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Copepod communities and secondary production in Portuguese coastal waters
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The study of zooplankton communities and estimates of copepod secondary production are of great importance to infer about the global organic matter fluxes in aquatic ecosystems and species-specific responses of zooplankton to hydrologic variability. However, there is still no routine method to determine copepods secondary production to eliminate time consuming experimental analyses. This thesis aims at improving the knowledge on copepods reproduction, with special emphasis on estimations of secondary production, and its relationship with environmental factors. For this purpose, different approaches (experimental and field studies) and time scales were used to study: 1) the effects of temperature and food on the physiology and metabolism of the climate change indicator copepod species Centropages chierchiae; 2) the effect of abiotic and biotic parameters on the production of the ubiquitous copepod genus Acartia in an interannual temporal scale (Guadiana estuary and adjacent coastal waters), as well as during a short temporal scale (Ria Formosa lagoon); 3) the effect of the environmental conditions on the mesozooplanktonic community in Ria Formosa lagoon; and, 4) the relationship between the biochemical method “RNA:DNA ratio” and the egg production rates of the genus Acartia, to infer if this could be a good method to estimate secondary production. Results showed that temperature influenced the feeding, reproductive and respiration rates of the calanoid C. chierchiae, with an optimal temperature at 19ºC for feeding and reproduction, while respiration increased exponentially with temperature and was sex independent. Reproduction rates and hatching success were influenced by different type of algae, a diatom and a dinoflagellate, respectively, and increased with food concentration. Food intake was always higher than the metabolic demands, except for the highest temperature tested (24ºC). During the interannual study in Guadiana estuary, the egg production rate (EPR) of Acartia tonsa was positively related with chlorophyll a concentration, freshwater inflow and dinoflagellates biomass, while Acartia clausi was only related to dinoflagellates. In the intensive field study conducted in Ria Formosa lagoon during summer, EPR of A. clausi was influenced by salinity and ammonia concentration. Moreover, salinity was the main factor affecting the short-term variability of mesozooplankton community, followed by tidal phase, semilunar cycle, temperature and food type. Estimates of Acartia females’ secondary production of both ecosystems were comparable to values of total production obtained in previous studies for other regions, indicating them as high productive areas. The biochemical index RNA:DNA was positively related to EPR in both in situ studies, indicating that it is a good proxy to infer copepod production. In conclusion, simple methods such as the egg production rate and the RNA:DNA ratio should be considered to estimate copepods secondary production in future studies using different species, taking into account the environmental factors that might influence them.
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Zooplankton Copepoda egg production rate RNA:DNA ratio secondary production