A field based assessment of predation impacts on planktonic egg capsules across depth and flow gradients

Abstract

The relative rates of mortality in benthic and pelagic environments have been proposed as a major factor structuring the evolution of complex benthic invertebrate life histories. Field methods, such as tethering, have provided indispensable measurements of mortality under natural conditions for the larvae of benthic invertebrates. However, few such field studies have examined mortality rates of benthic invertebrates' early life stages in size classes less than 1 mm. Here, we tethered egg capsules to quantify how rates of predation vary with environmental gradients, especially distance from the benthic substratum and flow velocity. We found that predation is consistently high on L. scutulata egg capsules and invariant at four positions in the water column and on the benthic substratum (average 34% loss across all treatments). Instead, the flow environment had the greatest effect on predation rate. We hypothesize that higher predation in the faster flow environment was due to higher encounter rates with advected predators.