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The South African West Coast rock lobster, Jasus lalandii (H. Milne-Edwards, 1837), has expanded its range to the southeast, where its abundance has increased radically. The ecological consequences of this "invasion" are likely to be considerable. We employed a minimally realistic model to simulate the "invasion" and to explore interactions of J. lalandii with the sea urchin, Parechinus angulosus (Leske, 1778), and the abalone, Haliotis midae Linnaeus, 1758, juveniles of which shelter beneath this urchin. Model fits to empirical data were good, although species-interaction terms were difficult to estimate. Base-case trajectories indicated: (1) Lobster biomass peaked at about 1000 t in 1994 and was then reduced by fishing to a stable value approximately 50% lower by 2008. (2) Urchins remained close to carrying capacity in "noninvaded" areas but collapsed to local extinction by 1997 in the invaded area. (3) Abalone declined over 2000-2008 in noninvaded areas because of illegal fishing and collapsed to near zero in the "invaded" area because of illegal fishing combined with increased lobster abundance. Sensitivity analyses favored the hypothesis that the invasion was due to adult immigration rather than larval recruitment. Modeled 50-yr projections indicated that urchins will remain locally extinct in the invaded area, even 50 yrs into the future. The abalone collapse in the invaded area would persist >50 yrs, even if lobsters were absent. We argue that the lobster "invasion" triggered an alternative stable state, making a return to pre-invasion conditions unlikely. [ABSTRACT FROM AUTHOR]

Abstract: Over the past two decades, several species have undergone distributional shifts in the southern Benguela. The commercially-important West Coast rock lobster Jasus lalandii is one of these, and its shift in distribution has had profound effects on the rest of the ecosystem along the south-west coast. Reasons for these shifts are not fully understood, but are probably linked to changes in environmental conditions. We applied a sequential t-test algorithm for analyzing regime shifts (STARS) to physical (wind and upwelling) and biological (rock-lobster catch and growth, Bank Cormorant abundance) data for the southern Benguela inshore region and performed sensitivity tests on each of the variables. Regime shifts were defined as ‘robust’ or ‘possible’ if they were detected for⩾70% or⩾60% of the sensitivity tests respectively. To corroborate the shifts detected by STARS, we then applied two additional methods: change point analysis and the Chow breakpoint test. The STARS method outperformed the other two methods because it could handle shorter time series and detect shifts towards the end of the time series, but most of the significant shifts detected by STARS were also detected by one or both of the other methods. A significant shift in Cape Point winter winds occurred in 1983, an El Niño year. However, measurement methodology changed during the same period and this is discussed in relation to the shift. A decline in rock-lobster growth rate occurred in the mid 1980s, and significant increases in upwelling variability and mean summer winds were detected in the early-to-mid 1990s – the same period in which rock lobster abundance underwent an eastward shift, declining on the west coast and increasing on the south-west coast. Bank Cormorants underwent respective declines and increases in the mid-to-late 1990s on the west and south-west coasts following the shift in lobsters. Further shifts in mean wind and upwelling were detected in the 2000s. These results are a step towards developing ecosystem indicators for the region, which can be monitored with the intended use of providing an early warning system for long-term, ecosystem-scale changes. [Copyright &y& Elsevier]

Abstract: An eastward shift in the center of abundance of the South African rock lobster Jasus lalandii occurred during the early 1990s into an area known as East of Cape Hangklip (EOCH). Given (1) the predatory capabilities of J. lalandii, (2) an intricate relationship between the urchin Parechinus angulosus and juveniles of the abalone Haliotis midae, and (3) existing over-exploitation of elements of the ecosystem, the ‘lobster invasion’ has major implications for the benthic ecosystem and associated fisheries. We surveyed the abundance of J. lalandii and the benthic community composition EOCH at six sites (three ‘invaded’ and three ‘non-invaded’ by J. lalandii), in three different depth zones (<5m, 6–12m and 13–20m). At all depths, J. lalandii was significantly more abundant in invaded areas than in non-invaded areas, and benthic communities were significantly different. The high densities of rock lobsters at invaded sites led to cascading effects including elimination of urchins and depletion of grazers, consequent enhancement of macroalgae, and diminishment of encrusting corallines. Non-invaded sites had few lobsters, abundant herbivores, less macroalgae and more encrusting corallines. Elimination of urchins in the invaded area has important implications, as juveniles of the commercially harvested abalone H. midae depend on shelter beneath urchins in this region. Floral species diversity was greater at invaded sites and increased with depth, whereas faunal species diversity was greater at non-invaded sites but also increased with depth. The depths at which strongest effects of J. lalandii were felt coincided with the depth of maximum abundance of the urchin P. angulosus, the abalone H. midae, the kelp Ecklonia maxima and encrusting corallines, with serious consequences for associated fisheries and the benthic community. We argue that the differences between invaded and non-invaded areas are sufficient to recognize that they are alternate stable-states and constitute a regime shift. [Copyright &y& Elsevier]