Congeneric and sympatric tropical mullets respond differently to environmental variability: insights into coexistence

Abstract

Context Disentangling mechanisms influencing the seasonal and spatial distribution of fish is essential to understanding population dynamics. In the south-western Atlantic, the sympatric mullets Mugil curema and M. rubrioculus are closely related and use habitat similarly. However, which processes allow their coexistence is unknown. Aims We tested the hypothesis that the two species exhibit temporally and spatially decoupled habitat-use patterns to allow sympatry due to different responses to environmental drivers. Methods Bayesian zero-inflated count models were used to unravel spatial and temporal distribution patterns of those species in a south-western Atlantic lagoon. Key results The two species display different distributions within the estuary, being spatially and temporally segregated, with M. curema mostly inhabiting the inner estuary and M. rubrioculus inhabiting coastal marine habitats. Conclusions This decoupling in habitat use might be driven by distinct responses to environmental variability: M. curema is influenced by factors such as temperature and dissolved oxygen, whereas M. rubrioculus is influenced by variations in salinity. We suggest that the studied species evolved divergent responses to environmental variation to allow coexistence. Implications This study suggests that environmental factors drive mullet abundance, and that zero-inflated count models incorporating those drivers are therefore useful in predicting their spatial and temporal distribution, as well as in standardising abundance trends for stock assessment efforts.