Tracking widespread climate-driven change on temperate and tropical reefs.

Warming seas, marine heatwaves, and habitat degradation are increasingly widespread phenomena affecting marine biodiversity, yet our understanding of their broader impacts is largely derived from collective insights from independent localized studies. Insufficient systematic broadscale monitoring limits our understanding of the true extent of these impacts and our capacity to track these at scales relevant to national policies and international agreements. Using an extensive time series of co-located reef fish community structure and habitat data spanning 12 years and the entire Australian continent, we found that reef fish community responses to changing temperatures and habitats are dynamic and widespread but regionally patchy. Shifts in composition and abundance of the fish community often occurred within 2 years of environmental or habitat change, although the relative importance of these two mechanisms of climate impact tended to differ between tropical and temperate zones. The clearest of these changes on temperate and subtropical reefs were temperature related, with responses measured by the reef fish thermal index indicating reshuffling according to the thermal affinities of species present. On low latitude coral reefs, the community generalization index indicated shifting dominance of habitat generalist fishes through time, concurrent with changing coral cover. Our results emphasize the importance of maintaining local ecological detail when scaling up datasets to inform national policies and global biodiversity targets. Scaled-up ecological monitoring is needed to discriminate among increasingly diverse drivers of large-scale biodiversity change and better connect presently disjointed systems of biodiversity observation, indicator research, and governance.

Detecting marine pests using environmental DNA and biophysical models.

The spread of marine pests is occurring at record rates due to globalisation and increasing trade. Environmental DNA (eDNA) is an emerging tool for pest surveillance, allowing for the detection of genetic material shed by organisms into the environment. However, factors influencing the spatial and temporal detection limits of eDNA in marine environments are poorly understood. In this study we use eDNA assays to assess the invasive ranges of two marine pests in south-eastern Australia, the kelp Undaria pinnatifida and the seastar Asterias amurensis. We explored the temporal and spatial detection limits of eDNA under different oceanographic conditions by combining estimates of eDNA decay with biophysical modelling. Positive eDNA detections at several new locations indicate the invasive range of both pest species is likely to be wider than currently assumed. Environmental DNA decay rates were similar for both species, with a decay rate constant of 0.035 h-1 for U. pinnatifida, and a decay rate constant of 0.041 h-1 for A. amurensis, resulting in a 57-73% decrease in eDNA concentrations in the first 24 h and decaying beyond the limits of detection after 3-4 days. Biophysical models informed by eDNA decay profiles indicate passive transport of eDNA up to a maximum of 10 to 20 km from its source, with a ~90-95% reduction in eDNA concentration within 1-3 km from the source, depending on local oceanography. These models suggest eDNA signals are likely to be highly localised, even in complex marine environments. This was confirmed with spatially replicated eDNA sampling around an established U. pinnatifida population indicating detection limits of ~750 m from the source. This study highlights the value of eDNA methods for marine pest surveillance and provides a much-needed description of the spatio-temporal detection limits of eDNA under different oceanographic conditions.

Restoring rocky intertidal communities: Lessons from a benthic macroalgal ecosystem engineer.

As coastal population growth increases globally, effective waste management practices are required to protect biodiversity. Water authorities are under increasing pressure to reduce the impact of sewage effluent discharged into the coastal environment and restore disturbed ecosystems. We review the role of benthic macroalgae as ecosystem engineers and focus particularly on the temperate Australasian fucoid Hormosira banksii as a case study for rocky intertidal restoration efforts. Research focussing on the roles of ecosystem engineers is lagging behind restoration research of ecosystem engineers. As such, management decisions are being made without a sound understanding of the ecology of ecosystem engineers. For successful restoration of rocky intertidal shores it is important that we assess the thresholds of engineering traits (discussed herein) and the environmental conditions under which they are important.