Assessing ecological patterns in Wellington south coast's nearshore rocky-reef communities for resource conservation and management
Authors:   , Byfield Tamsen 
Published: November 2021

<p>Many coastal marine communities are increasingly affected by terrestrial and maritime human activities and growing coastal populations. Protection of coastal assets and the sustainable use of coastal resources requires knowledge of nearshore benthic community status; the environmental processes that structure and connect them; the quality, abundance, and distribution of physical habitat; essential habitat for species requiring protective measures, and the spatio-temporal scales at which these patterns and processes occur. To assess the status of Wellington South Coast’s (WSC) rocky-reef assemblages prior to the enactment of the Taputeranga Marine Reserve in 2009, two annual baseline surveys were conducted during the austral summers of 2007/08 and 2008/09. These surveys evaluated the biotic and abiotic components of the assemblages in terms of diversity, abundance distribution, and size-class frequency patterns of key macroalgal and mobile macro-invertebrate species. These results were analysed to develop recommendations for best post-reserve monitoring practices, including the identification of “indicator” species for rapid yet representative field surveys to assess structural and status changes. In combination with patterns described by a previous pre-reserve baseline survey series (2000) that focussed on a reduced list of macro-algal and mobile macro-invertebrate species, this final pre-reserve survey forms the basis of a historical dataset for WSC rocky reefs that can be used for long-term monitoring of ecosystem shifts due to the new reserve and to possible changes caused by anthropogenic activity or altered natural processes. These aims were addressed by collecting information directly at local/site scale and remotely, at the larger area scale. Dived baseline surveys quantified nearshore WSC rocky-reef epibenthic assemblages at 9 sites at depths ranging from 5-13.6m and at a mean distance from shore = 113m. A survey design that included three sites west of the pending marine reserve, three sites to the east, and three sites within the designated reserve was selected to permit later BACI analyses of post-reserve changes. Species surveyed were those commonly encountered during daylight on exposed surfaces and in accessible crevices and belonged to one of three epibenthic groups: macro-algae (48 species), mobile macro-invertebrates (36 species), and sessile macro-invertebrates (30 morphotypes). These surveys did not include epizoa or smaller, cryptic newly recruited macro-invertebrates. Sessile macro-invertebrate cover was only logged if >0.1%/m2. To gauge possible spatio-temporal patterns in primary productivity as a measure of ecosystem function, biomass and plant size were measured semiannually (winter, summer) for dominant kelp and fucoid species and for two key recreationally and commercially important mobile macro-invertebrate species (sea urchin and abalone). Predictive regression equations developed from wet weight and plant size can be used for future non-destructive estimates of local primary productivity and in trophic modelling. [...] This mapping data forms the basis of a legacy dataset that will assist with monitoring changes in the integrity of critical physical habitat and associated biotic cover. It has also demonstrated that representative descriptions of both biotic and abiotic benthic components can be achieved with a minimum of sampling points and by using the quicker semi-quantitative visual analysis of video. These data can also be used to ground-truth a recently-completed multi-beam acoustic survey of the area. This work has used the approach of landscape ecology, which explains patterns in community structure, function, status and biophysical causes from a spatial perspective, to study biophysical patterns in WSC epibenthic rocky-reef communities. The work identified a high degree of spatial and temporal variation within the abiotic and biotic community within and outside of the reserve area and the limited availability of preferred habitat. The work also identified the need to include indicator species in monitoring to improve the chance of detecting impacted assemblages. These results, and the development of non-destructive sampling tools for assessing ecosystem status, are relevant locally and nationally for resource managers.</p>