Polychaete diversity and assemblage structure in the Oualidia Lagoon, Moroccan Atlantic coast

Abstract

The polychaete assemblages inhabiting the coastal waters of the Oualidia lagoon were studied during winter 2013 and summer 2013. Taxonomic composition and diversity were determined at 43 sample sites. Among the 13 species of polychaetes recorded, 10 were newly reported for Oualidia lagoon. Hediste diversicolor and Capitella sp. were the most abundant taxa in both seasons. Temperature and salinity were higher, and chl-a and OM were lower, in summer than in winter. The structure of the polychaete assemblages was characterized by forming three main clusters, either based on sampling stations or on polychaete species. These clusters were organized according to a downstream gradient, with the stations having fine sediments and a H. diversicolor assemblage in the inner lagoon being replaced by stations with medium grain-sized sediment and a Capitella sp. assemblage in the mid-lagoon, which were in turn replaced by stations having sandy sediments and assemblages dominated by Glycera alba (winter) and P. africana (summer) in the areas closer to the lagoon inlets. The shift was, in fact, from a classical, brackish, lacunar assemblage to two different, temporal aspects of a marine assemblage (close to the inlets), with a transition assemblage in between. This corresponded with a typically paralic spatial structure whose main descriptors responded to a confinement gradient. Despite the absence of a river, the organization of the polychaete assemblages closely resembled that of an estuarine system, with the tidal regime playing a major driving role.

Macrofaunal spatial distribution and community structure in a lagoon without a river discharge (the Oualidia lagoon, NW Morocco)

“…This species is promoted by the amount of particulate organic matter, but it could be also encountered on bare sediments with decreasing salinities and increasing temperatures (negative and positive correlations, respectively). The lower and upper parts of the lagoon supported low diversity with respect to the middle section as it was stated by El Asri et al (, ). This might be due to the decreased heterogeneity of habitats available and the unconstancy of abiotic factors.…”

“…The inconspicuous environmental gradients particularly those of OMC and silt content are mainly influenced by the pronounced seawater renewal and the lack of significant fluvial inputs (direct freshwater sources). Moreover, sediment and salinity distributions in this lagoon were typical of estuarine systems (El Asri et al, , , ; Zourarah et al, ).…”

“…The natural and typical distributions of the other environmental factors were also detected, and no impacts on physical regime (hydrological and sedimentological) and/or on biological components were found as it was expected. All of ecological gradients were not altered within this water body from down‐ to upstream areas (El Asri et al, ). Even with the lack of a direct freshwater riverine input into the Oualidia lagoon, and evaporation during summer and periods of drought, hypersaline conditions within its basin have never been detected.…”

“…Apart from studies of Azirar and Bayed (), Chbicheb (), El Asri, Zidane, Maanan, Tamsouri, and Errhif (), and El Asri et al (), macrozoobenthic communities of this transitional water system are scarcely studied and warrant further research. Here, we attempt to contribute towards filling this gap in our current knowledge through a baseline study conducted on the intertidal soft‐bottom‐inhabiting macrofauna of the Oualidia lagoon.…”

Social-Environmental Analysis for the Management of Coastal Lagoons in North Africa

“…The main pressure from the high nutrient inputs to the Oualidia lagoon in Morocco is from surface and groundwaters that drain from the cultivated areas that cover 78% of the catchment (Damsiri et al, 2015(Damsiri et al, , 2017 and where nitrogen and phosphate fertilizers are applied (Maanan et al, 2014). These nutrients promote a significant increase in chlorophyll a within the lagoon ecosystem (El Asri et al, 2017a). Another Moroccan example of pressures from agrochemicals is an irrigated agricultural area of 92 km 2 around the Nador lagoon (Re and Sacchi, 2017).…”