Biology and Ecology of Hexacorallians in the San Juan Archipelago

Abstract

Hexacorallians are one of the most conspicuous and dominant suspension feeders in temperate and tropical environments. While temperate hexacorallians are particularly diverse in the northeast Pacific, little work has been done in examining their biology and ecology. Within this dissertation, I describe a novel method for marking soft-bodied invertebrates such as hexacorallians (Chapter 1), examine the prey selectivity of the competitively dominant anemone Metridium farcimen with DNA metabarcoding (Chapter 2), and explore the distribution of the most common hard-bottom hexacorallians in the San Juan Archipelago (Chapter 3). In the first chapter, I found that both methylene blue and neutral red make excellent markers for long-term monitoring of M. farcimen with marked individuals identifiable for up to six weeks and seven months, respectively. I also found that fluorescein is lethal in small dosages to M. farcimen and should not be used as a marker. Neutral red could be used for long-term monitoring of growth and survival in the field, and in combination with methylene blue could be used to mark individuals in distinguishable patterns for short-term studies such as examining predator-prey interactions, movement of individuals, and recruitment survival. In the second chapter, I found that M. farcimen captures a wider variety of prey than has been previously described, likely all prey that are large enough to detect and that cannot escape. Additionally, comparisons between DNA metabarcoding and published results from traditional gut sampling techniques showed that many more taxa can be found by DNA metabarcoding. Terrestrial prey were surprisingly high in abundance within the diet of M. farcimen, likely due to the animals living on floating docks. These data highlight the need for consideration of space and time in a sampling regime and the usefulness of the metabarcoding method in identifying prey within the gut of planktivorous animals. In the final chapter, I found that depth, light, flow, and substratum slope had significant impacts on the distribution of hard-bottom hexacorallians, whereas predation pressure and temperature had no detectable effect. Depth and light have a strong relationship with algal cover and most hexacorallians were conspicuously missing from high algal cover surfaces. Additionally, nearly every species increased in density with increased flow. These data call attention to the need for experimental studies examining the interactions between temperate hexacorallians and algae as well the effects of flow on distribution of anthozoans.