Distribuição geográfica, morfologia dos dentículos dérmicos e níveis de contaminação por metais em elasmobrânquios do Atlântico Sudoeste: a raia costeira Zapteryx brevirostris e o tubarão pelágico Megachasma pelagios

Abstract

Sharks and rays play a crucial role in structuring marine ecosystems, occupying diverse trophic levels. However, this group faces increasing threats, such as overfishing and habitat degradation, necessitating urgent conservation strategies based on accurate biological data. The aim of this thesis was to review the distribution limits of the endemic ray Zapteryx brevirostris and to characterize the occurrence and ecology of the Megamouth Shark, Megachasma pelagios, in the Southwestern Atlantic. The study was divided into three main approaches. First, the distribution review of Z. brevirostris, based on scientific collections and literature, redefined its geographic limits from the Doce River mouth, Espírito Santo (19ºS), to the Falkland/Malvinas Islands (53ºS). This new southern limit extends the species' known distribution by over 2,000 km, suggesting the influence of biotic factors in the north and abiotic factors in the south. Regarding the shark M. pelagios, the third record in Brazil (Piauí) was described based on molecular identification using the ND2 gene. Scanning electron microscopy analysis revealed that the dermal denticles of this specimen (a neonate) exhibit a morphology distinct from that observed in adults, indicating ontogenetic changes. Finally, the isotopic composition of the neonate was investigated via δ13C and δ15N stable isotopes. Contradicting independent feeding, the isotopic signatures reflected maternal nutritional investment originating from oligotrophic waters of the Tropical Atlantic Ocean. The low mercury concentration corroborates the neonatal stage, while elevated levels of aluminum and lead indicate maternal offloading of these elements. These results establish a critical baseline for monitoring rare and data-deficient species in the Southwest Atlantic Ocean.