Effects of elevated CO2 and nutrients on the community metabolism of a Cymodocea nodosa bed

We assessed the combined effects of elevated CO2 and nutrients on the metabolism of a benthic community dominated by the seagrass Cymodocea nodosa (Ucria) Ascherson in a mesocosm experiment. C. nodosa plants and their associated community were exposed to two CO2 levels simulating future (700 ppm, pH 7.84) and current (360 ppm, pH 8.12) conditions, and two nutrient levels (enriched and ambient concentration) in a total of four treatments (-C-N, -C+N, +C-N, +C+N). Net community production (NCP) was estimated from changes in the concentration of dissolved inorganic carbon in the seawater in light incubations using benthic chambers. The variation pattern of NCP with the ordinance was consistent for all treatments. Although differences among treatments were not statistically significant, average NCP values were lowest under CO2 enrichment conditions. NCP was lower at a high CO2 level and ambient nitrogen concentration compared to when nutrient availability was higher, suggesting that the low nutrient availability may modulate the community response to CO2 enrichment. The results obtained suggest that the stimulation of the net community production of C. nodosa by elevated CO2 concentrations may be curtailed by low nutrient availability

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

An analysis of the impacts of climatic variability and hydrology on the coastal fisheries, Engraulis encrasicolus and Sepia officinalis, of Portugal

The notion that climate change may impact coastal fish production suggests a need to understand how climatic variables may influence fish catches at different time scales. Evidence suggests that the effect of climatic variability and fishing effort on landed catches (as proxy of fish abundance) may vary at the regional scale. This study aims to assess the sensibility of two commercial species with a short life cycle (Engraulis encrasicolus and Sepia officinalis) to climatic and fisheries effects across different regions of the coast of Portugal: northwestern, southwestern and southern Portugal. The effect of environmental explanatory variables, i.e. NAO index, sea surface temperature (SST), upwelling (UPW) index, river discharge, wind magnitude (WmaG), wind direction (Wdir), and fishing variables (fishing effort) on catch rates time series were studied between 1989 and 2009. The sensibility of the species studied to climatic variability differed among regions and were explained by different climatic variables. River discharge had a significant effect on catch rates of the two species, region independently. However, wind driven phenomenon and UPW were the variables that better explained the observed fishing trends across the three regions. Changes in catch rate trends among the studied regions, at a given time, were mostly associated with the reproduction periods of the species. Therefore, regional analyses will significantly contribute to a better understanding of the relationship between climate change and coastal fisheries, aiming to improve integrated coastal zone management

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

Establishing relationships between climatic variables and coastal fisheries of Portugal

The notion that climate change may impact coastal fish production suggests a need to understand how climate variables may influence fish catch on a small and large scale. The direct or indirect effects of climate change have been shown to affect catch in productive estuarine and coastal ecosystems. However, the effect of climatic variability and fishing effort on landing catches (as proxy of fish abundance) varied accordingly local and regional scale. Therefore, two studies were conducted. In the first study, an area with similar oceanographic environmental conditions, (Northwestern coast of Portugal) was selected, aiming to analyze the relationships between both climate and fishery variables on catch rates of important commercial and mostly short life cycle species (Alosa alosa, Alosa fallax, Engraulis encrasicolus, Sardina pilchardus, Sepia officinalis and Trachurus trachurus). In addition, particular emphasis was given to explore the effects of freshwater discharge from the three main rivers on the selected species landing trends. Therefore, time series of commercial landings of NW-Atlantic (northwestern Portugal) from 1989 to 2009 were analyzed using min/max autocorrelation factor analysis (MAFA) and dynamic factor analysis (DFA). These techniques were used to explore the relationships between the response variables (annual landings per unit effort) and explanatory variables [NAO index, sea surface temperature (SST), an upwelling (UPW) index, river discharge and fishing effort]. The results of the study confirmed that river discharge was the most important explanatory variables affecting coastal fisheries, followed by SST and UPW. In particular, seasonal river discharge became the explanatory variables that better explain the variability of the two most important small pelagic, Engraulis encrasicolus and Sardina pilchardus. Likewise, results also elucidated that change or reduction in river discharge during spawning event, might become detrimental for other species as well. The key finding of this study is that even within a small area with different rivers regimes and similar oceanographic conditions, the effect of environmental variables might be different on the same species/ population. In the other study, the sensibility of the species to climatic variability and fisheries was evaluated across regions: south, southwestern and northwestern Atlantic coast of Portugal. Similar statistical techniques were used for exploring data information that also includes the period from 1989 to 2009. The sensibility of the species studied to climatic variability differed accordingly the regions. However, results showed that wind and river discharge were the variables that mostly affect fishing trends, independently of different region. Thus, this study will significantly contribute to a better understanding of the relations between climate change and coastal fisheries variability, aspect that need to be considered for the integrated coastal management and development of new policies under the scope of climatic conditions.As alterações climáticas afectam os recursos pesqueiros e desta forma a productividade estuarina e marinha. O efeito da variabilidade climãtica e dos efeitos da pesca nas capturas da pesca (como indicador aproximado da biomassa pesqueira) variam no entanto à escala local e/ou regional. No primeiro estudo desta tese foi escolhida uma região com condições oceonográficas semelhantes (Costa Norte de Portugal) e o efeito das variáveis climãticas e o efeito da pressão da pesca sobre as capturas de espécies comerciais e de curto ciclo de vida (Alosa alosa, Alosa fallax, Engraulis encrasicolus, Sardina pilchardus, Sepia officinalis and Trachurus trachurus) foi estudado. Neste trabalho deu-se particular ênfase ao efeito das descargas de água de três rios principais do Norte (Douro, Vouga e Mondego). Os dados, relativos ao periodo compreendido entre 1989 e 2009, foram analisados utilizando procedimentos estatísticos para a análise de series temporais, nomeadamente “min/max autocorrelation factor analysis (MAFA) and dynamic factor analysis (DFA)” que permitem explorar relações entre as variãveis ambientais (oscilação do Atlântico Norte, temperatura de superficie da água, afloramento costeiro, descargas de água dos rios e esforço de pesca) e as capturas. O resultado deste estudo mostra que as descargas de água na região Norte de Portugal têm um efeito significativo sobre as capturas das espécies estudadas, seguidamente da temperatura e afloramento costeiro. De referir que o período (sazonalidade) da descarga é o factor que afecta com maior significância os valores, a curto período de tempo, das capturas para a maioria das espécies, com particular evidência para o caso do biqueirão (Engraulis encrasicolus) e sardinha (Sardina pilchardus). Dentro da mesma região os efeitos locais relacionados com as diferentes condições hidrolõgicas afectam diferentemente as capturas das espécies estudadas, embora as diferenças entre variáveis oceonográficas terem sido minímas. O segundo trabalho desta tese consistiu em avaliar se a a sensibilidade duma espécie aos efeitos climáticos e da pesca difere entre diferentes regiões (diferentes condições ambientais). A sensibilidade aos efeitos climáticos para a mesma espécies variou consideravelmente entre regiões (costa Norte, Centro e Sul de Portugal). Desta forma, este estudo integrado permitirá uma melhor compreensão dos fenómenos que mais efectam a productividade dos recursos marinhos. Esta informação é da maior importância para a gestão dos recursos pesqueiros nas zonas costeiras, uma vez que o desenvolvimento de estratégias para a regulação das pescarias devem considerar o efeito da variabilidade climãtica na previsão relacionada com a estimativa da biomassa dos stocks pesqueiros à escala regional.Universidade do Algarve, Faculdade de Ciências do Mar e do Ambient

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

Combining mesocosms with models reveals effects of global warming and ocean acidification on a temperate marine ecosystem

Ocean warming and species exploitation have already caused large‐scale reorganization of biological communities across the world. Accurate projections of future biodiversity change require a comprehensive understanding of how entire communities respond to global change. We combined a time‐dynamic integrated food web modeling approach (Ecosim) with previous data from community‐level mesocosm experiments to determine the independent and combined effects of ocean warming, ocean acidification and fisheries exploitation on a well‐managed temperate coastal ecosystem. The mesocosm parameters enabled important physiological and behavioral responses to climate stressors to be projected for trophic levels ranging from primary producers to top predators, including sharks. Through model simulations, we show that under sustainable rates of fisheries exploitation, near‐future warming or ocean acidification in isolation could benefit species biomass at higher trophic levels (e.g., mammals, birds, and demersal finfish) in their current climate ranges, with the exception of small pelagic fishes. However, under warming and acidification combined, biomass increases at higher trophic levels will be lower or absent, while in the longer term reduced productivity of prey species is unlikely to support the increased biomass at the top of the food web. We also show that increases in exploitation will suppress any positive effects of human‐driven climate change, causing individual species biomass to decrease at higher trophic levels. Nevertheless, total future potential biomass of some fisheries species in temperate areas might remain high, particularly under acidification, because unharvested opportunistic species will likely benefit from decreased competition and show an increase in biomass. Ecological indicators of species composition such as the Shannon diversity index decline under all climate change scenarios, suggesting a trade‐off between biomass gain and functional diversity. By coupling parameters from multilevel mesocosm food web experiments with dynamic food web models, we were able to simulate the generative mechanisms that drive complex responses of temperate marine ecosystems to global change. This approach, which blends theory with experimental data, provides new prospects for forecasting climate‐driven biodiversity change and its effects on ecosystem processes

Predicting impacts of climate change on forest tree species of Bangladesh: evidence from threatened Dysoxylum binectariferum (Roxb.) Hook.f. ex Bedd. (Meliaceae)

The impact of climate change on ecosystems, especially at the species level, can be currently observed in many parts of the world. Species distribution models (SDMs) are widely used to predict the likely changes in the distribution of species in future climate change scenarios. The aim of the present study is to predict the effect of climate change on a valuable threatened tree species Dysoxylum binectariferum in the northeastern part of Bangladesh using the maximum entropy (MaxEnt) model on species’ occurrence data. The future distribution of D. binectariferum was predicted under two scenarios from the IPCC 5 assessment (RCP 4.5, and RCP 8.5) in 2050 and 2070. Model results showed that approximately 32% (2177 km) of the studied area is currently suitable for this species to grow. However, future predictions obtained by the model projected a complete loss of suitable habitat for D. binectariferum in the studied area by both 2050 and 2070. Therefore, urgent measures are required for the conservation of D. binectariferum in northeastern Bangladesh. The application of species distribution models to simple inventory data (such as the occurrence of the species) may provide policymakers and conservationists with a useful tool for the prediction of future distribution (at both local and regional scales) of poorly known species with high preservation concerns

Seawater carbonate chemistry and trophic flows and the living biomass of detritivores, herbivores, and carnivores

Global warming and ocean acidification are forecast to exert significant impacts on marine ecosystems worldwide. However, most of these projections are based on ecological proxies or experiments on single species or simplified food webs. How energy fluxes are likely to change in marine food webs in response to future climates remains unclear, hampering forecasts of ecosystem functioning. Using a sophisticated mesocosm experiment, we model energy flows through a species-rich multilevel food web, with live habitats, natural abiotic variability, and the potential for intra- and intergenerational adaptation. We show experimentally that the combined stress of acidification and warming reduced 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). Warming in isolation also reduced the energy flow from herbivores to carnivores, the efficiency of energy transfer from primary producers and detritus to herbivores and detritivores, and the living biomass of detritivores, herbivores, and carnivores. Whilst warming and acidification jointly boosted primary producer biomass through an expansion of cyanobacteria, this biomass was converted to detritus rather than to biomass at higher trophic levels-i.e., production was constrained to the base of the food web. In contrast, ocean acidification affected the food web positively by enhancing trophic flow from detritus and primary producers to herbivores, and by increasing the biomass of carnivores. Our results show how future climate change can potentially weaken marine food webs through reduced energy flow to higher trophic levels and a shift towards a more detritus-based system, leading to food web simplification and altered producer–consumer dynamics, both of which have important implications for the structuring of benthic communities

Seawater carbonate chemistry and food web composition, productivity, and trophic architecture

As human activities intensify, the structures of ecosystems and their food webs often reorganize. Through the study of mesocosms harboring a diverse benthic coastal community, we reveal that food web architecture can be inflexible under ocean warming and acidification and unable to compensate for the decline or proliferation of taxa. Key stabilizing processes, including functional redundancy, trophic compensation, and species substitution, were largely absent under future climate conditions. A trophic pyramid emerged in which biomass expanded at the base and top but contracted in the center. This structure may characterize a transitionary state before collapse into shortened, bottom-heavy food webs that characterize ecosystems subject to persistent abiotic stress. We show that where food web architecture lacks adjustability, the adaptive capacity of ecosystems to global change is weak and ecosystem degradation likely