Phytoplankton patterns and processes in a tropical-subtropical transition region: Santa Catarina Coast, Southern Brazil

Abstract

The coast of Santa Catarina state is 561 km long and presents varied features and ecosystems. Bordered by the states of Paraná to the north and Rio Grande do Sul to the south, the coast of Santa Catarina shows a clear transition between these two neighboring states. In the coastal zone, this transition is marked by the limit of mangrove distribution (latitude 28°30'S) and the presence of the Cape of Santa Marta Grande, which induces upwelling and creates important oceanographic changes that affect the continental shelf. The Santa Catarina coast is one of the most important fishing regions of Brazil and contains 95% of the country's mariculture. Phytoplankton of the neritic zone presents considerable seasonality, as evidenced by moderate diatom blooms in the spring, reduction of phytoplankton biomass in the summer, and increased importance of dinoflagellates in the winter, patterns associated with peculiarities of local oceanography. Blooms of Trichodesmium spp. are also seasonal from early spring to late summer. Various estuaries impose strong influence over these seasonal patterns, forming estuarine or fluvial plumes where phytoplankton biomass increases at any time of the year. The high degree of pollution, most likely associated with climatic and oceanographic anomalies in some areas, has resulted in unusual blooms of diatoms, e.g., Pseudo-nitzschia spp. and Amphitetras antediluviana, and dinoflagellates, e.g., Dinophysis spp., posing a risk to both local ecology and mariculture. On sandy beaches, surf diatom blooms are quite frequent, especially Asterionellopsis glacialis sensu lato. The surf diatom Anaulus australis, which occurs along the entire Brazilian coast, alternating with A. glacialis, has its southern limit of distribution in Santa Catarina. These and other peculiarities characterize the Santa Catarina coast as an area of abrupt ecological transition and, hence, a genuine hotspot for ecological studies based on phytoplankton. This chapter reviews published data, including theses and difficult-to-access publications, in an attempt to characterize these transitional features but also to highlight emerging patterns to allow a greater understanding of western South Atlantic pelagic ecology.