Abstract
New Zealand’s heavily-calcified bryozoans are diverse, well-described, and capable of creating ecologically-important three-dimensional benthic habitat that hosts a taxonomically-rich fauna both on and around colonies. Economically-important species, including tarakihi (Nemadactylus macropterus), oysters (Ostrea chilensis), and blue cod (Parapercis colias) use bryozoan thickets as habitat and refugia. This association between commercial species and habitat-forming bryozoans has resulted in bryozoan beds being damaged by bottom fishing and, in some cases, intentionally cleared to ease fishing efforts. While protecting previously damaged ecosystems is important for re-establishing dynamic marine habitats, the effect of marine protection on bryozoan diversity and abundance has been unexplored in New Zealand, until now. The aim of the present thesis was to investigate the response of bryozoan communities to different types of marine protection around New Zealand’s three largest islands by using four locations as case studies: Cape Rodney – Ōkakari Point Marine Reserve (north-eastern North Island), Separation Point Exclusion Zone (north-eastern South Island), Ulva Island/Te Wharawhara Marine Reserve (Stewart Island), and the Otago shelf voluntary exclusion zone (south-eastern South Island).
In each of the four case studies presented within the present thesis, New Zealand’s protection of habitat-forming bryozoans has fallen short, regardless of whether bryozoans were the intended target of protection, although other examples of protection success could exist in other marine protected areas around the country. Within Cape Rodney – Ōkakari Point Marine Reserve and the Separation Point Exclusion Zone, bryozoan communities were less abundant and species-rich in modern surveys compared to historical collections. In the case of Ulva Island/Te Wharawhara Marine Reserve, bryozoan reefs were excluded from the marine reserve altogether. Results presented for the Otago shelf voluntary exclusion zone showed no increase in bryozoan abundance or species richness despite seventeen years of protection. Poor land management, ineffective marine protected area design, non-existent enforcement, and continued overuse are all potential explanations for why bryozoans are not thriving in these protected areas, with many of these diffuse stressors being uncontrolled by the implementation of fishing restrictions.
Existing protected areas that focus on heavily-calcified bryozoans (e.g., Separation Point Exclusion Zone, Otago shelf voluntary Exclusion Zone), however, have no targeted monitoring programs or recovery targets, which has made it impossible to quantify the success of management practices. Despite the uncertainty surrounding bryozoan protection and recovery timelines, bottom fishing is still one of the biggest threats to New Zealand’s bryozoans and marine reserves are an important tool for managing that threat. Risk-based approaches to management, like the one presented in the present thesis, can help identify threats and inform management decisions, although other approaches (e.g., precautionary approach) may be more proactive or adaptable to as we learn more about bryozoan biology and ecology. In the future, new marine protected areas should have well-defined, informed management goals, statistically-sound monitoring strategies, and a thorough understanding of the biology and ecology of target species to make reasonable management decisions that result in significant positive change to bryozoan-dominated biogenic habitat across New Zealand. To that end, the present thesis has also provided an overview of some fundamentals of monitoring program design, applied those broad fundamentals to a novel bryozoan management framework, and identified key aspects of bryozoan biology and ecology that must be investigated before effective management of bryozoan-dominated biogenic habitat is possible.