Análisis del estado trófico y microfitoplancton de la zona costera de la provincia del Guayas, Ecuador

Abstract

Most fishing and aquaculture activity in Ecuador is concentrated in the Gulf of Guayaquil. However, the nutrient loads from anthropic activities could affect the water quality and the diversity of fishery resources. Surface water samples were collected to determine the temperature, salinity, dissolved oxygen, nutrients, and the community structure of microphytoplankton to determine the trophic status of the coastal zone and the inner estuary. In addition, the relation between the hydrographic variables was established through principal component analysis (PCA), and redundancy analysis (RDA) was used to analyze the effect of the environmental variables on the microphytoplankton communities. Differences in community structure were determined using multidimensional scaling analysis of similarities (MDS-Anosim), and the trophic status was established through the Karydis index. Significant differences were detected between the coastal zone and the inner estuary. Overall, the inner estuary showed a higher trophic level, with higher temperature and nutrient concentrations, and lower values for the salinity, transparency, and dissolved oxygen. Seventeen species of microphytoplankton were identified, of which 78% were diatoms, 18% dinoflagellates, 2% cyanophytes, and 2% silicoflagellates. Significant differences were detected in equitability and diversity, with fewer records in the estuarine area. The RDA showed a positive correlation (0.54; p <0.05) between Paralia sulcata, Thalassionema nitzschioides, Thalassionema frauenfeldii and nutrients and a negative correlation with salinity. In the inner estuary, Nitzschia longissima, Chaetoceros decipiens, and Skeletonema costatum were positively correlated (0.64; p <0.05) with temperature and negatively correlated with phosphate and nitrate. Differences in the community structure existed between zones, with S. costatum, T. frauenfeldii, and T. nitzschioides dominating the inner estuary and N. longissima, Guinardia striata, and Leptocylindrus danicus dominating in the coastal zone. The study area was determined to be mesotrophic. However, in the inner estuary, the values of the trophic index were higher because this area probably receives more directly the contributions from anthropic activities. Surveys with samples less than a mile from the coast are recommended to determine the trophic status in an area closer to the coast and to develop management plans to avoid threats of eutrophication.