Symbiotic Relationship of Comasterschlegelii (Crinoidea: Comatulidae) and Gymnolophus obscura (Ophiuroidea: Ophiotrichidae) Derived from Stable Isotope and Fatty Acid Analyses.

This article focuses on the symbiotic relationship between the crinoid host *Comaster schlegelii* and its obligatory ophiuroid symbiont *Gymnolophus obscura* in coral reef environments near Wuzhizhou Island, China. Using stable isotope and fatty acid (FA) analyses, the study found that both species primarily consume particulate organic matter (POM) and phytoplankton, with *C. schlegelii* showing a higher intake of benthic microalgae. Elevated nitrogen isotope (δ¹⁵N) values and specific FA markers in *G. obscura* suggest it occupies a higher trophic level, likely feeding on materials filtered or expelled by its host, indicating a commensal relationship. These findings highlight distinct organic matter utilization strategies between the host and symbiont and contribute to understanding trophic interactions within coral reef symbiotic communities.