Implications of sea-level rise on estuarine benthic biodiversity and ecosystem functioning
Permanent link to Research Commons versionhttps://hdl.handle.net/10289/15027
Estuarine habitats are among the most productive ecosystems around the globe. The macroinvertebrate communities within these habitats underpin ecosystem functioning and therefore the provision of ecosystem services valued by society. Due to their geographic positioning, coastal areas represent a human-ocean interface and are consequently at the forefront of anthropogenic pressure. Sea-level rise (SLR) is one major consequence of anthropogenic climate change that poses a great threat to coastal environments and will result in extensive intertidal area loss. There is an evident bias within coastal SLR research towards the implications for the abiotic environment such as impacts on geomorphology but the ecological implications however, have been largely overlooked despite their likely significance. In this thesis, I aim to address this knowledge gap by investigating how benthic macroinvertebrate communities and their contributions to ecosystem function will respond to SLR within a large temperate estuary. To explore how benthic macroinvertebrate community structure will respond to future SLR, I employed a space-for-time approach. In this study, I considered site depth as a proxy for SLR to gauge how macroinvertebrate communities may shift with increasing depth as sea level is elevated. This study was based on data obtained from 119 unvegetated soft-sediment sampling locations throughout Tauranga Harbour. An initial hierarchical cluster analysis was performed on the macroinvertebrate abundance data to reveal groups of sites that shared significantly similar community structure. Three clusters of sites were identified at a > 34% similarity level with significantly different macroinvertebrate community structure. Clustered groups were generally characterised by different depth ranges that we could consider representative of intertidal, shallow subtidal and deep subtidal habitats. Similarly, depth was identified as the most important environmental variable for predicting variation in macroinvertebrate community structure using distance-based linear modelling (explaining 12%) and gradient forest analysis indicated it is important in explaining rates of compositional turnover (6%). Chl-a, mud content and average current speed were among the next most important predictors explaining variation in community structure (5%, 4% and 2%, respectively) and compositional turnover (6%, 3%, 4%, respectively). Functional trait analysis indicated low functional redundancy for a key intertidal suspension-feeding bivalve (Austrovenus stutchburyi) and the lack of a shallow subtidal functional replacement should intertidal habitats become inundated by SLR. The findings of this thesis strongly suggest SLR and the associated environmental changes will significantly alter estuarine macroinvertebrate communities, indicating implications for ecosystem function and resilience. Key findings of this thesis will complement management strategies of coastal areas and encourage they are not treated as static systems as ecological shifts are predicted to occur with SLR over time. Well- informed management of important estuarine habitats that recognises their spatial and temporal dynamicity will be critical for ensuring ecosystem functions and services they deliver will be conserved for future generations.
The University of Waikato
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- Masters Degree Theses