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

Seasonal variation of zooplankton and environmental conditions along a transect in the Gulf of Cádiz

This study presents seasonal variation in the zooplankton composition of the Gulf of Cádiz was studied between 2001 and 2012. Samples were collected three times per year, in the spring, summer and autumn at three stations situated along a transect perpendicular to the coast. The total zooplankton abundance during the summer was higher than in the spring and autumn. Zooplankton community is characterized by a seasonal cycle mirroring similar cycles in the physical environment. Differences in community composition were also found along the transect, particularly between the coastal station, under the influence of the Guadalquivir River, and the outer station, characterized by oceanic conditions. This study is the first description of the seasonal and spatial variation of this marine component of the Gulf of Cádi

Trophic control in the Guadalquivir estuary and neighbouring waters of the Gulf of Cadiz

The Guadalquivir estuary (SW Spain) is a non-stratified estuary with a gradual change in salinity. It supports an important biodiversity and functions as a nursery area for many commercial species (e.g. anchovy) in the Gulf of Cadiz (GoC). The understanding of the interplay between the environmental forcing (bottom-up) and the trophic regulation is essential to understand its functioning in relation to the GoC fisheries. Here, we seek to study the effects of environmental variables and predator-prey interaction (mysid-anchovy) in the estuary and surrounding marine areas with a particular focus on the zooplankton as key intermediaries between primary production and marine fish juveniles. A long-term (18 yr) monitoring program has been carried out in two sites: Tarfia and Bonanza (32 km and 8 km distance from the river mouth respectively). The latter station samples well the marine water masses advected into the estuary during the ebb flow. Our dataset includes mysids, anchovy larvae and juveniles, temperature, salinity, turbidity, freshwater discharges, precipitation and winds. We used time series-analysis (GAMs) to test the trophic, environmental and anthropogenic effects. Temperature was found to have a positive effect on mysids at both stations while salinity showed a positive effect only at Tarfia. Turbidity showed a strong negative effect on the whole estuary and so did the freshwater discharges at Bonanza, which are regulated by a dam. The results indicate that the trophic control in the estuary of the Guadalquivir is resource-driven. Our models also highlight that marine mysids have a positive effect on anchovy

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

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

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

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

A model for the future: Ecosystem services provided by the aquaculture activities of Veta la Palma

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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

Genetic differentiation between Mediterranean and Atlantic populations of the common prawn Palaemon serratus (Crustacea: Palaemonidae) reveals uncommon phylogeographic break

The Atlantic-Mediterranean transition zone between the Alboran Sea and the Gulf of Cadiz constitutes the most prominent marine geographic barrier in European waters and includes known phylogeographic breaks such as the Strait of Gibraltar and the Almeria-Oran Front. A genetic shift in this area has been previously documented for the European littoral shrimp Palaemon elegans. Here we carried out a phylogeographic analysis with the congeneric and sympatric species Palaemon serratus to test for similar intraspecific genetic differentiation and geographic structure. This littoral prawn is distributed in the Northeastern Atlantic Ocean, the Mediterranean Sea and the Black Sea. We compared DNA sequences from the mitochondrial genes Cox1 and to a lesser extent from 16S rRNA of several Atlantic and Mediterranean populations. Furthermore, sequences from the nuclear gene Enolase were included for corroborating differences between Mediterranean and Atlantic individuals. A pronounced genetic differentiation was detected between the Mediterranean and Atlantic populations, amounting to 10.14% in Cox1 and 2.0% in 16S, indicating the occurrence of two independent evolutionary lineages. Interestingly, specimens from the Atlantic Gulf of Cadiz cluster together with the Mediterranean individuals, indicating that a biogeographic barrier appears to be located west of the Strait of Gibraltar