Lipid profiles of deep-sea organisms.
University of Southampton, Faculty of Science, School of Ocean and Earth Science,
Lipids are a group of biologically important compounds that may be used as indicators of relationships
between an organism and its environment. Lipid class composition identifies types of storage lipid which
can suggest a pelagic or benthic existence and may be used to measure the condition of an organism. Fatty
acid composition may reflect trophic ecology. Lipid profiling has been used to elucidate elements of the
ecology of organisms from Mid-Atlantic and Juan de Fuca Ridge hydrothermal vents and shrimp from
below a permanent oxygen minimum zone. Lipid profiles of these organisms from extreme deep-sea
environments are compared.
Lipid profiles of adult Mid-Atlantic Ridge hydrothermal vent shrimp, Rimicaris exoculata. support a
benthic existence and primarily chemoautotrophic bacterial nutrition. Postlarval alvinocarid shrimp lipid
profiles suggest a pelagic life cycle stage with a reliance on phototrophically derived organic matter. This
result supports previous molecular evidence that Rimicaris exoculata travels between hydrothermal vents
on the Mid-Atlantic Ridge. The branchial area of Rimicaris exoculata has been reported to be colonised
with bacteria and elevated levels of bacterial fatty acids are present in these tissues. Lipid analyses of the
reproductive organs of Rimicaris exoculata reveal increases in triglycerides, sterols, phosphatidyl choline
and the proportion of n-3 fatty acids with advancing reproductive maturity. Preliminary studies of the lipid
profiles of the Mid-Atlantic vent shrimp Alvinocaris markensis support the hypothesis that it is a scavenger
and contains a lower proportion of bacterially derived fatty acids.
The lipid profiles of the deep-sea shrimp, Nematocarcinus gracilis, from the Indian Ocean, were
consistent with a benthic lifestyle, opportunistic feeding and a reliance on phototrophically derived organic
matter. Despite the presence of a permanent oxygen minimum zone above the habitat of the shrimp,
Nematocarcinus gracilis contain low levels of highly unsaturated fatty acids, reflecting a reduction in the
availability of labile organic matter with depth.
The hydrothermal vent tube worm Ridgeia piscesae contains only low levels of storage lipid, reflecting an
extreme reliance on endosymbiotic bacteria. Wax esters detected are thought to be stored in oocytes. The
fatty acid profile of Ridgeia piscesae reveal mainly bacterial biomarker fatty acids, but some
phototrophically derived fatty acids are also present. Adult Ridgeia piscesae have no gut, so the
mechanism by which these fatty acids are assimilated is uncertain.
Lipid profiles of the hydrothermal vent palm worm, Paralvinella palmiformis vary with the conditions of
the different microenvironments in which specimens were found. Fatty acids reflect a mixed diet based
mainly on chemoautotrophic bacteria, but with significant inputs of phototrophically derived organic
matter, such as diatom debris.
Phototrophically derived fatty acids were also detected in the hydrothermal vent clam Calyptogena
pacifica. suggesting that the reduced filter-feeding ability of this species is used to supplement nutrition
from endosymbiotic bacteria. Endosymbiont-bearing gill tissues contain the highest proportion of bacterial
fatty acids and also high concentrations of triglycerides. The presence of triglycerides in gill tissues
suggests that energy may be transferred from symbionts by hydrolysis of bacterial symbiont membrane
lipids and their conversion to triglyceride.
The lipid profiles presented in this work increase understanding of the life history strategies and ecology
of the species studied. This thesis shows that even the most highly adapted hydrothermal vent organisms
do not rely solely on a chemoautotrophic source of nutrition, but also appear to require phototrophically
derived elements in their diet.
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