Range shifts and the population dynamics of tropical, subtropical, and rare fishes in New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Auckland, New Zealand
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Date
2022
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Massey University
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Abstract
The rate of species re-distribution during the Anthropocene is unprecedented. The expectation is that as global temperatures continue to rise, tropical regions will become increasingly inhospitable, and temperate regions will become more tropicalised and biodiverse as species track favourable conditions poleward. Climate change mediated range shifts are causing the distinctness of species assemblages and biogeographic regions to erode, and the most significant biodiversity changes are currently occurring in the coastal marine environment. Identifying the species currently undergoing range shifts and predicting where and when future climate-mediated range shifts will occur is critical to proactively manage changes in resource-based human livelihoods and meet conservation goals. However, identifying range shifts is often hampered by a lack of baseline distributional data. In the marine environment, large areas remain under-surveyed, and given that marine species are often cryptic, wide-ranging, and highly mobile, our knowledge of geographic distributions is far from complete. This thesis aimed to fill this knowledge gap by using a combination of novel data sources and methods to set an accurate baseline for the spatio-temporal distribution of tropical, subtropical and rare teleost fishes in a temperate marine setting and develop methods to allow us to monitor future biodiversity change. Teleost fishes are valuable indicators of current and future change; they are early responders to climate-mediated ocean warming and are charismatic and highly visible, increasing the ease of monitoring, particularly by citizen scientists. First, data sourced from published accounts, scientific surveys, commercial catches, and citizen science sources were examined to determine the spatio-temporal distribution of tropical, subtropical, and rare fish in NZ waters. I characterise their contribution to New Zealand’s marine biodiversity and set a baseline for future monitoring of climate-driven biodiversity changes. I found that the contribution of tropical, subtropical, and rare fishes to New Zealand biodiversity is significant, and their occurrences and diversity have increased over the past 50 years. Second, I present and test a novel method that combines citizen science with expert knowledge to classify out-of-range occurrences for marine fishes as potential range extensions or human-mediated dispersal events. The stepwise approach uses qualitative decision making and scoring tools to classify citizen science observations of tropical, subtropical and rare fishes and combines these classifications with expert validation to increase confidence. By applying the method to a range of focal species, I successfully identified species that had undergone range shift into or within New Zealand waters and one species whose range shift was facilitated by human-mediated dispersal. The ease of our approach and the intuitive outputs should appeal to managers and science practitioners concerned with climate-induced biodiversity changes and alien species detection. Third, I apply the classification methods and distributional baselines from Chapters 2 and 3 to citizen science occurrence data for tropical, subtropical and rare fishes in New Zealand waters to identify those species that are tohu (indicators) of change and identify the areas where biogeographic change is occurring. Labrids and Pomacentrids disproportionately contributed to out-of-range occurrences, and 87% of all out-of-range occurrences represented potential and actual range extensions. Locations with a high occurrence of potentially range shifting fishes were centred in north-eastern New Zealand, with occurrences of potentially range shifting fishes decreasing with increasing latitude. I surmise that climate-mediated biodiversity change in New Zealand fishes is occurring and present a list of species contributing to range shifts by region to facilitate effective monitoring and impact mitigation. Overall, this thesis contributes new knowledge regarding the rate of poleward climate-mediated range shifts of marine teleost fishes to New Zealand and a suite of novel tools to facilitate future monitoring and impact mitigation of climate-mediated range shifts. I successfully demonstrate the capacity of ocean-going citizen scientists to identify range shifts in the marine environment and overcome some of the common biases and sampling errors associated with citizen science data by incorporating expert validation and knowledge. My results suggest that New Zealand is currently not a hotspot for climate-mediated biodiversity shifts but biodiversity shifts are occurring and the contribution of tropical, subtropical and rare fishes to New Zealand diversity is increasing. These contributions of this thesis will provide a baseline and framework for resource managers, science practitioners and citizens, to monitor range shifts and manage the impacts of climate change on New Zealand’s marine ecosystem.
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Keywords
Marine fishes, New Zealand, Geographical distribution, Fish populations, Tropics, Rare fishes