Feeding strategies and resource partitioning among mysids in oligotrophic marine caves

The understanding of how large populations of several mysids (Crustacea) species can co-exist and share resources in oligotrophic underwater marine caves from the northwestern Mediterranean Sea was investigated using carbon and nitrogen stable isotopes. The isotopic signatures indicated food partitioning among the five species of cave-dwelling mysids. Different diets provide an explanation for mysid co-existence in caves as resource partitioning reduces interspecific competition. The analysis of both the water column and cave sediments revealed that the quantity and quality of organic matter are strongly reduced compared to the outside, suggesting that mysids must find their food in another environment. Cave mysids might use the outside environment for feeding, since some species are documented to migrate outside of caves at night, where phytoplankton and zooplankton are available. These outside-inside movements make cave-dwelling mysids important drivers in the organic matter transfer from the open sea to different locations inside caves. The organic matter from the open sea accumulated by mysids is then made available to other cave-dwellers by fecal pellet production and predation by cave-dwelling predators such as teleost fishes, decapod crustaceans and carnivorous sponges