Vânia Freitas

Temperature tolerance and energetics: a dynamic energy budget-based comparison of North Atlantic marine species

Temperature tolerance and sensitivity were examined for some North Atlantic marine species and linked to their energetics in terms of species-specific parameters described by dynamic energy budget (DEB) theory. There was a general lack of basic information on temperature tolerance and sensitivity for many species. Available data indicated that the ranges in tolerable temperatures were positively related to optimal growth temperatures. However, no clear relationships with temperature sensitivity were established and no clear differences between pelagic and demersal species were observed. The analysis was complicated by the fact that for pelagic species, experimental data were completely absent and even for well-studied species, information was incomplete and sometimes contradictory. Nevertheless, differences in life-history strategies were clearly reflected in parameter differences between related species. Two approaches were used in the estimation of DEB parameters: one based on the assumption that reserve hardly contributes to physical volume; the other does not make this assumption, but relies on body-size scaling relationships, using parameter values of a generalized animal as pseudo-data. Temperature tolerance and sensitivity seemed to be linked with the energetics of a species. In terms of growth, relatively high temperature optima, sensitivity and/or tolerance were related to lower relative assimilation rates as well as lower maintenance costs. Making the step from limited observations to underlying mechanisms is complicated and extrapolations should be carefully interpreted. Special attention should be devoted to the estimation of parameters using body-size scaling relationships predicted by the DEB theory.

Modelling shellfish growth with dynamic energy budget models: an application for cockles and mussels in the Oosterschelde (southwest Netherlands)

Dynamic energy budget models for growth of individual cockles (Cerastoderma edule) and mussels (Mytilus edulis) are adjusted and calibrated to the Oosterschelde by formulating and parametrizing their functional responses using an extensive set of field observations. The resulting model predictions fit the observations satisfactorily. Results indicate that food quality and the importance of detritus as a food source are site-specific as well as species-specific. Despite these differences in their calibrated parameter values, both species show a very similar functional response. Compared with other systems, however, the functional responses of mussels in the present study are clearly higher than those of mussels in other systems. This may be explained by the absence of intra-specific competition in the measurement set-up that was used, and therefore supports the idea that the generally small functional response of M. edulis is caused by intra-specific competition.

Multi-year comparisons of fish recruitment, growth and production in two drought-affected Iberian estuaries

Climate extremes, such as drought and floods, are increasing and should be considered in ecosystem management plans. The effects of an extreme drought were studied in two estuaries of the Iberian coast, Minho and Mondego, by exploring fish recruitment, growth and production over four years. The two estuaries are located within an area with transitional climate, and differ considerably in size, availability of freshwater wetlands and freshwater inflow. Fishes from the Minho estuary, at higher latitude, generally had lower growth rates and later timing of recruitment. During the drought, freshwater inflow was severely reduced in both estuaries. The overall fish assemblage production in the Minho estuary decreased considerably, whereas in the Mondego estuary it showed an increase. However, the drought effects seemed highly species-specific and dependent on local geomorphology; the increase in the Mondego estuary was a result of an increase in a single species, whereas other species decreased or maintained similar production levels. Decreases in production in both estuaries were attributed to direct and indirect effects of changes in the freshwater inflow during the study period. This parameter should therefore be considered when undertaking management plans for transitional waters.

Factors influencing epibenthic assemblages in the Minho Estuary (NW Iberian Peninsula).

The epibenthic community of the Minho Estuary was studied during the summer of 2006. Diversity was generally low and a total of 14 fish and five crustacean taxa were identified. Multivariate analysis revealed two site clusters (A and B). Water conductivity and percentage of fine sand were the abiotic variables that most contributed to the spatial distinction between clusters. The species contributing the most to the average similarity within Cluster A were Crangon crangon and Pomatoschistus microps, while in Cluster B was Atyaephyra desmarestii. Possible factors responsible for the low diversity of the epibenthic community in Minho Estuary were the low macrozoobenthic abundance and diversity, and the high abiotic oscillations between tides (mainly salinity) acting on the ecosystem.

The European sea bass Dicentrarchus labrax in the Dutch Wadden Sea: from visitor to resident species

This paper analyses the population dynamics, growth and feeding ecology of Dicentrarchus labrax in order to gain a better understanding of its present role in the western Dutch Wadden Sea ecosystem. Otolith analysis showed that the population is mostly comprised of individuals aged 3–5 years old and between 20 and 45 cm in length. In autumn, 0-group juveniles are also an important part of the population. Both juveniles and adults use the area as a feeding ground exhibiting an opportunistic feeding strategy that relies on available prey, especially the brown shrimp Crangon crangon. Stomach content analysis and nitrogen stable isotope analysis showed an ontogenetic shift towards piscivory and a general decrease in the dominance of invertebrates with increasing size. Over the last 50 years, large between-year fluctuations in D. labrax abundance have been observed with an underlying increasing trend from about 1990 until 2007 followed by a subsequent decline. Spring abundance showed significant relationships with temperature and salinity while autumn abundance was only related to temperature. Spring and autumn D. labrax abundance were also strongly related to abundance of brown shrimp C. crangon prey. Long-term trends in temperature and salinity in the area suggest that environmental conditions for juvenile growth have become optimal, resulting in increased abundance since the mid-1980s. Continued monitoring of the dynamics of this species in the Dutch Wadden Sea is important to understand and anticipate the effects of climate change on the D. labrax population and its role in the local food web

High incidence of otolith abnormality in juvenile European flounder Platichthys flesus from a tidal freshwater area

ABSTRACT Otolith abnormality has been reported for a wide range of freshwater and marine fish species. In this study, the sagittal otolith morphology and mineralogy of juvenile European flounder, Platichthys flesus, were examined to describe the incidence and types of structural deformities in this species. Juvenile flounder were collected over the years 2013–2015 in the tidal freshwater section of an estuarine nursery (Minho estuary, NW Portugal). Otolith abnormality was found in 43% of the individuals and, in most cases, occurred in both otoliths. Despite an abnormal mineralogy confirmed by scanning electron microscopy, the morphometry and the mineral polymorph composition of abnormal otoliths did not differ from normal ones (i.e. aragonite). This contrasts with other studies where vaterite and/or calcite were found to replace aragonite in abnormal otoliths. Further studies are needed to elucidate whether abrupt salinity changes associated with habitat transitions may have played a role in the abnormal otolith biomineralization in this species.