Browsing by Author "Pastorinho, Ramiro"
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- Composition and trophic structure of zooplankton in a shallow temperate estuary (Mondego estuary, western Portugal)Publication . Morgado, Fernando; Quintaneiro, Carla; Rodrigues, Elsa; Pastorinho, Ramiro; Nicolau, Paula Bacelar; Vieira, Luís; Azeiteiro, UlissesThe south arm of Mondego Estuary, western Portugal is characterized by shallow depths and marked longitudinal spatial gradients, namely the tidally induced salinity gradient and an eutrophication gradient. The aims of this work were to study the zooplankton composition and trophic structure of the 335 μm taxocenosis in 2 different locations of the salinity and eutrophication gradients in the south arm. The 2 sampling stations displayed significantly different patterns of temporal variations in environmental variables. The total zooplankton density at each station showed significant spatial and temporal variabilities. However, the number of taxa did not show significant differences among months or between sites. The densities of the most abundant taxa significantly differed between the sampling stations and throughout the study period. The zooplankton assemblages were dominated by omnivores, representing 43.9% of the total zooplankton (with herbivores and carnivores representing 4.4% and 0.5%, respectively). Omnivores were significantly more abundant during autumn, winter, and spring, particularly in Oct., Mar., and May, at station 2, and during Jan., Mar., and Apr., at station 1. Herbivores were significantly more abundant during autumn, late winter, and spring particularly at station 1. Carnivores showed low densities throughout the year, being more abundant in summer and autumn. Despite the detected similarities to other temperate estuaries, the results of this work may indicate environmental stresses in this ecosystem: the spatial structure dominates seasonal patterns; and there are low diversities and high numbers of resident populations. This kind of ecological pattern has been previously reported for other biological communities. The prevailing conditions in Mondego Estuary, namely eutrophication, should result in the development of opportunistic adaptive strategies among invertebrates.
- Distribution, production histology and histochemistry in Acartia tonsa (Copepoda: Calanoida) as means for life history and determination in a temperate estuaryPublication . Pastorinho, Ramiro; Vieira, Luís; Ré, Pedro; Pereira, Mário; Nicolau, Paula Bacelar; Morgado, Fernando; Marques, João C.; Azeiteiro, UlissesAcartia tonsa is a key species in the Mondego estuary and a widespread species in all temperate estuarine zooplankton communities; a fact that bestows high relevance upon the outcome of this study. One of the purposes of this study was to estimate the distribution, production and production/biomass ratio values of A. tonsa. Biomass/length relationship was estimated as follows: Y = 0.15e3.04x. Length-weight relationships were used to estimate production taking into account cohort growth and mortality. The annual production was calculated to be 43.12 mg Cm–3 year–1 and the production/biomass (P/B) ratio was estimated to be 10.56. The other purpose of this study was to use histology, histochemistry and biometry to determine as to whether fecundity is a limiting factor in itself or are zooplankters constrained to respond to an ever changing environment. Analyses of the maturation stage of oocytes in adult ovigerous females performed in two different periods of opposed abundance (February— high abundance, representing maximum fertility—and September—low abundance, representing “sterility”) demonstrated the presence of all three considered oocytical development stages: immature, vitellogenic and mature; with emphasis on the latter since it indicates a permanent capability for reproduction despite the registered population abundances. Taking into account the relevance of the species, this fact demonstrates the modulating influence of ecological parameters on general zooplankton reproductive traits.