Spatial and temporal variations of hydrological conditions, nutrients and chlorophyll a in a Mediterranean coastal lagoon (Mar Menor, Spain)

Abstract

The Mar Menor is a sheltered and hypersaline lagoon, with salinity ranges between 38 and 51 psu. The lagoon is threatened by several pressures and in the last decades detrimental impact on the natural community structure and dynamics have increased. In the watershed, agricultural practices are rapidly evolving from extensive dry crop farming to intensively irrigated crops, with increasing loads of nutrient and pollutants to the lagoon. Hydrological conditions, nutrients and chlorophyll a concentrations were analysed in 1997 and 2002-2003 in a grid of 20 stations in the lagoon. Different time scales, from daily to interannual, were considered. In the considered periods, the dissolved inorganic nitrogen (DIN) increased whilst phosphate decreased significantly. These contrasting patterns depended upon the increased agricultural loading for DIN and were due to the implementation of the wastewater works for phosphates. In 1997 and 2002, the highest nitrate concentrations were usually found on the west coast of the lagoon, close to the mouths of the main watercourses. In parallel, the lowest concentrations were detected at the inner coastline along ''La Manga'' sandy bar and ''El Estacio'' channel. Based on weekly data, correlations between chlorophyll a concentrations and environmental variables disagreed with traditional eutrophication models. Relationships between chlorophyll a and nutrients were negative, suggesting that in the short term phytoplankton controlled nutrient concentrations. Moreover, nitrate and phosphorous seemed to alternate as limiting factors. The relationships between chlorophyll a became positive when considering time lags and analysed at longer time scales (monthly or seasonal means), thus suggesting a very rapid response of primary producers to nutrient enrichment. A significant correlation between chlorophyll a concentration and fish larvae density was also found at all time scales analysed, suggesting a top-down control of the trophic web.

Candidate gene variation in gilthead sea bream reveals complex spatiotemporal selection patterns between marine and lagoon habitats

“…However, the temporal analysis of genetic differentiation patterns at each candidate gene in each lagoon suggests a lack of stability for the patterns established in spring. This may be due to highly dynamic and heterogeneous environmental conditions of coastal lagoons (Pérez-Ruzafa et al 2005, Tournois et al 2013) that may generate within-year variations in the strength and direction of selection. This emphasises the need for increased spatiotemporal resolution to monitor the potentially complex responses to selection during early development of marine organisms (Broquet et al 2013, Hernández-Garcia et al 2015.…”

Coastal Lagoons in the Context of Water Management in Spain and Europe

“…This coincides with the findings in the seasonal patterns in productivity in the water column that also show time lags among lagoon basins at spatial scales involving only tens of kilometres (Pérez-Ruzafa et al, 2005a).…”

“…Chlorophyll a concentration and ichthyoplankton abundance showed spatial patterns at 10 0 -10 1 km, changing fortnightly, monthly and seasonally. The nearly identical scales of response of chlorophyll a and ichthyoplankton abundance confirms previous observations about the regular cycles in phyto and zooplankton assemblages, despite the high degree of variability in the planktonic habitat (Pérez-Ruzafa et al, 2005a;Smayda, 1998).…”

North East Atlantic vs. Mediterranean Marine Protected Areas as Fisheries Management Tool

“…However, it is also necessary to optimize trade-offs between connectivity and representation objectives, including species and habitat diversity, while minimizing the risk that multiple reserves will be impacted by catastrophic events (Almany et al, 2009). Spatio-temporal heterogeneity can play an important role in the emergence of homeostatic mechanisms of complex coastal ecosystems (Pérez-Ruzafa et al, 2005) and the introduction of restrictions to connectivity can develop complex structures that enhance biodiversity at genetic and taxonomic levels (Pérez-Ruzafa, 2015).…”