Oregon Sea Grant

Understanding the factors that control predation in pelagic communities can informpredictio​ns of community structure in marine ecosystems. Ubiquitous and selective predators such as cnidarian hydromedusae rely on their nematocysts to capture and retain prey but it is not clearhow the density and spatial distribution of these cells relate to predation mode. We examined the relationship between prey capture and nematocyst distribution in the tentacles of Aglantha digitaleand Proboscidactyla flavicirrata, which are considered ambush predators, and Clytia gregaria and Mitrocoma cellularia, which are considered feeding-current predators. First, we analyzedvideo of predator−prey interactions to compare capture locations of Artemia nauplii relative to thebell margin of each species. Second, tentacles of the same 4 species plus Sarsia tubulosa andAequorea victoria were analyzed using microscopy to determine nematocyst distribution alongtheir lengths. By analyzing behavior and morphology simultaneously, we found that the ambushpredators A. digitale and P. flavicirrata have higher nematocyst density far from the bell and tendto capture more prey in the same region. In contrast, the feeding-current predators C. gregariaand M. cellularia capture most of their prey close to the bell, where they also show a slight in -crease in nematocyst densities. The presence of high nematocyst densities in regions where preyare likely to contact feeding structures serves to increase capture efficiencies. Quantifying therelationship between prey capture and nematocyst locations for different foraging strategies willstrengthen the ability of researchers to predict feeding behavior based on morphological features.

Authors: Corrales-Ugalde, Marco; Colin, Sean P.; Sutherland, Kelly R.