Mp Marzloff

Impacts of Fishing Low-Trophic Level Species on Marine Ecosystems

High harvest levels of low–trophic level fishes may have cascading marine ecosystem effects. Low–trophic level species account for more than 30% of global fisheries production and contribute substantially to global food security. We used a range of ecosystem models to explore the effects of fishing low–trophic level species on marine ecosystems, including marine mammals and seabirds, and on other commercially important species. In five well-studied ecosystems, we found that fishing these species at conventional maximum sustainable yield (MSY) levels can have large impacts on other parts of the ecosystem, particularly when they constitute a high proportion of the biomass in the ecosystem or are highly connected in the food web. Halving exploitation rates would result in much lower impacts on marine ecosystems while still achieving 80% of MSY.

Building resilience against climate-driven shifts in a temperate reef system: staying away from context-dependent ecological thresholds

As climate-driven environmental changes and anthropogenic perturbations increasingly affect ecological systems, the number of abrupt phase shifts in ecosystem dynamics is rising, with far-reaching ecological, economic and social effects. These shifts are notoriously difficult to study, anticipate and manage. Although indicators of impending phase shifts in ecosystems have been described theoretically, they have only been observed empirically either after the fact or under controlled experiments. Here we demonstrate the usefulness of case-specific simulation models to estimate tipping points in the dynamics of real ecological systems, characterise how these thresholds may vary depending on local conditions and derive safe management targets associated with low risk of undesirable phase shifts. Under the combined effects of ocean changes and fishing, inshore rocky reefs in eastern Tasmania can transition from dense seaweed beds to sea urchin ‘barrens’ habitat, realising severe local loss of habitat, productivity and valuable fisheries. Using Monte-Carlo simulations with a validated model that realistically captures reef dynamics, we characterise the hysteresis in community dynamics and the variability in ecological thresholds along the gradient of environmental conditions. Simulation suggests that prevention of ongoing sea urchin destructive grazing of macroalgal beds is achievable but the yet-to-be-observed restoration of seaweed beds from extensive sea urchin barrens is highly unlikely. To guide management against undesirable phase shifts, we define target points associated with low risk of widespread barrens formation and show that, along with sea urchin culling, recognising the role of lobsters in mitigating sea urchin destructive grazing through predation is key to maintain reef productivity.

Modelling marine community responses to climate-driven species redistribution to guide monitoring and adaptive ecosystem-based management.

As a consequence of global climate-driven changes, marine ecosystems are experiencing polewards redistributions of species - or range shifts - across taxa and throughout latitudes worldwide. Research on these range shifts largely focuses on understanding and predicting changes in the distribution of individual species. The ecological effects of marine range shifts on ecosystem structure and functioning, as well as human coastal communities, can be large, yet remain difficult to anticipate and manage. Here, we use qualitative modelling of system feedback to understand the cumulative impacts of multiple species shifts in south-eastern Australia, a global hotspot for ocean warming. We identify range-shifting species that can induce trophic cascades and affect ecosystem dynamics and productivity, and evaluate the potential effectiveness of alternative management interventions to mitigate these impacts. Our results suggest that the negative ecological impacts of multiple simultaneous range shifts generally add up. Thus, implementing whole-of-ecosystem management strategies and regular monitoring of range-shifting species of ecological concern are necessary to effectively intervene against undesirable consequences of marine range shifts at the regional scale. Our study illustrates how modelling system feedback with only limited qualitative information about ecosystem structure and range-shifting species can predict ecological consequences of multiple co-occurring range shifts, guide ecosystem-based adaptation to climate change and help prioritise future research and monitoring.

Differential vulnerability to climate change yields novel deep-reef communities

The effects of climate-driven ocean change on reef habitat-forming species are diverse1,2 and can be deleterious to the structure and functioning of seafloor communities3–5. Although responses of shallow coral- or seaweed-based reef communities to environmental changes are a focus of ecological research in the coastal zone1,4–6, the ecology of habitat-forming organisms on deeper mesophotic reefs remains poorly known. These reefs are typically highly biodiverse7,8 and productive as a result of massive nutrient recycling9. Based on seafloor imagery obtained from an autonomous underwater vehicle8, we related change in community composition on deep reefs (30–90 m) across a latitudinal gradient (25–45° S) in southeastern Australia to high-resolution environmental and oceanographic data, and predicted future changes using downscaled climate change projections for the 2060s10–12. This region is recognized as a global hotspot for ocean warming13. The models show an overall tropicalization trend in these deep temperate reef communities, but different functional groups associate differentially to environmental drivers and display a diversity of responses to projected ocean change. We predict the emergence of novel deep-reef assemblages by the 2060s that have no counterpart on reefs today, which is likely to underpin shifts in biodiversity and ecosystem functioning.Deep reefs and their inhabitants are diverse, but environmental change, in particular warming, will cause these reefs found along southeastern Australia to tropicalize with different responses across functional groups, resulting in novel communities by the 2060s.