Ecosystem effects of a rock-lobster 'invasion': comparitive and modelling approaches
type: CreativeWork
description: An eastward shift in the West Coast rock lobster Jasus lalandii took place in the early 1990s along the south-west coast of South Africa in an area known as East of Cape Hangklip (EOCH). Given the predatory capabilities of J. lalandii, an intricate relationship between the urchin Parechinus angulosus and juvenile abalone Haliotis midae, and an already over-exploited ecosystem, the lobster âinvasionâ is assumed to have had serious consequences on the benthic community and associated fisheries. To investigate these effects, I used both empirical and modelling approaches. Based on field studies, I first analysed temporal changes in rock lobsters and the benthic community at two lobster-invaded sites EOCH. Prior to 1990, rock lobsters were rare EOCH, but from the mid 1990s onwards they achieved densities of 0.4- 0.8 m-2. The pre-invaded benthic community was significantly different from the postinvaded community at both sites. Three major changes followed the lobster invasion: (1) a decline or even a disappearance of herbivores (a direct effect), (2) macroalgal proliferation (an indirect effect) and (3) increases of a range of sessile taxa (unknown effect). This was followed by a detailed spatial analysis of J. lalandii densities and the benthic community EOCH, in which I surveyed six sites (three invaded and three noninvaded) at three different depth zones (< 5 m, 6-12 m and 13-20 m). At all three depth zones Jasus lalandii was significantly more abundant in invaded areas than in noninvaded areas, and invaded and non-invaded benthic communities were significantly different. Invaded sites were characterized by higher densities of rock lobsters, macroalgae and sessile species, whereas non-invaded sites had greater amounts of herbivores and encrusting corallines. Abalone abundance reflected their previouslyrecorded dependency on urchins and the effects of rampant poaching. Floral species diversity was on average greater at invaded sites and increased with depth, whereas f…
abstract: An eastward shift in the West Coast rock lobster Jasus lalandii took place in the early 1990s along the south-west coast of South Africa in an area known as East of Cape Hangklip (EOCH). Given the predatory capabilities of J. lalandii, an intricate relationship between the urchin Parechinus angulosus and juvenile abalone Haliotis midae, and an already over-exploited ecosystem, the lobster âinvasionâ is assumed to have had serious consequences on the benthic community and associated fisheries. To investigate these effects, I used both empirical and modelling approaches. Based on field studies, I first analysed temporal changes in rock lobsters and the benthic community at two lobster-invaded sites EOCH. Prior to 1990, rock lobsters were rare EOCH, but from the mid 1990s onwards they achieved densities of 0.4- 0.8 m-2. The pre-invaded benthic community was significantly different from the postinvaded community at both sites. Three major changes followed the lobster invasion: (1) a decline or even a disappearance of herbivores (a direct effect), (2) macroalgal proliferation (an indirect effect) and (3) increases of a range of sessile taxa (unknown effect). This was followed by a detailed spatial analysis of J. lalandii densities and the benthic community EOCH, in which I surveyed six sites (three invaded and three noninvaded) at three different depth zones (< 5 m, 6-12 m and 13-20 m). At all three depth zones Jasus lalandii was significantly more abundant in invaded areas than in noninvaded areas, and invaded and non-invaded benthic communities were significantly different. Invaded sites were characterized by higher densities of rock lobsters, macroalgae and sessile species, whereas non-invaded sites had greater amounts of herbivores and encrusting corallines. Abalone abundance reflected their previouslyrecorded dependency on urchins and the effects of rampant poaching. Floral species diversity was on average greater at invaded sites and increased with depth, whereas f…
author: Blamey, Laura Kate
language: eng
date published: 2010
date modified: 2026-07-22T22:22:46Z
provider: University of Cape Town
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Department of Biological Sciences

PropertyValue
property ID: Handle
value: http://hdl.handle.net/11427/6234