Lobster Jasus Lalandii Research Articles

Growth of the rock lobster Jasus lalandii and its relationship to benthos

Growth increments of the male rock lobster Jasus lalandii vary systematically with location within a small (38 km2) fishing ground off the South African west coast. High growth rates were recorded from an area where the availability of benthos suitable as rock-lobster food was also high. Increments could also be shown to vary significantly in different years, but over the size range examined, growth did not appear to be a function of size. Benthic biomass was found to be inversely related to depth. However, comparisons between biomass values from the same depths in two different areas of the fishing ground suggested that biomass was higher in areas which were in proximity to shallow water, where extensive kelp beds were found. Mussels (Aulacomya magellanica) formed an important constituent of the rock lobster's diet; these were prevalent at depths between 20 and 40 m, and especially in areas where rock-lobster growth rates were high.

A Mass Stranding of Rock Lobsters Jasus Lalandii (H. Milne Edwards, 1837) At Elands Bay, South Africa (Decapoda, Palinuridea)

Die sudafrikanische Languste (Jasus lalandii) fuhrt in der Gegend von Elands Bay (etwa 160 km nordlich von Kapstadt) jahreszeitliche Wanderungen zur Kuste durch. Dieses Verhalten wird verursacht durch die Anwesenheit einer sauerstoffarmen, bodennahen Wasserschicht, die sich, infolge winderzeugter Auftriebsbewegung, zur Kuste hin verlagert. Im Marz 1968 waren die Langusten in Strandnahe zusammengedrangt und konnten wahrend der Springflut bei ruhiger See in die sanft ansteigende Gezeitenzone vordringen. Bei einsetzender Ebbe sind die Langusten dann in grosser Zahl am Strand zuruckgeblieben und umgekommen. Das Massensterben war von solchem Ausmass, dass die Fange der nachsten Saison dadurch beeintrachtigt waren.

A symbiotic shell-encrusting bryozoan provides subtidal whelks with chemical defence against rock lobsters

The subtidal whelk Burnupena papyracea co-occurs with a voracious predator, the rock lobster Jasus lalandii, in situations where other potential prey are largely eliminated. The survival of B. papyracea has been ascribed to a symbiotic bryozoan, Alcyonidium nodosum, which characteristically encrusts the shells of this mollusc and deters feeding by J. lalandii. Although B. papyracea shells encrusted with A. nodosum were found to be stronger than non-encrusted shells, this bryozoan-induced physical defence was insufficient to deter predation by J. lalandii. However, laboratory bioassays using individual J. lalandii suggested a chemical basis for feeding deterrence originating from A. nodosum and highlighted the advantages of using ecologically relevant bioassays to monitor chemically mediated interactions between species in the marine environment. The nature of the chemical compound(s) responsible for the acquired chemical defence passively imparted by A. nodosum to B. papyracea is unknown.

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 Betty's 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.

The Cape Rock Lobster Jasus lalandii from the Bonteberg Excavation

The Cape Rock Lobster Jasus lalandii from the Bonteberg Excavation