Description
The distribution and abundance of organisms is typically shaped by multiple biotic and abiotic processes. Micropredators are parasite-like organisms that are smaller than their hosts and/or prey and feed on multiple hosts during a given life stage. Unlike typical parasites, they spend much of their time free-living, associating only temporarily with hosts. In the ocean, micropredators can impact multiple fish species. Like any natural enemy, they are thought to both influence and be influenced by host behavior and distribution. In Chapter 1, I aimed to investigate spatiotemporal patterns of distribution and abundance of three common demersal micropredators on subtidal temperate rocky reefs (families Cirolanidae, Cypridinidae, and Gnathiidae). Using lighted benthic emergence traps I sampled micropredators at two rocky reef sites in two substratum types (sand and rock) twice a month from May 2017-April 2018. There were differences in main effects (site, season) and interactions between these effects that differed among the three families of micropredators. For all families, substratum was not an important predictor of abundance. Cypridinids showed significant site and seasonal effects, whereas cirolanids showed an interaction between site, season, and substratum, and gnathiids revealed a site xseason interaction. These findings are likely a result of micropredator behavior, host distribution, and site-specific abiotic factors. In Chapter 2, my aim was to determine whether varying levels of gnathiid micropredation affected the swimming performance of small and large juvenile giant kelpfish, Heterostichus rostratus. Specifically, I measured swimming metrics associated with burst and ambient swimming. In addition, I assessed the lethal level of gnathiids for both small and large juvenile kelpfish. Surprisingly, we observed almost no influence of fish size or gnathiid level on burst and ambient swimming performance. There was also a significant difference in the probability of survival for small kelpfish compared to large fish at the highest gnathiid treatment, indicating that parasite-induced mortality is greater for smaller fish. Investigations of the effects of micropredators on subsequent predator-mediated mortality, including the susceptibility of fishes and their individual responses to micropredators, can further contribute to our understanding of processes affecting recruitment into resident reef fish populations.
