Mar Chiquita, an irregularly shaped brackish-water coastal lagoon, is located in the Buenos Aires province of Argentina and considered since 1996 by the Coordination Council of the Man and Biosphere Program of UNESCO as a World Reserve of Biosphere. The present paper aims to study both the spatial and temporal variation of fish composition in this coastal lagoon and the influence of some environmental variables on the relative abundance of the main fish species. Monthly sampling surveys over a two-year period in three different areas were conducted, using a beach-seine net and three monofilament-gill nets with different mesh size. Twenty-eight species belonging to four bio-ecological categories were identified, five of them are new records for Mar Chiquita fish community. The correspondence analysis showed strong relationships between high salinity range and the abundance of Brevoortia aurea, Cynoscion guatucupa and Pomatomus saltatrix. Conversely, low salinity range corresponded to high abundance of Mugil platanus and Odontesthes argentinensis. High temperatures were corresponded with abundance of Micropogonias furnieri and Brevoortia aurea. In contrast, high abundance of both Odontesthes argentinensis and Oligosarcus jenynsii were corresponded to low temperatures. Brevoortia aurea, Mugil platanus and Odontesthes argentinensis were the most abundant species, representing more than 80% of the total capture. The group of estuarine-nondependent-marine fish presented the highest species richness. Estuarine-dependent-marine species presented for both juveniles and adults specimens the highest abundance values.

The aim of this study was to assess the influence of environmental factors on the fish distribution and abundance in Mar Chiquita coastal lagoon. Seasonal fish sampling stations were distributed along the lagoon and grouped in three zones from a mixo-oligohaline waters zone with high contribution of freshwater to a mixo-eurihaline waters zone with high marine water influence. A mixo-mesohaline waters zone characterized the middle part of the lagoon. The results showed that the fish composition was dominated by marine estuarine dependent (ED) species in all three zones and in all seasons: Odontesthes argentinensis, Brevoortia aurea, Mugil liza and Micropogonias furnieri were the most representative species. The following important ecological category was freshwater fishes (FW), with Platanichthys platana and Jenynsia multidentata being the most representative species. According to the best model selected, by fitting generalized linear models, abundance of ED increased as water temperature increased during summer and autumn in all three zones. The highest abundance was recorded in the mixo-eurihaline waters zone. On the other hand, FW abundance increased with high rainfall and also when easterly winds blew. In conclusion, a differential habitat use by the species that occur in the Mar Chiquita coastal lagoon was observed. A few ED species dominated the fish composition but FW species also made use of the lagoon during periods of heavy rainfall.

We examined the fish larvae colonising pattern of the Mar Chiquita lagoon (Argentina). We hypothesised that in this microtidal lagoon, winds could regulate fish larvae dynamics. Ichthyoplankton samples were taken in marine waters, the surf zone and the estuary. Previous studies showed no reproduction by fishes with planktonic eggs inside the lagoon. However high abundance of eggs and larvae of Brevoortia aurea collected within the estuary also suggest possible spawning activity. Throughout the study period, the cumulated richness of fish larvae was slightly higher in the estuary. However, univariate analysis revealed a higher number of species per tow in marine waters than in the estuary. The lowest average values of fish density, number of species and diversity recorded in the surf zone suggest that this area is only used as a transient corridor between the sea and the lagoon. The canonical correspondence analysis (CCA) indicated that wind direction, tidal stage, temperature and rainfall contributed significantly to the fish larvae distribution patterns observed; being ‘onshore wind’ the most important variable affecting fishes. Our results show how winds, in addition to pushing seawater into the lagoon, contribute to larvae recruitment into this estuary. Finally, we discuss the role of small lagoons in the life-history of coastal fishes.