Environmental influences, particularly river flow alteration, on larval fish assemblages in the Douro Estuary, Portugal
2022
Rodrigues, Sabrina M. | Silva, Diogo | Cunha, Jacinto | Pereira, Rúben | Freitas, Vânia | Ramos, Sandra
Larval stages of fishes are highly vulnerable to environmental shifts and anthropogenic pressures can pose additional stress to such a critical phase. The present study aimed to investigate environmental controls on the larval fish assemblages of the Douro Estuary, a heavily modified water body with several anthropogenic pressures. Monthly sampling surveys were conducted over two years along the estuarine horizontal gradient. The estuarine larval fish assemblage was dominated by a few very abundant taxa. Resident Pomatoschistus microps and members of the marine Clupeidae and Soleidae families were the most abundant taxa, accounting for 87.5% of the total catch. Canonical correspondence analysis identified e.g., river flow and salinity as the main environmental variables regulating the larval fish assemblages in the Douro Estuary. River flow had a significant impact on larval fish abundances with the lowest abundances observed when river flow surpassed 900 m³ s⁻¹. Overall, the Douro larval fish assemblage exhibited similar features to other less impacted temperate estuaries. However, the results of this study highlighted the negative impact of regulating river flows that can compromise the connectivity of estuaries with adjacent coastal areas and, ultimately, their nursery function for the early life stages of fishes.
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