Sd Frusher

Overfishing reduces resilience of kelp beds to climate-driven catastrophic phase shift

A key consideration in assessing impacts of climate change is the possibility of synergistic effects with other human-induced stressors. In the ocean realm, climate change and overfishing pose two of the greatest challenges to the structure and functioning of marine ecosystems. In eastern Tasmania, temperate coastal waters are warming at approximately four times the global ocean warming average, representing the fastest rate of warming in the Southern Hemisphere. This has driven range extension of the ecologically important long-spined sea urchin (Centrostephanus rodgersii), which has now commenced catastrophic overgrazing of productive Tasmanian kelp beds leading to loss of biodiversity and important rocky reef ecosystem services. Coincident with the overgrazing is heavy fishing of reef-based predators including the spiny lobster Jasus edwardsii. By conducting experiments inside and outside Marine Protected Areas we show that fishing, by removing large predatory lobsters, has reduced the resilience of kelp beds against the climate-driven threat of the sea urchin and thus increased risk of catastrophic shift to widespread sea urchin barrens. This shows that interactions between multiple human-induced stressors can exacerbate nonlinear responses of ecosystems to climate change and limit the adaptive capacity of these systems. Management actions focused on reducing the risk of catastrophic phase shift in ecosystems are particularly urgent in the face of ongoing warming and unprecedented levels of predator removal from the worlds oceans.

Keystone species and mangrove forest dynamics: the influence of burrowing by crabs on soil nutrient status and forest productivity

Abstract The density of the burrowing crab fauna in a mangrove forest was reduced, using pitfall traps, to test the hypothesis that decreased burrowing would lead to: (1) increased soil sulphide concentrations; (2) altered nutrient concentrations; and (3) decreased forest productivity and growth. Experiments were conducted in Rhizophora -dominated forests in north Queensland, Australia, over a 12-month period. Crabs were trapped and removed from the experimental plots during 1 week each month for a year. Soil chemical and forest growth parameters were measured at monthly intervals in the experimental and appropriate control plots. Over the course of the experiment, soil sulphide and ammonium concentrations increased to levels which were significantly higher in plots from which crabs were being removed in comparison to controls. No differences were observed for either phosphate or nitrate plus nitrite. Cumulative forest growth, as measured by stipule fall, was significantly less in removal plots than in controls. Additionally, trees in the removal plots had significantly less reproductive output than did trees in control plots. These results support the hypothesis that burrowing by crabs is an important process in Australian Rhizophora forests. It appears that burrowing affects soil aeration which in turn affects the productivity and reproductive output of Rhizophora . Knowledge of the ecology of grapsid crabs from other continents, however, is very limited. It remains to be seen if the roles played by grapsid crabs are as important elsewhere as in Australia. This is particularly true for the Caribbean region from which many of our paradigms concerning mangrove forest ecology were developed.

Biodiversity redistribution under climate change : Impacts on ecosystems and human well-being

Consequences of shifting species distributions Climate change is causing geographical redistribution of plant and animal species globally. These distributional shifts are leading to new ecosystems and ecological communities, changes that will affect human society. Pecl et al. review these current and future impacts and assess their implications for sustainable development goals. Science, this issue p. eaai9214 BACKGROUND The success of human societies depends intimately on the living components of natural and managed systems. Although the geographical range limits of species are dynamic and fluctuate over time, climate change is impelling a universal redistribution of life on Earth. For marine, freshwater, and terrestrial species alike, the first response to changing climate is often a shift in location, to stay within preferred environmental conditions. At the cooler extremes of their distributions, species are moving poleward, whereas range limits are contracting at the warmer range edge, where temperatures are no longer tolerable. On land, species are also moving to cooler, higher elevations; in the ocean, they are moving to colder water at greater depths. Because different species respond at different rates and to varying degrees, key interactions among species are often disrupted, and new interactions develop. These idiosyncrasies can result in novel biotic communities and rapid changes in ecosystem functioning, with pervasive and sometimes unexpected consequences that propagate through and affect both biological and human communities. ADVANCES At a time when the world is anticipating unprecedented increases in human population growth and demands, the ability of natural ecosystems to deliver ecosystem services is being challenged by the largest climate-driven global redistribution of species since the Last Glacial Maximum. We demonstrate the serious consequences of this species redistribution for economic development, livelihoods, food security, human health, and culture, and we document feedbacks on climate itself. As with other impacts of climate change, species range shifts will leave “winners” and “losers” in their wake, radically reshaping the pattern of human well-being between regions and different sectors and potentially leading to substantial conflict. The pervasive impacts of changes in species distribution transcend single systems or dimensions, with feedbacks and linkages between multiple interacting scales and through whole ecosystems, inclusive of humans. We argue that the negative effects of climate change cannot be adequately anticipated or prepared for unless species responses are explicitly included in decision-making and global strategic frameworks. OUTLOOK Despite mounting evidence for the pervasive and substantial impacts of a climate-driven redistribution of Earth’s species, current global goals, policies, and international agreements fail to account for these effects. With the predicted intensification of species movements and their diverse societal and environmental impacts, awareness of species “on the move” should be incorporated into local, regional, and global assessments as standard practice. This will raise hope that future targets—whether they be global sustainability goals, plans for regional biodiversity maintenance, or local fishing or forestry harvest strategies—can be achievable and that society is prepared for a world of universal ecological change. Human society has yet to appreciate the implications of unprecedented species redistribution for life on Earth, including for human lives. Even if greenhouse gas emissions stopped today, the responses required in human systems to adapt to the most serious effects of climate-driven species redistribution would be massive. Meeting these challenges requires governance that can anticipate and adapt to changing conditions, as well as minimize negative consequences. As the global climate changes, human well-being, ecosystem function, and even climate itself are increasingly affected by the shifting geography of life. Climate-driven changes in species distributions, or range shifts, affect human well-being both directly (for example, through emerging diseases and changes in food supply) and indirectly (by degrading ecosystem health). Some range shifts even create feedbacks (positive or negative) on the climate system, altering the pace of climate change. Distributions of Earth’s species are changing at accelerating rates, increasingly driven by human-mediated climate change. Such changes are already altering the composition of ecological communities, but beyond conservation of natural systems, how and why does this matter? We review evidence that climate-driven species redistribution at regional to global scales affects ecosystem functioning, human well-being, and the dynamics of climate change itself. Production of natural resources required for food security, patterns of disease transmission, and processes of carbon sequestration are all altered by changes in species distribution. Consideration of these effects of biodiversity redistribution is critical yet lacking in most mitigation and adaptation strategies, including the United Nation’s Sustainable Development Goals.

Estimating the size-transition matrix for Tasmanian rock lobster, Jasus edwardsii

Assessment of the southern rock lobster (Jasus edwardsii) resource in Tasmania is based on a size-structured population dynamics model. One of the most important inputs to this model is the set of matrices that represent the season-specific probabilities of a lobster growing from one size-class to another. These matrices are estimated from tag–recapture data within a maximum-likelihood estimation framework. Measures of precision are determined from the asymptotic variance–covariance matrix. Various alternative models are contrasted for one site in the south-east of Tasmania, and a best model is selected by the likelihood ratio test. The growth model used is based on a generalization of the von Bertalanffy growth equation. Growth rates differ markedly among regions around Tasmania, being slowest in the south and fastest in the north. Growth of legal-size males is noticeably faster than that of legal-size females. It is shown that ignoring the effects of selectivity can lead to biased estimates of growth rate. An extension to the method is presented and applied that estimates size-specific selectivity in an attempt to eliminate this bias.

Distribution and abundance of grapsid crabs (Grapsidae) in a mangrove estuary: Effects of sediment characteristics, salinity tolerances, and osmoregulatory ability

Crabs (Grapsidae,Sesarma) are the dominant macrofaunal group of mangrove forest soils in northern Australia. Little is known about the ecology of these crabs or the factors that influence their distribution in mangrove forests. Pitfall traps were used to sample grapsid crabs in the Murray River estuary in north Queensland. Sampling was conducted at five sites along a salinity gradient from <1‰ at upstream sites to >35‰ at the river mouth. At each site, trapping was done in both low and high intertidal forests. We characterized the sediments at each site by measuring percent sand, silt, clay and organic matter, Eh, pH, and soil pore-water salinity. Four species of grapsids dominated the crab fauna along the Murray River (Sesarma semperi-longicristatum, S. messa, S. brevicristatum, andS. brevipes). Distinct zonation patterns were found along the salinity gradient and between high and low intertidal forests.S. messa was dominant in high intertidal, downstream forests, high and low intertidal forests in the middle to downstream portion of the river, and in low intertidal forests in the central reach of the river.S. brevipes was dominant in both low and high intertidal zone forests at low salinity upstream sites.S. brevicristatum was most abundant in the central reaches of the river and only in the high intertidal zone.S. semperi-longicristatum was found only in the low intertidal zone, downstream forest. Subsequently, tests of salinity tolerances of these crabs were carried out in the laboratory. These indicated very wide tolerances over salinities from completely fresh to hypersaline (60‰). The osmoregulatory abilities of the crabs were also found to vary. However, neither their salinity tolerance nor osmoregulatory ability adequately explain the zonation patterns were measured in the field. For example,S. brevicristatum had the most restricted distribution, but it had the second broadest salinity tolerance and osmoregulatory ability. Sediment characteristics explained a significant amount of the variation in abundance for two of the crab species. Pore-water salinity provided no explanatory power for any of the species. Individual species abundances are probably influenced by additional factors such as interspecific competition and predation.

The short history of research in a marine climate change hotspot: from anecdote to adaptation in south-east Australia

Climate change is not being felt equally around the world. Regions where warming is most rapid will be among those to experience impacts first, will need to develop early responses to these impacts and can provide a guide for management elsewhere. We describe the research history in one such global marine hotspot—south-east Australia—where a number of contentions about the value of hotspots as natural laboratories have been supported, including (1) early reporting of changes (2) early documentation of impacts, and (3) earlier development and promotion of adaptation options. We illustrate a transition from single discipline impacts-focused research to an inter-disciplinary systems view of adaptation research. This transition occurred against a background of change in the political position around climate change and was facilitated by four preconditioning factors. These were: (1) early observations of rapid oceanic change that coincided with (2) biological change which together provided a focus for action, (3) the strong marine orientation and history of management in the region, and (4) the presence of well developed networks. Three case studies collectively show the critical role of inter-disciplinary engagement and stakeholder participation in supporting industry and government adaptation planning.

Rapid assessment of fisheries species sensitivity to climate change

Climate change driven alterations in the distribution and abundance of marine species, and the timing of their life history events (phenology), are being reported around the globe. However, we have limited capacity to detect and predict these responses, even for comparatively well studied commercial fishery species. Fisheries provide significant socio-economic benefits for many coastal communities, and early warning of potential changes to fish stocks will provide managers and other stakeholders with the best opportunity to adapt to these impacts. Rapid assessment methods that can estimate the sensitivity of species to climate change in a wide range of contexts are needed. This study establishes an objective, flexible and cost effective framework for prioritising future ecological research and subsequent investment in adaptation responses in the face of resource constraints. We build on an ecological risk assessment framework to assess relative sensitivities of commercial species to climate change drivers, specifically in relation to their distribution, abundance and phenology, and demonstrate our approach using key species within the fast warming region of south-eastern Australia. Our approach has enabled fisheries managers to understand likely changes to fisheries under a range of climate change scenarios, highlighted critical research gaps and priorities, and assisted marine industries to identify adaptation strategies that maximise positive outcomes.

Relationship between settlement of southern rock lobster pueruli, Jasus edwardsii, and recruitment to the fishery in Tasmania, Australia

Puerulus catches on artificial collectors were measured monthly at four sites around Tasmania from 1991 to April 2000, with the aim of predicting future changes in recruitment to the fishery. Support for the potential of catch-rate prediction in Tasmania was provided at the two sites that have overlap of several years between indices of puerulus settlement and indices of the abundance of recruits to the fishery. At Bicheno, on the northeast coast, correlations between annual puerulus index and commercial catch rates were highly significant, with a lag of 5 years (P< 0.01). Similar interannual trends in puerulus index and estimates from a stock-assessment model of the biomass of recruits to the fishery provided additional support for a link with puerulus index. A 5-fold interannual variation in puerulus index detected at Bicheno, with a peak in 1995, was preceded by 3 years of relatively low puerulus catch. The peak in puerulus index appears to lead to an increase in the abundance of sublegal males in research sampling 3 years later. Correlation between annual measures of puerulus index and catch rate also appeared significant at King Island (P= 0.06) although data at this site had less contrast.

Space-time variation in catchability of southern rock lobster Jasus edwardsii in Tasmania explained by environmental, physiological and density-dependent processes

A seasonal catchability model for the rock lobster Jasus edwardsii, which had been developed previously for a population in a scientific reserve, was applied to catchability estimates over several years in northern and southern fishing regions off Tasmania, Australia. Catchability was estimated from commercial catch and effort data and fishery-independent estimates of exploitation rates. The seasonal catchability models describe the effects of water temperature, moulting and mating on catchability. They suggest that similar environmental and physiological processes underpin seasonal catchability in the two regions of the fishery, but that the relative importance of these factors varies considerably between the two regions. Physiological processes dominate the pattern of catchability in the north while water temperature contributes significantly to the model only in the south. Interannual variation in relative catchability was correlated with density-dependent processes. Full models described 72% of the total variation in catchability over 6 years in the south and 80% of the total variation over 4 years in the north.

Seasonal occurrence and population structure of the broadnose sevengill shark Notorynchus cepedianus in coastal habitats of south-east Tasmania

Research longline sampling was conducted seasonally from December 2006 to February 2009 to investigate the occurrence and population structure of the broadnose sevengill shark Notorynchus cepedianus in coastal areas of south-east Tasmania. Notorynchus cepedianus showed a consistent temporal trend in seasonal occurrence in Norfolk Bay characterized by high abundances in summer to near absence in winter. This pattern was less pronounced in the Derwent Estuary, where fish were still caught during winter. The absence of smaller total length (L(T) ) classes (<80 cm) from the catches suggests that N. cepedianus are not using these coastal habitats as nursery areas. Of the 457 individuals tagged, 68 (15%) were recaptured. Time at liberty ranged from 6 days to almost 4 years and all but one of the recaptures were caught in its original tagging location, suggesting site fidelity. The large number of N. cepedianus in these coastal systems over summer indicates that these areas are important habitats for this species and that N. cepedianus may have a significant influence on community dynamics through both direct and indirect predator-prey interactions.