Time Variation in Phytoplankton Assemblages in a Subtropical Lagoon System after the 1982-1983 "El Nino" Event (1984 to 1986)

An analysis of seasonal and geographical distribution and abundance of the total and separate fractions of phytoplankton (nanno- and microphytoplankton) in the Magdalena-Almejas lagoon system was done after the 1982-1983 "El Nino" event. In spite of its being in a subtropical region, the annual variation of phytoplankton abundance in the area was similar to the annual cycle of production of coastal lagoons in temperate regions. There were two peaks of phytoplankton abundance, in spring and in autumn. The upwelling and tidal currents enriching the waters of Bahia Magdalena were responsible for the high concentrations of phytoplankton in the bay. Microphytoplankton was the most important fraction throughout the study period. Nannophytoplankton was somewhat abundant. Using principal component analysis, seasonal variation and frequency were the two factors determining the structure of species assemblages. Lowest values of diversity and dominance were related to circulation patterns and to the phytoplankton blooms that occurred throughout the year in Bahia Magdalena-Almejas. High values of diversity and low dominance were estimated at those areas under the influence of oceanic waters. The 1982-1983 El Nino caused a drastic drop in phytoplankton abundance during 1984. The recuperation process was slow, starting in 1985 and completed by 1986. Recorded increases in phytoplankton abundance surpassed all previous records. "El Nino" caused changes in the structure of the microphytoplankton assemblages. Species richness and specific diversity diminished because of the occurrence of few species

First Record of a Rhizosolenia debyana Bloom in the Gulf of California, Mexico

A bloom of the diatom Rhizosolenia debyana H. Peragallo was observed in the southwestern Gulf of California. This bloom was estimated to be about 22 Ian long and represents the first record of this species for the area. Total abundance of R. debyana ranged from 2,576,000 to 3,684,000 cells liter^-1. Chlorophyll a concentrations ranged from 17.15 to 41.45 mg/m^3. Rhizosolenia debyana has a tropical and subtropical distribution

Dinoflagellate cyst distribution in recent sediments along the south-east coast of India

The spatial variation in the dinoflagellate cyst assemblage from the south-eastcoast of India is presented along with a comparison of the cyst abundance from other regions of the world. Samples from 8 stations revealed the presence of 24 species from the genera <i>Protoperidinium</i>, <i>Zygabikodinium</i>, <i>Gonyaulax</i>, <i>Lingulodinium</i> and <i>Gyrodinium</i>. Cyst abundance was comparatively high at northern stations and was well correlated with the fine-grained (silt-clay dominated) sediments. In contrast, low cyst abundance was recorded in sandy sediments at southern stations. Fourteen cyst-forming dinoflagellate species previously unrecorded in planktonic samples were detected in the sediments. Thecyst abundance recorded here is low (29-331 cysts g<sup style="font-size:0.6em">-1</sup> dry sediment) as compared to sub-tropical and temperate regions, but it is on a par with tropical regions, including the west coast of India. Comparison of the cyst assemblage along the Indian coast revealed a smaller number of potentially harmful and red-tide-forming dinoflagellate species on the south-east coast (6 species) than on the west coast (10 species). Furthermore, calcareous cysts of the genus <i>Scrippsiella</i> reported from the west coast were not observed in this study although their planktonic cells have been reporte