The shallow inshore areas of coastal lagoons function as nursery grounds for the early life stages of marine fish. Multi-species approaches and the assessment of several population variables are of great value in studies focused upon the ecological importance of estuarine systems as fish nursery areas. Therefore, the objective of this study was to analyse the spatial differences in the abundance, biomass, growth and condition indexes of juveniles from three marine species: Sparus aurata, Liza aurata and Liza ramada, in order to assess the nursery role of the Mar Menor coastal lagoon for these species. Results showed high spatial variability of the studied variables, with higher abundance and biomass values at those sites closest to the inlet connecting the lagoon with the Mediterranean Sea. Moreover, there were significant relationships between the growth and condition of the fish with hydrographical circulation patterns within the lagoon, indicating the suitability of the Mar Menor as a nursery area for the three studied fish species.

Context: For the success of future conservation and management programs, it is necessary to better understand the resilience mechanisms of invasive species and their invasive potential. In this sense, the study of the effects that management actions have on their biological traits is essential. Aims: The present study aimed to assess the effects of removal control on the abundance and biology of an isolated population of the top invasive fish Gambusia holbrooki (eastern mosquitofish). Methods: Experimental removal control with traps and handnets was carried out on a population of mosquitofish inhabiting a small semiarid stream in south-eastern Spain. Mosquitofish were periodically captured for more than 3 years. Temporal variations in abundance, fish somatic condition and reproductive investment, percentage of mature females, size at maturity and population recruitment were analysed. Key results: Individuals of the 1+ age class increased their reproductive investment when population abundance was lower, thus increasing recruitment rate during the first months of the recruitment period. Individuals of the 0+ age class were responsible for expanding the reproductive period in conditions of low fish abundance. Conclusions: The mosquitofish population showed variations of reproductive parameters that could indicate a compensatory density-dependent phenotypic response under diminished abundance conditions. However, its removal by the constant use of a combination of active and passive capture methods, reinforced by increased extraction effort according to its local biology, has led to an eradication of the population. The target mosquitofish population showed distinct ecological features that may have contributed to the effectiveness of local control, namely, low initial fish density, isolation in a headwater stretch and the prevalence of individuals in sunlit shallow ponds. Implications: The compensatory mechanisms of this invasive species in low-density conditions should be considered in the design of management programs. Moreover, further research into removal control methods for mosquitofish or similar species is also needed.

The fish community that inhabits shallow littoral areas of the Mar Menor coastal lagoon was studied seasonally. Three different habitat types were compared: deep sandy habitats, vegetated habitats and shallow muddy habitats. The results indicated that the dominant fish families in the lagoon were Mugilidae, Gobiidae, Sparidae and Atherinidae. In general, vegetated habitats and shallow muddy habitats showed higher fish abundance, biomass and fish diversity than deep sandy habitats. Moreover, fish community structure differed significantly among habitats. Vegetated habitats and shallow muddy habitats seems to play an important nursery role, mainly for marine migrant species of the Mugilidae and Sparidae families, and constituted essential habitats for species of conservationist interest such Aphanius iberus and Syngnathus abaster. Deep sandy habitats were dominated by the resident goby Pomatoschistus marmoratus. These habitat-related differences are probably related to variations in structural complexity.