Maria D. Bordalo

Ambient fauna impairs parasite transmission in a marine parasite-host system

To understand possible factors controlling transmission of trematode larvae between first and second intermediate hosts we examined the impact of ambient fauna on parasite transmission in a marine intertidal parasite-host association. Cockle hosts (Cerastoderma edule) kept together with selected co-occurring macrozoobenthic species in mesocosms acquired a lower parasite load compared to cockles kept alone, when targeted by cercariae of the trematode Himasthla elongata. The reduction of parasite load in the cockles differed between the 7 macrozoobenthic species tested and was between 35 and 91%. Three different types of reduction could be distinguished: (1) predators (Carcinus maenas, Crangon crangon) actively preying upon cercariae, (2) non-host filter feeders (Crepidula fornicata, Mya arenaria, Crassostrea gigas) filtering cercariae but not becoming infected and (3) alternative hosts (Mytilus edulis, Macoma balthica) becoming infected by the cercariae and thus distracting cercariae from the target hosts. In addition, interference competition may occur in the form of disturbance of cockles by ambient organisms resulting in lower filtration rates and subsequently lower parasite loads. Our results suggest that the species composition and relative abundance of the ambient fauna of parasite-host systems play an important role in controlling trematode transmission rates in benthic marine systems.

Implications of nutrient decline in the seagrass ecosystem success

The Mondego estuary (Portugal) suffered major changes in environmental quality due to eutrophication, however, in the late 1990 s a restoration project was implemented in order to return the system to its original condition. The main goal of this paper is to evaluate the ecosystem response to the restoration measures applied at three different levels: water quality, primary producers and primary consumers. In post-restoration period a clear decline was observed in dissolved inorganic nitrogen which was reflected in the gradual recovery of Zostera noltii and a concomitant decline in green macroalgae. Macrobenthic assemblages responded variably to the recovery process. In the seagrass bed and intermediate area, there was a large increase in total biomass, but in the eutrophic area species diversity increased. Despite improvement in the ecological status of the system, full recovery has not been achieved yet, possible due to hysteresis in the dynamics of this system.

Trematode fauna of Hydrobia ulvae (Gastropoda: Prosobranchia) in a eutrophic temperate estuary

Digenean trematodes infecting the mud snail Hydrobia ulvae were studied at two key sites of the Mondego Estuary (Portugal), from January 1993 to September 1995: a mud flat covered by the seagrass Zostera noltii , and a bare sand flat where seasonal macroalgal blooms occurred as a result of eutrophication. Digeneans belonging to Microphallidae, Notocotylidae, Haploporidae and Heterophyidae were recorded in snails from both sites whereas representatives from Echinostomatidae were only found in snails from the seagrass bed. The density of infected snails was higher at the seagrass bed than at the eutrophic area partly reflecting the difference in population structure of H. ulvae between sites. The Zostera noltii bed supports an abundant and well-structured mud snail population, with all size-classes represented, in contrast to a less abundant and juvenile dominated population in the eutrophic area. In the Z. noltii bed no clear seasonal and interannual patterns emerged in the infection densities. In the eutrophic area, the density of infected individuals increased in the presence of algae, and decreased during the occurrence of occasional flood events. Small scale spatial and temporal patterns in the prevalence of digenean trematodes in mud snails were therefore demonstrated within the Mondego Estuary that has experienced a mixture of anthropogenic impact and climate instability.

Exposure to chlorantraniliprole affects the energy metabolism of the caddisfly Sericostoma vittatum

Caddisflies have been included in ecotoxicological studies because of their sensitivity and ecological relevance. The present study aimed to assess the sublethal effects of an anthranilic diamide insecticide, chlorantraniliprole (CAP), to Sericostoma vittatum. Used worldwide, CAP is a persistent compound that has been found in surface waters at concentrations from 0.1 μg/L to 9.7 μg/L. It targets the ryanodine receptors, and the present ecotoxicological assessment focused on biomarkers related to neurotransmission, biotransformation, oxidative stress damage, and endpoints related to energy processing (feeding, energy reserves, and cellular metabolism). Six days of exposure trials revealed that feeding activity was significantly decreased in S. vittatum larvae exposed to 0.9 μg/L CAP. Concomitantly, a reduction in cellular metabolism and a significant decrease in protein content were also observed in caddisfly larvae exposed to CAP, suggesting metabolic depression. The results show that sublethal concentrations of CAP can cause detrimental sublethal effects on S. vittatum total glutathione content at concentrations as low as 0.2 μg/L. Bioenergetics can be used to assess physiological effects of contaminants, and the present results show that exposure to low, environmentally relevant, concentrations of CAP alter energy acquisition and metabolism in nontarget aquatic insects with potential population level effects. Environ Toxicol Chem 2017;36:1584-1591.

Combined effects of predation risk and food quality on freshwater detritivore insects

Because both predation risk and resource quality have a pivotal role in ecological communities, their combined effects were assessed in stream detritivores. Bioassays were conducted using a simplified trophic chain, coupling effects of predation risk and basal resources with different nutritious qualities, namely, a predator planarian Dugesia subtentaculata, a caddisfly shredder Sericostoma vittatum, a dipteran collector Chironomus riparius, native alder Alnus glutinosa and invasive eucalypt Eucalyptus globulus. We investigated whether individual performance of C. riparius larvae is affected under predation risk and whether the response can be mediated by resource quality. We also assessed whether shredder–collector interactions are altered under these conditions. Predation risk and food quality influenced leaf decomposition and C. riparius growth independently. Chironomus riparius fed preferentially on alders, resulting in increased growth rate. Litter processing decreased under planarian presence, in both leaf types, impairing the growth of C. riparius larvae, this effect being exacerbated with eucalypts. Chironomus riparius growth was also reduced in the presence of the caddisfly, suggesting competition between these species, irrespective of planarian presence, but dependent on leaf type. The present study highlighted the importance of assessing predator influence along detritus-based processing chains, because predation risk may result in sublethal costs, with potential cascading effects.

Invasive Species Mediate Insecticide Effects on Community and Ecosystem Functioning

Anthropogenic activities increase pesticide contamination and biological invasions in freshwater ecosystems. Understanding their combined effects on community structure and on ecosystem functioning presents challenges for an improved ecological risk assessment. This study focuses on an artificial stream mesocosms experiment testing for direct and indirect effects of insecticide (chlorantraniliprole - CAP) exposure on the structure of a benthic macroinvertebrate freshwater community and on ecosystem functioning (leaf decomposition, primary production). To understand how predator identity and resource quality alter the community responses to chemical stress, the mediating effects of an invasive predator species (crayfish Procambarus clarkii) and detritus quality (tested by using leaves of the invasive Eucalyptus globulus) on insecticide toxicity were also investigated. Low concentrations of CAP reduced the abundance of shredders and grazers, decreasing leaf decomposition and increasing primary production. Replacement of autochthonous predators and leaf litter by invasive species decreased macroinvertebrate survival, reduced leaf decomposition, and enhanced primary production. Structural equation modeling (SEM) highlighted that CAP toxicity to macroinvertebrates was mediated by the presence of crayfish or eucalypt leaf litter which are now common in many Mediterranean freshwaters. In summary, our results demonstrate that the presence of these two invasive species alters the effects of insecticide exposure on benthic freshwater communities. The approach used here also allowed for a mechanistic evaluation of indirect effects of these stressors and of their interaction on ecosystem functional endpoint, emphasizing the value of incorporating biotic stressors in ecotoxicological experiments.