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Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2023., 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 hos, I extend my thanks to the grantors and funding agencies who supported my research, including NSF grants OCE-1829773 and OCE-84773500, the Grassle Student Fellowship Fund, and the Ocean Ventures Fund.

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dykman, L. N., Beaulieu, S. E., Mills, S. W., Solow, A. R., & Mullineaux, L. S. Functional traits provide new insight into recovery and succession at deep-sea hydrothermal vents. Ecology, 102(8), (2021): e03418, https://doi.org/10.1002/ecy.3418., Investigation of communities in extreme environments with unique conditions has the potential to broaden or challenge existing theory as to how biological communities assemble and change through succession. Deep-sea hydrothermal vent ecosystems have strong, parallel gradients of nutrients and environmental stress, and present unusual conditions in early succession, in that both nutrient availability and stressors are high. We analyzed the succession of the invertebrate community at 9°50′ N on the East Pacific Rise for 11 yr following an eruption in 2006 in order to test successional theories developed in other ecosystems. We focused on functional traits including body size, external protection, provision of habitat (foundation species), and trophic mode to understand how the unique nutritional and stress conditions influence community composition. In contrast to established theory, large, fast-growing, structure-forming organisms colonized rapidly at vents, while small, asexually reproducing organisms were not abundant until later in succession. Species in early succession had high external protection, as expected in the harsh thermal and chemical conditions after the eruption. Changes in traits related to feeding ecology and dispersal potential over succession agreed with expectations from other ecosystems. We also tracked functional diversity metrics over time to see how they compared to species diversity. While species diversity peaked at 8 yr post-eruption, functional diversity was continuing to increase at 11 yr. Our results indicate that deep-sea hydrothermal vents have distinct successional dynamics due to the high stress and high nutrient conditions in early succession. These findings highlight the importance of extending theory to new systems and considering function to allow comparison between ecosystems with different species and environmental conditions., Funding for L. Dykman, L. Mullineaux, and S. Beaulieu was provided by NSF OCE-1829773. The Synthesis Centre of the German Centre for Integrative Biodiversity Research (sDiv) funded the sFDvent working group and database.

Dataset: EPR vent colonists functional traits, Functional traits of colonists collected from colonization surfaces at the East Pacific Rise (EPR) deep-sea vents (1998-2017) (Dykman et al., 2021). A dataset of trait modality assignments for 8 functional traits of 58 invertebrate species or higher taxa (when species ID was uncertain) collected from colonization surfaces deployed at hydrothermal vents at 9° 50’N on the East Pacific Rise. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/844993, NSF Division of Ocean Sciences (NSF OCE) OCE-1829773

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Mullineaux, L. S., Mills, S. W., Le Bris, N., Beaulieu, S. E., Sievert, S. M., & Dykman, L. N. Prolonged recovery time after eruptive disturbance of a deep-sea hydrothermal vent community. Proceedings of the Royal Society B: Biological Sciences, 287(1941), (2020): 20202070, https://doi.org/10.1098/rspb.2020.2070., Deep-sea hydrothermal vents are associated with seafloor tectonic and magmatic activity, and the communities living there are subject to disturbance. Eruptions can be frequent and catastrophic, raising questions about how these communities persist and maintain regional biodiversity. Prior studies of frequently disturbed vents have led to suggestions that faunal recovery can occur within 2–4 years. We use an unprecedented long-term (11-year) series of colonization data following a catastrophic 2006 seafloor eruption on the East Pacific Rise to show that faunal successional changes continue beyond a decade following the disturbance. Species composition at nine months post-eruption was conspicuously different than the pre-eruption ‘baseline' state, which had been characterized in 1998 (85 months after disturbance by the previous 1991 eruption). By 96 months post-eruption, species composition was approaching the pre-eruption state, but continued to change up through to the end of our measurements at 135 months, indicating that the ‘baseline' state was not a climax community. The strong variation observed in species composition across environmental gradients and successional stages highlights the importance of long-term, distributed sampling in order to understand the consequences of disturbance for maintenance of a diverse regional species pool. This perspective is critical for characterizing the resilience of vent species to both natural disturbance and human impacts such as deep-sea mining., Support was provided by NSF grant nos. OCE-1356738, DEB-1558904 and OCE-1829773 to L.S.M., and NSF grant nos. OCE-0452333, OCE-1136727, OCE-1131095, and OCE-1559198 to S.M.S. Support from Ifremer ‘Geobiology of Extreme Environment', EU ITN SENSENET no. 237868, CNRS INEE, and Fondation Total was provided to N.L.B., and from the French Oceanographic Research Fleet, CNRS and Sorbonne University for the MESCAL cruise (doi:10.17600/12010020).