Aim: To present an updated database of fish species recorded on south‐western Atlantic reef environments and to explore the ecological drivers of the structure, the latitudinal gradient of biodiversity and the centre of endemism in this peripheral province.Location: South‐western Atlantic (SWA): Brazilian and Argentinian Provinces.Methods: A database composed of 733 fish species along 23 locations in the SWA (00°55′ N to 43°00′ S) was compiled based on primary data, literature and museum records. Cluster and beta diversity analyses were carried out to evaluate faunal overlaps among locations and subprovinces. “Target‐area‐distance effect” and “stepping stones dispersal” hypotheses for assemblage composition were tested through Mantel tests. Relationships between the distribution patterns and ecological traits of reef fish species were investigated through generalized linear mixed‐effect models.Results: Out of the 733 fish species, 405 are SWA resident reef fishes, of which 111 (27%) are endemics and 78 are threatened with extinction. Cluster analysis detected six subprovinces in the SWA structured following the target‐area‐distance model, and with no evidence for a latitudinal gradient in diversity. The greatest overall richness and endemic species richness were found in the east–south‐eastern region. Depth range, habitat use and body size were the main drivers of SWA reef fish assemblage structure.Main conclusions: The Brazilian and Argentinian coasts constitute different provinces structured by oceanographic barriers and environmental filters. Similarities among oceanic islands indicate connectivity driven by stochastic and ecological factors. Species richness and endemism indicate that peripheral provinces may also bear centres of origin and biodiversity, patterns driven by parapatric/ecological speciation and the overlap between tropical and subtropical reef fish species. Ecological drivers of reef fish distribution, such as habitat specialization and body size, support hypotheses of speciation in the periphery. New approaches for spatial planning, marine protected areas and off‐reserve marine management are essential for the conservation and sustainability of SWA reef fishes.

Top predators have a strong influence on the structure and dynamics of marine ecosystems. These organisms have been largely used as indicators of the effectiveness of marine protected areas (MPAs). In Brazil, the impact of fisheries on reef species, such as groupers and sea basses, and the importance of local marine reserves in the maintenance of these fish communities are still poorly understood. Here we assessed the assemblage of groupers and sea basses (Epinephelidae and Serranidae) inside and outside the Arvoredo Marine Reserve (AR), a MPA in Santa Catarina State, southern Brazil. Density and biomass of 13 fish species (7 Epinephelidae and 6 Serranidae) were recorded. The most abundant groupers were Epinephelus marginatus and Mycteroperca acutirostris, while Serranus flaviventris and S. balwini were the most abundant sea basses. Grouper biomass was significantly higher inside the reserve, indicating the effectiveness of this MPA for target and threatened species, such as E. marginatus. In contrast, biomass of sea basses was higher outside the MPA, as a possible result of prey release effect. Despite the higher biomass of groupers inside AR, spearfishing records from the 1960s indicate that there is still a long way to a full recovery of the biomass of top predators, especially groupers and sharks. Thus, a more effective enforcement and longer-term protection are necessary to restore fish stocks and ecosystem health in these reefs.9 page(s

Long-distance dispersal is one of the main drivers structuring the distribution of marine biodiversity. This study reports the first occurrence of Macrocystis pyrifera and Durvillaea antarctica rafts on the southwestern warm temperate coast of the Atlantic Ocean. Our results indicate that an extreme meteo-oceanographic event, characterized by a northward, displacement of cold sub-Antarctic oceanic waters driven by an extratropical cyclone, could account for these unusual occurrences. A niche model based on known current distribution and maximum entropy principle (MAXENT), revealed the availability of suitable habitats at lower latitudes, outside their actual distribution edges. The distributional boundaries, mainly driven by temperature and irradiance, suggest the existence of environmental suitability in warm temperate areas, as well as in the Northern Hemisphere off Atlantic and Asian coasts. These theoretical edges and respective environmental drivers agree with the physiological affinities of both species, supporting the hypothesis that these variables act as limiting factors for their occurrences in tropical or warmer areas. Emerging regions can function as refuges and stepping-stones, providing substrate with adequate habitat conditions for recruitment of propagules, allowing eventual colonization. Long dispersal events reinforce the need for an extensive discussion on selective management of natural dispersion, biological invasions, refuge mapping and conservation initiatives in a transnational perspective.

We present a checklist of 278 species of reef fishes recorded along the coastline of Santa Catarina state, the southernmost limit of distribution of tropical ichthyofauna on the coast of Brazil. Twelve new species records for this state are presented: Acanthurus coeruleus, Acanthurus monroviae, Apogon americanus, Cantherhines macrocerus, Chaetodon sedentarius, Chromis flavicauda, Clepticus brasiliensis, Decapterus punctatus, Gymnothorax vicinus, Herpetoichthys regius, Muraena retifera and Stegastes partitus. Stegastes partitus and H. regius are reported for the first time, respectively, from the Southwestern Atlantic and for the coastal part of this region, while Acanthurus monroviae is reported for the second time for the Southwestern Atlantic. We present habitat distribution, trophic structure and comment on biogeographic affinities of this transitional region, discussing both remarkable species presences and absences.