Temporal and spatial changes in the megabenthic invertebrate fauna of Cockburn Sound; a heavily-utilised coastal embayment

Ben J Roots

Coastal waters are biodiverse and highly productive ecosystems, supporting various habitats and providing refuge, nutrition, and favourable physical conditions for many species. These ecosystems are also valuable for commercial, industrial, and recreational purposes, and consequently, many have been negatively impacted by anthropogenic activities. Despite their importance, relatively little information is known about how these activities impact the biota coastal waters support, particularly the invertebrate communities. This study examined the longand short-term temporal and spatial variation in the megabenthic invertebrate fauna of Cockburn Sound, a heavily utilised coastal embayment in temperate Western Australia, within which there is a proposal to construct a new container port. Firstly, a suite of interdecadal analyses were conducted by comparing trawl data from seven sites across Cockburn Sound sampled in two seasons in 2007/08 and 14 years later in 2021/22 to determine whether there had been a shift in the characteristics of the megabenthic invertebrate community. Secondly, a contemporary analysis focussing on seasonal, short-term interannual, and spatial variation was conducted using the data from 2021/22 and additional samples collected in 2022/23. From the interdecadal analyses, a total of 214 invertebrate taxa representing 17 classes and six phyla were recorded for the two surveys. There was a substantial decline in abundance, biomass, and diversity measures between decades, with a clear shift in community composition. The largest temporal declines in abundance were for arthropods and echinoderms, two pollution and disturbance-sensitive phyla. Abundance-biomass curves revealed a contrasting viewpoint of undisturbed ecosystem condition due to the dominance of large-bodied opportunistic crustaceans in both decades. A total of 175 taxa from 15 classes and six phyla were recorded in the contemporary sampling, with the community significantly differing in diversity measures, abundance, and biomass across sites and between seasons, highlighting finer-scale spatial and seasonal influences that act on the community. Fluctuating abundances of crustacean, mollusc, and echinoderm taxa were apparent, with greater abundances in autumn of 2022/23. A gradient of declining diversity measures moving southwards in the Sound was apparent, most clearly expressed by taxa richness. The findings of this study document concerning patterns in the invertebrate communities of Cockburn Sound across decades and likely display the cumulative detrimental effects of press (e.g. sediment eutrophication, increased industrialisation) and pulse (e.g. marine heatwave, hypoxia event) disturbances. This study showcases the value of historical data sets in forming a comprehensive view of contemporary invertebrate community trends and the data will be useful in the environmental impact assessment of the proposed container port development.

Temporal and spatial changes in the megabenthic invertebrate fauna of Cockburn Sound; a heavily-utilised coastal embayment

Files and links (1)

Abstract

Details

Metrics