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Mesoscale distribution and community composition of zooplankton in the Mozambique 1 Channel 2 3 Jenny A. Huggetta,b,* 4 5 aDepartment of Environmental Affairs, Oceans and Coasts, Private Bag X2, Roggebaai 8012, 6 Cape Town, South Africa 7 bMarine Research Institute, University of Cape Town, Private Bag, Rondebosch 8001, Cape 8 Town, South Africa 9 10 *Corresponding author. Tel.: +27214023174; fax: +27214023330. 11 E-mail address: jhuggett@environment.gov.za (J. Huggett). 12 13 Abstract 14 15 The biovolume, biomass, vertical distribution and community composition of mesozooplankton 16 (>200 µm) associated with mesoscale eddies in the Mozambique Channel was investigated 17 during four cruises in September 2007, December 2008, November 2009 and April/May 2010. 18 Stations were categorised according to their location in cyclonic or anticyclonic eddies, frontal, 19 divergence or shelf regions. Mean mesozooplankton biovolume in the upper 200 m was 0.33 ml 20 m-3. Moderate to high concentrations of zooplankton (0.3-0.7 ml m-3) were associated with 21 relatively cool water (<20°C) at a depth of 100 m and negative sea level anomalies (SLA <-15 22 cm) characteristic of cyclonic eddies. Low concentrations of zooplankton (<0.2 ml m-3) were 23 associated with relatively warm temperatures (>23°C) at 100 m and positive sea level anomalies 24 (SLA >20 cm) characteristic of anticyclonic eddies. Zooplankton biovolume was largely 25 concentrated in the upper 100 m during all four cruises. Sampling depth was the most important 26 predictor of biovolume, which was greatest for net samples with a mid-depth of 0-40 m (0.62 ml 27 m-3), followed by 40-80 m (0.46 ml m-3). Biovolume was greatest for shelf stations overall (0.42 28 ml m-3), but was highly variable. Biovolume was next highest for cyclonic eddies (0.37 ml m-3) 29 followed by divergence stations (0.33 ml m-3), intermediate for frontal stations (0.26 ml m-3), and 30 lowest for anticyclonic stations (0.18 ml m-3). Mean biovolume was significantly higher during 31 2008 and 2010 (0.38 and 0.35 ml m-3 respectively) compared to 2007 and 2009 (0.25 and 0.27 32 ml m-3), and was also significantly higher for samples collected at night (0.35 ml m-3) than 33 during the day (0.27 ml m-3). The mesozooplankton community in 2007 was strongly dominated 34 by small copepods (~70-80% abundance) followed by appendicularians (10%), ostracods (8%) 35 and chaetognaths (7%). The most abundant copepods were the Paracalanids, Oncaea spp, 36 Oithona spp. and Corycaeus spp. Multivariate analysis showed the communities in 2007 and 37 2008 were most strongly structured by depth, but classification was also important in 2007 when 38 mesoscale features were more strongly developed. Zooplankton assemblages showed a high 39 degree of homogeneity, with differences between mesoscale features largely due to differing 40 abundances of similar species. These results suggest that mesoscale eddy and shelf interactions 41 play a fundamental role in shaping the Mozambique Channel pelagic ecosystem through the 42 concentration, enhanced growth and redistribution of zooplankton communities. 43 44 Keywords: Zooplankton; Mesoscale eddies; Biomass; Vertical distribution; Community 45 composition; Mozambique Channel 46

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1. Introduction 47 48 Remote sensing and modeling studies have shown the Mozambique Channel to be a region of 49 high mesoscale variability (Biastoch and Krauss, 1999; Schouten et al., 2003; Tew-Kai and 50 Marsac, 2009), particularly in the central region (16°S-24°S). The general circulation is 51 dominated by large anticyclonic eddies (300-350 km in diameter) that form near the narrows of 52 the Channel at 16°S and propagate southwards along the African shelf edge at speeds of 3-6 km 53 per day (Biastoch and Krauss, 1999; de Ruiter et al., 2002; Schouten et al., 2003; Backeberg and 54 Reason, 2010). The mid-channel islands of Bassas da India and Europa (at approximately 22°S) 55 serve to restrict the passage of eddies to the western side of the channel (Quartly and Srokosz, 56 2004), although eddies are also occasionally observed in the eastern Mozambique Channel. 57 58 Eddies are important structures in oligotrophic systems, such as the Mozambique Channel, as 59 they provide mechanisms by which the physical energy of the ocean system can be converted to 60 trophic energy to support biological processes (Bakun, 2006; Godø et al., 2012). Cyclonic eddies 61 facilitate enhanced primary production in their centres (Falkowski et al., 1991) through the 62 upwelling of nutrients from deeper layers to the euphotic zone (McGillicuddy et al., 1998; Seki 63 et al., 2001; Benitez-Nelson et al., 2007), whereas anticyclonic eddies are characterized by 64 convergent flow in their surface layer which promotes development of frontal structures and 65 retention of passive organisms (Bakun, 2006). Furthermore, anticyclonic eddies that pass close to 66 the Mozambique coast appear to entrain and export chlorophyll-rich shelf waters offshore, seen 67 in images of ocean colour as curved trails or filaments of chlorophyll (Quartly and Srokosz, 68 2004; Tew-Kai and Marsac, 2009). 69 70 Several studies have shown the importance of the frontal regions between eddies as favourable 71 foraging areas for higher trophic levels, particularly seabirds, as demonstrated by large daytime 72 aggregations of micronekton (small fish, crustaceans and cephalopods) associated with areas of 73 high sea level anomaly (SLA) gradient (Sabarros et al., 2009), and the high abundance of great 74 frigatebirds, which feed on micronekton, associated with peripheries of eddies in the 75 Mozambique Channel (Weimerskirch et al., 2004; Tew Kai and Marsac, 2010). 76 Zooplanktivorous, surface-foraging seabirds were also most abundant in cold-core eddies along 77 the western frontal boundary of the Gulf Stream (Haney, 1986), which was attributed to higher 78 primary production associated with eddy-centre upwelling, and thus presumably high secondary 79 production leading to increased zooplankton abundance and biomass. 80 81 Enhanced zooplankton biomass and abundance in cold-core eddies relative to surrounding areas 82 has been documented for a number of oligotrophic systems, e.g. the Sargasso Sea (Goldthwait 83 and Steinberg, 2008), the Gulf of Mexico (Zimmerman and Biggs, 1999), the Hawaiian islands 84 (Landry et al., 2008) and the Bay of Bengal (Fernandes, 2008; Fernandes and Ramaiah, 2009). In 85 contrast, higher zooplankton associated with warm-core or anticyclonic eddies has been observed 86 for the Canary Islands (Hernandez-Leon et al., 2001) and off Western Australia (Strzelecki et al., 87 2007). To date, information is lacking on zooplankton biomass, distribution and community 88 structure associated with cyclonic and anticyclonic eddies in the Mozambique Channel, and for 89 the frontal regions between these eddies. 90 91

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This study brings together information on zooplankton biovolume and species composition from 92 depth-stratified net samples, environmental conditions from in situ sensors, and satellite-derived 93 water mass classification from four cruises to characterize the zooplankton biomass and 94 community structure of eddy systems off Mozambique. This is the first detailed study of 95 zooplankton assemblages associated with eddies in the region. 96 97 98 2. Methods 99 100 2.1 Cruise descriptions: 101 102 Cruises were conducted to investigate mesoscale eddy functioning in the Mozambique Channel 103 during September 2007 (MC07), December 2008 (MC08A), November 2009 (MC09B) and 104 April/May 2010 (MC10A), as described in Ternon et al. (submitted, this volume). For a 105 description of the hydrographic sampling during these cruises see Lamont et al. (submitted). 106 Note that fluorescence profiles were not available for MC09B or MC10A. Locations of stations 107 where zooplankton sampling was conducted are shown in Figure 1. Discriminant functional 108 analysis (DFA) was used to categorise each station according to its location in a cyclonic or 109 anticyclonic eddy, frontal, divergence or shelf (<1300 m) region, using processed altimetry data 110 (sea level anomaly and geostrophic current speed) and high resolution bathymetry (see Lamont 111 et al.; submitted, this volume). 112 113 2.2. Field sampling and analysis: 114 115 Mesozooplankton was collected using a Hydrobios MultiNet (0.25 m2 mouth area; 200-µm 116 mesh). During cruise MC07, vertical tows were made in the upper 400 m, with the following 117 depth strata sampled: 400-300, 300-200, 200-100 and 100-0 m. The finding of (a) relatively 118 small sample volumes, and (b) the bulk of the mesozooplankton biomass being confined to the 119 upper 200 m, prompted an altered sampling strategy for subsequent cruises in this region. During 120 cruises MC08A, MC09B and MC10A, tows were conducted obliquely to increase the volume of 121 water filtered, and sampling was restricted to the upper 200 m. Vertical profiles of temperature 122 and fluorescence from each station were used to select MultiNet depth strata representative of the 123 water column structure, including strata above, through and below the thermocline and depth of 124 maximum fluorescence (Fmax). The volume of water filtered was calculated using flow data 125 from built-in Hydrobios flowmeters. 126 127 In the laboratory, zooplankton samples were poured into measuring cylinders and left to settle 128 for 24 hours, after which the settled volume was recorded. Biovolume (ml m-3) was calculated by 129 dividing the settled volume by the volume filtered through the net. Samples were then divided 130 into two halves using a Folsom splitter, with one half retained for microscope analysis of 131 taxonomic composition, and the other half used to measure wet and dry biomass. Wet biomass 132 was determined after sample filters were blotted on paper towel to remove excess water. Samples 133 were then dried for 24 h at 60 °C and re-weighed. Wet and dry biomasses (mg m-3) were 134 determined by dividing the sample weights by the volume filtered. Biomass analysis was not 135 conducted for MC07 as most of the samples volumes collected by the vertical MultiNet tows 136 were too small (<5 ml). Wet and dry biomass (mg m-3) was estimated using regressions between 137

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settled volume (ml) and wet and dry biomass (g) from cruises MC08A, MC09B and MC10A: 138 wet biomass = 0.191 * settled volume (r2 = 0.78; n = 292), and dry biomass = 0.012 * settled 139 volume (r2 = 0.50; n = 292).. 140 141 Some of the sample volumes from the MultiNet oblique tows during cruises MC08A, MC09B 142 and MC10A were also too small (<5 ml) for accurate wet or dry biomass analysis. The biomass 143 of these samples was estimated using the above regressions or a regression between wet biomass 144 (g) and dry biomass (g), for the remaining samples collected during these cruises: dry biomass = 145 0.066 * wet biomass (r2 = 0.59; n = 292). Biovolume (which may considered a proxy for 146 biomass) was used for all analyses and graphical output, as it was the only consistent bulk 147 measurement for all four cruises 148 149 Data from the MultiNet tows were used to calculate the mean vertical position (weighted mean 150 depth, WMD) of zooplankton biovolume in the water column as follows: WMD = Σ(ni × zi × 151 di)/Σ(ni × zi), where di is the depth of a sample i (center of the depth interval, m), zi is the 152 thickness of the depth interval (m), and ni is the biomass or abundance of individuals in the depth 153 interval (mg or no m-3) (Steinberg et al., 2008). There were no bimodal vertical distributions. 154 155 Correlation analysis was used to investigate linear relationships between mean zooplankton 156 biovolume (Biovol) in the upper 200 m and selected environmental variables: sea surface 157 temperature (SST), temperature at 100 m (T100), sea surface salinity (SSS), surface chlorophyll 158 a concentration (SSChl), the depth of maximum fluorescence (Fmax), chlorophyll a 159 concentration at the depth of maximum fluorescence (MaxChl), integrated chlorophyll a in the 160 upper 200 m (IntChl), sea surface height anomaly (SLA) and geostrophic current speed (GCS). 161 162 Analysis of variance (ANOVA) was used to explore variability in zooplankton biovolume (using 163 each MultiNet sample from the upper 200 m) as a function of Year, the year of sampling (2007, 164 2008, 2009 or 2010); Class, the station classification (anticyclonic, cyclonic, divergence, frontal 165 or shelf); Depth, sampling depth; and Time, the time of sampling (night or day). To investigate 166 variability with regard to sampling depth, the mid-depth point of each net tow was used to assign 167 the sample to one of five 40 m-interval depth ranges in the upper 200 m (0-40 m, 41-80 m, 81-168 120 m, 121-160 m or 161-200 m). For cruise MC07, only samples from the upper 200 m were 169 used (3 samples per station), whereas all 5 samples were used from the other cruises. To test the 170 influence of daytime vs night-time sampling, samples collected during twilight (broadly defined 171 as the period from 30 minutes before to 30 minutes after both sunrise and sunset) were excluded 172 from the analysis. 173 174 2.3 Microscope identification of zooplankton: 175 176 Zooplankton samples from cruises MC07 and MC08A were identified to taxonomic level, and 177 copepods from MC07 were identified to genus or species level. Samples were split up to four 178 (vertical hauls, MC07) or seven (oblique tows, MC08A) times using a Folsom splitter, depending 179 on the density of each sample. Small samples (≤1.0 - 1.5 ml) were counted in their entirety. 180 181 2.4 Multivariate analysis: 182 183

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Multivariate analysis was used to investigate the mesozooplankton community composition 184 during MC07 and MC08A, and to test whether knowledge of copepod species composition 185 (available for MC07 cruise), in addition to knowledge of zooplankton taxa, improves 186 understanding of the zooplankton assemblages in relation to structuring variables (compared to 187 understanding based on knowledge of zooplankton taxa alone). 188 189 Multivariate analysis was performed using PRIMER v6 software according to Clarke and 190 Warwick (2001). Species abundance data was transformed using the fourth root transformation, 191 which strongly down-weights abundant species, and allows rare species to exert some influence 192 on the calculation of similarity (Clarke and Warwick, 2001). The Bray-Curtis measure of 193 similarity was used to create a resemblance matrix, on which the SIMPROF (similarity profile) 194 permutation testing procedure was run to identify statistically significant clusters of samples. 195 Non-metric multi-dimensional scaling (MDS) was used to produce 2-dimensional and 3-196 dimensional ordinations of samples in relation to selected grouping variables (Year, 197 Classification and Time of Day). One-way ANOSIM (analysis of similarities) was used to test 198 for significant differences in the community composition according to depth, station 199 classification and time of day. The SIMPER (similarity percentages) routine was used to 200 determine which zooplankton taxa or copepod species contributed most to similarities within and 201 dissimilarities between groups. 202 203 204 3. Results 205 206 3.1. Biovolume and biomass 207 208 Mean mesozooplankton biovolume in the upper 200 m from all four cruises was 0.33 ml m-3, 209 with a maximum of 1.9 ml m-3 sampled near the Mozambique coast, south of Nacala, during 210 2010 (Table 1). Mean dry biomass was 5.00 mg m-3, with a maximum of 28.5 mg m-3 measured 211 on the eastern side of the Channel in 2010 near Madagascar. Wet biomass was on average 13.2 212 times dry biomass. 213 214 3.2. Horizontal distribution of zooplankton 215 216 Moderate to high concentrations of zooplankton biovolume (>40 ml 100 m-3) during September 217 2007 (Fig 2a) were associated with relatively cool water (<20°C) at a depth of 100 m (Fig 2b) 218 and negative sea level anomalies (SLA <-15cm) indicative of the core of the cyclonic eddy (Fig 219 2c). Biovolume was also elevated near Hall Tablemount and Jaguar Seamount (stns 21 and 22), 220 situated to the south-west of Bassas da India, but was low at shelf-edge stations off Mozambique. 221 Low zooplankton concentrations (<20 ml 100 m-3) were associated with relatively warm 222 temperatures (>23°C) at 100 m, and positive sea level anomalies (SLA >20cm). Spatial 223 associations between zooplankton biovolume and integrated chlorophyll suggested a broadly 224 positive relationship; areas of low zooplankton biovolume were associated with low 225 concentrations of integrated chlorophyll (<30 mg m-3; Fig. 2d). 226 227 During December 2008, discrete areas of high zooplankton biovolume (>70 ml 100 m-3) 228 coincided with steep shelf-edge regions on either side of the Mozambique Channel (Fig 3a). 229

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Moderate concentrations (30-60 ml 100 m-3) were associated with areas of cooler water (<20°C) 230 at depth (Fig 3b) and negative SLA (Fig 3c), whereas low zooplankton biovolumes (<30 ml 100 231 m-3) were again associated with warm temperatures (>22°C) at depth and positive SLA (>15 232 cm). High zooplankton biovolume along the shelf-edge off the Mozambique coast (e.g. stations 233 16 and 18) was accompanied by high concentrations of integrated chl a (>80 mg m-3; Fig 3d). 234 235 Zooplankton biovolume was relatively low during November 2009, ranging from 15-40 ml 100 236 m-3 at the cyclonic stations, and <15 ml 100 m-3 at the anticyclonic stations (Fig 4a). There were 237 greater contrasts in temperature and SLA between cyclonic and anticyclonic stations compared 238 to previous years, resulting in strong frontal boundaries (Fig 4b and 4c). Cyclonic eddy stations 239 were characterized by colder water (<18°C) at 100 m and more strongly negative SLA (<-25cm) 240 compared to 2007 and 2008, whereas anticyclonic stations were characterized by warmer water 241 (>24°C) at 100 m and SLA>25cm. In contrast to previous years, integrated chlorophyll a was 242 higher at the anticyclonic stations (>65 mg m-3) compared to the cyclonic stations (<30 mg m-3; 243 Fig 4d). 244 245 Patterns of zooplankton biovolume during April 2010 (Fig 5a) were mostly well coupled to the 246 oceanographic structure inferred from hydrography and altimetry. Cool (<19°C at 100 m) 247 cyclonic features were observed to the north and south of the relatively large survey area, with a 248 warm (>23°C at 100 m) but dividing anticyclonic eddy in the central region (Figs 5b and 5c). 249 Zooplankton biovolume was low (<30 ml 100 m-3) at most of the anticyclonic stations as well as 250 in the northern divergence area caused by the dividing eddy (stns 17-20). Moderate to high 251 zooplankton biovolume (30-70 ml 100 m-3) was observed elsewhere, in conjunction with 252 cyclonic and other divergence areas (Fig 5a). Highest integrated chlorophyll a was associated 253 with the northern cyclonic eddy (Fig 5d). 254 255 3.3. Vertical distribution of zooplankton 256 257 Mesozooplankton biovolume was largely concentrated in the upper 100 m during all four cruises 258 (Fig. 6). Mean weighted mean depth (WMD) for the upper 200 m ranged from 54.7 m during 259 2008 to 84.4 m during 2009. During September 2007, elevated concentrations of biovolume 260 (>0.8 ml 100 m-3) clearly corresponded to cyclonic and divergence areas, characterized by a 261 doming of the isotherms (Fig 6a). Maximum zooplankton biovolume fluctuated between the 262 upper 50 m and 50-100 m depth intervals, suggesting some synchrony with vertical fluctuations 263 of the isotherms. The vertical distribution of chlorophyll a showed similar undulations to those in 264 temperature, but over a narrower depth range, and did not appear to correspond to any particular 265 isotherm. The bulk of the phytoplankton biomass occurred between 30 and 120 m, with highest 266 concentrations (>0.9 mg m-3) corresponding to the cyclonic and divergence areas where 267 zooplankton biovolume was greatest. 268 269 Highest zooplankton biovolume during 2008 occurred within the upper 50 m of the water 270 column (Fig 6b), with peak values (>3 ml m-3) between 25 and 50 m on the shelf-edge north of 271 Angoche, Mozambique (stn 16). High zooplankton biovolumes associated with the shelf-edge 272 farther south (stns 17-19) and off Madagascar (stn 12) were concentrated in the upper 25 m of 273 the water column. The vertical distribution of chlorophyll a again appeared to broadly reflect the 274 vertical structuring of the isotherms, with very high concentrations (>1 mg m-3) between 30 and 275

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70 m, in relatively cool water (21-24°C) associated with the Mozambican shelf-edge stations and 276 the divergence region to the south-west of station 18. Areas of high phytoplankton concentration 277 broadly corresponded to areas of high zooplankton concentration. 278 279 During November 2009, zooplankton was fairly evenly distributed throughout the upper water 280 column in the vicinity of the cyclone as well as in the broad frontal region, with peak 281 zooplankton biovolume concentrated below 50 m at the southernmost shelf station (stn 13; Figs 282 4c and 6c). Zooplankton distribution appeared to extend deeper at the frontal stations compared 283 to the cyclonic stations, where doming of the isotherms may have compressed the vertical 284 distribution of zooplankton. 285 286 Highest densities of zooplankton biovolume during April/May 2010 were concentrated between 287 25 and 50 m at the northern and southern cyclonic eddies, and between 25 and 75 m in the 288 divergence area off the south-western Madagascar shelf-edge (Figs 5 and 6d). 289 290 3.4. Factors influencing variability in zooplankton 291 292 The correlation analysis indicated strong positive correlations between the temperature at 100 m 293 (T100) and SLA, and between T100 and the depth of maximum fluorescence (Fmax) over all 294 four cruises (Table 2). Zooplankton biovolume was significantly negatively correlated with 295 T100, SLA, Fmax and geostrophic current speed, and positively correlated with surface salinity. 296 There was a weak but significant positive correlation between zooplankton biovolume and 297 maximum chlorophyll a in the water column, but no correlation with integrated chlorophyll or 298 surface chlorophyll. 299 300 Analysis of variance (ANOVA) showed that year, classification, depth and time of sampling 301 (day or night) were all significant predictors of mesozooplankton biovolume (F=26.76; 302 p<0.001). Only main factors were considered, as not all station classifications were identified 303 each year, precluding a full analysis of interactions. Depth was the most important factor, 304 explaining almost 21% of variability in zooplankton biovolume, followed by classification 305 (2.6%), year (1.3%) and time of day (0.8%). 306 307 Zooplankton biovolume showed a strong depth gradient (Fig. 7(A)), with greatest biovolume for 308 net samples with a mid-depth of 0-40 m (0.62 ml m-3), followed by those with a mid-depth of 40-309 80 m (0.46 ml m-3). Biovolume was not significantly different for samples collected from the 3 310 deepest depth strata (mid-depths of 80-200 m). In terms of water type classification, biovolume 311 was greatest for shelf stations overall (0.42 ml m-3), but was highly variable (Fig. 7(B)). 312 Biovolume was next highest for cyclonic eddy stations (0.37 ml m-3) followed by divergence 313 stations (0.33 ml m-3), intermediate for frontal stations (0.26 ml m-3), and lowest for anticyclonic 314 eddy stations (0.18 ml m-3). Biovolume at the cyclonic eddy stations was significantly greater 315 than at both frontal and anticyclonic eddy stations, but frontal and anticyclonic eddy biovolume 316 did not differ significantly. Mean biovolume was significantly higher during 2008 and 2010 317 (0.38 and 0.35 ml m-3 respectively) compared to 2007 and 2009 (0.25 and 0.27 ml m-3; Fig. 318 7(C)), and was also significantly higher for samples collected at night (0.35 ml m-3) than during 319 the day (0.27 ml m-3; Fig. 7(D)). 320 321

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Further analysis of depth-related patterns of biovolume for the different water type classifications 322 highlighted the strong depth gradient but also extreme variability in mean biovolume in the upper 323 water column (mid-depths ≤ 80 m) for the shelf stations (Fig. 8). The depth gradient was also 324 notable for divergence and cyclonic eddy stations, but considerably dampened for anticyclonic 325 eddy stations. The patterns of relative biovolume associated with the various mesoscale features, 326 in particular significantly greater biovolume for cyclonic eddy stations than anticyclonic eddy 327 stations, and high variability for shelf stations, was consistent for all cruises (Fig. 9). 328 329 3.5. Abundance and community structure 330 331 Zooplankton abundance in the upper 400 m during 2007 varied strongly with depth, with much 332 larger numbers of zooplankton in the upper 100 m of the water column compared to the depths 333 below, and a gradual decline in abundance from the 100-200 m stratum to the 300-400 m stratum 334 (Table 3). Small calanoid, cyclopoid and poecilostomatoid copepods (mostly ≤ 1 mm) dominated 335 the zooplankton community in the upper 200 m, as well as each water type, comprising 70-80% 336 of total abundance (Table 4). Appendicularians, ostracods, chaetognaths and siphonophores were 337 the next most abundant taxa after copepods. Copepod nauplii were relatively abundant at 338 cyclonic eddy (8.4%) and divergence stations (5.2%), but not at anticyclonic eddy stations. 339 Different euphausiid developmental stages characterized the different mesoscale features, with 340 nauplii present at cyclonic eddy stations (1.7%), calyptopes present at divergence (1.8%), frontal 341 (0.8%) and shelf stations (1.7%), and furcilia at anticyclonic eddy stations (0.8%). 342 343 Mean zooplankton abundance in the upper 200 m was greater during 2007 (277 m-3) than 2008 344 (192 m-3). During both cruises, abundance was highest (but also most variable) at the shelf 345 stations, followed by the cyclonic eddy and divergence stations during 2007, with lowest 346 abundance at the anticyclonic eddy stations (Table 5). The pattern was slightly different for 347 2008, with second highest abundance at the divergence stations, but equally low abundance at 348 both cyclonic and anticyclonic eddy stations (~100m-3), although only 2 stations were classified 349 as cyclonic during this cruise. 350 351 Multivariate analysis of the zooplankton taxa and copepod species abundance data within the 352 upper 400 m for 2007 indicated that sampling depth was a significant factor influencing the 353 zooplankton assemblages (ANOSIM, R=0.50, p<0.1%). Two main clusters with approximately 354 50% similarity corresponded to samples collected mostly within the upper 100 m, and those 355 between 100 and 400 m (Fig. 10(A)). Clusters at a higher level of similarity (60%, not shown) 356 confirmed a depth gradient in community composition. The assemblages from the deepest (300-357 400 m) and shallowest (0-50 m) strata were most dissimilar (SIMPER, 60.5%), whereas those 358 from the 200-300 m and 100-200 m strata were least dissimilar (SIMPER, 38.7%). There were 359 no evident taxonomic discriminators of the different groups, since dissimilarity between groups 360 was largely due to different relative abundances of a wide range of species or taxa, as opposed to 361 the presence or absence of species. However, pair-wise comparisons of groups indicated greater 362 relative abundances of Pleuromamma indica and Gaetanus minor in the deeper groups, and G. 363 minor was absent from the shallowest (0-50 m) samples. The most abundant and consistently 364 present species or taxa for all depth strata were the Paracalanidae, Oncaea spp, Oithona spp, 365 Corycaeus spp and chaetognaths. There was also a depth gradient in the number of species or 366

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taxa responsible for within-group similarity, with fewest for the deepest group (8 species/taxa) 367 and most for the shallowest group (17 species/taxa), suggesting a decline in diversity with depth. 368 369 Station classification was also a significant factor shaping community composition (ANOSIM, 370 R=0.08, p<0.1%), although an R value close to zero indicates a high degree of overlap between 371 the assemblages, as observed in the 2-d ordination (Fig. 10(B)). Dissimilarity was greatest 372 between cyclonic eddy and shelf communities (SIMPER, 49.4%), due to higher abundance of 373 most taxa at shelf stations compared to cyclonic eddy stations, and between cyclonic and 374 anticyclonic eddy communities (SIMPER, 48.5%), due to higher abundance of many taxa at 375 cyclonic eddy stations, although Oithona spp., shelled pteropods, euphausiid furcilia and several 376 copepod species were relatively more abundant at anticyclonic eddy stations. There was a 377 marginally significant effect of time of day on community composition (ANOSIM, R=0.03; 378 p<4.8%), but again the very low R value indicates a high degree of overlap between groups. 379 380 Similar analyses using data from the upper 400 m in 2007 on copepod species alone, and 381 zooplankton taxa alone, indicated that zooplankton assemblages were significantly influenced by 382 both depth and classification, but not time of day (Table 5; Fig. 11(A & B)). When abundance of 383 zooplankton taxa from just the upper 200 m was analysed, depth, classification and time all had a 384 significant influence on zooplankton assemblages, in contrast to 2008, when only depth was 385 shown to have a significant influence on the zooplankton assemblages (Table 5; Fig. 11(C)). The 386 3-d ordination suggests some separation of communities from different water types (Fig. 11(D)), 387 as in 2007 (Fig. 11(B)), but the differences in 2008 were not significant. Analyses using data on 388 copepod species composition yielded higher R values compared to data on zooplankton taxa 389 alone, but did not alter the main finding of depth as the most important factor discriminating the 390 zooplankton assemblages in 2007, with a lesser influence from station (i.e. water type) 391 classification. 392 393 394 4. Discussion 395 396 4.1. Patterns of zooplankton distribution within the eddies 397 398 There are many factors that may influence the distribution of zooplankton within a mesoscale 399 eddy landscape, such as the characteristics of the source water (temperature, nutrient 400 concentrations, phytoplankton biomass and productivity, zooplankton biomass, life cycles and 401 behaviour of the zooplankton populations within the eddies), the age, size, intensity and 402 evolution of the eddies, the type of forcing mechanism (e.g. topographic, such as headland-, 403 seamount- or island-induced, or dynamic, such as rings shed from ocean currents or frontal 404 meanders), as well as interactions with the coast and other eddies, and wind events (Owen, 1981; 405 Benitez-Nelson and McGillicuddy, 2008; Morales et al, 2010). Both cyclonic and anticyclonic 406 eddies are zones of horizontal recirculation, and thus locally maintain and transport their 407 contained populations and substances (Owen 1981). 408 409 The passage of mesoscale eddies through the Mozambique Channel clearly has a strong 410 influence on the distribution of zooplankton. Mesozooplankton biovolume and biomass in the 411 cold-core cyclonic eddies were on average twice that in the warm-core anticyclonic eddies 412

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sampled during this study, with intermediate biovolume in the frontal zones between eddies. This 413 pattern suggests that these eddies were in their “spinning up” phase (Bakun, 2006), with 414 upwelling in the cyclonic eddies resulting in enhanced nutrient concentrations, primary 415 production and phytoplankton biomass in the upper water column, and hence increased 416 production of the zooplankton community already present from the source water (supported by 417 higher abundance of copepod and euphausiid nauplii), leading to relatively high concentrations 418 of zooplankton in the eddy centres. Divergent surface flow would tend to distribute zooplankton 419 towards the peripheries of these eddies, resulting in the intermediate/high biovolumes measured 420 at the frontal/divergence areas. The lack of such enrichment in the anticyclonic eddies, although 421 also retaining zooplankton from the source waters and entraining some material from the frontal 422 region, would render them comparatively poor in zooplankton biomass compared to the cyclonic 423 eddies. 424 425 Similar results from oligotrophic systems include those of Landry et al., (2008), who 426 documented an 80% increase in mesozooplankton biomass in the core of a subtropical cyclonic 427 eddy (“Cyclone Opal”) relative to surrounding waters near the Hawaiian islands, and of 428 Fernandes and Ramaiah (2009), where a 5-fold increase in biomass and an 18-fold increase in 429 abundance of zooplankton was observed in cold-core eddies in the Bay of Bengal. Acoustic 430 backscatter intensity (ABI) reflected from epipelagic zooplankton communities in the Gulf of 431 Mexico was significantly enhanced within cold-core eddies compared to warm-core eddies 432 (Zimmerman and Biggs, 1999). However, Goldthwait and Steinberg (2008), who sampled a 433 more mature, post-phytoplankton bloom cyclonic eddy in the Sargasso Sea, recorded higher 434 biomass in the periphery of the eddy compared to the centre, and even higher biomass within the 435 centre of the mode-water anticyclonic eddy. Similarly, Hernandez-Leon et al. (2001) recorded 436 elevated zooplankton biomass at the periphery of a cyclonic eddy compared to its core near the 437 Canary Islands, and high biomass associated with the nearby anticyclonic eddy. 438 439 The varying ages of the eddies in the studies described above most likely contributed to the 440 different patterns of zooplankton biomass and distribution. Cyclone Opal was a large “mature” 441 eddy of 4-6 weeks age at the time of study, with doming of isopycnals and nutriclines, above-442 ambient phytoplankton biomass and growth rates, and elevated biomass and grazing rates of 443 heterotrophic protists (Landry et al., 2008), whereas the Sargasso Sea cyclonic eddy C1 sampled 444 by Goldthwait and Steinberg (2008) was thought to be winding down, i.e. decaying or in the 445 “spinning down” phase as described by Bakun (2006). This was also thought to be the case for 446 the cyclonic eddy studied by Hernandez-Leon et al. (2001), with initial enhancement of 447 zooplankton metabolism at the eddy centre in response to increased primary production, 448 followed by outward drift of the zooplankton toward the eddy periphery (Goldthwait and 449 Steinberg, 2008). 450 451 In a study off Western Australia, both biomass and abundance of mesozooplankton >355 µm 452 were twice as high in a warm-core (anticyclonic) eddy compared to the adjacent cold-core 453 (cyclonic) eddy, contrary to initial expectations (Strezelecki et al., 2007). This was attributed to 454 the more productive source water of the warm-core eddy (largely Leeuwin Current water) 455 compared to the cold-core eddy (subtropical Indian Ocean water), as well as the fact that 456 upwelling within the cold-core eddy did not penetrate the euphotic zone. These eddies were 457 sampled five months after their formation, yet still retained a strong biological signature of their 458

11

origin. Other examples of high biomass in association with anticyclonic eddies are those that 459 form off the continental margins, such as the Haida eddies of the northeast Pacific, which may 460 transport planktonic biota of coastal origin over long distances into the oceanic region (Batten 461 and Crawford, 2005; Crawford et al., 2007; Mackas and Galbraith, 2002; Mackas et al., 2005). 462 Cyclonic eddies may also be responsible for such offshore dispersion, as demonstrated by 463 Morales et al., (2010) for the Humboldt Current System. 464 465 The high variability in zooplankton biomass between years may reflect varying conditions in the 466 source waters, as well as a varying influence of entrainment from the shelf regions, which also 467 varied considerably in terms of biomass. There was no clear seasonal pattern, as the first three 468 cruises were conducted during summer, and the fourth during winter. There could be a latitudinal 469 effect, as sampling was concentrated in the northern part of the Mozambique Channel during the 470 years of higher biomass (2008 and 2010), but was concentrated farther south during 2007 and 471 2009, when biomass was lower. Mean shelf biomass was greatest during 2008, particularly in the 472 Angoche region, with apparent offshore entrainment of shelf material in the strong frontal region 473 between the cyclonic and anticyclonic eddies situated to the south of Angoche. Shelf-edge 474 upwelling and subsequent elevated chlorophyll concentration is common in this region during 475 summer (August to March), and is thought to be largely driven by weak northeasterly monsoon 476 winds (Malauene et al., submitted, this volume; Nehring et al., 1987). Mean biomass during 2010 477 was strongly influenced by above average zooplankton concentrations off the Madagascar shelf, 478 and this region was also characterised by relatively high values of integrated chlorophyll a. 479 Although zooplankton biovolume showed varying relationships with several indices of 480 phytoplankton biomass in the water column, high chlorophyll values in these shelf regions 481 suggest elevated primary production, which would lead to enhanced growth of the zooplankton 482 population over time. 483 484 Zooplankton biovolume was strongly correlated with the broad physical signature of the cyclonic 485 eddies, namely a relatively shallow thermocline (indicated by a low T100) and Fmax, a negative 486 SLA, as well as slow current speeds likely to favour retention. The weak or lack of correlation 487 between zooplankton biovolume and various chlorophyll a parameters, also noted by Fernandes 488 and Ramaiah (2009), may well be a result of grazing impact. Although grazing by zooplankton 489 and microzooplankton was not measured during this study, Landry et al., (2008) found that 490 herbivory by both micro- and mesozooplankton balanced out phytoplankton growth within 491 Cyclone Opal. This may also account for the lack of significant difference in phytoplankton 492 biomass between the cyclonic and anticyclonic eddies observed by Lamont et al., (submitted, 493 this volume), compared to the significant difference in zooplankton biomass between opposing 494 eddies observed in this study. 495 496 Mesozooplankton biovolume and abundance was markedly concentrated in the upper 100 m of 497 the water column. The difference in WMD between the cyclonic and anticyclonic stations (~12 498 m) was not significant, hence diminished biovolume in the upper 200 m of the water column in 499 association with the anticyclonic eddies was a true reduction in absolute water column 500 biovolume, and not a vertical displacement of biovolume to deeper in the water column. 501 Furthermore, there was greater variability in WMD between cruises than between mesoscale 502 features. Although biovolume was significantly greater at night, usually a consequence of 503 nocturnal ascent by larger migrating zooplankton, this only amounted to a 30% increase in 504

12

biovolume, and did not manifest as a noticeable change in species composition of the dominant 505 taxa. This disparity is fairly minor compared to other studies, for example Goldthwait and 506 Steinberg (2008) measured a more than 2-fold increase in biomass at night in both cyclonic and 507 anticyclonic eddies for zooplankton >150 µm in the Sargasso Sea, and Biggs et al. (1997) found 508 that biovolume was 2.4 times higher at night on average for zooplankton >333 µm in a cold-core 509 eddy in the Gulf of Mexico, largely due to an increase in euphausiids. Older (thus larger and 510 more migratory) euphausiid stages were not particularly abundant during the present study, 511 which may contribute to the reduced diel vertical migratory response for the mesozooplankton 512 component compared to other regions. 513 514 4.2. Community structure within the eddies 515 516 Although the eddies differed significantly in terms of biomass, the differences in species 517 assemblages were largely due to differences in total abundance between the water types, with 518 minor variation in species composition. This suggests that the region is quite homogeneous with 519 respect to species composition, and that differences between the features are largely due to 520 differential concentration or dilution of the ambient communities, and not to extended isolation 521 of the eddies. Landry et al. (2008) also found species composition to be similar in both Cyclone 522 Opal, where biomass was significantly elevated, and the control stations in the southeastern lee 523 of the Hawaiian islands, suggesting a broad community increase in Cyclone Opal. Similarly, 524 Strzelecki et al. (2007) found differences between the warm-core and cold-core assemblages off 525 Western Australia to be due to different proportions and abundances of the taxa rather than to 526 differences in a few indicator species. The similar patterns in assemblages obtained in this study 527 using either broad taxonomic information or more detailed knowledge of copepod species 528 composition suggests knowledge of the former alone will provide sufficient insight for a basic 529 understanding of community structure, reducing the need for long hours behind the microscope. 530 However, it is also possible our taxonomic resolution for both copepods and other zooplankton 531 taxa was insufficient to reveal subtle differences in distribution or to identify suitable 532 discriminators of the different water masses. 533 534 Abundance data was only available for two of the cruises, but revealed a greater difference in 535 abundance between cyclonic and anticyclonic eddies during 2007, which featured a well 536 developed eddy dipole, compared to 2008 when the cyclonic features in particular were less 537 developed (smaller SLA), and areas of negative SLA were classified mainly as areas of 538 divergence. As the mesoscale features sampled during 2008 were farther north than those in 539 2007, the eddy field was likely to have been in an earlier stage of development, consistent with 540 eddy genesis even farther north in the narrows of the Channel (Ridderinkhof and de Ruiter, 2003; 541 Tew-Kai and Marsac, 2009). The reason for higher mean biomass but lower mean abundance in 542 2008 is unclear, but could indicate a difference in size composition for some or all of the taxa. 543 544 The strong dominance of the zooplankton assemblage (70-80%) by small (≤ 1 mm total length) 545 copepods is typical of tropical and subtropical ecosystems (Hopcroft et al., 1998; Schnack-Schiel 546 et al., 2010). This community structure suggests that the measurements of mesozooplankton 547 biomass in this study are likely to be conservative, as many juvenile stages of these small 548 copepods would have been undersampled by the 200-µm mesh of the MultiNet used here. 549 Hopcroft et al. (1998) conducted comparative sampling with 64- and 200-µm mesh nets in 550

13

Kingston Harbour, Jamaica, and found that all nauplii, most copepodites and many adults of 551 these small copepods, equivalent to half of the biomass and production, were missed by a 552 standard 200-um plankton net. Furthermore, small copepods are known to have relatively fast 553 growth rates, and are rarely food-limited compared to larger copepods (Hirst and Bunker, 2003), 554 such that tropical ecosystems are now thought to have productivities comparable to, or 555 exceeding, temperate ecosystems (Hopcroft et al., 1998). Accordingly, an expected fast growth 556 of the copepod assemblages in the cyclonic eddies supports the likelihood of their grazing impact 557 matching growth of the phytoplankton assemblages enhanced by elevated nutrient 558 concentrations. 559 560 In conclusion, these results suggest that mesoscale eddy and shelf interactions play a 561 fundamental role in shaping the Mozambique Channel pelagic ecosystem through the 562 concentration, enhanced growth and redistribution of zooplankton communities. 563 Mesozooplankton populations were significantly enriched within cyclonic eddies compared to 564 anticyclonic eddies, as shown by the doubling of mean biomass from four cruises, and a 565 significant increase in abundance of the entire assemblage when eddy features were strongly 566 developed, as in 2007. Biomass in the frontal areas was not as high as in the cyclonic eddies, but 567 was still elevated relative to the anticyclonic eddies. The productive cores of the cyclonic eddies 568 are relatively small areas compared to the larger anticyclonic eddies, whereas the frontal and 569 divergence areas, which are constantly “fed” by divergence from the cyclonic eddies, between 570 them likely constitute an extensive area of above average biomass. The probability of higher 571 trophic levels (e.g. micronekton or planktivorous avifauna) encountering such areas is likely to 572 be greater than for the relatively small hotspots of production in the cyclone cores, and the faster 573 current speeds associated with the frontal areas may facilitate the identification of these 574 relatively favourable foraging zones. 575 576 The wide spacing between sampling stations for the four cruises in this study has helped to 577 elucidate the “big picture” of zooplankton distribution in relation to mesoscale features in the 578 Mozambique Channel, but was too coarse to determine fine-scale gradients in biomass from a 579 cyclone core across the frontal area to an anticyclone. We hope to address this in future cruises, 580 as well as to investigate rates of zooplankton grazing and secondary production. 581 582 Acknowledgements 583 584 Tamaryn Morris, Andre Miggel, Hans Verheye, Marco Worship, Sven Kaehler, Marcel van den 585 Berg, Tore Mork, Jean-François Ternon and Pascal Cotel are warmly thanked for assistance with 586 sampling, as well as the Captains and crew of the FRV Algoa, the RV Dr Fridjtof Nansen and 587 the RV Antea. Kholeka Batyi, Samantha Ockhuis, Lauren Abels, Susan Jones, Elana Wright, 588 Asanda Mkiva, Michelle Pretorius and Cornelia Nieuwenhuys provided invaluable assistance 589 with laboratory analysis and microscope identification. The African Coelacanth Ecosystem 590 Programme (ACEP), Agulhas and Somali Currents Large Marine Ecosystem (ASCLME) 591 Project, Western Indian Ocean Marine Science Association (WIOMSA) and l'Institut de 592 recherche pour le développement (IRD) are gratefully acknowledged for logistical and/or 593 financial support. 594

595

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Morales, C.E., Torreblanca, M.L., Hormazabal, S., Correa-Ramírez, M., Nuñez, S., Hidalgo. P., 688 2010. Mesoscale structure of copepod assemblages in the coastal transition zone and oceanic 689 waters off central-southern Chile. Progress in Oceanography 84, 158–173. 690 691 Nehring, D., Hagen, E., da Silva, A.J., Schemainda, R., Wolf, G., Michelchen, N., Kaiser, W., 692 Postel,L., Gosselck, F., Brenning, U., Kuhner, E., Arlt, G., Siegel, H., Gohs, L., Bublitz, G., 693 1987. Results of oceanological stuies in the Mozambique Channel in February-March 1980. 694 Beiträge zur Meereskunde, Berlin, 56, 51-63. 695 696 Owen, R.W., 1981. Fronts and eddies in the sea: mechanisms, interactions and biological effects. 697 In: Owen, R.W. (Ed.), Fronts and Eddies in the Sea. Academic Press, London. 698 699 Quartly, G.D., Srokosz, M.A., 2004. Eddies in the southern Mozambique Channel. Deep-Sea 700 Research II 51, 69-83. 701 702 Ridderinkhof, H., de Ruiter, W.P.M., 2003. Moored current observations in the Mozambique 703 Channel. Deep-Sea Research II 50, 1933-1955. 704 705 Sabarros, P.S., Ménard, F., Lévénez, J.-J., Tew-Kai, E., Ternon, J.-F., 2009. Mesoscale eddies 706 influence distribution and aggregation patterns of micronekton in the Mozambique Channel. 707 Marine Ecology Progress Series 395, 101–107. 708 709 Schnack-Schiel, S. B., Mizdalski, E., Cornils, A., 2010. Copepod abundance and species 710 composition in the Eastern subtropical/tropical Atlantic. Deep-Sea Research II 57, 2064-2075. 711 712 Schouten, M.W., de Ruijter, W.P.M., van Leeuwen, P.J., Ridderinkhof, H., 2003. Eddies and 713 variability in the Mozambique Channel. Deep-Sea Research II 50, 1987–2003. 714 715 Seki, M.P., Polovina, J.P., Brainard, R.E., 2001. Biological enhancement at cyclonic eddies 716 tracked with GEOS thermal imagery in Hawaiian waters. Geophysical Research Letters 28(8), 717 1583-1586. 718 719 Steinberg, D.K, Cope, J.S, Wilson, S.E., Kobari, T., 2008. A comparison of mesopelagic 720 mesozooplankton community structure in the subtropical and subarctic North Pacific Ocean. 721 Deep-Sea Research II 55, 1615– 1635. 722 723 Strzelecki, J., Koslowa, J.A., Waite, A., 2007. Comparison of mesozooplankton communities 724 from a pair of warm- and cold-core eddies off the coast of Western Australia. Deep-Sea Research 725 II 54, 1103-1112. 726 727 Ternon, J-F., Barlow, R., Huggett, J., Kaehler, S., Marsac, F., Menard, F., Potier, M., Roberts, R., 728 submitted. An overview of recent field experiments on the ecosystem's mesoscale signature in the 729 Mozambique Channel: from physics to upper trophic levels. Deep-Sea Research II (this issue) 730 731 Tew-Kai, E., Marsac, F., 2009. Patterns of variability of sea surface chlorophyll in the 732 Mozambique Channel: a quantitative approach. Journal of Marine Systems 77, 77–88. 733 734

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Tew Kai, E., Marsac, F., 2010. Influence of mesoscale eddies on spatial structuring of top 735 predators’communities in the Mozambique Channel. Progress in Oceanography 86, 214–223. 736 737 Weimerskirch, H., Le Corre M, Jaquemet, S., Potier, M., Marsac, F., 2004. Foraging strategy of 738 a top predator in tropical waters: great frigate birds in the Mozambique Channel. Marine Ecology 739 Progress Series 275, 297-308. 740 741 Zimmerman, R.A., Biggs, B.C., 1999. Patterns of distribution of sound-scattering zooplankton in 742 warm- and cold-core eddies in the Gulf of Mexico, from a narrowband acoustic Doppler current 743 profiler survey. Journal of Geophysical Research 104 (C3), 5251-5262. 744

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Table 1 746

Mean ± standard deviation (and range) of settled biovolume (ml m-3) and wet and dry biomass 747 (mg m-3) in the upper 200 m, for mesozooplankton (>200 µm) for all stations sampled during 748 each cruise. 749

Cruise  Biovolume (ml m‐3)  Wet biomass (mg m‐3) Dry biomass (mg m‐3)  n

MC07  0.27 ± 0.14 (0.10‐0.63)  51.20 ± 26.50 (19.26‐120.66)a  3.22 ± 1.66 (1.21‐7.58)a  33 MC08A  0.40 ± 0.19 (0.16‐0.96)  87.31 ± 33.09 (43.97‐173.70)  5.73 ± 2.86 (0.82‐11.11)b  39 MC09B  0.23 ± 0.11 (0.09‐0.43)  48.35 ± 21.81 (13.84‐82.86)  3.29 ± 1.48 (1.18‐6.85)b  17 MC10A  0.37 ± 0.30 (0.15‐1.94)  65.32 ± 26.77 (28.59‐165.89)c  6.75 ± 4.97 (1.88‐25.88)b,c  33 mean  0.33 ± 0.22 (0.09‐1.94)  66.13 ± 32.40 (13.84‐173.70)  5.00 ± 3.56 (0.82‐25.58)  122 

750 a all values estimated from settled volume. 751 b some values estimated from wet weight. 752 c some values estimated from settled volume. 753 754

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Table 2 755

Correlation analysis showing positive or negative linear correlations between zooplankton 756 biovolume and selected environmental variables. Significant correlations (p < 0.05) are shown in 757 bold. 758

SST T100 SSS SChl Fmax MaxChl IntChl SLA GCS Biovol

SST 1.00

T100 0.08 1.00

SSS 0.27 -0.20 1.00

SChl 0.39 -0.21 0.05 1.00

Fmax -0.10 0.75 0.00 -0.28 1.00

MaxChl 0.08 -0.35 0.10 0.32 -0.34 1.00

IntChl 0.24 -0.19 0.06 0.39 -0.13 0.75 1.00

SLA 0.15 0.82 -0.10 -0.09 0.57 -0.16 -0.09 1.00

GCS -0.27 0.20 -0.15 -0.02 0.16 0.02 -0.07 0.03 1.00

Biovol 0.19 -0.55 0.25 0.11 -0.39 0.22 0.18 -0.48 -0.31 1.00

759

20

Table 3 760

Mean abundance (no m-3) of zooplankton within the different depth strata during 2007. 761

Depth  Mean  SD  n 

0 ‐ 50 m  560.79  375.13  33 50 ‐ 100 m  418.37  324.32 33100 ‐ 200 m  86.45  67.90  33 200 ‐ 300 m  44.00  49.03  33 300 ‐ 400 m  29.13  13.26  33 

762

21

Table 4 763

Mean and % abundance (no m-3) of the 20 most abundant zooplankton taxa or species from all stations in the upper 200 m, and 764 according to station classification, during cruise MC07. 765

766

767

768

Taxon no m‐3 % Taxon no m‐3 % Taxon no m‐3 %Paracalanidae 106.85 38.59 Paracalanidae 64.31 33.74 Paracalanidae 158.31 45.16

Oncaea spp. 44.85 16.20 Oithona spp. 44.92 23.57 Oncaea spp. 49.27 14.05

Oithona spp. 35.79 12.93 Oncaea spp. 27.00 14.16 Oithona spp. 25.93 7.40

Corycaeus spp. 18.21 6.58 Corycaeus spp. 17.81 9.35 Corycaeus spp. 18.04 5.15

Appendicularians 9.97 3.60 Chaetognaths 5.24 2.75 Appendicularians 11.02 3.14

Ostracods 8.28 2.99 Ostracods 4.59 2.41 Chaetognaths 8.95 2.55

Chaetognaths 7.03 2.54 Lucicutia spp. 2.91 1.53 Copepod nauplii 8.44 2.41

Siphonophores 4.42 1.60 Euchaeta indica 2.04 1.07 Ostracods 8.40 2.39

Copepod nauplii 3.85 1.39 Shelled pteropods 2.02 1.06 Siphonophores 6.02 1.72

Lucicutia spp. 2.93 1.06 Siphonophores 2.01 1.06 Euterpina spp. 4.98 1.42

Shelled pteropods 2.50 0.90 Nannocalanus minor 1.39 0.73 Pareucalanus attenuatus 4.81 1.37

Pareucalanus attenuatus 2.41 0.87 Scolecithrix spp. 1.13 0.59 Subeucalanus spp. 3.30 0.94

Euchaeta indica 2.27 0.82 Polychaete larvae  1.10 0.58 Lucicutia spp. 3.09 0.88

Pleuromamma indica 1.83 0.66 Pareucalanus attenuatus 1.08 0.57 Polychaete larvae  2.85 0.81

Scolecithrix spp. 1.75 0.63 Haloptilis spp. 1.05 0.55 Lubbockia squillimana 2.83 0.81

Polychaete larvae  1.68 0.61 Appendicularians 0.98 0.51 Scolecithrix spp. 2.70 0.77

Subeucalanus spp. 1.20 0.43 Pleuromamma indica 0.91 0.48 Temora spp. 2.24 0.64

Euphausiid calyptopis 1.15 0.42 Macrosetella gracilis 0.88 0.46 Shelled pteropods 2.01 0.57

Euterpina spp. 1.13 0.41 Amphipods 0.88 0.46 Pleuromamma indica 1.97 0.56

Haloptilis spp. 1.05 0.38 Euphausiid furcilia 0.76 0.40 Euphausiid nauplii 1.74 0.50

All stations from upper 200m Anticyclonic stations (n=4) Cyclonic stations (n=7)

22

Table 4 (continued) 769

770

771

Taxon no m‐3 % Taxon no m‐3 % Taxon no m‐3 %Paracalanidae 101.36 34.89 Paracalanidae 86.51 38.64 Paracalanidae 148.41 35.18

Oncaea spp. 50.45 17.37 Oncaea spp. 38.66 17.27 Oncaea spp. 73.87 17.51

Oithona spp. 37.81 13.02 Oithona spp. 32.01 14.29 Oithona spp. 63.83 15.13

Corycaeus spp. 16.25 5.59 Corycaeus spp. 16.95 7.57 Corycaeus spp. 35.41 8.39

Appendicularians 15.06 5.18 Appendicularians 7.14 3.19 Appendicularians 16.96 4.02

Ostracods 11.11 3.82 Ostracods 6.70 2.99 Ostracods 11.23 2.66

Chaetognaths 7.41 2.55 Chaetognaths 5.54 2.47 Chaetognaths 10.34 2.45

Siphonophores 5.19 1.79 Siphonophores 3.15 1.41 Siphonophores 7.20 1.71

Copepod nauplii 5.19 1.79 Lucicutia spp. 2.98 1.33 Shelled pteropods 5.98 1.42

Lucicutia spp. 3.10 1.07 Shelled pteropods 2.76 1.23 Euchaeta indica 5.20 1.23

Pareucalanus attenuatus 3.04 1.05 Euchaeta indica 2.22 0.99 Copepod nauplii 3.50 0.83

Pleuromamma indica 2.56 0.88 Bivalve larvae 1.58 0.71 Scolecithrix spp. 2.86 0.68

Euchaeta indica 2.44 0.84 Pleuromamma indica 1.52 0.68 Polychaete larvae  2.60 0.62

Scolecithrix spp. 2.07 0.71 Haloptilis spp. 1.14 0.51 Pareucalanus attenuatus 2.16 0.51

Shelled pteropods 1.99 0.68 Copepod nauplii 1.06 0.47 Naked pteropods 2.02 0.48

Polychaete larvae  1.97 0.68 Scolecithrix spp. 0.91 0.41 Bivalve larvae 1.99 0.47

Salps 1.76 0.61 Pareucalanus attenuatus 0.91 0.40 Macrosetella gracilis 1.72 0.41

Euphausiid calyptopis 1.75 0.60 Euphausiid calyptopis 0.83 0.37 Lucicutia flavicornis 1.71 0.41

Subeucalanus spp. 1.42 0.49 Polychaete larvae  0.74 0.33 Euphausiid calyptopis 1.70 0.40

Rhincalanus rostrifrons 1.26 0.43 Nannocalanus minor 0.72 0.32 Pleuromamma indica 1.62 0.39

Shelf stations (n=2)Divergence stations (n=9) Frontal stations (n=11)

23

Table 5 772

Mean abundance (± SD) of mesozooplankton (no m-3) at all stations in the upper 200 m, and for 773 each station classification. 774

Classification  2007  2008 

All stations in upper 200m  276.66 ± 36.34 (n = 33)  192.07 ± 19.45 (n = 39) Anticyclonic stations  190.56 ± 26.35 (n = 4)  96.10 ± 10.23 (n = 6) Cyclonic stations  350.26 ± 46.58 (n = 7)  100.27 ± 11.66 (n = 2) Divergence stations  290.21 ± 36.80 (n = 9)  190.83 ± 19.99 ( n = 17) Frontal stations  223.79 ± 29.71 (n = 11)  128.57 ± 13.04 (n = 7) Shelf stations  421.02 ± 54.91 (n = 2)  367.09 ± 34.81 (n = 7)  775

776

24

Table 6 777

Results of ANOSIM routine to test the significance of factors shaping zooplankton assemblages 778 during 2007 and 2008. Significant effects shown in bold. 779

Year: taxonomic level and depth  Depth  Class  Time 

2007: species & taxa to 400m  R = 0.504; p < 0.1%  R = 0.083; p < 0.1%  R = 0.032; p < 4.8% 2007: species only to 400m  R = 0.511; p < 0.1%  R = 0.090; p < 0.1%  R = 0.028; p <5. 8% 2007: taxa only to 400m  R = 0.483; p < 0.1%  R = 0.060; p < 0.7%  R = 0.021; p <10.8% 2007: taxa only to 200m  R = 0.359; p < 0.1%  R = 0.097; p < 0.3%  R = 0.054; p < 3.3% 2008: taxa only to 200m  R = 0.230; p < 0.1%  R = 0.048; p < 8.6%  R = 0.034; p <5. 8%  780

781

25

List of figures 782 783 Fig. 1. Map showing zooplankton sampling locations during four cruises in the Mozambique 784 Channel. 785 786 Fig. 2. Contour plots of (A) mesozooplankton biovolume (ml 100 m-3), (B) temperature at 100 787 m, (C) sea level anomaly (cm) and (D) integrated chlorophyll a (mg m-3) during cruise MC07 788 (September 2007). Station numbers reflect sampling sequence. Depth contours indicated for 200, 789 500, 1000 and 2000 m. 790 791 Fig. 3. Contour plots of (A) mesozooplankton biovolume (ml 100 m-3), (B) temperature at 100 792 m, (C) sea level anomaly (cm) and (D) integrated chlorophyll a (mg m-3) during cruise MC08A 793 (December 2008). Station numbers reflect sampling sequence. Depth contours indicated for 200, 794 500, 1000 and 2000 m. 795 796 Fig. 4. Contour plots of (A) mesozooplankton biovolume (ml 100 m-3), (B) temperature at 100 797 m, (C) sea level anomaly (cm) and (D) integrated chlorophyll a (mg m-3) during cruise MC09B 798 (November 2009). Station numbers reflect sampling sequence. Station classification is indicated 799 by C (cyclonic), A (anticyclonic), D (divergence, F (frontal) or S (shelf). Depth contours 800 indicated for 200, 500, 1000 and 2000 m. 801 802 Fig. 5. Contour plots of (A) mesozooplankton biovolume (ml 100 m-3), (B) temperature at 100 803 m, (C) sea level anomaly (cm) and (D) integrated chlorophyll a (mg m-3) during cruise MC10A 804 (April/May 2010). Station numbers reflect sampling sequence. Station classification is indicated 805 by C (cyclonic), A (anticyclonic), D (divergence, F (frontal) or S (shelf). Depth contours 806 indicated for 200, 500, 1000 and 2000 m. 807 808 Fig. 6. Vertical distribution of (top) mesozooplankton biovolume (ml m-3), (middle) temperature 809 (°C) and (bottom) chlorophyll a (mg m-3) in the upper 200 m during cruises (A) MC07 and (B) 810 MC08A, and (top) mesozooplankton biovolume (ml m-3) and (bottom) temperature (°C) during 811 cruises (C) MC09B and (D) MC10A. Stations are displayed in order of sampling. C, A, D and S 812 indicate approximate location of cyclonic, anticyclonic, divergence and shelf stations. 813 814 Fig. 7. Zooplankton biovolume (ml m-3) as a function of (A) sampling depth (m), (B) water type 815 classification, (C) year of sampling, and (D) time of day for four cruises in the Mozambique 816 Channel. Least squares means and 95% confidence intervals are shown. 817 818 Fig. 8. Zooplankton biovolume (ml m-3) as a function of sampling depth and water type 819 classification for four cruises in the Mozambique Channel. Least squares means and 95% 820 confidence intervals are shown. 821 822 Fig. 9. Zooplankton biovolume (ml m-3) as a function of year and water type classification for 823 four cruises in the Mozambique Channel. Least squares means and 95% confidence intervals are 824 shown. 825 826

26

Fig.10. Results of non-metric multidimensional scaling analysis based on zooplankton 827 abundance within the upper 400 m during cruise MC07 showing (A) a gradient in 828 mesozooplankton assemblages from relatively shallow sampling strata (0-50 m) to relatively 829 deep strata (300-400 m), with clusters from a dendrogram at similarity levels of 40% (green line) 830 and 50% (blue line) superimposed; (B) relation of zooplankton assemblages according to water 831 type classification (divergence, cyclonic, frontal, anticyclonic or shelf). 832 833 Fig. 11. 3-d ordination plots resulting from non-metric multidimensional scaling analysis based 834 on abundance of zooplankton taxa within the upper 200 m showing (A) a gradient in 835 mesozooplankton assemblages with depth during cruise MC07, (B) grouping of zooplankton 836 assemblages according to water type classification (divergence, cyclonic, frontal, anticyclonic or 837 shelf) during MC07, (C) a gradient in mesozooplankton assemblages with depth during MC08A, 838 and (D) grouping of zooplankton assemblages according to water type classification during 839 MC08A. 840

841

27

Figure 1

28

Figure 2

(B) Temperature at 100 m (°C)

(D) Integrated chlorophyll a (mg m‐3)(C) Sea level anomaly (cm)

(A) Zooplankton biovolume (ml 100 m‐3)

29

Figure 3

(B) Temperature at 100 m (°C)

(D) Integrated chlorophyll a (mg m‐3)(C) Sea level anomaly (cm)

(A) Zooplankton biovolume (ml 100 m‐3)

30

Figure 4

(B) Temperature at 100 m (°C)

(D) Integrated chlorophyll a (mg m‐3)(C) Sea level anomaly (cm)

(A) Zooplankton biovolume (ml 100 m‐3)

31

Figure 5

(B) Temperature at 100 m (°C)

(D) Integrated chlorophyll a (mg m‐3)(C) Sea level anomaly (cm)

(A) Zooplankton biovolume (ml 100 m‐3)

32

Figure 6

(A) MC07 – September 2007 (B) MC08A ‐ December 2008

(C) MC09B ‐ November 2009 (D) MC10A ‐ April 2010

C C

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33

Figure 7

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34

Figure 8

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35

Figure 9

Mean Mean±0.95 Conf. Interval

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36

Figure 10

Transform: Fourth rootResemblance: S17 Bray Curtis similarity

2D Stress: 0.15

deep

shallow

Depth0-5050-100100-200200-300300-400

Similarity4050

(A)

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Transform: Fourth rootResemblance: S17 Bray Curtis similarity

2D Stress: 0.15

ClassDCFAS

MC07

MC07

37

Figure 11

Transform: Fourth rootResemblance: S17 Bray Curtis similarity

3D Stress: 0.13

Transform: Fourth rootResemblance: S17 Bray Curtis similarity

3D Stress: 0.13

Transform: Fourth rootResemblance: S17 Bray Curtis similarity

3D Stress: 0.13

Transform: Fourth rootResemblance: S17 Bray Curtis similarity

3D Stress: 0.13

Depth0-5050-100100-200

Depth0-5050-100100-200

ClassDCFAS

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(A) (B)

(C) (D)

MC07 MC07

MC08A MC08A