Trophic interactions between jellyfish and fish ... · Trophic interactions between jellyfish and...
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Year 1980 1985 1990 1995 2000 2005 2010 2015 Forage fish biomass (kg ha -1 ), thousands 60 80 100 120 140 160 180 200 220 240 Jellyfish biomass (kg/ha), thousands 0 50 100 150 200 250 Forage fish 3-yr ave Jellyfish 3-yr ave Trophic interactions between jellyfish and fish: investigating the ecosystem impacts of jellyfish variability in the Bering Sea Mary Beth Decker 1 , *Kristin Cieciel 2 , Richard Brodeur 3 , James Ruzicka 4 Fig. 5. BASIS Surface Trawl survey grid Goal To measure spatial overlap of EBS jellyfish and forage fish by comparing spatial distributions observed in AFSC BASIS surveys from 2004 to 2012 (Fig. 5). Methods • Compared the center of gravity distributions of jellyfish and 4 forage fish species. • Calculated fish - jellyfish overlap using the Global Index of Colocation (GIC) statistic. • Significance of overlap tested with a Cramér-von Mises randomization test . Results • Capelin distributed in central Bering Sea; had the highest overlap with Chrysaora (Figs. 6 & 7). • Pacific herring distributed to the north; and overlapped the least with Chrysaora (Figs. 6 & 7). • Overall decrease in spatial overlap (except capelin) between the warm period (2004-2007) and the cooler period, 2009-2012 (Fig. 6). Did fish distributions change with climate? • Capelin and walleye pollock had the most years of significant overlap (4 of 8); cod and herring had significant overlap in only one year. Fig. 1B Fig. 9 Goal To investigate the role of jellyfish as competitors with forage fishes, as predators of the early life- history stages of commercial species and as ecosystem structuring agents. Model Development • The foundation of our analyses is the EBS food web model developed by Aydin et al. (2007). • We are redefining the lower trophic components of this model: 1) zooplankton community composition and biomass will be set using pelagic survey data; 2) Jellyfish biomass, diet, and consumption rates will be based on field and experimental observations obtained during this project Analyses • Structural scenarios visualize immediate implications of imposed changes (i.e., jellyfish abundance) to the food web. • Dynamic scenarios run across decades will reveal long-term compensatory responses and top-down feedback pressures. • Performed trial analyses (Figs. 8 & 9) with an updated version of the 2007 EBS model; Chrysaora biomass was redefined using BASIS survey data (2004-2013) and physiological parameters were redefined based upon a global review of zooplankton physiology compiled by Hirst (2003). Figure 8 shows the network of major trophic interactions in the EBS. • Top panel highlights in green the energy flow pathways supporting forage fish groups (walleye pollock, herring, capelin, smelts, sandlance), and highlights in red the higher trophic groups that are, in turn, supported by forage fishes. • Bottom panel shows the energy flow patterns supporting and supported by jellyfishes (Chrysaora). Line width and color intensity reflects strength of the trophic connections. Note that jellyfish are supported by a larger proportion of lower trophic level production but pass much less energy on to higher trophic levels than do forage fishes. Figure 9 shows the results of a structural scenario. Here, jellyfish biomass was reduced by 10%, and the effect on other groups is shown as relative changes in their production rates. • The effect upon other pelagic groups was a general increase in productivity. • Benthic groups also benefitted, but to a lesser extent than do groups in the pelagic food web. Chrysaora Fig. 7. Centers of gravity & variation Surface Trawl, 2004-2012 Herring Capelin Pollock Pac. cod cod Fig. 6. Comparison of Global Index of Collocation between Chrysaora and forage fishes Year 2004 2005 2006 2007 2008 2009 2010 2011 2012 Global index of collocation 0.0 0.2 0.4 0.6 0.8 1.0 Pacific Herring Walleye Pollock Capelin Pacific Cod Fig. 4. 3-year running means of forage fish & jellyfish in Bottom Trawl Survey Goals 1. To quantify interannual changes in jellyfish predation potential by examining jellyfish diets, prey digestion rates, and jellyfish abundances and distributions in AFSC surveys. 2. To measure dietary overlap of EBS jellyfish and forage fish by comparing diets collected during AFSC surveys. 3. Examine the interannual relationships between forage fish and jellyfish biomass to assess indices of potential jellyfish competition. Diet Collection • 43 jellyfish were collected with dip nets at 9 stations for diet analysis. • Preliminary diet results indicate presence of Limacina helicina, small copepods, and possible commensals: polychaetes and hyperiid amphipods. • Digestion experiments will be conducted in 2015-2016 • Additional stomach samples will be collected in 2015 & 2016 Competition • Time series of summer EBS Bottom Trawl surveys (Fig. 4) show an inverse relationship between jellyfish biomass and combined forage fish biomass (Pacific herring, age-0 walleye pollock, age-0 Pacific cod and capelin). • Jellyfish may be negatively impacting fish via predation and/or competition. • Where jellyfish-fish overlap is high, predation by jellyfish on fish and fish prey may be an important factor controlling the dynamics of commercially important fish species. Jellyfish predation on zooplankton and ichthyoplankton Ecosystem model analyses Project Objectives • Large scyphozoan jellyfish feed on zooplankton and early life stages of fish; they are competitors and predators of fish (Fig. 1). • Eastern Bering Sea (EBS) fishery surveys indicate that jellyfish populations have fluctuated widely over decades (Figs. 2 & 3). • Jellyfish population changes are related to variability in climate and prey. • An understanding of the role of jellyfish in the EBS is required for fishery and ecosystem management. • We lack measurements of the direct and indirect impact of changes in jellyfish abundance on the ecosystem and the fish species it supports. • We seek to estimate the scale and impact of competition between EBS forage fish and jellyfish. • Our goal is to determine the role of jellyfish in the ecosystem as a predator and as an ecosystem structuring agent. 1 Yale University, 2 Alaska Fisheries Science Center, 3 Northwest Fisheries Science Center, 4 Oregon State University Fig. 8 The recommendations and general content presented in this poster do not necessarily represent the views or official position of the Department of Commerce, the National Oceanic and Atmospheric Administration, or the National Marine Fisheries Service. Photo credits: Photos taken by NOAA employees and diet photos by Jared Weems Chrysaora melanaster collected for diet analysis Dip-netting for Chrysaora melanaster Chrysaora melanaster prey items Jellyfish collected with Surface Trawl Fig. 1. Conceptual diagram of energy transfer pathways in the EBS pelagic food web. Fig. 2. Time series of large jellyfish collected during the EBS Bottom Trawl survey. Fig. 3. Time series of large jellyfish collected during the EBS Surface Trawl survey. Spatial overlap analyses References: Aydin K, Gaichas SK, Ortiz I (2007) NOAA Tech. Memo. NMFS-AFSC-178. 298 pp. Hirst AG, Roff JC, Lampitt RS (2003) Advances in Marine Biology 44: 1-142.
Transcript of Trophic interactions between jellyfish and fish ... · Trophic interactions between jellyfish and...
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Trophic interactions between jellyfish and fish: investigating the ecosystem impacts of jellyfish variability in the Bering Sea
Mary Beth Decker1, *Kristin Cieciel2, Richard Brodeur3, James Ruzicka4
Fig. 5. BASIS Surface Trawl survey grid
Goal To measure spatial overlap of EBS jellyfish and forage fish by comparing spatial distributions observed in AFSC BASIS surveys from 2004 to 2012 (Fig. 5). Methods • Compared the center of gravity distributions of jellyfish and 4 forage fish species. • Calculated fish - jellyfish overlap using the Global Index of Colocation (GIC)
statistic. • Significance of overlap tested with a Cramér-von Mises randomization test . Results • Capelin distributed in central Bering Sea; had the highest overlap with Chrysaora
(Figs. 6 & 7). • Pacific herring distributed to the north; and overlapped the least with Chrysaora
(Figs. 6 & 7). • Overall decrease in spatial overlap (except capelin) between the warm period
(2004-2007) and the cooler period, 2009-2012 (Fig. 6). Did fish distributions change with climate?
• Capelin and walleye pollock had the most years of significant overlap (4 of 8); cod and herring had significant overlap in only one year.
Fig. 1B
Fig. 9
Goal To investigate the role of jellyfish as competitors with forage fishes, as predators of the early life-history stages of commercial species and as ecosystem structuring agents. Model Development • The foundation of our analyses is the EBS food web model developed by Aydin et al. (2007). • We are redefining the lower trophic components of this model:
1) zooplankton community composition and biomass will be set using pelagic survey data; 2) Jellyfish biomass, diet, and consumption rates will be based on field and experimental
observations obtained during this project Analyses • Structural scenarios visualize immediate implications of imposed changes (i.e., jellyfish
abundance) to the food web. • Dynamic scenarios run across decades will reveal long-term compensatory responses and
top-down feedback pressures. • Performed trial analyses (Figs. 8 & 9) with an updated version of the 2007 EBS model;
Chrysaora biomass was redefined using BASIS survey data (2004-2013) and physiological parameters were redefined based upon a global review of zooplankton physiology compiled by Hirst (2003).
Figure 8 shows the network of major trophic interactions in the EBS. • Top panel highlights in green the energy flow pathways supporting forage fish groups
(walleye pollock, herring, capelin, smelts, sandlance), and highlights in red the higher trophic groups that are, in turn, supported by forage fishes.
• Bottom panel shows the energy flow patterns supporting and supported by jellyfishes (Chrysaora). Line width and color intensity reflects strength of the trophic connections. Note that jellyfish are supported by a larger proportion of lower trophic level production but pass much less energy on to higher trophic levels than do forage fishes.
Figure 9 shows the results of a structural scenario. Here, jellyfish biomass was reduced by 10%, and the effect on other groups is shown as relative changes in their production rates. • The effect upon other pelagic groups was a general increase in productivity. • Benthic groups also benefitted, but to a lesser extent than do groups in the pelagic food web.
Chrysaora
Fig. 7. Centers of gravity & variation Surface Trawl, 2004-2012
Herring Capelin Pollock Pac. cod cod
Fig. 6. Comparison of Global Index of Collocation between Chrysaora and forage fishes
Year2004 2005 2006 2007 2008 2009 2010 2011 2012
Glo
bal i
ndex
of c
ollo
catio
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0.2
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Pacific HerringWalleye PollockCapelinPacific Cod
Fig. 4. 3-year running means of forage fish & jellyfish in Bottom Trawl Survey
Goals 1. To quantify interannual changes in jellyfish predation potential by examining jellyfish
diets, prey digestion rates, and jellyfish abundances and distributions in AFSC surveys. 2. To measure dietary overlap of EBS jellyfish and forage fish by comparing diets
collected during AFSC surveys. 3. Examine the interannual relationships between forage fish and jellyfish biomass to
assess indices of potential jellyfish competition. Diet Collection • 43 jellyfish were collected with dip nets at 9 stations for diet analysis. • Preliminary diet results indicate presence of Limacina helicina, small copepods, and
possible commensals: polychaetes and hyperiid amphipods. • Digestion experiments will be conducted in 2015-2016 • Additional stomach samples will be collected in 2015 & 2016
Competition
• Time series of summer EBS Bottom Trawl surveys (Fig. 4) show an inverse relationship between jellyfish biomass and combined forage fish biomass (Pacific herring, age-0 walleye pollock, age-0 Pacific cod and capelin).
• Jellyfish may be negatively impacting fish via predation and/or competition.
• Where jellyfish-fish overlap is high, predation by jellyfish on fish and fish prey may be an important factor controlling the dynamics of commercially important fish species.
Jellyfish predation on zooplankton and ichthyoplankton Ecosystem model analyses
Project Objectives • Large scyphozoan jellyfish feed on zooplankton and early life stages of
fish; they are competitors and predators of fish (Fig. 1).
• Eastern Bering Sea (EBS) fishery surveys indicate that jellyfish populations have fluctuated widely over decades (Figs. 2 & 3).
• Jellyfish population changes are related to variability in climate and prey.
• An understanding of the role of jellyfish in the EBS is required for fishery and ecosystem management.
• We lack measurements of the direct and indirect impact of changes in jellyfish abundance on the ecosystem and the fish species it supports.
• We seek to estimate the scale and impact of competition between EBS forage fish and jellyfish.
• Our goal is to determine the role of jellyfish in the ecosystem as a predator and as an ecosystem structuring agent.
1 Yale University, 2 Alaska Fisheries Science Center, 3 Northwest Fisheries Science Center, 4 Oregon State University
Fig. 8
The recommendations and general content presented in this poster do not necessarily represent the views or official position of the Department of Commerce, the National Oceanic and Atmospheric Administration, or the National Marine Fisheries Service. Photo credits: Photos taken by NOAA employees and diet photos by Jared Weems
Chrysaora melanaster collected for diet analysis
Dip-netting for Chrysaora melanaster
Chrysaora melanaster prey items
Jellyfish collected with Surface Trawl
Fig. 1. Conceptual diagram of energy transfer pathways in the EBS pelagic food web.
Fig. 2. Time series of large jellyfish collected during the EBS Bottom Trawl survey.
Fig. 3. Time series of large jellyfish collected during the EBS Surface Trawl survey.
Spatial overlap analyses
References: Aydin K, Gaichas SK, Ortiz I (2007) NOAA Tech. Memo. NMFS-AFSC-178. 298 pp. Hirst AG, Roff JC, Lampitt RS (2003) Advances in Marine Biology 44: 1-142.
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