Natural heterotrophic feeding by a temperate octocoral with symbiotic zooxanthellae: a contribution to understanding the mechanisms of die-off events
- 329 Downloads
Octocorals are among the most emblematic and representative organisms of sublittoral communities in both tropical and temperate seas. Eunicella singularis is the most abundant gorgonian in shallow waters and the only gorgonian with symbiotic zooxanthellae in the Mediterranean Sea. We studied the natural diet and prey capture rate of this species over an annual cycle and characterized prey digestion time over the natural temperature regime. The species captured zooplankton prey between 40 and 920 µm. A mean content of 0.14 ± 0.02 prey polyp−1 was observed throughout the year. The strong pattern of decrease in digestion time with temperature increase (from 25 h at 13 °C to 8 h at 21 °C) allowed us to estimate that the prey capture rate was 0.017 ± 0.002 prey polyp−1 h−1 (mean ± SE); the ingestion rate exhibited a seasonal pattern with higher values in spring (0.007 µg C polyp−1 h−1). Feeding on zooplankton had a low contribution to the respiratory expenses of E. singularis except in early spring. Then, heterotrophic nutrition in the natural environment seems unable to meet basal metabolic requirements, especially in summer and fall. This result, in conjunction with the documented collapse of photosynthetic capacity above a warm temperature threshold, indicates the occurrence of a resource acquisition limitation that may play a role in the repeated summer die-off events of the species.
KeywordsNatural diet Capture rate Digestion time Feeding ecology Gorgonians Eunicella singularis
We thank Esther Jordana and Antonio Canepa for helping with the research. We are grateful to the “Parc Natural del Montgrí, les Illes Medes i el Baix Ter” and “Parc Natural del Cap de Creus” for their continuous support. Financial support was provided by the Spanish Government under the projects ENCHANGES (CGL2010-18466) and CSI-Coral (CGL2013-43106-R). This is a contribution from the Marine Biogeochemistry and Global Change Research group from the Generalitat de Catalunya (2014SGR1029).
- Ballesteros E (2006) Mediterranean coralligenous assemblages: a synthesis of present knowledge. Oceanogr Mar Biol Annu Rev 44:123–195Google Scholar
- Barangé M, Zabala M, Riera T, Gili JM (1989) A general approach to the in situ energy budget of Eudendrium racemosum (Cnidaria, Hydrozoa) in the Western Mediterranean. Sci Mar 53:423–427Google Scholar
- Biswas AK, Biswas MR (1979) Handbook of environmental data and ecological parameters, vol 6. Environmental sciences and applications, Pergamon, OxfordGoogle Scholar
- Dobson AJ, Barnett AG (2008) An introduction to generalized linear models. CRC Press, Boca Raton, FloridaGoogle Scholar
- Estrada M (1996) Primary production in the northwestern Mediterranean. Sci Mar 60:55–64Google Scholar
- Faganeli J, Malej A, Pezdič J, Malačič V (1988) C:N: P ratios and stable isotopic ratios as indicators of sources of organic matter in the Gulf of Trieste (Northern Adriatic). Oceanologica Acta 11:377–382Google Scholar
- Gori A, Viladrich N, Gili JM, Kotta M, Cucio C, Magni L, Bramanti L, Rossi S (2012) Reproductive cycle and trophic ecology in deep versus shallow populations of the Mediterranean gorgonian Eunicella singularis (Cap de Creus, northwestern Mediterranean Sea). Coral Reefs 31:823–837CrossRefGoogle Scholar
- Kinzie RA III (1973) The zonation of West Indian gorgonians. Bull Mar Sci 23:93–155Google Scholar
- Llorente-Llurba E (2011) Dieta i taxes de captura estacionals en Eunicella singularis Esper 1794. M.Sc. thesis, University of Barcelona, p 34Google Scholar
- Martinussen MB, Båmstedt U (2001) Digestion rate in relation to temperature of two gelatinous planktonic predators. Sarsia 86:21–35Google Scholar
- Rossi S (2002) Environmental factors affecting the trophic ecology of benthic suspension feeders. Ph.D. thesis, University of Barcelona, p 200Google Scholar