Proportion Of Dinoflagellates Research Articles

Phytoplankton Seasonal Dynamics under Conditions of Climate Change and Anthropogenic Pollution in the Western Coastal Waters of the Black Sea (Sevastopol Region)

The studies of seasonal phytoplankton dynamics, its growth rate, and microzooplankton grazing were conducted on two stations in the western Black Sea coastal waters near Sevastopol from January 2021 to December 2022. The phytoplankton species composition has remained relatively the same during recent years compared to the end of the last century and the beginning of the 2000s. However, significant changes have occurred in the ratio between different species of diatoms, and the proportion of dinoflagellates was increased, especially in the autumn. Large diatoms and dinoflagellates play a crucial role in forming the phytoplankton biomass seasonal peaks. The first central maximum was observed in July, and the second smaller one was in September–November. Whereas two decades ago, the small diatoms generated three peaks annually: in February, May, and September–October. The maximum values of the phytoplankton growth rate and the rate of its consumption by microzooplankton decreased 2–3 times compared to the beginning of the 2000s. The relative share of primary production consumed by microzooplankton annually averages 35%, two times lower than before.

Regional disparities of phytoplankton in relation to different water masses in the Northwest Pacific Ocean during the spring and summer of 2017

The West Pacific Ocean is considered as the provenance center of global marine life and has the highest species diversity of numerous marine taxa. The phytoplankton, as the primary producer at the base of the food chain, effects on climate change, fish resources as well as the entire ecosystem. However, there are few large-scale surveys covering several currents with different hydrographic characteristics. This study aimed to explore the relationships between the spatio-temporal variation in phytoplankton community structure and different water masses. A total of 630 water samples and 90 net samples of phytoplankton were collected at 45 stations in the Northwest Pacific Ocean (21.0°–42.0°N, 118.0°–156.0°E) during spring and summer 2017. A total of 281 phytoplankton taxa (>5 µm) belonging to 61 genera were identified in the study area. The distribution pattern of the phytoplankton community differed significantly both spatially and temporally. The average abundances of phytoplankton in spring and summer were 797.07×102 cells/L and 84.94×102 cells/L, respectively. Whether in spring or summer, the maximum abundance always appeared in the northern transition region affected by the Oyashio Current, where nutrients were abundant and diatoms dominated the phytoplankton community; whereas the phytoplankton abundance was very low in the oligotrophic Kuroshio region, and the proportion of dinoflagellates in total abundance increased significantly. The horizontal distribution of phytoplankton abundance increased from low to high latitudes, which was consistent with the trend of nutrient distributions, but contrary to that of water temperature and salinity. In the northern area affected by the Oyashio Current, the phytoplankton abundance was mainly concentrated in the upper 30 m of water column, while the maximum abundance often occurred at depths of 50–75 m in the south-central area affected by the Kuroshio Current. Pearson correlation and redundancy analysis (RDA) showed that phytoplankton abundance was significant negatively correlated with temperature and salinity, but positively correlated with nutrient concentration. The phytoplankton community structure was mainly determined by nutrient availability, especially the N:P ratio.

The role of life cycle processes on phytoplankton spring bloom composition: a modelling study applied to the Gulf of Finland

Abstract Diatoms are typical representatives of the spring bloom worldwide. In several parts of the Baltic Sea, however, cold-water dinoflagellates such as Biecheleria baltica have become dominant during the past decades. We have investigated the mechanisms behind this trend by using an ecosystem model which includes the life cycles of three main phytoplankton groups (diatoms, dinoflagellates and cyanobacteria). Coupled to a water column model we have applied the model system for the period 1981–2010 to the Gulf of Finland. In agreement with observations, the model results show an increasing trend in the proportion of dinoflagellates in the Gulf of Finland. Temperature and life cycle-related processes explain the relative increase of dinoflagellates and corresponding decrease of diatoms. Warming over the 30 years has enabled a head start of dinoflagellates by reducing the time lag between germination and growth of vegetative cells. Although diatoms have a much higher growth rate, they cannot compete with the high dinoflagellate concentrations that result from the inoculum. Diatoms will only dominate in years when the inoculum concentrations of dinoflagellates or the temperatures are low. Overall, the model results suggest that consideration of life cycle dynamics of competing phytoplankton groups may be crucial to understand trends and shifts in community composition.

Mercury concentration in phytoplankton in response to warming of an autumn – winter season

Among other climate changes in the southern Baltic, there is a tendency towards warming, especially in autumn-winter. As a result, the ice cover on the coastal zone often fails to occur. This is conducive to the thriving of phytoplankton, in which metals, including mercury, can be accumulated. The dry deposition of atmospheric Hg during heating seasons is more intense than in non-heating seasons, owing to the combustion of fossil fuels for heating purposes. This has resulted in studies into the role of phytoplankton in the introduction of Hg into the first link of trophic chain, as a function of autumn and winter warming in the coastal zone of the lagoon. The studies were conducted at two stations in the coastal zone of the southern Baltic, in the Puck Lagoon, between December 2011 and May 2013. The obtained results show that, in the estuary region, the lack of ice cover can lead to a 30% increase and during an “extremely warm” autumn and winter an increase of up to three-fold in the mean annual Hg pool in phytoplankton (mass of Hg in phytoplankton per liter of seawater). The Hg content in phytoplankton was higher when Mesodinium rubrum was prevalent in the biomass, while the proportion of dinoflagellates was small.

Spatio-temporal variation of microphytoplankton in the upwelling system of the south-eastern Arabian Sea during the summer monsoon of 2009

The phytoplankton standing crop was assessed in detail along the South Eastern Arabian Sea (SEAS) during the different phases of coastal upwelling in 2009. During phase 1 intense upwelling was observed along the southern transects (8°N and 8.5°N). The maximum chlorophyll a concentration (22.7mgm −3) was observed in the coastal waters off Thiruvananthapuram (8.5°N). Further north there was no signature of upwelling, with extensive Trichodesmium erythraeum blooms. Diatoms dominated in these upwelling regions with the centric diatom Chaetoceros curvisetus being the dominant species along the 8°N transect. Along the 8.5°N transect pennate diatoms like Nitzschia seriata and Pseudo-nitzschia sp. dominated. During phase 2, upwelling of varying intensity was observed throughout the study area with maximum chlorophyll a concentrations along the 9°N transect (25mgm−3) with Chaetoceros curvisetus as the dominant phytoplankton. Along the 8.5°N transect pennate diatoms during phase 1 were replaced by centric diatoms like Chaetoceros sp. The presence of solitary pennate diatoms Amphora sp. and Navicula sp. were significant in the waters off Kochi. Upwelling was waning during phase 3 and was confined to the coastal waters of the southern transects with the highest chlorophyll a concentration of 11.2mgm−3. Along with diatoms, dinoflagellate cell densities increased in phases 2 and 3. In the northern transects (9°N and 10°N) the proportion of dinoflagellates was comparatively higher and was represented mainly by Protoperidinium spp., Ceratium spp. and Dinophysis spp.

Long-term changes of basic biological and chemical parameters at two stations in the middle Adriatic

Since the early 1960s regular monthly observations of basic hydrographic, chemical and biological parameters have been carried out at two stations in the middle Adriatic which are influenced to a varying degree by the coastal and open Adriatic waters. Based on the analysis of the relationship between diatom/dinoflagellate and primary production, it was established that the proportion of dinoflagellates in the phytoplankton community increased with an increase in primary production. All these changes were accompanied by a steady increase in percent oxygen saturation in the surface layers and a decrease in the bottom layers. The increase in primary production and changes in percent oxygen saturation in the open Adriatic occurred ten years after those in Kaštela Bay. Even though all the relevant data indicate that the changes in Kaštela Bay are closely related to an increase of anthropogenic nutrient loading, similar changes in the open sea suggest that primary production increase in the Bay might, at least partly, be due to global climatic changes.

Composition of benthic protozoan communities along a depth transect in the eastern Mediterranean Sea

The benthic protozoans were investigated along a transect in the eastern Mediterranean Sea from the Ionian to the Levantine Sea. Sediment samples were taken during Meteor cruise 25/1 in May and June 1993 at water depths of between 156 and 4617 m with a box corer and a multiple corer. A semi-quantitative cultivation technique was applied by placing sediment in petri dishes and diluting with sterile biotope water. Microscopic analyses of the protozoan taxa were conducted immediately after sampling, and then daily after enrichment with organic substrate. A total of 134 protozoan morphospecies were recorded, including 87 flagellates, 12 naked amoebae and 35 ciliates. 58% of the species could be attributed to genera known from shallow waters, demonstrating the wide distribution of these taxa. The number of recorded species per location ranged from 0 to 35 and decreased with increasing water depth. At stations deeper 1300 m very low species numbers as well as low potential abundances were recorded. Qualitative changes in the taxonomic composition with increasing depth were recorded as a decrease in the proportion of amoebae and euglenid flagellates and as an increase in the proportion of dinoflagellates. Ciliates were found down to a depth of 4260 m. The number of species was also dependent on the chloroplastic pigment equivalent (CPE), indicating a dependency on sedimented phytodetritus. The observed species included picophagous species, which feed mostly on bacteria, as well as nano- and microphagous species, which generally feed on protists, suggesting the existence of several trophic levels within the deep sea microbial food web.