Mecanismos associados à vulnerabilidade da ictiofauna estuarina às alterações climáticas globais

Abstract

Biodiversity conservation in the face of climate change relies on identifying mechanisms associated with species persistence in their original habitat, in order to prevent impacts at higher ecological levels (i.e. community, ecosystem). The present thesis assessed (I) the relative importance of shifts in species dominance and occupancy for reshaping communities under warming (Chapter 1); (II) the influence of local-scale heterogeneity in temperature and salinity on the thermal tolerance of Brazilian silversides Atherinella brasiliensis (Quoy & Gaimard, 1825), which is a resident species in tropical estuaries (Chapter 2); and the relationship between non-native species’ thermal niche and their geographic area of introduction, and drivers of non-native richness (Chapter 3). In order to achieve the 1o goal, a meta-analysis was performed using studies with a time series equal or greater than 20 years. Trends in beta-diversity and the mean thermal affinity of estuarine fish assemblages were assessed using the compiled database (Chapter 1). For the 2o goal, experiments were performed with A. brasiliensis’ juveniles captured at Guanabara Bay, RJ. Fish were acclimated under distinct temperature and salinity levels in the laboratory, previous to their exposure to a thermal ramp (+1oC each 15 minutes until specimens’ reached endpoint) for detecting their Critical Thermal Maxima (CTMax) (Chapter 2). To achieve the 3o goal, model selection was performed using proxies of anthropogenic activities and environmental filtering, to assess the primary drivers of non-native fish species in estuaries. The relationship between non-native species’ thermal limits and latitude of invaded estuary was also investigated. Tropicalization of estuarine fish assemblages in the temperate realm was primarily driven by shifts in abundance of resident species with distinct thermal affinities, disagreeing with previous expectations regarding a central role of immigration. Estuarine species’ persistence may be related to several mechanisms, including thermal tolerance. Experimental tests revealed A. brasiliensis tolerates temperatures up to 40.6oC. Plasticity on thermal limits in response to acclimation temperature and salinity was also detected. These results indicate A. brasiliensis’ has potential to persist in the estuary under heatwaves and intermediate warming scenarios. Nonetheless, lack of acclimation in the thermal maxima after exposure to temperatures predicted in “worst-case” scenarios, suggests A. brasiliensis heat tolerance is close to reaching a “ceiling”. Thermal limits were also related to the geographic area of introduction of non-native fish species, suggesting conservatism of the climatic niche during invasions. Shipping traffic and salinity were also associated with richness of non-native species, revealing a central role of colonization pressure and habitat filtering for non-native occurrence. These represent novel and timely insights for advancing theory and practice on biodiversity change in response to warming.