Effects of a red tide on the structure of estuarine fish assemblages in northeastern Brazil

Abstract

The present study evaluated changes in an estuarine fish community caused by blooms of the dinoflagellate Akashiwo sanguinea. Samples were collected before, during and after the red tide using seine nets and surface and bottom nets in three areas near the affected area. The area was around the mouth of the Paraguaçu River. A total of 144 samples were collected, containing 1,989 individuals, with a total weight of 51.4 kg, belonging to 42 species in 29 families. During the red tide, fish density, richness and biomass decreased significantly. Atherinella brasiliensis and Sphoeroides greeleyi were the most abundant species during the red tide, indicating some possible resistance to the effects of the red tide. One month after the red tide, there was a rapid recovery of the density, biomass and richness of fish, and Cetengraulis edentulus was the most captured species. An important result of the present study is the finding that the dynamics of small populations of fish are often influenced by fortuitous events, and stochasticity may dominate. The establishment of a continuous and adequate monitoring program in the area may contribute to understanding the effects of red tides on fish population dynamics.