Main functional groups of the plankton in front of the fishing port of Anconcito, Santa Elena-Ecuador

Abstract

Coastal marine plankton is an indicator of the link in the pelagic food chains of the first level (phytoplankton) and the second trophic level (zooplankton); therefore, it is of great ecological, fisheries and economic importance. In this context, the objective of this study was to describe the main components of two plankton communities (phytoplankton and zooplankton) and environmental variables (temperature, salinity, oxygen) at three distances (1, 5 and 10 miles) off the fishing port of Anconcito from May 2019 to February 2020, as an indicator of the ecosystem health of a fishing sector. Samples were collected horizontally using plankton nets with 55 and 300 μm mesh eyes for 10 minutes. Temperature, salinity, pH and dissolved oxygen were measured in situ with a multiparameter probe at the surface level. Mean temperature values were recorded among the three study areas of 25°C, salinity of 31 ups, dissolved oxygen of 4.6 mg.L-1 and pH of 8.
The results showed that the first trophic level recorded the abundance of centric diatoms, considered indicators of productive zones mainly in August, while their density in the other months was lower. The phytoplankton composition recorded 167 species; only 12 species of centric diatoms and 13 species of dinoflagellates recorded higher algal density (> 2%), with 142 species present/scarce, the same that evidenced slight differentiation in the three zones. Therefore, diatoms and dinoflagellates were the phytoplankton functional groups that contributed a heterogeneous diversity index in the three sites. Twenty-three zooplanktonic groups were identified, with an average of six species of jellyfish, twelve siphonophores, two cladocerans, two appendicularians and various larval forms of different taxa. Copepods presented the highest mean abundance (48639.3 ind. (100m3 )-1 and 33.3 % respectively), followed by invertebrate eggs (48434.3 ind. (100m3 )-1 and 36. The ANOSIM analysis showed that there is no significant difference between the population densities of the three fixed stations, and in the Bonferroni pairwise comparison between stations 1 and 10 miles, there is no significant difference. In contrast, between stations (10 and 5), (5 and 1) miles there are significant differences, through the SIMPER application, it was found that the group that contributed to the dissimilarity was the copepods, with 38.29% between stations of 10 and 5 miles. The principal component analysis reported that the groups of cladocerans, crustaceans, mollusks, quetognathans, jellyfish and ichthyoplankton were associated with temperature. In conclusion, this line of research on phytoplankton and zooplankton recorded nutritional indicators such as diatoms and copepods very important in the trophic web, combined with local ecological and oceanographic aspects, indicate that the state of health of the coastal margin in front of Anconcito Bay is optimal.