Response of temperate marine food webs to climate change and ocean acidification: bridging the gap between experimental manipulation and complex foodwebs

Global warming and ocean acidification are forecast to exert significant impacts on marine ecosystems, while intensive exploitation of commercial marine species has already caused large-scale reorganizations of biological communities in many of the world’s marine ecosystems. Whilst our understanding on the impact of warming and acidification in isolation on individual species has steadily increased, we still know little on the combined effect of these two global stressors on marine food webs, especially under realistic experimental settings or real-world systems. We particularly lack evidence of how the top of the food web (piscivores and apex predators) will respond to future climate change (ocean warming and acidification) because responses of ecological communities could vary with increasing trophic level. The picture is further complicated by the interaction of global and local stressors that affect our oceans, such as fishing pressure. Accurate predictions of the potential effects of these global and local stressors at ecosystem-levels require a comprehensive understanding of how entire communities of species respond to climate change. Mechanistic insights revealed by a combination of different approaches such as experimental manipulation of food webs, and integrated with ecosystem modelling approaches provide a way forward to improve our understanding of the functioning of future food webs. In this thesis, I show how the combined effect of such global and local stressors could affect a three trophic level temperate marine mesocosm food web and how these outcomes could be translated to predict the response of ecological communities in a four trophic level natural food web. Using a sophisticated mesocosm experiment (elevated pCO2 of approximately 900 ppm and warming of +2.8°C), I first modelled how energy fluxes are likely to change in marine food webs in response to future climate. I experimentally show that the combined stress of acidification and warming could reduce energy flows from the first trophic level (primary producers and detritus) to the second (herbivores) and from the second to the third trophic level (carnivores). Although warming and acidification jointly boosted primary producer biomass, most of it was constrained to the base of the food web as consumers were unable to transfer unpalatable cyanobacterial production up the food web. In contrast, ocean acidification affected the food web positively by increasing the biomass from producers to carnivores. I then developed a unique approach that combines the empirical data on species response to climate change from our mesocosms experiments with historical population data (fisheries biomass and catch data) to predict future changes in a natural food web. I incorporated physiological and behavioural responses (complex species-interactions) of species from primary producers to top predators such as sharks within a time-dynamic integrated ecosystem modelling approach (Ecosim). I show that under continuation of the present-day fishing regime, warming and ocean acidification will benefit most of the higher trophic level community groups (e.g. mammals, birds, demersal finfish). The positive effects of warming and acidification in isolation will likely be reduced under their combined effect (antagonistic interaction) which is likely to be further negated under increased fishing pressure, decreasing the individual biomass of consumers. The total future fisheries biomass, however, will likely still remain high compared to the present-day scenario. This is because unharvested species in present day fishery will likely benefit from decreased competition and an increase in biomass. Nevertheless, ecological indicator such as the Shannon diversity index suggests a trade-off between biomass gain and loss of functional diversity within food webs. The mechanisms behind the increase in biomass at higher trophic level consumers and a decrease in the biomass of lower trophic levels is mostly driven by the increasing top down control by consumers on their prey through increasing trophic interaction strength and a positive response of some of the prey groups under warming irrespective of acidification. I show that in a future food web, temperature-driven changes in direct trophic interactions strength (feeding and competition) will largely determine the direction of biomass change (increase or decrease) of consumers due to higher mean interaction strength (magnitude of change). In contrast, although acidification induces a relatively small increase in trophic interaction strength it shows a much larger change in the percent interactions altered for indirect interactions. Hence, ocean acidification is likely to propagate boosted primary consumer biomass to higher trophic levels. The findings of this thesis reveal that warming in combination with acidification can increase trophic interaction strengths (top down control), resulting in a reorganization of community biomass structure by reducing or increasing the biomass of resources and consumers and a loss of functional diversity within the food web. Also, the degree to which warming and acidification will be beneficial or detrimental to functional groups in future food webs will largely depend on how interaction strengths affects individual consumers or resource groups due to multi-trophic species interaction, the availability of prey resources and the complexity of the food web considered (e.g. three or four trophic level and more diverse ecological communities).Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 201

The Fisheries Co-Management Guidebook: Emerging research for the effective management of small-scale fisheries

Small-scale fisheries account for 40% of global fish catch and employ more than 90% of the world’s fishers, defining the livelihoods, nutrition, and culture of a substantial and diverse segment of humankind. In recent decades collaborative forms of fisheries management, including co-management, have gained popularity as the most appropriate, fair, and effective form of governance for small-scale fisheries. Fisheries co-management is envisioned as a process by which to reverse the interconnected crises of hunger, poverty, and biodiversity loss, transforming small-scale fisheries into engines of prosperity, inclusion, and sustainability. Yet co-management can succeed or fail, and implementation does not mean positive impacts for food security, nutrition, livelihoods, or biodiversity. Nor does it imply programs will respect human rights, gender equality, or principles of justice and equity. Fewer management programs implemented well might achieve far more than many implemented poorly, and poorly implemented co-management can be worse than no management. This guide was designed to assist practitioners in understanding the latest research on what constitutes successful fisheries co-management, and how to reach this objective. The aim is to synthesize emerging research that, if adopted, would substantially improve impacts across both ecological and social dimensions. The guide is presented as an infographic series with each infographic summarizing a substantial body of research from a particular field. This work was undertaken through a growing partnership between the Wildlife Conservation Society and WorldFish, aiming to increase collaboration between conservation and development sectors. This partnership represents a milestone towards integrated approaches for the benefit of both ecosystems and local communities

Bioeconomics of Commercial Marine Fisheries of Bay of Bengal: Status and Direction

The fishery of the Bay of Bengal (BOB) is assumed to be suffering from the overexploitation. This paper aims to assess the sustainability of current level of fishing effort as well as possible changes driven by anthropogenic and climate driven factors. Therefore, the commercial marine fishery of BOB for the period of 1985/86 to 2007/08 is analyzed by applying Gordon-Schaefer Surplus Production Model on time series of total catch and standardized effort. Static reference points such as open-access equilibrium, maximum economic yield, and maximum sustainable yield are established. Assumptions about potential climatic and anthropogenic effects on r (intrinsic growth rate) and K (carrying capacity) of BOB fishery have been made under three different reference equilibriums. The results showed that the fishery is not biologically overexploited; however, it is predicted to be passing a critical situation, in terms of achieving reference points in the near future. But, on the other hand, economic overfishing started several years before. Higher fishing effort, and inadequate institutional and legal framework have been the major bottlenecks for the proper management of BOB fisheries and these may leads fishery more vulnerable against changing marine realm. Thus, the present study calls for policy intervention to rescue the stock from the existing high fishing pressure that would lead to depletion

Bioaccumulation of heavy metals in some commercially important fishes from a tropical river estuary suggests higher potential health risk in children than adults.

The Karnaphuli River estuary, located in southeast coast of Bangladesh, is largely exposed to heavy metal contamination as it receives a huge amount of untreated industrial effluents from the Chottagram City. This study aimed to assess the concentrations of five heavy metals (As, Pb, Cd, Cr and Cu) and their bioaccumulation status in six commercially important fishes, and also to evaluate the potential human health risk for local consumers. The hierarchy of the measured concentration level (mg/kg) of the metals was as follows: Pb (13.88) > Cu (12.10) > As (4.89) > Cr (3.36) > Cd (0.39). The Fulton's condition factor denoted that fishes were in better 'condition' and most of the species were in positive allometric growth. The bioaccumulation factors (BAFs) of the contaminants observed in the species were in the following orders: Cu (1971.42) > As (1042.93) > Pb (913.66) > Cr (864.99) > Cd (252.03), and among the specimens, demersal fish, Apocryptes bato appeared to be the most bioaccumulative organism. Estimated daily intake (EDI), target hazard quotient (THQ), hazard index (HI) and carcinogenic risk (CR) assessed for potential human health risk implications suggest that the values were within the acceptable threshold for both adults and children. However, calculated CR values indicated that both age groups were not far from the risk, and HI values demonstrated that children were nearly 6 times more susceptible to non-carcinogenic and carcinogenic health effects than adults