Changes in the Composition and Abundance of Phytoplankton in a Coastal Lagoon of Baja California, México, During 2011

Abstract

A time series with weekly sampling was conducted from February 20, to December 16, 2011 at a station in the interior of the San Quintín Bay to estimate seasonal changes in the composition and abundance of phytoplankton. Water temperature was recorded and the upwelling index was calculated for the period. Phytoplankton abundance was estimated and phytoplankton were identified by using an inverted microscope and the CHEMTAX program. There were 16 positive phytoplankton anomalies during the year, but only three were considered to be blooms. The blooms were dominated by diatoms and were recorded in the winter, spring and summer. Different genera composed 80% of the total phytoplankton abundance of each of the blooms. The first bloom consisted of diatoms of the genera Pseudo-nitzschia sp. (15.7%), Skeletonema sp. (14.6%), Eucampia sp. (7%), and Navicula sp. (7%) a haptophyte of the genus Imantonia sp. (13.1%) and dinoflagellates of the genus Prorocentrum sp. (4.6%). The second bloom consisted mainly of diatoms of the genera Guinardia sp. (30.6%), Pseudo-nitzschia sp. (21.5%), Skeletonema sp. (14.5%), Chaetoceros sp. (8.4%) and Eucampia sp. (5.3%). The third bloom consisted of Chaetoceros sp. (46.3%), Pseudo-nitzschia sp. (22.6%), Skeletonema sp. (7.29%), and Imantonia sp. (6%). Dinoflagellates were observed in the winter, summer and autumn, but they contributed less biomass than diatoms. Prorocentrum sp., Gymnodinium sp., and Ceratium sp. were among the dinoflagellates that were observed. The differences in abundance and composition of phytoplankton groups in the blooms in San Quintín Bay during 2011 were due primarily to seasonal changes in the physical and chemical factors of the seawater and to upwelling events.