High Phytoplankton Diversity Research Articles

Global patterns of organic‐walled phytoplankton biodiversity during the late Silurian to earliest Devonian

Numerous environmental factors as well as oceanic circulation patterns and geographic constraints all contribute to the abundance, distribution, and diversity of present‐day marine phytoplankton assemblages. These same factors presumably affected the Paleozoic marine phytoplankton, which was dominated by organic‐walled acritarchs and prasinophytes. During the Late Silurian (Gorstian, Ludfordian, and Prídolf) and earliest Devonian (Lochkovian), important paleogeographic, paleooceanographic, and geochemical changes were occurring as well as major compositional changes and diversity fluctuations in the marine organic‐walled phytoplankton. Innovative morphologies appeared during the Late Silurian, in both low and high latitude assemblages, but with significant quantitative differences. This was followed by a turnover in assemblage composition during the Silurian/Devonian transition, and an initial radiation of new acritarch and prasinophyte taxa in the Early Devonian. Observed changes in total phytoplankton diversity during the Gorstian through earliest Lochkovian are based on organic‐walled microphytoplankton data derived from published and unpublished key stratigraphic sections where independent age control has been firmly established. These key sections are from: Missouri and Oklahoma, U.S.A. and western Newfoundland, Canada (Laurentia); Gotland, Sweden, and Podolia, Ukraine (Baltica); the Welsh Basin and Borderland (Avalonia); northern France and northern Spain (Armorica); and Libya in northern Africa, and Argentina and Bolivia, South America (Gondwana). Regional biodiversity changes for the organic‐walled microphytoplankton were determined for the warm low latitude areas (Baltica, Laurentia, and Avalonia) and temperate to cool higher latitude areas (northern and southern Gondwana). The Late Silurian‐earliest Devonian organic‐walled phytoplankton was divided into three major categories to facilitate comparison of compositional fluctuations, both within stratigraphic sections as well as between geographic areas. The three categories, based on overall morphology, are marine chlorophytes and prasinophytes, marine acritarchs, and nonmarine types, including coenobial forms. This triparate grouping is both broad and detailed enough to mark critical changes in both the phytoplankton assemblages, as well as the paleoenvironment. In general, high phytoplankton diversity peaks occurred during the Early and Late Gorstian in the warm low latitude areas, followed by varying fluctuations during the Ludfordian and Prídolí for both the warm low latitude and cool high latitude areas. An initial radiation of new phytoplankton taxa and the appearance of more cosmopolitan assemblages mark the beginning of the Lochkovian.

Imbalance of fatty acids in the base of the Baltic Sea food web — a mesocosm study

A reproductive disturbance in Baltic Sea Atlantic salmon (Salmo salar), the M74 syndrome, has been reported since early 1970s and has occasionally caused up to 90% mortality for newborn fry. Previous research has revealed that the M74 syndrome may be due to reduced levels of the vitamin thiamin, the carotenoid astaxanthin, and elevated ratios of ω3/ω6 fatty acids in salmon eggs. Using mesocosm experiments, we compared the quantity (µg·L–1) and quality (mg·g–1 C) of fatty acids in microalgae and copepods in the southern Baltic Sea where the M74 syndrome is common with those in a habitat in the Norwegian Sea where the syndrome has not been observed. Daily additions were made of the nutrients N and P or N, P, and Si, copepods were added after 6–7 days, and nutrient additions were stopped after 9–10 days. Flagellates dominated completely in the Baltic Sea, whereas higher phytoplankton diversity was found in the Norwegian Sea. We found elevated ω3/ω6 ratios in phytoplankton and abnormally high docosahexaenoic acid/arachidonic acid ratios (22:6ω3/20:4ω6) in copepods in the Baltic Sea mesocosms compared with those in the Norwegian Sea. Our results suggest that imbalance in fatty acid composition may prevail in the basic food web of the Baltic Sea.

Phytoplankton composition, dominance and abundance as indicators of environmental compartmentalization in Jurumirim Reservoir (Paranapanema River), Sao Paulo, Brazil

Patterns in the spatial and temporal composition, dominance and abundance of the phytoplankton community of the Jurumirim Reservoir (Brazil) were studied during one year at ten different sampling stations. The main phytoplankton associations were characterized by diatoms and blue-green algae, in distinctive patterns of dominance. The main species were Microcystis aeruginosa Kuetz, Anabaena circinalis Rabenhorst, A. spiroides Kleb., A. solitaria Kleb., Aulacoseira cf. italica Grunow and A. granulata (Ehr.) Simon. A high growth of Aulacoseira was observed in the upstream zones of the reservoir in spring, at the beginning of the seasonal rainy period. This growth was a response to increased flow rates and input of fresh nutrients by the main feeder rivers. A high concentration of blue-green algae, especially Anabaena circinalis and A. spiroides, was observed in winter (dry season) in the lacustrine part of the reservoir, towards the dam. These algae benefitted from the longer water retention times and greater internal circulation of nutrients in the absence of a thermocline at this time of the year. Among the Cyanophyceae, there was an alternation between M. aeruginosa, more abundant in summer, and Anabaena, dominant in autumn and winter. A conspicuous growth of Anabaena occurred in a diverticle of the reservoir, sheltered from the main advective processes that predominate in the central channel. Higher phytoplankton diversity was associated with the contact zone between riverine and lacustrine systems.