The trophic level of Mytilicola intestinalis Steuer (Copepoda: Poecilostomatoida) in Mytilus edulis L., as determined from Stable Isotope Analysis

Abstract

Mytilicola intestinalis inhabits the digestive tract of the commercially important European blue mussel Mytilus edulis. Early researchers believed that Mytilicola damaged the host by feeding directly upon the epithelial lining of the host intestine, whilst more recent work indicated that it does not seriously affect the host and feeds upon excess food (phytoplankton and detritus) which passes through the mussel intestine. Comparative analysis of the stable isotope 15N shows that it is 2.8 ppt higher in whole Mytilicola than in mussel intestine, suggesting that Mytilicola occupies a higher a trophic level than Mytilus and therefore is unlikely to use the same food source. Whilst the limitations and pitfalls of this method are recognised and discussed, it is concluded from these observations (and from evidence provided by other techniques) that Mytilicola utilizes mussel breakdown products such as mucus and sloughed-off cells as its major food source and thus feeds indirectly upon the host.