In the characteristic mat-like communities of the seaweed Caulerpa, preliminary observations show that there is a positive relationship between the species diversity indices for the animals and the algae. Since some of the animals are obligate herbivores or otherwise related trophieMly within the community, they can be expected to contain some of the peculiar or toxic algal components and to vary in trophic biomass with the food biomass, at least when food is limiting. However, there is little relationship apparent between the biomass of the animals and that of the Caulerpa.
Mollusc communities are getting endangered in the aftermath of urban sprawl because artificial structures do not surrogate natural substrates. In this study, we compared the diversity, community and trophic arrangements of molluscs among different models of artificial substrate and their adjacent natural rock, to detect relationships between some abiotic variables and the mollusc communities. Complexity, chemical composition and age were tested as potential drivers of the community. Diversity, community and trophic structure differed between natural and artificial substrates. Complexity at the scale of cm was detected as the most important factor driving the community structure. In addition, a chemical composition based on silica and/or scarce calcium carbonates seems to be relevant for molluscs, as well as for the secondary substrate where they inhabit. However, age did not seem to be a driving factor. Among the different artificial structures, macroscale complexity was detected as the main factor diverging a drastically poor community at seawall from other artificial structures. In this context, macro and microscale complexity, chemical composition and mineral type are variables to consider in future designs of artificial substrates.
The Atlantic blue crab, native from the east coast of the American continent, is a portunid, estuarine crab that has been recently considered invasive in many areas of the European and African continents, being cited in the Guadalquivir estuary in 2017 for the first time. The feeding habits of the Atlantic blue crab were studied as predictor of food web interactions and potential impacts in the study area. Depending on the availability of food, C. sapidus can adapt to a diverse resource utilization in the Guadalquivir estuary. The main consumed preys were fish, molluscs, and crabs, but they also consumed sediments and vegetation, although in smaller quantities and with a lower frequency. Diet composition was very generalist, and no seasonal or sexual effects were detected. However, diet seems to be more diverse in summer, while in winter blue crabs seem to switch trophic strategies to cannibalism or scavenging on fishing discarded nets. In addition, sexual dimorphism of chela and different spatial distribution seem to diverge the diet composition between males and females during the different sampled seasons. This requires the establishment of many diverse trophic interactions between the Atlantic blue crab and the native food web, which could lead to future impacts on the native community. Consequently, we believe that prey monitoring and control over this non-native species should be considered a priority for the management and conservation of the Guadalquivir estuary. Other methodological approaches as laboratory experiments and feeding habits predictors should be considered as future studies to better describe the trophic behaviour in the whole C. sapidus species.
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