Marine parasites in island-like disturbed habitats

Abstract

Parasites are taxonomically and functionally diverse members of biological communities, and can play key roles in species interactions, community structure, and ecosystem functioning. For their reliance on host species, parasites are theorized to be particularly sensitive to disturbances that alter host diversity and abundance, especially in isolated habitats, which present challenges to introduction and establishment. In this thesis, I investigate habitat isolation and disturbance as drivers of parasite diversity, with an emphasis on parasite life history strategies related to colonization and persistence. I focus on an island-like, frequently disturbed habitat, deep sea hydrothermal vents at 9°50’N on the East Pacific Rise, to explore the boundaries of parasite persistence in an extreme environment. First, I analyze recovery in the vent community for 11 years after a catastrophic eruption in 2006 to test successional hypotheses in a new setting with distinct fauna and a chemosynthesis-based food web. Second, I compare parasite diversity at isolated, disturbed vents to marine ecosystems that are similarly isolated but undisturbed (atoll sandflat) and both well connected and undisturbed (kelp forest). Overall, parasite diversity within host species was not significantly lower at vents, but the vent community had many fewer parasite species because there are fewvertebrate predator species (fish). Parasites with indirect (multi-host) life cycles were relatively diverse in the disturbed environment, which contradicts expectation based on theory. To explore this further, I investigate the three-host life cycles of trematodes at vents, whichwas the most diverse and abundant parasite taxon. All life stages of the trematode life cyclewere discovered in vent fauna and several taxawere traced across multiple life stages via morphology and genetics. Finally, I use a computational model to investigate how different parasite strategies (colonization capability and impact on hosts) contribute to parasite success under a range of disturbance conditions in island habitats. Parasites that reduce host reproduction reached higher densities than parasites that cause mortality across all disturbance frequencies explored, and disturbance facilitated the evolution of more virulent parasites. These studies demonstrate that life history traits and the ability to adapt allow diverse parasite taxa to persist in isolated, ephemeral environments.