Seasonal Variation of Functional Traits in the Fish Community in a Brackish Lagoon of the Po River Delta (Northern Italy)

Abstract

Brackish lagoons are highly productive systems that support fishing and aquaculture activities with important revenue. At the same time, they function as fundamental habitats for the conservation of a number of species that use lagoons for reproduction and feeding. The present study aims at describing the seasonal structural and functional variations of fish communities in the Fattibello lagoon, a small but important nursery ground of the Po River delta (northern Italy), historically exploited for fishing. The fish community was sampled monthly over a six-years’ period (2009–2014). The results were normalized in catch per unit of effort (CPUE) and are expressed both as individual abundances (ind/CPUE) and biomass (g/CPUE). Higher biodiversity levels were observed in autumn, when both lagoon residents and marine species coexist, and summer, for individual abundances and biomass. Biomass was a better descriptor than individual abundance of the functional use of the lagoon. In autumn, the lagoon resident species increased significantly, while marine feeding ground species decreased. Vice versa, lagoon residents decreased in winter, when the lagoon were mainly used as feeding ground by marine fishes. Marine migrating species were present throughout the whole year. Overall, the lagoon serves as (i) reproduction habitats for different species, as well as habitat for the pre-reproductive period for the European anchovy; (ii) nursery grounds for a number of commercial species; and (iii) habitats for lagoon resident species, supporting them for the whole life cycle. Overall, the results highlight the fundamental conservation role of the lagoon throughout the whole year, and that seasonal structural and functional patterns of fish communities should be carefully considered when seeking to harmonize direct uses, such as fishing and bivalve farming, as well as nature conservation.

The paradoxical need for human intervention in the conservation of natural environments in Venice lagoon

“…In contrast, the valli da pesca that maximize hunting implement a series of landscape modifications to maintain suitable wintering and nesting habitats, despite the main water body of the lagoon having lost several of such natural characteristics 34 , 36 , 37 , 70 . Besides enhancing provisioning ESs, those efforts can also maintain the presence of some species and support their lifecycles in the long run, confirming the observation of other authors 34 , 50 .…”

“…In Italy, traditional ecological knowledge about the migratory behavior of fish that migrate from the sea to shallow brackish waters 36 , 37 , 48 – 50 has driven the development of particular enclosures to entrap juvenile fish and hold them until they reach commercial size 32 , 51 – 54 . The Venice lagoon made no exception, and today is home to the most emblematic examples of this type of extensive capture-based aquaculture, which often integrates with waterfowl hunting 20 , 31 , 33 .…”

Like little lagoons: the contribution of valli da pesca to the Ecosystem Services supply of the Venice Lagoon

“…On the other hand, while the fish migration and the recruitment processes taking place outside in the lagoon plays a fundamental role for sustaining fish lifecycle (Lanzoni et al 2021;Scapin et al 2022;Cavraro et al 2017) and the aquaculture ES in the valli da pesca, we could in turn affirm that the aquaculture ES in the valli da pesca could positively affect the regulating ES of lifecycle support in the entire lagoon. As happens for waterbirds, indeed, the persistency of suitable habitats in the valli da pesca depends on human maintenance, which in turn depend on economic resources that come from the provisioning ESs incomes.…”

Fish community, seasonal movement and habitat use in a subtropical coastal lagoon

“…Studies of community structure and life stages in coastal lagoons in temperate, tropical, and subtropical regions agree that ichthyofauna is mainly constituted by juveniles using these spaces for feeding and nursery (Ramos et al 2016, Cabrera-Páez et al 2018, Lanzoni et al 2021, which are the main functions of the lagoons since they contribute to growth and survival and later recruited to the adult population inhabiting the adjacent areas (Cabrera-Páez et al 2020). Adult fish use the coastal lagoons as feeding and breeding grounds, but generally, spawning occurs in areas adjacent to the lagoon (Nagelkerken 2009, Ramos et al 2016.…”

“…In coastal lagoons, fish species are among the most rich and abundant communities (Arceo-Carranza et al 2010). Temporal variations of community structures and their interactions throughout the year are determined by seasonal changes in environmental variables in coastal lagoons (Lanzoni et al 2021). These changes cause different fish species to use them permanently or temporarily throughout their life cycle (Díaz-Ruiz et al 2018), which is ecologically important since the marine ichthyofauna perform functions related to energy flow, establishing connectivity between the lagoon systems and the marine environment (Albaret 2017, Padilla-Serrato et al 2017.…”