Laura K. Blamey

Global regime shift dynamics of catastrophic sea urchin overgrazing

A pronounced, widespread and persistent regime shift among marine ecosystems is observable on temperate rocky reefs as a result of sea urchin overgrazing. Here, we empirically define regime-shift dynamics for this grazing system which transitions between productive macroalgal beds and impoverished urchin barrens. Catastrophic in nature, urchin overgrazing in a well-studied Australian system demonstrates a discontinuous regime shift, which is of particular management concern as recovery of desirable macroalgal beds requires reducing grazers to well below the initial threshold of overgrazing. Generality of this regime-shift dynamic is explored across 13 rocky reef systems (spanning 11 different regions from both hemispheres) by compiling available survey data (totalling 10 901 quadrats surveyed in situ) plus experimental regime-shift responses (observed during a total of 57 in situ manipulations). The emergent and globally coherent pattern shows urchin grazing to cause a discontinuous ‘catastrophic’ regime shift, with hysteresis effect of approximately one order of magnitude in urchin biomass between critical thresholds of overgrazing and recovery. Different life-history traits appear to create asymmetry in the pace of overgrazing versus recovery. Once shifted, strong feedback mechanisms provide resilience for each alternative state thus defining the catastrophic nature of this regime shift. Importantly, human-derived stressors can act to erode resilience of desirable macroalgal beds while strengthening resilience of urchin barrens, thus exacerbating the risk, spatial extent and irreversibility of an unwanted regime shift for marine ecosystems.

Temporal changes in kelp forest benthic communities following an invasion by the rock lobster Jasus lalandii

The rock lobster Jasus lalandii expanded its centre of distribution south-eastwards into an area known as ‘East of Cape Hangklip’ on the south-west coast of South Africa in the early 1990s. Using historical and present data, we analysed differences in the abundance of key species and functional groups between the pre- and post-rock lobster invasion periods at two sites along that coast: Cape Hangklip and Bettys Bay. Pre-1989, lobsters were absent, but after 1995 they reached densities approximating 0.4–0.8 m−2. Benthic community composition also changed significantly with herbivores being abundant whereas macroalgae and sessile invertebrates were scarce pre-invasion. We attribute the decline of herbivores to the direct effects of lobster predation, in turn indirectly promoting macroalgae. Post-invasion sessile invertebrates and macroalgae increased by 2 600% and 453% respectively, whereas herbivores declined by 99.3%. The virtual elimination of the sea urchin Parechinus angulo-sus by rock lobsters has substantial implications for the commercial harvesting of the abalone Haliotis midae, because its juveniles are intimately associated with this urchin. The lobster invasion has thus not only led to a regime shift of the ecosystem but has also substantial economic consequences, which calls for an ecosystem approach to the management of the pool of commercially exploited resources in this region.

Human-mediated drivers of change — impacts on coastal ecosystems and marine biota of South Africa

Coastal ecosystems are highly vulnerable to human-mediated drivers of global change because they are located at the land–ocean interface and often host centres of urbanisation and development. The South African coastline comprises several distinct coastal ecoregions that support a wide range of coastal (inshore) ecosystems, including rocky, sandy and mixed shores, kelp beds, estuaries and seagrass communities. A growing body of evidence indicates that local air and sea temperatures, wind patterns, ocean current speed and upwelling regimes are all being affected by human-mediated climate change. In addition, anthropogenic activities, such as shipping (introducing coastal bioinvasives), exploitation of coastal marine resources, industry (releasing pollutants) and urban development, act synergistically with climate change to place pressure on coastal ecosystems and their biota. The aim of this review was primarily to synthesise and update research into causes of direct and indirect human-mediated global change and their effects on South African coastal systems. It incorporates both historic and the latest regional research on climate change and anthropogenic threats across the ecosystems listed above, much of which was supported by the South African Network for Coastal and Oceanic Research (SANCOR), specifically the SEAChange programme in recent years. It is evident that all these ecosystems are vulnerable to all the drivers considered, albeit to differing degrees, depending on their location on the coast. Whereas some bioinvasives have had a dramatic impact on rocky shore systems on the West Coast, their impact has been moderate on the South Coast and minimal on the East Coast; exploitation shows the reverse pattern. Furthermore, the impacts of human-mediated drivers on coastal ecosystems are synergistic. Of major interest is the fact that the West Coast and parts of the South Coast are exhibiting cooling trends in offshore sea surface temperatures, rather than warming. Correspondingly, a geographical spread of organisms associated with West and South-West Coast rocky shores and kelp beds has tended to be eastwards around Cape Point, rather than northwards along the West Coast as would have been expected with warming sea temperatures. Overall, significant progress has been made toward a better understanding of the combined pressures on each ecosystem and knowledge gaps have been identified, thus helping to direct future research themes.

Spatial characterisation of the Benguela ecosystem for ecosystem-based management

The three countries of the Benguela Current Large Marine Ecosystem (BCLME), namely Angola, Namibia and South Africa, have committed to implementing ecosystem-based management (EBM) including an ecosystem approach to fisheries (EAF) in the region, to put in practice the principles of sustainable development in ocean-related matters. There is also recognition of the need for marine spatial planning (MSP) as a process for informing EBM with regard to the allocation and siting of ocean uses so that ecosystem health is ensured and trade-offs between ecosystem services are appropriately dealt with. Marine spatial planning is both an integrated and an area-based process, and this paper produces a spatial characterisation of the BCLME for achieving a common basis for MSP in the region, focusing on the oceanography, biology and fisheries. Recognising spatial variation in physical driving forces, primary and secondary production, trophic structures and species richness, four different subsystems are characterised: (1) north of the Angola–Benguela Front, (2) from the Angola–Benguela Front to Lüderitz, (3) from Lüderitz to Cape Agulhas, and (4) from Cape Agulhas to Port Alfred on the south-east coast of South Africa. Research and monitoring requirements of relevance for MSP and EBM in the region are identified, focusing on understanding variability and change, including with regard to the boundary areas identified for the system. To this end, 14 cross-shelf monitoring transects are proposed (including seven that are already being monitored) to estimate fluxes of biota, energy and materials within and between the subsystems. The usefulness of models for understanding ecosystem variability and changes is recognised and the need for fine-scale resolution of both sampling and modelling for adequate MSP as input to EBM for the often-conflicting interests of conserving biodiversity, and managing fisheries, recreation, offshore oil and gas exploration and exploitation, offshore mining and shipping routes, is emphasised.

Southern African Sea Life: A Guide for Young Explorers

What I would have given for a book like this twenty-something years ago when I was a kid playing in rock pools. And I am just as excited about it now as I would have been back then. Dr Sophie von der Heyden, marine biologist and geneticist at the University of Stellenbosch and mother of two young children, has presented us with an informative, colourful and easy-to-read guide to southern African sea life and marine habitats. And the vivid photographs by underwater photographer Guido Zsilavecz help bring the book to life. Although primarily aimed at children ranging from primary to early high school, older children and adults alike will enjoy this book.