• Energy Research

Climate change is expected to affect marine mercury (Hg) biogeochemistry and biomagnification. Recent modeling work suggested that ocean warming increases methylmercury (MeHg) levels in fish. Here, we studied the influence of El Niño Southern Oscillations (ENSO) on Hg concentrations and stable isotopes in time series of seabird blood from the Peruvian upwelling and oxygen minimum zone. Between 2009 and 2016, La Niña (2011) and El Niño conditions (2015-2016) were accompanied by sea surface temperature anomalies up to 3 °C, oxycline depth change (20-100 m), and strong primary production gradients. Seabird Hg levels were stable and did not co-vary significantly with oceanographic parameters, nor with anchovy biomass, the primary dietary source to seabirds (90%). In contrast, seabird Δ199Hg, proxy for marine photochemical MeHg breakdown, and δ15N showed strong interannual variability (up to 0.8 and 3‰, respectively) and sharply decreased during El Niño. We suggest that lower Δ199Hg during El Niño represents reduced MeHg photodegradation due to the deepening of the oxycline. This process was balanced by equally reduced Hg methylation due to reduced productivity, carbon export, and remineralization. The non-dependence of seabird MeHg levels on strong ENSO variability suggests that marine predator MeHg levels may not be as sensitive to climate change as is currently thought.

Abstract Along the coast of North-West Africa, fish supply is important at both socio-economic and cultural levels while threatened by climatic changes. To assess the impact of climate change on the distribution of small pelagic fish, a comprehensive trend analysis was conducted using data from 2,363 trawl samplings and 170,000 km of acoustics sea surveys spanning the period 1995–2015. The approach included estimating eight northern small pelagic species' presence and acoustics spatial distribution of the sardinella. The analysis incorporated key environmental variables, including sea temperature, chlorophyll-a concentration, and a wind-based Ekman upwelling index. The Southern Canary Current Large Marine Ecosystem (CCLME) was divided into five distinct ecological areas, extending from Morocco to Senegal, providing a spatialized perspective on the dynamic changes unfolding within these characteristic areas. Then, yearly averages of the monthly data per area were calculated. Strong warming is reported in all five areas. Over 34 years, from 1988 to 2021, several discernible trends emerged, with the southern CCLME experiencing increases in both wind speed and upwelling intensity, particularly in areas where the coastal upwelling was already the strongest. Despite upwelling-induced cooling mechanisms, sea surface temperature increased in most areas, indicating the complex interplay of climatic-related stressors in shaping the marine ecosystem. Concomitant northward shifts in the distribution of sardinella and other species were attributed to long-term warming trends in sea surface temperature (SST). As a result, the abundance of Sardinella aurita, the most abundant species along the coast, has increased in the subtropics (north part) and fallen in the intertropical region (south part). Independent environmental and ecological observational time series confirm a northward shift of around 180 km in one decade for S. aurita, while S. maderensis did not move significantly. Spatial shifts in biomass from 30 to 145 kilometers were observed for six other exploited small pelagic species, similar to those recorded for surface isotherms. An intensification in upwelling intensity within the northern and central regions of the system is documented without change in marine primary productivity. In contrast, a stable upwelling intensity is reported in the southern region (Senegal), which is associated with a decline in primary productivity. These environmental differences were associated with several small pelagic species beyond national boundaries whose recent overexploitation adds a new threat to their sustainable future in the whole region. Such changes must motivate common regional policy considerations for food security and sovereignty in all West African countries sharing the same stocks.

The southern Alboran Sea is a highly dynamic region in the Mediterranean. However, there is few data on microphytoplankton which is, an important component of the marine ecosystem. We therefore collected microphytoplankton samples and related the biomass and diversity patterns to ambient variability, considering cross-shore and longitudinal gradients. There was a general eastward decrease in both species richness and biomass, with Cape Three Forks as a transitional point. Diversity increased in coastal areas and decreased with depth. High chlorophyll-a concentrations corresponded to low temperature and low-salinity waters, indicating the Atlantic origin. Microphytoplankton biomass was low in comparison with total chlorophyll, suggesting a dominance of nano- and picophytoplankton. Biomass values increased in the stretch between Cape Three Forks and Al Hoceima Bay, an area highly influenced by upwelled water originating from the northern Alboran Sea. We suggest that the Western Alboran Gyre enhances the development of dinoflagellates while local upwelling enhances the development of diatoms. A statistical relationship was found between microphytoplankton biomass and diversity, especially when diversity was estimated as species richness. These results are crucial for understanding microphytoplankton dynamics and trends in an area that is undergoing climate-derived changes and biodiversity losses.

Shin, Yunne-Jai ... et al.-- This is a contribution to the IndiSeas Working Group, co-funded by IOC-UNESCO and the Euromarine Consortium in 2015.-- 10 pages, 4 figures, 2 tables, supplementary data https://doi.org/10.1016/j.ecolind.2018.01.010 Ecological indicators are widely used to characterise ecosystem health. In the marine environment, indicators have been developed to assess the ecosystem effects of fishing to support an ecosystem approach to fisheries. However, very little work on the performance and robustness of ecological indicators has been carried out. An important aspect of robustness is that indicators should respond specifically to changes in the pressures they are designed to detect (e.g. fishing) rather than changes in other drivers (e.g. environment). We adopted a multi-model approach to compare and test the specificity of commonly used ecological indicators to capture fishing effects in the presence of environmental change and under different fishing strategies. We tested specificity in the presence of two types of environmental change: “random” representing interannual climate variability and “directional” representing climate change. We used phytoplankton biomass as a proxy of the environmental conditions, as this driver was comparable across all ecosystem models, then applied a signal-to-noise ratio analysis to test the specificity of indicators with random environmental change. For directional change, we used mean gradients to apportion the quantity of change in the indicators due to fishing and the environment. We found that depending on the fishing strategy and environmental change, ecological indicators could range from high to low specificity to fishing. As expected, the specificity of indicators to fishing almost always decreased as environmental variability increased. In 55–76% of the scenarios run with directional change in phytoplankton biomass across fishing strategies and ecosystem models, indicators were significantly more responsive to changes in fishing than to changes in phytoplankton biomass. This important result makes the tested ecological indicators good candidates to support fisheries management in a changing environment. Among the indicators, the catch over biomass ratio was most often the most specific indicator to fishing, whereas mean length was most often the most sensitive to change in phytoplankton biomass. However, the responses of indicators were highly variable depending on the ecosystem and fishing strategy under consideration. We therefore recommend that indicators should be tested in the particular ecosystem before they are used for monitoring and management purposes L.J.S was supported through the South African Research Chair Initiative, funded through the South African Department of Science and Technology and administered by the South African National Research Foundation. J.E.H., L.V., and Y.J.S were funded by the EMIBIOS project (FRB Fondation pour la Recherche sur la Biodiversité, contract n°APP-SCEN-2010-II). J.E.H. was supported by a Beaufort Marine Research Award carried out under the Sea Change Strategy and the Strategy for Science Technology and Innovation (2006–2013), with the support of the Marine Institute, funded under the Marine Research Sub-Programme of the Irish National Development Plan 2007–2013. L.J.S and Y.J.S. were funded by the European project MEECE (FP7, contract n°212085). M.C. was supported by a Marie Curie CIG grant to BIOWEB project and the Spanish Research Program Ramon y Cajal. Funding from CSIRO and the Australian Fisheries Research and Development Corporation on behalf of the Australian Government supported the development of Atlantis-SE. J.J.H was supported by the UK Natural Environment Research Council and Department for Environment, Food and Rural Affairs under the project MERP: Grant No. NE/L003279/1, Marine Ecosystems Research Programme Peer Reviewed

In the Canary Current System (CCS), coherent structures and concurrent movements of surface waters such as meanders, filaments and eddies strongly control the ocean bio-optical proprieties response to the coastal upwelling process. One of the outstanding problems is to understand the mechanisms of the bio-optical proprieties transfer and the connection mechanism between the coastal band and the ocean interior. We use a combination of satellite data and derived mesoscale indicators to provide a comprehensive view of the relationship between the physical and bio-optical proprieties off Moroccan upwelling region (part of the CCS) in terms of wind impulse responsible of sea turbulence, sea surface temperature (SST) response of the wind stress and ocean color proprieties considered as bio-optical ocean proxy response. To optimize the predicted ranges of these parameters, Generalized Additive Model (GAM) was applied. We conclude that the energetic mesoscales structures as seen from the satellite climatology observations can provide insight into dominant transport pathways controlling the bio-optical exchange from the coastal area to the ocean interior structured as an oceanic corridor connecting the Moroccan area to the Canary archipelagos.

AbstractFisheries constitute an important economic sector for Morocco, where the species Sardina pilchardus represents the main landings. In acoustic evaluations conducted along the Moroccan coast since 1995, the absence of juveniles in 1996 and 1998 and the collapse of the sardine stock between 1996 and 1997 represent the main events until 2002. Sardines are known to be microphageous planktivores and thus are sensitive to environmental variability. A biogeochemical model coupled to a hydrodynamic model (ROMS) was run over the Canary Current System (1991–2002) to investigate the environmental factors that could have played a role in the variability of the sardine spawning. A grid refinement (1/12°) centred on the Saharan Bank (SB) region was built to study the main spawning ground of sardines off northwest Africa. The volume of the potential spawning habitat (PSH) of sardines was defined as a function of depth, temperature and salinity, which are included in the ranges 0–200 m, 15–21°C and 35.8–36.8, respectively. Our modelling frame was able to reproduce the seasonal cycle of temperature, phytoplankton concentration and PSH over the SB. It also captured the warming associated with the negative index of the North Atlantic Oscillation of 1995–1997 and allowed a description of the inter‐annual variability of the PSH. Our experiment shows that the volume of PSH was much reduced in 1996 compared to the other years. The results suggest that the delay between high abundance of plankton and favourable spawning conditions is a good proxy for determining the recruitment failure of sardine in this oceanic region.