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The trophic chain, its interactions and the effects of the different variables at two estuary spots in Guadalquivir. (Graphic: IEO)
Anthropogenic and natural effects on juvenile anchovy quantified in Guadalquivir estuary
(SPAIN, 8/3/2018)
A new study suggests that temperature, turbidity and fresh water discharges are key factors in the regulation of the anchovy breeding area that provides the Guadalquivir estuary.
The work, carried out by researchers from the Oceanographic Center of Cádiz of the Spanish Institute of Oceanography (IEO), Fisheries Research and Training Institute (IFAPA) and Institute of Marine Sciences of Andalusia (CSIC), describes the natural and anthropogenic effects derived from sector activities studies on juvenile anchovy and its main prey in the Guadalquivir estuary by analyzing 18 years of monthly data from the ecological monitoring of the estuary.
Estuaries are habitats known for their large biological production and the ecosystem services they provide, such as carbon capture, climate regulation and their function as a breeding area for many species. Thousands of crustaceans and fish such as prawn, eels or anchovy depend on these essential habitats to live, feed and reproduce.
Juvenile anchovies from the Gulf of Cádiz enter the estuary of the Guadalquivir River, one of the largest ones in Europe, in spring and summer in search of refuge and food. They also play a fundamental role in the structure of the estuarine ecosystem, since the anchovy is one of the most abundant species and an important predator of copepods and mysidaceans.
During this period, the survival of its early stages depends on the environmental conditions and availability of food as well as on the effects of those human activities that develop along the watershed. Among these sectoral activities, agriculture (eg. rice cultivation) stands out due to its influence on environmental conditions (eg., area to cultivate, fresh water for irrigation).
The aforementioned study develops a model that quantifies the effect of natural (eg. temperature, salinity) and anthropogenic (eg. freshwater discharges) variables on the abundance of anchovy and its prey.
"The model is able to quantify the direct and indirect effects on these groups and reproduce the evolution of the ecosystem, including distant factors such as human activities", explains Gustavo de Carvalho-Souza, doctoral candidate at the IEO and principal author of the work.
Another important aspect that scientists have investigated are the implications regarding the deployment of ecosystem management. The anthropogenic variables have the particularity that, up to a certain point, they are influenced by the way in which humans perceive and manage the ecosystem.
The most important infrastructure with respect to the flow of fresh water in the estuary is Alcalá del Río dam, which contributes 80 per cent of the total. The fresh water discharges have direct effects on the Guadalquivir's trophic network and indirect effects, since they affect salinity and turbidity, which in turn has a domino effect on the anchovy and the mysidaceans. "These effects can spread to the adult population, via recruitment, which is an important fishing resource in the Gulf of Cádiz," says de Carvalho-Souza.
The scientists point out that in order to achieve an ecosystem management in this region, it is necessary to make the economic development (agricultural and fishing) and the maintenance of the good ecological status of this essential habitat compatible.
The paper was published in the Marine Ecology Progress Series.
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