Life-history data of a key amphipod species from three NE Atlantic estuaries under different levels of anthropogenic pressure.

Knowledge on population dynamics of ecosystem's key-species is invaluable to understand how populations will respond to natural and human-induced perturbations. The amphipod Echinogammarus marinus is a key-species from European estuarine habitats with a distribution ranging from Norway to Portugal [1]. The present article contains supportive data related to a research article entitled 'Comparing production and life-history traits of a key amphipod species within and between estuaries under different levels of anthropogenic pressure' [2]. The present dataset presents the density, biomass, fecundity, and production of E. marinus in three estuaries under different anthropogenic pressure and, within each estuary, at three sampling sites, which differed in terms of the distance to the estuary mouth, vegetation cover, and organic matter content. Monthly environmental abiotic data and seasonal concentration of PAH and other contaminants are also provided. Sampling took place monthly for 13 months at low tide on intertidal mudflats. At each site, Fucus fronds containing E. marinus individuals were randomly collected. All E. marinus individuals were counted, sexed, and measured under a binocular stereo microscope to estimate the density and the biomass of E. marinus in Fucus fronds. Finally, the annual production of E. marinus at each sampling site was estimated through the size-frequency method. This dataset may be used to compare population traits of E. marinus populations across different estuaries and it may overall assist designing studies regarding population dynamics and designing management strategies in coastal systems, namely targeting at habitat conservation and restoration.

Comparing production and life-history traits of a key amphipod species within and between estuaries under different levels of anthropogenic pressure.

Inter-population variability may arise as a response to adverse natural and anthropogenic stressors. The dynamics of a key amphipod species (Echinogammarus marinus) was followed during ≈ 1-year at its southerly range (NW Portugal), in three estuaries with different levels of anthropogenic pressure (High - Ave estuary; Moderate - Mondego estuary; Low - Minho estuary). We hypothesised that E. marinus populations would present lower production and fitness, and higher intersexuality incidence with increasing anthropogenic pressure. According to a GAM model explaining ≈70% of the observed variability, E. marinus biomass depends on temperature, organic matter, Fucus area and time of the year. Significant differences were found between the gammarid biomass in Minho and Mondego estuaries and within sites from the same estuary. As expected, Ave estuary exhibited the lowest average annual production, abundance and fecundity rates. However, the highest average production was found in Mondego and not in Minho estuary, although the turnover ratio (P/B) of both estuaries was very similar. Besides the system's global ecological status, E. marinus also seems to respond to microhabitat conditions, which may explain the spatial heterogeneity observed in the amphipod production within the same estuary. Intersexuality prevalence was negligible in the three populations, which does not support the idea of a link between anthropogenic pressure and intersexuality in E. marinus. We argue that the dependence of E. marinus on Fucus sp. should be further investigated to fully understand the role of both fucoids and the gammarid in coastal foodwebs.

Evidence of low dose effects of the antidepressant fluoxetine and the fungicide prochloraz on the behavior of the keystone freshwater invertebrate Gammarus pulex.

In recent years, behavior-related endpoints have been proposed as rapid and reliable ecotoxicological tools for risk assessment. In particular, the use of detritivores to test the toxicity of pollutants through feeding is currently becoming a well-known method. Experiments combining feeding with other behavioral endpoints can provide relevant information about direct and indirect toxicological effects of chemicals. We carried out a feeding experiment with the shredder Gammarus pulex in order to detect indirect (through leaf conditioning) and direct effects (through water exposure) of two pollutants at environmentally relevant concentrations: the fungicide prochloraz (6 µg/L) and the antidepressant fluoxetine (100 ng/L). Prochloraz inhibited fungal growth on leaves, but it did not affect either the microbial breakdown rates or the C:N ratio of the leaves. Individuals of G. pulex that were fed with treated leaves presented lower consumption rates, not only those fed with prochloraz-treated leaves, but also those fed with fluoxetine-treated leaves, and those fed with the mixture-treated leaves. Mixed-effects models revealed that the swimming velocity of the amphipods after the experiment was modulated by the exposure to fluoxetine, and also by the exposure to prochloraz. We demonstrate that both the antidepressant and the fungicide may cause significant sublethal effects at low concentrations. The combination of behavioral endpoints together with the application of mixed models provided a useful tool for early detection of the effects of toxicity mixtures in freshwater ecosystems.

A widespread and distinctive form of amphipod intersexuality not induced by known feminising parasites.

Intersexuality occurs in a diverse range of animals, and its study offers insights into basic reproductive biology. Investigations in amphipods suggest intersexuality results from incomplete feminisation caused by sex-distorting parasites. It has also been noted that 2 intersex phenotypes occur in males of the amphipod Echinogammarus marinus, an external phenotype, in which males possess rudimentary brood plates, and an internal phenotype, in which only an ovotestis is present. This study examines the relationship between these phenotypes and finds their prevalences are independent. In addition, a cross-species microarray reveals the testicular transcriptomes of the intersex phenotypes are distinct from that of normal males and, most crucially, each other. Furthermore, the internal intersex phenotype, unlike the external phenotype, shows no correlation with infection by known feminising parasites. These findings suggest the male intersex phenotypes should not be considered stages on a single spectrum of intersexuality. Rather, they support the hypothesis that internal and external intersexuality are divergent phenotypes with separate causal mechanisms and point to the existence of a distinct and geographically widespread form of amphipod intersexuality caused by an unknown factor.