Indirect Effects Of Marine Reserve Protection On New Zealands Rocky Coastal Marine Communities

Marine reserves are often effective in allowing the recovery of targeted species within their boundaries, which potentially have indirect effects on non-‐ target species. While the direct effects of protection on targeted species are fairly well understood, the indirect effects have been less well researched. In New Zealand’s oldest marine reserve at Leigh, the recovery of snapper Pagrus auratus and spiny lobster Jasus edwardsii populations has indirectly resulted in the increase of macroalgal habitats due to increased predation on sea urchins. Increased abundances of snapper and other targeted fish species may also affect other fish species via competition or predation. The main aim of this thesis was to investigate how these indirect effects, especially large-‐scale change in habitats, have affected reef fish species relative to the direct effects of protection. Reef fish abundances and sizes were estimated using habitat-‐ stratified underwater visual censuses inside and outside of the Leigh and Tawharanui marine reserves, which allowed for assessment of reef fish habitat associations. Based on these densities and the estimated extents of each habitat (from a drop-‐camera survey) the total population size of a number of key species was estimated for both reserves and surrounding coast. These estimates were then compared to historic population sizes in the Leigh Reserve that were estimated prior to habitat change. The main habitat change between 1978 and 2014 was the conversion of barrens into shallow kelp inside the Leigh reserve. In 2014 there were clear differences between reserve and fished sites at both locations, with virtually no urchin barrens and substantially more kelp habitat inside the reserves. Some species had clear habitat associations, with brown seaweed-‐associated species such as butterfish and silver drummer indirectly benefitting from increased kelp habitats in the Leigh Reserve. Overall changes in population sizes of most targeted species are most likely a direct response to protection. Some species (spotty and goatfish) were less abundant in the reserves, which may be due to increased competition or predation from snapper or other predators. In 2014 the majority of species showed a reserve effect, with greater abundance and/or average size in the reserves. However, aside from red moki, butterfish and silver drummer, which increased in abundance, and leatherjacket and banded wrasse, which showed no change, most species have declined in abundance inside the Leigh Reserve. These population declines may be a reflection of increased fishing pressure being placed on the surrounding coast, environmental change (e.g., sedimentation), or simply due to natural fluctuations in abundance. In summary, the patterns observed in this study, coupled with historic data, suggest that responses of most fish species to protection within northern New Zealand marine reserves are directly attributable to the absence of removal by fishing, with relatively few species showing indirect responses to large-‐scale habitat change or altered levels of competition or predation.

The results of a survey of New Zealand and international literature to identify negative impacts associated with visitors to marine protected areas are presented. It is suggested that further research is needed to assess the biological significance of visitor impacts and that there is a need for long-term research to assess the sustainability of visitor activities.

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Marine reserves are established to protect marine ecosystems from fishing, allowing harvested fishes to recover: these are the "direct effects" of protection. However, changes may also occur among species not typically exposed to fishing mortality, via "indirect effects" . Most marine reserve studies have focused on direct effects, and the prevalence and relative importance of indirect effects is poorly understood. Understanding both direct and indirect effects is key to understanding how fishing affects wider fish assemblages. To investigate the direct and indirect effects of marine reserve protection on reef fish assemblages I examined monitoring data from four northeastern New Zealand marine reserves. This long-term analysis also provided a wider assessment of how reef fish have changed over the last 2-4 decades in this region. Across all reserves examined, the large predatory sparid Chrysophrys auratus responded strongly to protection. This response was hypothesised to drive indirect effects on other species, as a result of increased predation, competition, or predator-induced habitat changes. Long-term changes in reef fish assemblages in New Zealand's oldest marine reserve at Leigh suggested that along with direct effects on six targeted species, snapper recovery had indirect effects on three small-bodied non-target fishes and one herbivorous fish. Comparisons across three reserves revealed that the potential indirect effects identified in Leigh were not ubiquitous. While direct effects on target species like snapper and cheilodactylid Cheilodactylus spectabilis were largely predictable, potential indirect effects were more location-specific and difficult to differentiate from the effects of environmental gradients. At an offshore island marine reserve, with a more speciose temperate-subtropical fish fauna, potential indirect effects existed for just 3 wrasses, despite dramatic direct effects of protection on snapper. There was no evidence of tropicalisation of fish assemblages at this offshore island marine reserve over the last two decades. This study demonstrated that while protected fish assemblages are distinct, this is mostly driven by the recovery of harvested species. Potential indirect effects of long-term protection were identified, but were rarely consistent across multiple reserves. Trophic links between reef fishes appear weak, and the role of indirect effects is likely overwhelmed by the direct effects of fishing.

A comprehensive account of how abiotic and biotic interactions shape patterns of coastal marine biodiversity and ecosystem processes globally.