Papers and Publications: Interdisciplinary Journal ofUndergraduate Research

Volume 3 Article 14

8-26-2014

Coral preference of the polychaete Spirobranchusgiganteus in the Belize Barrier ReefEthan EvansSewanee: The University of the South,

Callie OldfieldSewanee: The University of the South,

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Recommended CitationEvans, Ethan and Oldfield, Callie (2014) "Coral preference of the polychaete Spirobranchus giganteus in the Belize Barrier Reef,"Papers and Publications: Interdisciplinary Journal of Undergraduate Research: Vol. 3, Article 14.Available at: http://digitalcommons.northgeorgia.edu/papersandpubs/vol3/iss1/14

INTRODUCTION

On coral reefs, there are numerous symbiotic relationships among reef organisms

(Goldberg 2013). Many of these symbioses are commensalisms, in which one participant (the

commensal) benefits while the other participant (the host) is unaffected. However, there are

some instances of reef commensalisms in which the host inadvertently benefits (Glynn and

Nochs 2011). For example, xanthid crabs that carry coral fragments as protection can potentially

help these fragments become established in different areas (Lamberts and Garth1977).

Spirobranchus giganteus (the Christmas tree worm) is a polychaete that commonly burrows in

corals in what is likely a commensalistic relationship (Gibbs 1969). The polychaete may offer

benefits to the coral host, such as greater water circulation from filter-feeding and nutrients from

its waste (Ben-Tzvi et al. 2006). Further, coral colonies in the immediate vicinity of the

polychaete may be protected from coral-feeding fish, facilitating coral colony regrowth after

heavy predation (DeVantier et al. 1986). This polychaete-coral relationship occurs in only certain

species of coral, because of the settlement preferences of the polychaete larvae (Marsden 1987).

The Christmas tree worm reproduces by mass spawning. Larvae are not sessile like adults

and swim until they find a suitable coral colony for settlement (Qian 1999). In a laboratory

preference study, Marsden (1987) demonstrated larval settlement preference on the coral species

Acropora prolifera. Populations of the genus Acropora have been severely reduced in the Belize

Barrier Reef over the last 30 years because of extreme weather and disease (Aronson et al. 2002).

A field study of coral preference performed in Barbados (Conlin 1988) determined that the coral

genus Diplora was the most preferred by S. giganteus. Hunte et al. (1990) demonstrated that S.

giganteus individuals thrive and grow larger on Diplora when compared to other coral

substrates.

Goldberg (2013) hypothesized that S. giganteus host preference may vary within large

geographical areas. In addition, coral preference by S. giganteus could result from preference of

larvae for a particular coral substrate color. Little is known about the abundance of S. giganteus

color morphs, but investigations on color morph spatial patterns in other genera of polychaetes

have been published. Crisp and Ekaratne (1984) noted that the distribution of Pomatoceros

triqueter color morphs was correlated with latitudinal gradients, but found no spatial pattern in P.

lamarckii. Rankin (1946) determined that the distribution of color morphs in Clymenella

torquata was related to environmental conditions, with flesh-colored individuals associated with

sandy substrates and green individuals associated with muddy areas.

The purpose of this study was two-fold. We investigated (1) whether S. giganteus prefers

a specific coral host in the Belize Barrier Reef (the second largest barrier reef system in the

world), thus testing Goldberg’s (2013) hypothesis that geographic variations exist in host

preference behavior of this polychaete. The Conlin (1988) study in Barbados was used for

comparison. In addition, we investigated (2) whether S. giganteus color morphs are associated

with coral preference.

METHODS

Data was collected from two patch reefs: Whale Shoals (16° 46’ 39.39”N 88° 06’

53.41”W) and Long Reef (16° 46’ 43.78”N, 88° 04’ 44.09”W), in May 2013 along the Belize

Barrier Reef south of Carrie Bow Cay. To assess coral composition, six 10 m length transects

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Evans and Oldfield: Coral preference of Spirobranchus giganteus in the Belize Barrier Reef

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were placed parallel and at regular intervals within a 100 by 100 m study area at each site. We

identified all mounding corals to the level of genus including Diplora, Porites, and Montastraea.

Five 0.5 by 0.5 m quadrats were placed at 1.5 m intervals along each transect. In each quadrat, an

estimate was made of the percent composition of each genus. To determine S. giganteus settling

patterns, an investigator searched the study area in each site by moving at a constant pace along

parallel transects. We searched for S. giganteus individuals for the duration of 40 min at each

site. For each individual, we recorded the color of the stalk of the worm’s branchial crown and

coral substrate on which it was found. Color was classified as red, white, or yellow (Fig. 1).

To calculate the expected number of S. giganteus per coral species, the total number of

worms found for each site was multiplied by the percent cover of each coral species. Chi-squared

tests were used to test for patterns of substrate preference and for color morph association with

coral genera.

RESULTS

In both sites, S. giganteus preferred Diplora to the genera Porites and Montastraea (Fig.

2). At Whale Shoals, despite making up a small percentage of the overall coral cover (7.7%),

Diplora hosted a significantly higher (χ2 = 150.29, df = 2, p < 0.0001) percentage of S.

giganteus. Porites, even though it was the most abundant coral (80.5% of coral cover), hosted a

significantly lower percentage (χ2 = 12.12, df = 2, p = 0.0023) of S. giganteus. The number of S.

giganteus found on Montastraea was insufficient for proper analysis, despite having a similar

percent coral cover (11.9%) to Diplora. The S. giganteus individuals exhibited similar

preferences in Long Reef; the majority of the coral composition was Porites (77.9%), but fewer

than predicted S. giganteus were observed on the coral (χ2 = 9.75, df = 2, p = 0.0076). Diplora

made up slightly more of the coral composition at Long Reef (18.2%), and more worms than

expected were observed there (χ2 = 50.01, df = 2, p < 0.0001).

In both sites, red was the dominant color morph, regardless of coral substrate (Fig. 3).

The two study sites showed different trends in S. giganteus color morph in relation to coral genus

distributions. In Whale Shoals, there was no significant color morph association with coral

genus. In Long Reef, there was a significant positive color association between Diplora and red

color morphs (χ2 = 10.01, df = 2, p = 0.0067) (Fig. 1), and a significant negative association

between Diplora and yellow color morphs (χ2 = 9.33, df = 2, p = 0.0094).

Figure 1. Red

color morph S.

giganteus on

Diplora coral

substrate

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A.

B.

Figure 2. Percent coral composition and percent S. giganteus individuals found on coral

substrate at Whale Shoals (A) and Long Reef (B)

A. Significantly fewer S. giganteus were found on Porites and significantly more S. giganteus on

Diplora at Whale Shoals. The number of S. giganteus found on Montastraea was insufficient for

proper analysis. B. The S. giganteus individuals exhibited similar preferences in Long Reef;

Porites made up the majority of the coral composition, but more worms were found on Diplora.

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Evans and Oldfield: Coral preference of Spirobranchus giganteus in the Belize Barrier Reef

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A.

B.

Figure 3. Percentage of color morphs per coral genus at Whale Shoals and Long Reef

A. Data from Whale Shoals shows a random distribution of color morphs on Porites, but non-

random trends on Diplora for yellow and red color morphs. B. Long Reef had a slightly different

distribution, with significant negative association with yellow and positive association with red

morphs. The white color morph displayed no significant association in either site. We did not

observe S. giganteus on Montastrea coral on Long Reef.

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DISCUSSION

S. giganteus were most frequently found on corals in the genus Diplora. This settlement

preference for Diplora in the Belize Barrier Reef matches a similar pattern found by Conlin

(1988) in Barbados and therefore does not support the Goldberg (2013) hypothesis that there is

likely to be geographical variation in substrate preference. Diplora made up a small percentage

of the overall coral composition, yet settlement rates were significantly higher than on Porites or

Monastraea, so it is evident that S. giganteus were not randomly distributed among corals. The

non-random distribution may be a result of larval preference or differential mortality (Conlin

1988). Data regarding settlement on Montastraea was inconclusive due to the rarity of the coral

at the two study sites. The limited S. giganteus settlement could be related to the depth at which

the coral is found within the study site (Conlin 1988).

Although there were site-specific associations between worm color and coral substrate,

there were no significant overall trends between the two sites. The random distribution of color

morphs may reflect density-independent pressure from predation and habitat constraints.

Previous studies in the Red Sea have shown that a wide variety and even distribution of different

color morphs prevents predators from forming an association of S. giganteus with a certain color

morph (Grassle 1973). Further, the Indo-Pacific region hosts a variety of S. giganteus colors not

found in the Caribbean, such as blue, brown, and purple. The cause of these regional effects is

unclear. Even in our small-scale study, the color morphs varied greatly between the two sites.

Environmental stress and other abiotic factors, such as depth and temperature, may also

contribute to varying color morph distribution (Etter 1988). Whether these factors relate to S.

giganteus settlement preferences is an area of future research.

While our data and that of Conlin (1988) suggests S. giganteus preference is strongly

linked with Diplora in the Caribbean basin, studies on the Great Barrier Reef (Marsden 1988)

and in Taiwan (Dai and Yang 1995) demonstrated that S. giganteus is not solely dependent on

one species of coral for survival. Many factors influence S. giganteus larval preference, including

depth, prevalence of light, and percent coral cover (Marsden 1984). It is likely that the larval

preference towards Diplora is due to the expansive size and surface area of Diplora colonies, as

well as the relative depth of Diplora in the Belize Barrier Reef (Conlin 1988).

In reef ecosystems, mutualistic and commensalistic relationships among organisms are

common (Goldberg 2013). This interdependence between species makes them vulnerable to the

loss of either partner (Kohl et al. 2004). Corals are especially vulnerable to environmental threats

such as acidification, bleaching, extreme weather, eutrophication, or disease. Each coral species

has a different susceptibility to these threats (Burke and Maidens 2004). Diplora coral have been

shown to be less susceptible to coral bleaching in the Caribbean as compared to species in other

coral genera (van Hooidonk et al. 2012). Our results show a strong preference by S. giganteus

towards Diplora as a coral substrate. If this commensalism is a result of the resilience of Diplora

to environmental pressures, S. giganteus may be showing a preference towards coral types that

are less susceptible to bleaching. However, if this preference is obligatory, a future decline in

Diplora could cause a decline in S. giganteus abundance. Our study was located in the Caribbean

region, which contains some of the most endangered reef systems in the world (Burke and

Maidens 2004). In the two coral reefs we studied, we found a lower density of polychaete worms

(fewer than five per square meter) than seen in previous studies of other systems (Conlin 1988).

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Evans and Oldfield: Coral preference of Spirobranchus giganteus in the Belize Barrier Reef

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Whether S. giganteus abundance is linked to coral decline is a question that is worthy of future

study in the Caribbean region.

LITERATURE CITED

Aronson, R., I. G. Macintyre, W. F. Precht, T. J. Murdoch, and C. M. Wapnick. 2002. The

expanding scale of species turnover events on coral reefs in Belize. Ecological

Monographs 72: 233-249.

Ben-Tzvi, O., S. Einbinder, and E. Brokovich. 2006. A beneficial association between a

polychaete worm and a scleranctinin coral. Coral Reefs 25: 98.

Burke, L. and J. Maidens. 2004. Reefs at risk in the Caribbean. World Resources Institute,

Washington, D.C. 4: 41-51.

Conlin, B. 1988. Aspects of habitat selection by a tropical serpulid polychaete Spirobranchus

giganteus. PhD Thesis. McGill University.

Crisp, D. J. and K. Ekaratne. 1984. Polymorphism in Pomatoceros. Zoological Journal of the

Linnean Society 80: 157-175.

Dai, C. F. and P. H. Yang. 1995. Distribution of Spirobranchus giganteus corniculatus (Hove)

on the coral reefs of southern Taiwan. Zoological Studies 34: 117-125.

DeVantier, L. M., R. E. Reichelt, and R. H. Bradbury. 1986. Does Spirobranchus giganteus

protect host Porites from predation by Acanthaster planci: predator pressure as a

mechanism of coevolution? Marine Ecology – Progress Series 32: 307-310.

Etter, R. J. 1988. Physiological stress and color polymorphism in the intertidal snail Nucella

lapillus. Evolution 42: 660-680.

Gibbs, P. E. 1969. Aspects of polychaete ecology with particular reference to commensalism.

Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences

255: 443-458.

Glynn, P. W. and I. C. Nochs. 2011. Invertebrates and their roles in coral reef ecosystems. Coral

Reefs: An Ecosystem in Transition. Springer 273-325.

Goldberg, W. M. 2013. The biology of reefs and reef organisms. University of Chicago Press,

Chicago, Illinois, USA.

Grassle, J. F. 1973. Variety in coral reef communities. Biology and Geology of Coral Reefs

Volume II, ed. O. A. Jones and R. Endean. Academic Press.

Hunte, W., B. E. Conlin, and J. R. Marsden. 1990. Habitat selection in tropical polychaete

Spirobranchus giganteus. Marine Biology 104: 87-92.

Kohl, L. P., R. R. Dunn, N. S. Sodhi, R. K. Colwell, H. C. Proctor, and V. S. Smith. 2004.

Species coextinctions and the biodiversity crisis. Science 305: 1632–1634.

6

Papers and Publications: Interdisciplinary Journal of Undergraduate Research, Vol. 3 [2014], Art. 14

http://digitalcommons.northgeorgia.edu/papersandpubs/vol3/iss1/14

Lamberts, A. E. and J. S. Garth. 1977. Coral-crab commensalism in xanthids. Pacific Science

31(3): 245-247.

Marsden, J. R. 1984. Swimming in response to light by larvae of the tropical serpulid

Spirobranchus giganteus. Marine Biology 83: 13-16.

Marsden, J. R. 1987. Coral preference behaviour by planktotrophic larvae of Spirobranchus

giganteus corniculatus (Serpulidae: Polychaeta). Coral Reefs 6: 71-74.

Qian, P. 1999. Larval settlement of polychaetes. Developments in Hydrobiology 142: 239-253.

Rankin, J. S. 1946. Notes on the ecology of the polychaete annelid Clymenella torquata

(Leidy), with particular reference to color variation. Ecology 27: 262-264.

van Hooidonk, R. J., D. P. Manzello, J. Moye, M. E. Brandt, J. C. Hendee, C. McCoy, and C.

Manfrino. 2012. Coral bleaching at Little Cayman, Cayman Islands 2009. Estuarine,

Coastal, and Shelf Science 106: 80-84.

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Evans and Oldfield: Coral preference of Spirobranchus giganteus in the Belize Barrier Reef

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