Temporal changes in the trophic ecology of the asymbiotic gorgonian Leptogorgia virgulata
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Gorgonians are widespread sub-littoral benthic suspension feeders in the world oceans. However, data on their trophic ecology and role in benthic–pelagic coupling and biogeochemical cycles remain limited. This study assesses the trophic ecology of Leptogorgia virgulata in the Skidaway River estuary, USA (31.9896N, 81.0242W) by analysing carbon and nitrogen isotopic signatures of its soft tissue and different-sized fractions of particulate organic matter (POM) in its environment. Samples were taken in 5 April, 2 August, and 15 October 2012 and 11 January 2013. Results support a distinct temporal shift in the diet of L. virgulata from the POM fraction <10 µm (i.e. pico- and nanoplankton) to the 10–63-µm fraction (i.e. microplankton). This trophic regime is likely associated with the natural abundance of prey items within these size classes, thus suggesting that L. virgulata may be an opportunistic feeder, and seasonal shifts in food availability in the water column affect its diet. As such small prey items affect the bioenergetics of L. virgulata, it is important to understand the implications of changes in food availability associated with environmental drivers on the physiology and population dynamics of this dominant species in the western Atlantic Ocean.
KeywordsParticulate Organic Matter Particulate Organic Carbon Isotopic Signature Trophic Ecology Western Atlantic Ocean
We are grateful to two anonymous reviewers for their comments. This project benefited from collaboration with the Skidaway River Monitoring Program (SRiMP) and the SRiMP team. SRiMP members who contributed to data collection and analysis included Laura Birsa, Tina Walters, Victoria Baylor, Megan Thompson, LaGina Fraizer, Kevin McKenzie, Paul Arkwright and Thais Bittar. The SRiMP program was partially funded by the US National Science foundation’s LTREB program (Award # 054312). Additional student support for SRiMP activities was provided by the US National Science Foundation under the auspices of the GK-12 program (Award # 0841162 to MEF) and the EDGE program (Award # GEO 0914633 to MEF). M.C.L. was supported by a PhD scholarship (SFRH/BD/63783/2009) funded by the Fundação para a Ciência e Tecnologia (QREN-POPH-Type 4.1—Advanced Training, subsidized by the European Social Fund and national funds Ministério da Educação e Ciência). Partial support was also provided by the US National Science Foundation to M.E.F. (awards OCE 0825999 and OCE 1031263) and J.C.N. (award OCE 0824499), C.F.P. was supported by the government of the Principality of Monaco.
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