Trends in the species composition at the southernmost estuary of the Atlantic coast of Europe.

Climate change may enhance the establishment of introduced species, as well as the poleward shift in distribution of numerous species over decades. Long-term research and monitoring of an ecosystem at the southernmost point of the Atlantic coast of Europe should be an important priority in order to detect and understand trends in species composition and the related environmental changes. The Guadalquivir estuary (South Spain) is more likely to suffer the exacerbated effects of climate change due to its location in the Mediterranean-climate zone. The long-term data set between 1997 and 2015 in this estuary has allowed us to analyse the variability of the natural and anthropogenic stressors, especially in some dry years and how records of new species have been stabilised as a consequence of expanded connectivity (shipping) and “African Creep”. The mean interannual dissimilarity of the estuarine fauna (Bray–Curtis dissimilarity index) has showed important differences throughout the years, and the species that most contributed to these differences were the exotic species capable of completing their life cycles. Their average annual density has shown a continuous increase during the years of study in a period of expansion. This long-term monitoring of the estuarine community has allowed us to anticipate future events and ecological risk assessment in Europe due to climate change. Management implications are mainly related to the catching of exotic species to control their impact on native communities and reduce the shipping in this sort of ecosystem, which have been especially sensitive in the last 10 years

The nursery role of the Guadalquivir estuary for marine fish. A long-term ecological research

Trabajo presentado en el 23rd Biennial CERF Conference (Grand challenges in coastal and Estuarine Science: securin our future), celebrado en Portland (Oregón, US) del 8 al 12 de noviembre de 2015.N

Salinity tolerance as a factor controlling spatial patterns in composition and structure of zooplankton in the Guadalquivir estuary

Trabajo presentado en ECSA 56 (Coastal systems in transition: From a 'natural' to an 'anthropogenically-modified' state), celebrado en Bremen del 4 al 7 de septiembre de 2016.N

Feeding Habits of the Invasive Weakfish (Cynoscion regalis) in the Gulf of Cadiz

Weakfish (Cynoscion regalis) has been present in Iberian waters since at least 2011, when it was first recorded in the Guadalquivir estuary. Little is known about the preferences and feeding strategies of weakfish outside of its native range; therefore, in this work, we carried out a comprehensive study between March 2021 and September 2021 to elucidate these matters. In total, the stomach contents of 300 fish were examined. The fish were collected in spring and summer in the Gulf of Cadiz (Spain), with individuals caught ranging from 185 to 590 mm in total length. Due to the sampling period and size range of individuals, ontogenic and seasonal (spring–summer) variations in the diet were also explored. Overall, fish and crustaceans were the dominant groups consumed by weakfish. The European anchovy (Engraulis encrasicolus) and caramote prawn (Penaeus kerathurus) were the most abundant prey in each group. While no differences were found in the percentage of occurrence of fish in the non-empty stomachs analyzed in spring and summer (83%), a small increase was found in the percentage of occurrence of crustaceans from spring (20%) to summer (29%). In addition, the analysis of the results also suggested that weakfish of smaller sizes feed more on crustaceans, while bigger individuals feed mainly on fish. Our findings indicate that weakfish is a fully carnivorous species with a preference for fish. All this is in line with the diet and strategy that weakfish exhibits in its native area and with the first assessment made with the existing population in the Sado Estuary (Portugal). In recent years, due to the appearance of non-native species, there is increasing concern among local fishermen and the local authorities about the reduction in captures of certain species such as Penaeus kerathurus; therefore, this study could help researchers to understand the role of weakfish concerning this matter. The present study contributes to the ecological knowledge about this species in the Iberian Peninsula and the Gulf of Cadiz, helping the local authorities to establish, if needed, an appropriate management program to cope with this recently introduced species

Assessing the trophic ecology of the invasive Atlantic Blue Crab Callinectes sapidus in the coastal waters of the Gulf of Cadiz

Callinectes sapidus, the invasive blue crab from the west of the Atlantic Ocean, has extended its distribution along the Atlantic coast around the Gulf of Cadiz and increased massively since 2016. Food web studies are useful for understanding changes in ecosystems caused by exotic species. Stable isotope analysis (δ13C and δ15N) were used to assess the potential carbon sources and its trophic relationships among different ecosystems (estuaries and saltmarshes), sexes (male and females) and seasons (summer vs. autumn). Significant differences were found in the δ13C of blue crabs from the estuaries and salt-marshes (-21.2 ±2.6 vs -14.2 ±0.9, respectively). These differences may be explained by an increase in the 13C of the blue crabs from the salt-marshes, probably due to the enrichment of this isotope in the primary producers such as the salt marsh plants [1] and its preys inhabiting this ecosystem. Meanwhile, the more depleted 13C values in the estuary crabs seem to reflect a carbon source from mollusks and fish derived from decomposing detritus. Among the ecosystems analyzed, δ15N was only significantly enriched in the crabs of the Guadalquivir estuary and was higher in males than females. Also, seasonal differences were found in this estuary in both sexes, by a decrease in the 15N values between summer and autumn. Those differences, can be explained by the fact that the Guadalquivir estuary suffers nitrogen hyper-nitrification due to intensive agriculture and is more noticeable in the upper part of the estuary, to which the males are more associated due to their life cycle. Previous studies reported, the diet of C. sapidus seems to be opportunistic, dependent on the food availability in different habitats [2], with a divergence in sexes induced by different spatial distributions. Future studies analyzing the stomach content and trophic behavior should be conducted to clarify our results

Population dynamic and trophic position of mysid community demonstrates its key role for nursery function in a temperate estuary

Guadalquivir Estuary is a main nursery ground of marine goal species for Gulf of Cadiz fisheries. It is a well-mixed temperate estuary with horizontal salinity gradient and clear seasonal water temperature trend. Mysid community with Mesopodopsis slabberi, Neomysis integer and Rhopalophthalmus tartessicus make up to over 80% of total macrofauna biomass in the estuary. Life history, population structure, secondary production, trophic level and community spatio-temporal dynamic were unravelled combining analysis of long term 16y monitoring data with 2y of in depth population analysis and trophic biomarker studies. Results show a key trophic role in food web, a seasonal trend showing density peaks ( 23, 3 and 6 mg/m3, respectively) in spring-summer and winter marine coastward migration. Despite being euryhaline, the three species of showed unevenly spatial distribution, being salinity the variable best explaining structure changes of mysid assemblage. Inter- and intra-specific euryhalinity differences both for prey and predators seem to determine the entire spatial estuarine community distribution. High secondary production (P/B rates 38.2, 10.3 and 10.7) and food web studies confirm key role of mysids transferring energy up to juveniles (fish and crustaceans) arriving yearly in spring to their nursery area

Multidecadal (1997-2020) telecoupling of water management for terrestrial agriculture and a marine fishery at southern Spain

Climate change is decreasing water supplies globally while water demand is rising, making water access and distribution essential for sustainability, equity, and efficiency. In response, water management has shifted towards practices that improve water efficiency. However, links between geographically separated socioecological systems, known as telecouplings, can obscure the potential consequences of water use. This study focuses on a telecoupling between terrestrial water use and marine fisheries for the period 1997 to 2020. We develop a case study in southern Spain using multidecadal time series of the Guadalquivir river’s hydrology, its estuarine community, and the European anchovy (Engraulis encrasicolus) fishery in the Gulf of Cadiz. We found that water extracted to irrigate crops decreased the river’s flow and seasonality. However, anchovies used the estuary as a nursery before recruiting to the ocean, where they were harvested. Anchovy recruitment improved when estuary hydrology matched the Guadalquivir River’s historical hydrology (i.e., high discharge and seasonality). Then using hydro-economic modeling, we explored the outcomes of different water policies on the telecoupled socioecological systems. Our models predicted that improved water efficiency incentivized agricultural expansion. In contrast, continued marine fishery yields required management values that supported the value of the marine fishery. We highlight estuaries’ critical role in driving marine systems; yet, upriver processes drive estuaries dynamics. Overall, marine-terrestrial telecouplings provide evidence that marine fisheries that rely on estuarine reliant species would benefit of water policy and management being extended beyond the water basin

Decadal variability 2010-2021 of zooplankton community at the Guadalquivir estuary (southern Spain)

A Long Term Ecological Research Program has been monitoring the Guadalquivir estuary meso- and macro- zooplankton community monthly since January 2010. As an important nursery area for many marine species (fish and crustacean) from the Gulf of Cadiz, whose juveniles and recruits depend on zooplankton as main prey, understanding how abiotic and biotic factors determine zooplankton community structure it´s necessary to unreveal recruitment variability. We sampled throughout the whole salinity gradient, 2 locations, the two diurnal ebb and flood tides during the new moon days using a 100 μm zooplankton net. Zooplankton community is mainly composed by copepods and mysids. While the exotic Acartia tonsa calanoid copepod is the most abundant specie by abundance, mysid Mesopodopsis slabberi contribute the most to total biomass, followed by mysids Rhopalophthalmus tartessicus and Neomysis integer. Other abundant groups were copepods Acartia bifilosa and Acartia clausii, Calanipeda aquaedulcis, Paracalanus parvus and Acanthocyclops robustus, cladocera Pleopis polyphaemoides, together with veliger larvae, Cirripeda and Ostracoda, and Decapoda larvae. About total biodiversity, we found up to 183 species, estimating a total mean Species Richness of 9.7 (minimum 2- maximum 33) per sample, mean Shannon Diversity Index 3.27, Pielou Evenness 0.50 and mean betadiversity 0.630. While copepods area abundant form fall to early spring and summer, mysid density peaks form spring to fall. Community is structured by Salinity, but Temperature, Turbidity, Nitrate, Nitrite and Dissolved Oxygen were also important variables leading spatio-temporal variability, mainly when estuary recives high freshwater discharges from Alcala del Río dam

Distribution and salinity tolerance of the invasive isopod Synidotea laticauda in the Guadalquivir estuary (SW Spain): Field and laboratory observations

Trabajo presentado en ECSA 56 (Coastal systems in transition: From a 'natural' to an 'anthropogenically-modified' state), celebrado en Bremen del 4 al 7 de septiembre de 2016.The effects of the exotic species in native communities are unpredictable and ecological studies should be required for environmental management. In Europe, the exotic species Synidotea laticauda has been introduced in several estuaries but there was not any previous biological study about these non-native populations. The spatio-temporal field distribution of S. laticauda in the last 30 km of the Guadalquivir estuary (salinities 0 to 30) was assessed during 7 years (August 1997-June 2004) by sampling at each new moon with a mesh size net of 1 mm. Survival and osmoregulatory patterns of the species under different experimental salinity conditions were also estimated. This exotic species is a permanent resident of the estuary, with presence of juveniles and adults during most of the year, but showing maximum densities in the warmest period (summer to early autumn). Spatial patterns were closely related to the salinity gradient: the highest densities were observed between 10 and 30 of salinity, with a maximum at 20 (≈ isosmotic point). In fact, the isopod is a weak osmoregulator, which maintains the osmolality of the hemolymph partially independent of the medium osmolality (in a salinity range of 5 to 25). Moreover, survival experiments showed a high tolerance (mortality < 30%) to sudden salinity changes between 2 and 35 and virtually no mortality in salinities (15-25) close to the isosmotic point (20). Osmoregulatory and survival patterns were not dependent on sex but they seemed to be specific-dependent on salinity acclimation. Although it is a euryhaline species, its weak osmoregulatory capacity explains its salinity-dependent distribution pattern. Our results provide a framework to predict the distribution of this invasive species under sceneries of climate change and consequent freshwater scarcity.N