Trophic interactions and life strategies of epi- to bathypelagic calanoid copepods in the tropical Atlantic Ocean

Abstract

Copepods play central roles in pelagic food webs linking primary production to higher trophic levels. Biomarkers (lipids, stable isotopes) provide modern approaches to study dietary preferences and trophic interactions. A cluster analysis based on the fatty acid (FA) and fatty alcohol compositions of calanoid copepods (copepodids C4/C5 and adult stages) from the southeastern tropical Atlantic identified five distinct groups according to lipid composition and storage strategy, coinciding with differences in vertical distribution from the surface to 1800 m depth. Most epipelagic species were characterized by low lipid levels ( 10% of dry mass, DM), low quantities of wax esters (WE) and low dN ratios indicating low trophic positions. In contrast, surface-dwelling Rhincalanus cornutus had higher lipid levels (.29% DM) and stored WE (.90% of total lipid), whereas vertically migrating Pleuromamma species did not store WE. Most mesopelagic copepods belonged to another cluster, defined by high lipid level (max. 47% DM), high amounts of the FA 18:1(n-9) and high dN ratios .9‰ indicating carnivorous feeding at a higher trophic level. Diapausing Calanoides carinatus (copepodids C5), collected at great depth, formed a separate cluster with low dN ratios and high amounts of herbivory markers. The latter were apparently accumulated during active feeding on phytoplankton in surface waters and transferred to the deep sea during ontogenetic vertical migrations. In conclusion, these tropical calanoid copepod species from the surface to the deep sea have adopted diverse feeding strategies and occupy a wide range of ecological niches, affecting energy flux and carbon cycling in the tropical Atlantic.