New South Wales rocky reefs are under threat

Abstract

Rocky reefs of New South Wales (NSW) are characterised by a mosaic of habitats, including kelp forest and urchin-grazed barrens. These habitats support a diversity of dependent species. Decades of research have demonstrated that kelps form extensive forests with distinctive fish and invertebrate faunas and the ‘barrens’ boulder habitat provides shelter and other resources for commercial fishes, charismatic fishes and invertebrates; the barrens are not deserts! The feeding activities of herbivorous invertebrates, particularly the black sea urchin (Centrostephanus rodgersii) determine the presence of barrens habitat. Some invertebrates survive only in the presence of urchins and are the food resources for many predatory fishes. The barrens habitat in NSW has been highly stable for decades and is critical for the diversity of reef-based organisms. Because of climate change, Tasmanian waters have warmed and as a result C. rodgersii larvae have dispersed southward from NSW. Importantly, the situation regarding C. rodgersii in Tasmania differs from the established pattern in NSW and this needs to be recognised in the approach to management of this species in the two states. Urchins in NSW should be appreciated as important habitat determiners and the removal of them for whatever purpose would have to be managed carefully.

Taxa‐dependent temporal trends in the abundance and size of sea urchins in subtropical eastern Australia

“…This study adds to the growing body of knowledge regarding C. rodgersii within its historic range in NSW (Davis et al., 2023 ; Glasby & Gibson, 2020 ; Kingsford & Byrne, 2023 ; Przeslawski et al., 2023 ) and shows that that C. rodgersii populations in this coral associated habitat in NSW are currently stable (Glasby & Gibson, 2020 , summarised by Przeslawski et al., 2023 ). Although the poleward range expansion of C. rodgersii has altered the sea scape in Tasmania (Ling, 2008 ), in NSW, the barrens‐macroalgae mosaic is a natural and stable part of the ecosystem that promotes local biodiversity and is characteristic of this coastal ecosystem (Glasby & Gibson, 2020 ; Kingsford & Byrne, 2023 ; Przeslawski et al., 2023 ). Any management action in our study region, such as culling or expansion of the C. rodgersii fishery in NSW, must be carefully considered and informed by research (Kingsford & Byrne, 2023 ).…”

“…Although the poleward range expansion of C. rodgersii has altered the sea scape in Tasmania (Ling, 2008 ), in NSW, the barrens‐macroalgae mosaic is a natural and stable part of the ecosystem that promotes local biodiversity and is characteristic of this coastal ecosystem (Glasby & Gibson, 2020 ; Kingsford & Byrne, 2023 ; Przeslawski et al., 2023 ). Any management action in our study region, such as culling or expansion of the C. rodgersii fishery in NSW, must be carefully considered and informed by research (Kingsford & Byrne, 2023 ). Further, it should be a research priority to understand the ecological role of the barren forming sea urchin C. rodgersii within its preindustrial range, including its interaction with corals and other organisms on subtropical reefs in the biogeographic transition zone.…”

“…Ocean warming and changes to the EAC have driven the poleward range expansion of Centrostephanus rodgersii from New South Wales (NSW) to Tasmania, with major impacts on receiving ecosystems resulting in the shift from macroalgal reefs to ‘barrens’ habitats (Byrne & Andrew, 2020 ; Ling, 2008 ). Within its native distribution in NSW, C. rodgersii contributes to the formation of a mosaic of ‘barren’ and kelp forest habitats characteristic of the region and is important for local biodiversity (Curley et al., 2002 ; Kingsford & Byrne, 2023 ; Underwood et al., 1991 ). Understanding spatial and temporal dynamics of common sea urchin species including C. rodgersii on subtropical reefs in NSW is critical to understanding future trajectories of associated ecosystems.…”

Variation in faunal assemblages under the sea urchin Centrostephanus rodgersii

“…It has been estimated that the area of nearshore macroalgal habitat in NSW, of which fringe is a component, is ~ 3,000 ha and that of extensive barrens within 65 m from the shore is 2,000 ha, and within these habitats Given these large extents of habitat and densities, our results suggest that the diverse assemblages living under C. rodgersii in both fringe and barrens may be an important component of the overall biodiversity on the benthic reefs of NSW (also see Kingsford & Byrne, 2023). The abundance of small crustaceans associated with C. rodgersii, for example, is notable given these highly productive invertebrates are key to bentho-pelagic trophic transfer.…”

Urchin grazing of kelp gametophytes in warming oceans

“…Overgrazing commonly results in the formation of “urchin barrens” characterized by the absence of canopy‐forming macrophytes and high cover of encrusting coralline algae (Andrew & Underwood, 1993). These are natural habitats on temperate rocky reefs and part of a mosaic with kelp habitats (Estes & Steinberg, 1988; Kingsford & Byrne, 2023; Konar & Estes, 2003); however, barrens are thought to have increased due to anthropogenic factors (Filbee‐Dexter & Scheibling, 2014; Harris & Tyrrell, 2001; Ling, Johnson, Ridgway, et al, 2009). Shifts between kelp‐dominated states and urchin barrens are well studied, but the interactions that trigger these shifts can be complex (Beas‐Luna et al, 2020; Filbee‐Dexter & Scheibling, 2014; Rinde et al, 2014).…”