Jasus Lalandii Research Articles

The ecological and socioeconomic implications of future total allowable catch decisions and illegal fishing scenarios for South Africa’s West Coast rock lobster fishery

The West Coast rock lobster fishery, vital to South Africa, is in a critical state with only 1.1 % of its original exploitable biomass remaining. This study evaluates effects of various total allowable catch (TAC) decisions on biomass and economic performance, taking illegal fishing, currently a serious problem, into account. TAC options included two sustainable options and an option (1500 mt), which could only be feasible if illegal fishing is stopped. Biomass projections, from 2022 to 2050, are modelled from a length-based model incorporating a Beverton and Holt stock-recruit relationship. The impacts of different TAC decisions on biomass, net seasonal incomes (NSI) and net present value (NPV) are assessed. Sensitivity to different discount rates is also considered. Biomass projections suggest an imminent collapse if legal fishing limits are set too high or if IUU fishing is not substantially reduced. The NPVs for the entire sectors are found to be highest under a 1500 mt TAC but unless accompanied by a halt to IUU fishing, would result in unsustainable catch rates and rapidly declining NSI in areas where many quota holders are located. Under the 550 mt TAC scenario, there is less risk of biomass declines but the quotas for many stakeholders would be economically unviable. Lower TAC options are forecast to lead to the functional exclusion of many rights holders and reduction in employment. The most secure and economically successful strategy is considered to be adjusting annual TACs in response to the effectiveness of controlling IUU fishing and changes in biomass.

Plastic gear loss estimates from a major Australian pot fishery

Abstract The quantity of plastic fishing gear lost to the ocean remains largely undocumented despite its importance for understanding the magnitude of fishery contributions to plastic marine debris and mitigating contamination at the source. This study estimated plastic gear loss from a major Australian pot fishery by interviewing 50 commercial fishers from the West Coast Rock Lobster Managed Fishery in 2021 to document the plastic gear components used, the number of pots lost, and the causes for gear loss. The estimated annual percentage of gear lost (10.8%) and rate of “active” gear loss by fishing effort (0.2%) were lower than global estimates for other pot fisheries indicating that plastic gear loss from this commercial fishery is relatively low. Plastic gear loss was attributed to rope (47.0%), pot components (30.7%), and floats (22.3%), of which 78.0% were polypropylene and polyethylene. The composition of pots, measures used to prevent gear loss, and changes to management could influence plastic gear loss from this fishery. This is the first study to examine plastic gear loss from an Australian pot fishery with a dynamic approach that provides robust estimates for better understanding plastic gear loss from fisheries and informing plastic mitigation efforts.

Estimating the economic income and social contributions derived from the South African west coast rock lobster fishery

The west coast rock lobster Jasus lalandii fishery is South Africa’s third-most-valuable fishery, although the stock is currently estimated at <2% of its pristine biomass. Recent ecologically necessary reductions in the total allowable catch (TAC) had negative economic impacts on stakeholders; however, these have not been quantified as current research into the socio-economic aspects of this fishery is limited. This study explored trends in the net seasonal income and employment opportunities of the fishery in the seasons 2016/17–2018/19 for its different sectors and representative individuals, by analysing records from the government authority and data collected from stakeholders in this fishery through interviews (n = 30) and surveys (n = 19). The results indicate that though the fishery was profitable over the three seasons, with the estimated contribution to gross national income ranging from R453 185 000 (US$33 302 714) in 2018/19 to R564 721 000 (US$41 499 039) in 2017/18, the decreasing quotas had a disproportionate negative effect on some of the representative individuals examined within the different sectors. These worrying economic trends for the different stakeholders indicate that, for effective resource recovery and equitable distribution of fishing opportunities, the socio-economic context of the fishery must be studied more extensively and must be included more directly in management decisions.

Distribution of astaxanthin in the spiny lobster Jasus lalandii: trends during biological cycles

ABSTRACT Astaxanthin, the dominant carotenoid pigment in the South African spiny lobster, Jasus lalandii, was quantified in haemolymph and tissue extracts by means of reverse phase-high pressure liquid chromatography and analysed with respect to growth and reproduction cycles of adults. Haemolymph, exoskeleton, muscle, gonads and hepatopancreas from both sexes, as well as egg parcels from berried females were collected within days of removing the animals from the ocean. The astaxanthin profile is, therefore, representative of spiny lobsters in the wild. Astaxanthin is significantly more in exoskeleton, ovaries and egg parcels, and is influenced by the ovarian cycle in females: it accumulated in growing oocytes and remained in the extruded eggs ostensibly for protection as antioxidant. Radioactive inulin was used to determine total haemolymph volume of a spiny lobster and the gravimetric contribution of body organs and various tissues to the total weight of these animals were measured: muscle tissue constitutes 33% of the total wet weight of J. lalandii, while haemolymph (22%) and exoskeleton (20%) are other major contributors. For maximal harvesting of astaxanthin from carcases, it would thus, be best to focus only on the exoskeleton with an emphasis on the carapace, which can be easily removed.

Development of an individual-based tag recapture model to benchmark biomass and harvest rates in an iconic lobster fishery

The West Coast Rock Lobster Managed Fishery (WCRLMF) moved from input to output controls in 2010. This change affected the relativity of fishery-based data sources (e.g., catch rates and landed size composition), making the assessment of the fishery problematic. A novel examination of the stock dynamics was required to ensure the robustness of the stock assessment and associated management arrangements. This study derived estimates of current biomass levels and harvest rates from the release of over 60,000 tagged western rock lobsters (Panulirus cygnus). A Brownie tag-recapture (BTR) model was initially implemented to provide an assessment on a fishery-wide basis. Estimates from this were compared to those derived from a novel purpose-built tag-recapture individual-based model (IBM) that accounted for sex, size, month, and location-specific changes in catchability. The two models produced similar estimates on a fishery-wide scale—harvest rate (HR 0.26 vs 0.30, respectively) and legal-sized biomass (about 24,500 vs 20,735 t, respectively)—while the IBM also provided estimates on a far finer spatial and temporal scale. Both models indicate that the WCRLMF is currently in a very sustainable condition and is being fished at a rate below maximum economic yield (HRmey is about 0.39). These findings were in concert with estimates derived for this fishery based on two separate catch-rate based population models, an integrated population model and a biomass-dynamics model. Such strong agreement among all models provides great certainty in the current assessment and management of this important marine resource.

World wide fund for nature South Africa (WWF) and the case of the West Coast rock lobster

Subject area The following subjects are addressed through the case: Integrated thinking; professional skills; ethics and values; sustainability; and responsible leadership. Study level/applicability This teaching case is aimed at Postgraduate accounting honours or masters students or MBA students. Case overview The case begins on 16 May 2018, with Jason Roberts, Head of Environmental Programmes at World wide fund for nature (WWF), reflecting over bad news. The Department of Agriculture, Forestry and Fisheries (“DAFF”, also referred to as “government”), have just approved the 2017/2018 Total Allowable Catch (“TAC”) for the West Coast (WC) rock lobster at 1,924 tons, almost three times the amount recommended by the scientific community. The events describe a history of tension between the primary objectives of the WWF and the government; difficulties in stakeholder management, and the potential consequences for the survival of the WC rock lobster and those who depend on it for their livelihood. The different perspectives held by different stakeholders; the relevance of the scientific evidence; the legal provisions in place and the process applicable to making the TAC decision; all highlight the complex environment in which decisions were made; to which the WWF is wondering how to respond. Expected learning outcomes The case’s primary learning objective is to highlight the variety of considerations involved in complex decision-making, also known as “integrated thinking”. Students will be required to critically analyse and evaluate the information in the case, as well as the exhibits; to comment on the appropriateness of various decisions and recommendations; evaluate the ethical/moral responsibilities of WWF; understand different perspectives and the reasons for these perspectives; identify actions and statements that reflect responsible leadership, as well as those that reflect the contrary; and apply learnings from this case to personally reflect on one’s role as a responsible business leader. Supplementary materials Teaching Notes are available for educators only. Subject code CSS 1: Accounting and Finance.

Analysis of biological and biochemical parameters of adult male spiny lobsters Jasus lalandii for identification of possible growth predictors

Biological body parameters of adult male West Coast rock lobsters, Jasus lalandii, of commercial size were analysed over two years to determine reserve accumulation during two moult (i.e. growth-) cycles. Two fishing areas were compared that were historically known for fast- and slow growth, respectively. In addition, setagenic development for moult stage determination and the biochemistry of the hepatopancreas were investigated from the fast growth area. This information was intended to confirm previously proposed predictors of annual male moult increment and identify potential new ones. Annual moult increments in these areas were determined from tag-and-recapture studies, including the seasons for which reserve accumulation was analysed. Data from the present study were not robust enough to confirm previously proposed predictors from peak accumulation months (March – May). Data arranged per moult stage were also unsuitable for prediction. Further results analysis, however, identified a subset of data that are potentially more useful: Hepatosomatic index HSI (+ 6 %), lipid content (+ 9 % ww, + 12 % wD) and lipid per whole hepatopancreas (+ 24 %) are all significantly higher in July 2011 than in July 2010, the last sampled months before the respective annual moult. These differences correlate with a 26 % (0.7 mm) faster growth during subsequent moult in 2011 than in 2010. Aspects of hepatopancreas lipid metabolism in the months prior to moult have therefore the potential to provide simple and robust predictors of growth in adult male J. lalandii. However, more research is required that also includes the months adjacent to July in more than one area and for a longer period than two years.

Changes in food-web structure and energy flow in kelp forest ecosystems on the south-west coast of South Africa following the invasion of Jasus lalandii

In the early 1990s, the West Coast rock lobster Jasus lalandii underwent an eastward shift in distribution into an area known as East of Cape Hangklip, where they had previously been rare. This shift has also been termed an invasion and resulted in a complete change in the benthic community structure, changing from a state dominated by herbivores and encrusting algae, to another state dominated by lobsters, sessile species, kelp and understory algae. Using the trophic modelling software Ecopath with Ecosim, baseline models of the pre- and post-invasion systems were created to better understand trophic pathways between the two different states and assess how fishing pressure may have driven the shift in ecosystem state. Using the baseline models, different fishing management strategies were tested to see whether the post lobster-invaded ecosystem could be shifted back or close to the pre-invasion state. Baseline models that were developed to describe the shift in ecosystem state reflected an increase in the presence of kelp, sessile species and lobsters, and the decline of encrusting algae and herbivores. Furthermore, the post-invasion system was more productive and less diverse than the pre-invasion system. Simulations using an Ecosim model showed that, with a reduction in fishing pressure on reef fish and abalone, and a simulated increase in fishing pressure on rock lobster, reef fish recovered to pre-invasion levels, but juvenile abalone, adult abalone and urchin biomass did not recover, probably due to the difficulty in capturing non-trophic interactions in the trophic models. Further functional groups such as sessile species, turf and foliose algae, also did not return to the pre-invasion state. This study concluded that a reduction in fishing pressure on abalone and reef fish, and the removal of rock lobster through increased fishing pressure, would allow the post-invasion ecosystem to partially recover to the pre-invasion state, but not completely, suggesting a hysteresis effect. Further exploration of management strategies through model simulations is needed, including those that can account for non-trophic processes.

Reorganising the lobster fishery value chain

In South Africa, approximately 38% of the net revenue attained from the near-shore lobster fishery value chain accrues to small-scale fishers. The remainder accrues to industrial processors and export marketeers. Moreover, the median annual net income attained by a typical small-scale fisher is less than a State Welfare grant recipient, which is problematic.This study examines the impact of reorganising the value chain for the high value West Coast rock lobster species—Jasus lalandii—on the economic welfare of fishers. The 2016–17 fishing season in the Northern and Western Cape provinces is examined through a mixed research method and various scenarios are presented. The measures presented in the scenarios of value chain reorganisation ought to improve the economic welfare of fishers by at least 136%. The potential for growth is even more profound with the introduction of market timing. This study provides insight into a coordinated developmental approach to improve the livelihoods of coastal community fishers.

Geographical and temporal variation in the diet of Bank Cormorants Phalacrocorax neglectus in South Africa

The Bank Cormorant Phalacrocorax neglectus is endemic to the Benguela upwelling ecosystem off southwest Africa and is classified as Endangered owing to a recent large reduction in its number. It is thought that food scarcity, including a decreased abundance of West Coast rock lobster Jasus lalandii, has been a major driver of the decrease, yet its diet in South Africa is poorly known. We collected 941 pellets regurgitated by Bank Cormorants, at 18 South African breeding colonies during 1975–1985, and 1 523 pellets at 17 colonies during 1995–2002. The species composition of the diet (% numbers) was significantly different between the two periods, with widespread decreases in proportions of rock lobster in the west and of octopus and cuttlefish Sepia spp. at most localities. These taxa were replaced in the diet by fish, including Gobiidae and Clinidae. The pelagic goby Sufflogobius bibarbatus, an important prey of Bank Cormorants in Namibia, was absent from pellets collected in 1975–1985 but common at northern localities from 1995–2002. Composition of the diet by frequency of occurrence was only determined for 1995–2002, when rock lobster was present in 67% of all samples collected, cuttlefish in 39%, and Clinidae in 32%. Data for 1975–1985 and 1995–2002 showed that carapace lengths of rock lobsters eaten by Bank Cormorants averaged 56 mm (range 22–82 mm) and 50 mm (range 22–75 mm), respectively, which compares to the minimum legal size of 75 mm for fisheries in South Africa. This energy- rich prey item was an important constituent of the diet in the winter breeding period.

A diagnosis of the status and effectiveness of marine fisheries management in South Africa based on two representative case studies

Effective fisheries management is crucial for ensuring resource sustainability, economic stability and food security for those depending on the fisheries. This study assessed the current state of management in South Africa by examining two case studies: the fisheries for West Coast rock lobster (WCRL) and small pelagic species (SP). The WCRL fishery includes small-scale and larger scale commercial sectors and the resource is valuable and accessible from the shore. The SP fishery is offshore, more capital-intensive, requiring specialized vessels and gear and harvests a lower-value product. The methods consisted of a review of available information and structured assessment of stakeholder opinions. Opinions were obtained through specifically-designed questionnaires and sent to stakeholders from diverse perspectives, selected for their broad knowledge and experience with one or both fisheries. The management framework used for the questionnaire has potential for international application in other fisheries, with some adaptation to local circumstances.The results revealed significant differences in overall performance of management of the two fisheries, with that for SP being satisfactory to good but that for WCRL being below the necessary standards overall and across many criteria. Weakest performance in both fisheries was related to Capacity in the management authority and Enforcement and compliance. Stakeholder engagement, socio-economic research, and effective implementation of required management measures were other particular concerns in the WCRL fishery. In the SP fishery, most of the other functions assessed were being performed adequately to well. Management efficiency in both fisheries had decreased over the last five to 10 years.

Effects of chronic hypercapnia and elevated temperature on the immune response of the spiny lobster, Jasus lalandii

The West Coast rock lobster (WCRL), Jasus lalandii, inhabits highly variable environments frequented by upwelling events, episodes of hypercapnia and large temperature variations. Coupled with the predicted threat of ocean acidification and temperature change for the coming centuries, the immune response in this crustacean will most likely be affected. We therefore tested the hypothesis that chronic exposure to hypercapnia and elevated seawater temperature will alter immune function of the WCRL. The chronic effects of four combinations of two stressors (seawater pCO2 and temperature) on the total number of circulating haemocytes (THC) as well as on the lobsters’ ability to clear (inactivate) an injected dose of Vibrio anguillarum from haemolymph circulation were assessed. Juvenile lobsters were held in normocapnic (pH 8.01) or hypercapnic (pH 7.34) conditions at two temperatures (15.6 and 18.9 °C) for 48 weeks (n = 30 lobster per treatment), after which a subsample of lobsters (n = 8/treatment), all at a similar moult stage, were selected from each treatment for the immune challenge. Baseline levels of haemocytes (THC ml−1) and bacteria (CFU ml−1) in their haemolymph were quantified 24 h prior to bacterial challenge. Lobsters were then challenged by injecting 4 × 104V. anguillarum per g body weight directly into the cardiac region of each lobster and circulating haemocyte and culturable bacteria were measured at 20 min post challenge. No significant differences in THC ml−1 (p < 0.05) were observed between any of the treatment groups prior to the bacterial challenge. However lobsters chronically exposed to a combination of hypercapnia and low temperature had significantly higher (p < 0.05) THCs post-challenge in comparison with lobsters chronically exposed to hypercapnia and high temperature. A significant interactive effect was recorded between temperature and pH for the post-challenge THC data (two-way ANOVA, p = 0.0025). Lobster were very efficient at rendering an injected dose of bacteria non-culturable, with more than 83% of the theoretical challenge dose (∼1.7 × 105Vibrio ml−1 haemolymph) inactivated within the first 10 min following injection. Although differences in the inactivation of V. anguillarum were observed between treatment groups, none of these differences were significant. Clearance efficiency was in the following order: Hypercapnia/low temperature > normocapnia/high temperature > normocapnia/low temperature > hypercapnia/high temperature. This study demonstrated that despite chronic exposure to combinations of reduced seawater pH and high temperature, the WCRL was still capable of rapidly rendering an injected dose of bacteria non-culturable.

Macro-benthic invertebrate assemblages in the Betty’s Bay Marine Protected Area (Kogelberg region South Africa)

The Betty’s Bay Marine Protected Area (MPA) was established to protect endangered species like the African penguin (Spheniscus demersus), abalone (Haliotis midae) and the west coast rock lobster (Jasus lalandii). Very little is known about the effects their protection has had on other assemblages within the MPA. To this end, a photo-quadratic survey of the macro-benthic invertebrates was conducted to provide more information on these communities. The photo-quadratic survey was conducted within two depth zones at 10 sites, seven inside and three outside the MPA. Representative samples were collected to assist in the identification of organisms. Eight hundred and eighty one photo-quadrats were analysed to determine percentage cover, diversity and community structure of the invertebrate assemblages. A mean evenness of 0.88 species was recorded for the entire study area and a total of 250 species were documented. Location (inside or outside MPA) had a significant effect on species richness (F1,637.4=32, p<0.001) and diversity (F1,5.47=24.18, p<0.001), while depth had a significant effect on percentage cover (F1,761=5.9, p<0.05) and community structure. Colonial taxa such as Porifera, Cnidaria and algae were dominant, while semi-motile Mollusca were in relatively low abundance.

A red tide forming dinoflagellate Prorocentrum triestinum: identification, phylogeny and impacts on St Helena Bay, South Africa

:A non-toxic red tide with resulting anoxia was the cause of a major harmful algal bloom in St Helena Bay, South Africa, in February and March 2015. The red tide was observed along approximately 200 km of the Namaqua coastline extending well north of the Olifants River and southward into the bay. A maximum cell concentration of 14.32 × 106 cells l−1 was recorded in the southern reaches of the bay, and oxygen concentrations declined to as low as 0.06 ml l−1 in the shallow waters off Dwarskersbos. The hypoxia induced ecological fallout was significant with massive marine mortalities, including an estimated 415 tons of rock lobster (Jasus lalandii). The causative organism was identified morphologically, ultrastructurally and phylogenetically (using partial sequences of the 18S small subunit rDNA and the 28S large subunit rDNA) as Prorocentrum triestinum (Dinophyceae). Light and electron microscopy (both scanning and transmission) also facilitated identification of P. triestinum and addressed possible confusion with similar taxa. The global incidence of P. triestinum blooms is low, with hot spots limited to coastal areas in eastern China and the Mediterranean Sea, where blooms are sometimes associated with anthropogenic nutrient pollution. The harmful bloom documented here is the first exceptional bloom event with anoxic-related marine mortalities induced by P. triestinum in a major eastern boundary upwelling system such as the Benguela.

Defining ecologically relevant scales for spatial protection with long-term data on an endangered seabird and local prey availability.

Human activities are important drivers of marine ecosystem functioning. However, separating the synergistic effects of fishing and environmental variability on the prey base of nontarget predators is difficult, often because prey availability estimates on appropriate scales are lacking. Understanding how prey abundance at different spatial scales links to population change can help integrate the needs of nontarget predators into fisheries management by defining ecologically relevant areas for spatial protection. We investigated the local population response (number of breeders) of the Bank Cormorant (Phalacrocorax neglectus), a range-restricted endangered seabird, to the availability of its prey, the heavily fished west coast rock lobster (Jasus lalandii). Using Bayesian state-space modeled cormorant counts at 3 colonies, 22 years of fisheries-independent data on local lobster abundance, and generalized additive modeling, we determined the spatial scale pertinent to these relationships in areas with different lobster availability. Cormorant numbers responded positively to lobster availability in the regions with intermediate and high abundance but not where regime shifts and fishing pressure had depleted lobster stocks. The relationships were strongest when lobsters 20-30 km offshore of the colony were considered, a distance greater than the Bank Cormorant's foraging range when breeding, and may have been influenced by prey availability for nonbreeding birds, prey switching, or prey ecology. Our results highlight the importance of considering the scale of ecological relationships in marine spatial planning and suggest that designing spatial protection around focal species can benefit marine predators across their full life cycle. We propose the precautionary implementation of small-scale marine protected areas, followed by robust assessment and adaptive-management, to confirm population-level benefits for the cormorants, their prey, and the wider ecosystem, without negative impacts on local fisheries.

The economic value of South African kelp forests and temperate reefs: Past, present and future

Abstract In South Africa, kelp forests and associated temperate reefs dominate the nearshore subtidal zone in the southern Benguela, with kelp forests covering approximately 1000 km of the coastline. These ecosystems provide a range of goods and services that are of immense ecological, social and economic importance. A number of valuable species on these subtidal reefs are overexploited and have reached a state of crisis since the 1990s. Many linefish stocks are considered collapsed or overexploited, West Coast rock lobster populations are estimated to be at

Potential application of baited remote underwater video to survey abundance of west coast rock lobster Jasus lalandii

AbstractThe first assessment of the baited remote underwater video system (BRUVs) for monitoring rock lobster Jasus lalandii (Milne‐Edwards) in South Africa was compared to annual ring net and trap survey data. Count data from 58 BRUVs, 36 ring net and 95 trap samples were fitted with generalised additive models using depth, habitat, time and spatial gradient as independent variables. A power analysis was used to determine the number of samples needed per annum to detect a 5 and 10% increase and decrease in population size. The BRUVs outperformed the nets and traps in terms of sampling effort and were better at detecting changes in abundance of lobster than abundance of three fish species. Considering factors such as cost, analysis time, additional data and environmental impact, traps are the most feasible method in deeper waters but BRUVs could replace nets and traps in depths less than 60 m, low‐density areas and marine reserves.

The effects of hypercapnia on the West Coast rock lobster (Jasus lalandii) through acute exposure to decreased seawater pH — Physiological and biochemical responses

The cold water palinurid Jasus lalandii (“West Coast rock lobster”) is a commercially important crustacean in South Africa and Namibia and inhabits the Benguela Current Eastern Boundary System. This habitat is characterised by strong upwelling events in summer and algal blooms with their subsequent decay in autumn. Upwelling can lead to acute hypercapnia whereas the algal decay is associated with acute hypercapnic hypoxia. Both types of hypercapnic events could become more frequent and severe in the future due to ongoing climate change. The aim of the present study was, however, to study the capability and mechanisms of response in J. lalandii to hypercapnia exclusively. Accordingly, the following research questions were formulated: 1) To what extent is haemocyanin oxygen-binding affinity of adult J. lalandii pH-sensitive? 2) Can adult male J. lalandii respond swiftly to drastic changes in pH? 3) What physiological mechanisms facilitate a potential response to a drastically declining pH, i.e. acute hypercapnia? These questions were answered by analysing 1) the pH sensitivity of the haemocyanin's oxygen binding properties and 2) in vivo changes in the acid–base balance of adult J. lalandii during acute exposure to hypercapnia (pH7.4). Results showed the following: 1) Haemocyanin displays a strong Bohr shift (whole haemolymph: ΔlogP50/ΔpH=−1.17; dialysed haemolymph: ΔlogP50/ΔpH=−0.84) in response to lowering of pH. 2) Acute hypercapnia leads to a decline in extracellular pH within the initial 1.5h of exposure. 3) Thereafter, active compensation becomes apparent as the bicarbonate levels start to increase, with complete compensation reached after 5h of exposure (+2.3mmoll−1; +48%). 3) This bicarbonate increase is reversed when returning lobsters to normocapnia (pH7.9). 4) Levels of molecular modulators of haemocyanin oxygen affinity (Ca2+, Mg2+ and l-lactate) do not change during acute exposure to hypercapnia.Our results show the capability of adult J. lalandii to rapidly and fully compensate the experienced extracellular acidosis, protecting oxygen carrying capacity of haemocyanin and ensuring an outward gradient of CO2. The West Coast rock lobster is therefore well equipped for its habitat where these hypercapnic events are known to occur frequently.

Acid–base balance and changes in haemolymph properties of the South African rock lobsters, Jasus lalandii, a palinurid decapod, during chronic hypercapnia

Few studies exist reporting on long-term exposure of crustaceans to hypercapnia. We exposed juvenile South African rock lobsters, Jasus lalandii, to hypercapnic conditions of pH 7.3 for 28 weeks and subsequently analysed changes in the extracellular fluid (haemolymph). Results revealed, for the first time, adjustments in the haemolymph of a palinurid crustacean during chronic hypercapnic exposure: 1) acid-base balance was adjusted and sustained by increased bicarbonate and 2) quantity and oxygen binding properties of haemocyanin changed. Compared with lobsters kept under normocapnic conditions (pH 8.0), during prolonged hypercapnia, juvenile lobsters increased bicarbonate buffering of haemolymph. This is necessary to provide optimum pH conditions for oxygen binding of haemocyanin and functioning of respiration in the presence of a strong Bohr Effect. Furthermore, modification of the intrinsic structure of the haemocyanin molecule, and not the presence of molecular modulators, seems to improve oxygen affinity under conditions of elevated pCO2.

Was overfishing of predatory fish responsible for a lobster-induced regime shift in the Benguela?

The top-down effects of predators have been demonstrated for terrestrial, freshwater and marine systems and their removal can cause a shift in ecosystem state. In many cases, the depletion of top-predators occurred long before humans began monitoring these systems, but models can elucidate likely ecosystem changes. In this paper we use a multispecies model to demonstrate that the abundance of predators can induce different ecosystem states, emphasising the importance of sustainable harvesting. Our model is founded on empirical data documenting a regime-shift that took place in the kelp-forest ecosystem along the south-west coast of South Africa following an ‘invasion’ by the West Coast rock lobster Jasus lalandii in the early 1990s. Formerly dominated by herbivores and encrusting corallines, the ecosystem became dominated by lobsters and macroalgae. A combination of illegal fishing of abalone Haliotis midae and the lobster-induced extermination of the urchin Parechinus angulosus (which shelters juvenile abalone) depleted abalone stocks severely. In this currently over-fished ecosystem where predators of lobsters are scarce, the regime-shift appears irreversible. Using an intermediate complexity model of lobster, urchin and abalone relationships, we simulated the effects of predatory fish at various population levels on the course of development of the currently lobster-dominated system. Our results indicate that current levels of fish biomass (<10% of the pristine population) would have been too small to significantly affect the lobster population. However, at pristine levels of fish abundance (or even 50% less), the invasion of lobsters would have been controlled by linefish, and urchin and abalone populations would not have collapsed. The effect of the lobster invasion had a greater influence on abalone abundance than illegal fishing, but together they severely depleted the abalone. Ecosystem effects of historical exploitation of top predators are of central concern, and our ecosystem model indicates that depletion of linefish had severe consequences for lobsters, urchins and abalone, illustrating how overfishing of top predators may precipitate regime shifts, with profound socio-economic consequences.