Composition and diversity of the phytoplankton community in two adjacent sectors of the bay of Manta, Ecuador

Abstract

Phytoplankton is the basis of the food chains in many aquatic ecosystems and is susceptible to environmental changes caused by physical, biological or chemical parameters. In this sense, the study of the parameters that potentially affect the phytoplankton will allow better control of environments where there are important economic activities under development such as fishing, tourism, among others. The purpose of the present study was to evaluate the composition and diversity of the phytoplankton in two sectors which divide Manta Bay, subjected to different level of environmental impact, Muricielago (M) and Esteros (E). The study was conducted between July and August of 2017 taking phytoplankton samples once a week at 21:00 and 08:00 with a net made with 50 µm mesh size. Tows were made from a boat in three transepts of 300 m long parallel to the coast, the first located at 1.8 km off shore and the other two at 2 km and 2.2 km offshore, respectively. Sector M is predominantly more exposed to the ocean currents and showed greater thermal variability. Sector E receives the discharge of two rivers and was considered more polluted than M. Found a positive correlation between temperature and the abundance of phytoplankton in M. Phytoplankton was composed of 32 families: 22 Bacillariophyta, 4 Dinoflagellata, 4 Haptophyta and 1 Chlorophyta. In M, phytoplankton was most abundant (average ± 610,7 780,1 cel ml^-1) and diverse (H'= 3, 27), compared to E, where abundance was in average 13.6 ± 4.8 cel ml-1 and diversity (H') was 3.1. The lower diversity and abundance in sector E, was attributed to a greater environmental deterioration and it was considered that the families present there could serve as indicators of environmental pollution; in particular: Chaetocerotaceae, Lithodesmiaceae, Rhopalodiaceae, Melosiraceae diatoms and dinoflagellates Ceratiaceae.