Comparisons of fatty acid and stable isotope ratios in symbiotic and non-symbiotic brittlestars from Oban Bay, Scotland

The bed-forming brittlestars Ophiothrix fragilis, Ophiocomina nigra and Amphiura chiajei from Oban Bay, Scotland were studied using methods previously employed to study chemoautotrophic symbioses. Ophiothrix fragilis and A. chiajei both contain symbiotic bacteria (SCB) while Ophiocomina nigra is non-symbiotic. Samples were taken of Ophiothrix fragilis at approximately two-week intervals for one year. Symbiotic bacteria numbers were determined by direct counting of homogenates of the arms of 50 individual brittlestars. Water samples were analysed for chlorophyll content. Stable isotope ratios for carbon and nitrogen were determined for each homogenate sample. Regular SCB counts were made on the infaunal brittlestar A. chiajei. Homogenate samples of Ophiothrix fragilis, A. chiajei and the non-symbiotic Ophiocomina nigra were analysed to produce fatty acid profiles for each species. Symbiotic bacteria count varied by up to one order of magnitude in both Ophiothrix fragilis and A. chiajei with no evidence of seasonality in this variation. Symbiotic bacteria number was inversely correlated with δ15N but no relationship was established with δ13C. 16:1ω7 and 18:1.ω7 fatty acids were used as putative bacterial markers. Both symbiotic species had higher percentages of 16:1ω7 than the non-symbiotic Ophiocomina nigra. However, only Ophiothrix fragilis appeared to receive appreciable quantities of 18:1ω7 from its SCB. The SCB are heterotrophic and may contribute to the nitrogen budget of the host. The two symbiotic species studied here derive the bulk of their nutrition from conventional feeding but SCB make significant, additional contributions.

[1]  J. Buchanan.  A Comparative Study of Some Features of the Biology of Amphiura Filiformis and Amphiura Chiajei [Ophiuroidea] Considered in Relation to their Distribution , 1964, Journal of the Marine Biological Association of the United Kingdom.

[2]  K. Nealson,et al.  The Fine Structure of the Echinoderm Cuticle and the Subcuticular Bacteria of Echinoderms , 1978 .

[3]  D. Siebers.  Transintegumentary Uptake of Dissolved Amino Acids in the Sea Star Asterias rubens. A Reassessment of its Nutritional Role with Special Reference to the Significance of Heterotrophic Bacteria , 1979 .

[4]  G. J. Perry,et al.  Fatty acids of bacterial origin in contemporary marine sediments , 1979 .

[5]  J. Waterbury,et al.  Prokaryotic Cells in the Hydrothermal Vent Tube Worm Riftia pachyptila Jones: Possible Chemoautotrophic Symbionts. , 1981, Science.

[6]  G. Rau.  Hydrothermal Vent Clam and Tube Worm 13C/12C: Further Evidence of Nonphotosynthetic Food Sources. , 1981, Science.

[7]  J. Sargent,et al.  Fatty acid compositions of neutral glycerides from the ovaries of the asteroids Ctenodiscus crispatus, Asterias lincki and Pteraster militaris from Balsfjorden, northern Norway , 1983 .

[8]  G. Duineveld,et al.  Observations on the population dynamics of amphiura filiformis (ophiuroidea: echinodermata) in the southern north sea and its exploitation by the dab, Limanda limanda , 1986 .

[9]  W. Christie.  Gas Chromatography and Lipids , 1989 .

[10]  P. Nichols,et al.  Fatty acid and lipid composition of 10 species of microalgae used in mariculture , 1989 .

[11]  F. Neidhardt,et al.  Physiology of the bacterial cell : a molecular approach , 1990 .

[12]  M. Janquín,et al.  Ammonium excretion by the ophiuridOphiothrix fragilis as a function of season and tide , 1991 .

[13]  T. Boutton.  11 – Stable Carbon Isotope Ratios of Natural Materials: II. Atmospheric, Terrestrial, Marine, and Freshwater Environments , 1991 .

[14]  C. Hily.  Is the activity of benthic suspension feeders a factor controlling water quality in the Bay of Brest , 1991 .

[15]  J. Brooks,et al.  Stable isotope partitioning in seep and vent organisms: chemical and ecological significance , 1992 .

[16]  M. Johnson,et al.  Endosymbiotic Bacterial Contribution in the Carbon Nutrition of Loripes lucinalis (Mollusca: Bivalvia) , 1994 .

[17]  J. Mckenzie,et al.  Comparative study of sub-cuticular bacteria in brittlestars (Echinodermata: Ophiuroidea) , 1994, Marine Biology.

[18]  R. Michener.  Stable isotope ratios as tracers in marine aquatic food webs , 1994 .

[19]  P. Dando,et al.  Fatty Acids of Hydrothermal Vent Ridgeia Piscesae and Inshore Bivalves Containing Symbiotic Bacteria , 1995, Journal of the Marine Biological Association of the United Kingdom.

[20]  J. Mckenzie,et al.  Echinoderms and oil pollution: A potential stress assay using bacterial symbionts , 1995 .

[21]  J. Mckenzie,et al.  Survey of the occurrence and morphology of sub-cuticular bacteria in shelf echinoderms from the north-east Atlantic Ocean , 1995 .

[22]  I. Gilmour,et al.  Carbon isotopic analysis of the free fatty acids in a tridacnid―algal symbiosis: interpretation and implications for the symbiotic association , 1995, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[23]  M. Barker,et al.  The Incidence and Morphology of Subcuticular Bacteria in the Echinoderm Fauna of New Zealand. , 1995, The Biological bulletin.

[24]  J. Sargent,et al.  Lipid and lipid carbon stable isotope composition of the hydrothermal vent shrimp Mirocaris fortunata: evidence for nutritional dependence on photosynthetically fixed carbon , 1997 .

[25]  J. Sargent,et al.  Stable-Carbon-Isotope Composition of Fatty Acids in Hydrothermal Vent Mussels Containing Methanotrophic and Thiotrophic Bacterial Endosymbionts , 1998, Applied and Environmental Microbiology.