Abstract
Understanding how natural systems are structured and function is a fundamental goal in ecological research. Without this knowledge, researchers cannot accurately predict how natural systems will change in response to natural or anthropogenic pressures. However, in recent decades, the approach used by ecologists to explore the functioning of natural systems has broadened with growing appreciation of certain previously ignored or underrepresented groups of organisms. Parasites are one such group whose seemingly hidden presence within natural systems has led to misunderstanding and underestimation of their significance. Due to their ubiquitous nature and potential to impact whole ecosystems, it is not surprising that including parasites in ecological research is essential for ‘full picture resolution’ of ecosystems. Without their inclusion, our knowledge of how natural systems are structured, function, and how they will change in response to natural and anthropogenic pressures, is potentially flawed.
This thesis focuses on the helminth parasites (acanthocephalans, cestodes, trematodes and nematodes) that infect a range of host animals (vertebrates – seabirds, teleost fish, elasmobranchs and marine mammals – and invertebrates) within a localised ecosystem, Otago’s coastal marine ecosystem. Overall, this thesis aims to characterise parasite biodiversity, and resolve their life cycles and roles in the surrounding ecosystem.
Beginning with a review of what is currently known regarding parasite biodiversity in New Zealand’s marine environment, I identify areas of research particularly lacking in study. This paints a worrying picture of how extremely little is known about parasite biodiversity in New Zealand’s marine environment. I make some recommendations for how to improve our knowledge, including further large-scale biodiversity surveys, utilization of integrative taxonomy and inclusion of a wider range of host groups from opportunistic and collaborative sampling methods.
From those recommendations on how to improve our knowledge, I conducted a large-scale localised biodiversity survey in Otago’s coastal marine ecosystem (incorporating multiple host and parasite taxa) that revealed the wide phylogenetic biodiversity of parasites present. Between June 2019 and August 2021, I dissected almost 7000 animals of 168 host species to uncover and characterise the parasite biodiversity they harboured, using an integrative taxonomic approach (utilizing both morphological and molecular tools to identify parasites to the lowest taxonomic level possible). Overall, 95% of vertebrate and 29% of invertebrate species were found to host parasites, which comprised 188 parasite species. By uncovering over 160 new host records, 66 new geographic records and at least 23 species new to science, this survey significantly advances our knowledge of what parasites are present in this ecosystem, and what hosts they infect.
Next, by matching up larval and adult forms of parasites within intermediate and definitive hosts, I provide insights into the ecology and evolution of complex parasite life cycles. Using genetic data, I identified over 400 transmission routes (i.e. predator-prey interactions) that are exploited by parasites in order to complete their life cycles. Some parasites appear to converge on particular transmission routes, while others are constrained to infect specific host taxa by their shared evolutionary histories. I determined which host species and higher taxa are the most important for allowing completion of parasite life cycles, and provided new data regarding how parasites move through food webs by following predator-prey trophic links to complete their life cycles.
Lastly, by constructing and analysing a series of increasingly complex food webs (first excluding, then including parasite data), I investigate the role of parasites in the structure and functioning of Otago’s ecosystem. This ecosystem is parasite-dominated not only in species richness, but in the number of links involving parasites (over 80% of links include parasites). When incorporating parasite data, the results showed that the resilience of the ecosystem to withstand change was drastically decreased, underlining the importance of including parasites in future predictions regarding ecosystem change.
Not only are parasites extraordinarily ubiquitous and biodiverse, infecting a range of vertebrate and invertebrate animals within Otago’s coastal marine ecosystem, they also contribute significantly to both the structure and functioning of the system. Overall, this thesis stands as a testament pleading for parasite inclusion in ecological research pertaining to natural systems. Until they are routinely included, we risk losing sight of how natural systems will change in response to natural and anthropogenic pressures.