Abstract
Coastal lagoons are often exposed to intense short-term environmental changes and strong anthropogenic pressures influencing zooplanktonic communities and production. However, most works focus on long-term temporal scales using monthly or seasonal sampling strategies. The present study analysed the structure of the mesozooplanktonic assemblages, the production (egg production rates) and physiological condition (RNA:DNA ratio) of the copepod Acartia clausi in a temperate coastal lagoon (Ria Formosa) during the summer, using an intensive sampling approach. Salinity was the main factor affecting the short-term variability of mesozooplankton composition, followed by tidal phase (ebb tides) and semilunar cycle (spring tides). There was a positive relationship between the abundance of Appendicularia and the cladoceran Penilia avirostris with the toxic dinoflagellate Gymnodinium catenatum, suggesting no deleterious effects. The egg production rate of A. clausi was influenced by salinity and ammonia concentration, with a positive correlation between the egg productivity and the macronutrient, showing a possible adaptation of this calanoid species. The RNA:DNA index was positively related to egg production rate, suggesting that it is a good proxy for the reproductive output of copepods, even in short-term periods. This study shows that different timescales need to be included in regular monitoring of planktonic assemblages in coastal lagoons in order to understand the influence of environmental and anthropogenic variables on marine organisms.
Highlights
Coastal lagoons are shallow nutrient-rich ecosystems, being a typically unstable environment threatened by climate changes and usually under intense anthropogenic pressures (Barbosa and Chícharo, 2011)
We aim to analyze the short-term variability of the mesozooplanktonic assemblage structure in a temperate coastal lagoon (Ria Formosa) during the peak production period that occurs during summer, which is typical of the unimodal annual cycle of planktonic production that occurs in the temperate coastal lagoons (Barbosa and Chícharo, 2011)
The lower values of the copepod species and Cirripedia larvae abundances observed at the beginning of the present study indicate that the salinity values (> 36) inside the Ria Formosa lagoon were above their optimal metabolic conditions
Summary
Coastal lagoons are shallow nutrient-rich ecosystems, being a typically unstable environment threatened by climate changes and usually under intense anthropogenic pressures (Barbosa and Chícharo, 2011). Tidal dynamics is usually strong and the major mechanical energy input in coastal lagoons, forcing water circulation through turbulent mixing and driving the physical, chemical and biological interactions inside these ecosystems (Schelske and Odum, 1962). Daily variability in wind stress on the water surface and freshwater input generally provide part of the mechanical energy necessary for the structuring of coastal lagoons (Barbosa, 2010). The dynamics of planktonic communities in transitional systems highlights the unsteadiness of their spatial and temporal features. Most studies in these areas are developed under a monthly sampling strategy There is a significant number of studies on zooplankton communities in coastal lagoons worldwide, the patterns of planktonic production and the trophic interactions of their assemblages are poorly known (e.g. Repelin, 1985; Heerkloss et al, 1991; Sprung, 1994; Marques, 2005)
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