Shifts In Phytoplankton Community Structure Research Articles

Toxicological effects of cypermethrin to marine phytoplankton in a co-culture system under laboratory conditions

The growth of three marine phytoplankton species Skeletonema costatum, Scrippsiella trochoidea and Chattonella marina and the response of the antioxidant defense system have been investigated on exposure to commercial cypermethrin for 96 h and 32 days in a co-culture system. Growth of the three species was generally comparable over 96 h with an inoculation of 1:3:6.5 (C. marina:S. trochoidea:S. costatum), with stimulation at 5 μg l(-1) and inhibition under higher concentrations (50, 100 μg l(-1)). However, when inoculating at ratios of 1:1:1 during a 32 day test, S. costatum became the most sensitive species and was significantly inhibited in all test groups under the dual stresses of cypermethrin and interspecies competition. The growth of C. marina was significantly inhibited at the concentrations higher than 5 μg l(-1), while the growth of S. trochoidea was significantly promoted at low concentrations. Superoxide dismutase (SOD) activities significantly increased during 6-12 h exposure periods in test treatments at low concentrations, and enhanced in the control as well due to interspecies competition. The lipid peroxidation product malondialdehyde was enhanced at high concentrations, but did not increase in control and low concentration cultures with high SOD activities, indicating that algal cells activated the antioxidant enzymes promptly to protect the cells from lipid membrane damage. Results from this study suggested that cypermethrin pollution in maricultural sea waters might lead to a shift in phytoplankton community structure from diatom to harmful dinoflagellate species, and thus potentially stimulatory for harmful algal blooms.

Phytoplankton Community Indicators of Short- and Long-term Ecological Change in the Anthropogenically and Climatically Impacted Neuse River Estuary, North Carolina, USA

Estuarine and coastal systems represent a challenge when it comes to determining the causes of ecological change because human and natural perturbations often interact. Phytoplankton biomass (chlorophyll a) and group-specific photopigment indicators were examined from 1994 to 2007 to assess community responses to nutrient and climatic perturbations in the Neuse River Estuary, NC. This system experienced nutrient enrichment and hydrologic variability, including droughts, and an increase in hurricanes. Freshwater input strongly interacted with supplies of the limiting nutrient nitrogen (N) and temperature to determine the location, magnitude, and composition of phytoplankton biomass. Multi-annual, seasonal, and episodic hydrologic perturbations, including changes in the frequency and intensity of tropical storms, hurricanes and droughts, caused significant shifts in phytoplankton community structure. Climatic oscillations can at times overwhelm anthropogenic nutrient inputs in terms of controlling algal bloom thresholds, duration, and spatial extent. Eutrophication models should incorporate climatically driven changes to better predict phytoplankton community responses to nutrient inputs and other anthropogenic perturbations.

Phosphorus availability, phytoplankton community dynamics, and taxon‐specific phosphorus status in the Gulf of Aqaba, Red Sea

The relationships among phytoplankton taxon‐specific phosphorus‐status, phytoplankton community composition, and nutrient levels were assessed over three seasons in the Gulf of Aqaba, Red Sea. During summer and fall, stratified surface waters were depleted of nutrients, and picophytoplankton populations comprised the majority of cells (80% and 88%, respectively). In winter, surface nutrient concentrations were higher and larger phytoplankton were more abundant (63%). Cell‐specific alkaline phosphatase activity (APA) derived from enzyme‐labeled fluorescence was consistently low (<5%) in the picophytoplankton population throughout the year, whereas larger cells expressed increased APA (up to 68% labeling in some taxa) during the summer and fall but less in the winter. A nutrient addition bioassay during the fall showed that after addition of orthophosphate along with a nitrogen source, APA in larger cells was reduced by half relative to the control, whereas the APA of picophytoplankton groups remained low (<1%) across all treatments. These results indicate that the most abundant phytoplankton in the gulf are not limited by orthophosphate, and only some subpopulations (particularly of larger cells) exhibit orthophosphate limitation throughout the year, and more so in the summer and fall. Our results indicate that orthophosphate availability influences phytoplankton ecology, correlating with shifts in phytoplankton community structure and the nutrient status of individual cells. The role of dissolved organic phosphorus as an important phosphorus source for marine phytoplankton in oligotrophic settings and the need for evaluating nutrient limitation at the taxa and/or single cell level (rather than inferring it from nutrient concentrations and ratios or bulk enzyme activity measurements) are highlighted.

Alteration of the food web along the Antarctic Peninsula in response to a regional warming trend

AbstractIn the nearshore coastal waters along the Antarctic Peninsula, a recurrent shift in phytoplankton community structure, from diatoms to cryptophytes, has been documented. The shift was observed in consecutive years (1991–1996) during the austral summer and was correlated in time and space with glacial melt‐water runoff and reduced surface water salinities. Elevated temperatures along the Peninsula will increase the extent of coastal melt‐water zones and the seasonal prevalence of cryptophytes. This is significant because a change from diatoms to cryptophytes represents a marked shift in the size distribution of the phytoplankton community, which will, in turn, impact the zooplankton assemblage. Cryptophytes, because of their small size, are not grazed efficiently by Antarctic krill, a keystone species in the food web. An increase in the abundance and relative proportion of cryptophytes in coastal waters along the Peninsula will likely cause a shift in the spatial distribution of krill and may allow also for the rapid asexual proliferation of carbon poor gelatinous zooplankton, salps in particular. This scenario may account for the reported increase in the frequency of occurrence and abundance of large swarms of salps within the region. Salps are not a preferred food source for organisms that occupy higher trophic levels in the food web, specifically penguins and seals, and thus negative feedbacks to the ecology of these consumers can be anticipated as a consequence of shifts in phytoplankton community composition.

Long-term changes in plankton community structure and productivity in the North Pacific Subtropical Gyre: The domain shift hypothesis

Oceanic productivity, fishery yields and the net marine sequestration of atmospheric greenhouse gases are all controlled by the structure and function of planktonic communities. Detailed paleoceanographic studies have documented abrupt changes in these processes over timescales ranging from centuries to millennia. Most of these major shifts in oceanic productivity and biodiversity are attributable to changes in Earth's climate, manifested through large-scale ocean–atmosphere interactions. By comparison, contemporary biodiversity and plankton community dynamics are generally considered to be “static”, in part due to the lack of a suitable time frame of reference, and the absence of oceanic data to document ecosystem change over relatively short timescales (decades to centuries). Here we show that the average concentrations of chlorophyll a (chl a) and the estimated rates of primary production in the surface waters of the North Pacific Subtropical Gyre (NPSG) off Hawaii have more than doubled while the concentrations of dissolved silicate and phosphate have decreased during the past three decades. These changes are accompanied by an increase in the concentration of chl b, suggesting a shift in phytoplankton community structure. We hypothesize that these observed ecosystem trends and other related biogeochemical processes in the upper portion of the NPSG are manifestations of plankton community succession in response to climate variations. The hypothesized photosynthetic population “domain shift” toward an ecosystem dominated by prokaryotes has altered nutrient flux pathways and affected food web structure, new and export production processes, and fishery yields. Further stratification of the surface ocean resulting from global warming could lead to even more enhanced selection pressures and additional changes in biogeochemical dynamics.

200 000 yr diatom records from Atlantic upwelling sites reveal maximum productivity during LGM and a shift in phytoplankton community structure at 185 000 yr

Time series of diatom accumulation rates (DAR) and assemblage composition for the last 200 000 yr from the Atlantic major coastal upwelling loci of the eastern boundary currents and eastern Equator are compared together with independent proxies of export production, to upper ocean productivity and to nutrient concentration and utilization. Fluctuations in DAR are concomitant at all sites and in good correspondence to the other independent productivity proxies indicating glacial periods as the most productive times of the past 200 000 yr in both hemispheres of the eastern Atlantic. Maximum productivity, about one order of magnitude higher than at present, occurred at the last glacial maximum (LGM). Despite the ‘Atlantic’ similarities in both coastal and equatorial upwelling types, important regional and site specific variations emerge. In the southern Hemisphere site, a contradiction of proxies, diatoms and Corg, is noted at the base of stage 6 (185 000 yr). The good correlation found between the Corg and the benthic foraminifera fluxes is interpreted as a reflection of a shift in the phytoplankton community structure related to either a change in the N:P:Si ratio, or similar nutrient conditions associated with increased water column stratification.

Effects on aquatic ecosystems

Effects on aquatic ecosystems

Introduction to the short communications

The shift in phytoplankton community structure towards an increased proportional abundance of cyanobacteria∗ has wide‐ranging ecological as well as water management implications. Certain species, typically representatives of the genera Ana‐baena, Aphanizomenon, Nodularia, and Nostoc, can fix gaseous nitrogen and their rise to dominance within the community can result in a major input of new nitrogen to the ecosystem. Most bloom‐forming species consist of long trichomes or large colonies which may inhibit grazing by zooplank‐ton, and dominance by these forms may reduce the transfer of carbon and energy through to higher trophic levels. Bloom‐forming cyanobacteria contain gas vesicles within their cells which allow them to float to the top of the water column, and their sudden and striking appearance at the surface during conditions of low water turbulence often creates public concern. Cyanobacteria can additionally produce unpleasant tastes and odours in drinking water by releasing volatile organic substan...

Influence of Amphibian Larvae on Primary Production, Nutrient Flux, and Competition in a Pond Ecosystem

In a pond ecosystem near St. Louis, Missouri, natural variations in tadpole biomass during 1971—1972 were accompanied by shifts in patterns of nutrient cycling and primary production, particularly when metamorphoses caused abrupt removal of these transient consumers. In the field, increased tadpole biomass was associated with: (1) reduced standing crop of suspended particles, including phytoplankton, the tadpoles' major food source; (2) a shift in the state of nitrogen from largely particulate to largely dissolved; (3) reduced rates of primary production, from both H14CO3 uptake and diurnal oxygen methods; (4) a nonliner effect on phytoplankton specific growth rates; (5) a shift in phytoplankton community structure away from filamentous blue—green algae; and (6) a reduced proportion of active chlorophyll @a in the photosynthetic pigments of phytoplankton. From laboratory experiments, the potential impact of tadpoles on nitrogen flux, through feeding and nutrient release, was estimated. Several conclusions were made: (1) Suspensions feeding by tadpoles reduced concentrations of suspended particles. Under conditions of low particles: high tadpoles, the specific growth rates of tadpoles reduced. Recruitment was absent except under conditions of high particles: low tadpoles; the most diverse community of new tadpole recruits (four species) was observed under such conditions. All four species (three genera) had similarly sized particles in their guts. These field observations are consistent with an hypothesis of competition among the tadpoles. (2) Tadpoles apparently were regulatory consumers; they became a large component with respect to phytoplankton. Nitrogen flux through tadpoles was within the same order of magnitude, and sometimes exceeded the estimated N uptake by phytoplankton. (3) Tadpoles probably regulated primary production by both reducing standing crop and altering specific growth rates of algae. At maximum tadpole biomass, suspended particle concentrations were stabilized near the laboratory—determined threshold concentration for feeding by these Rana tadpoles. When metamorphosis removed these transient consumers, rates of primary production increased dramatically. (4) Interactions within the pond ecosystem apparently determined aquatic—terrestrial nutrient balances for the amphibian communities. Some species deposited more nutrient in their eggs than was assimilated by larvae, but the community as a whole extracted nutrient from the ecosystem. Nutrient input in eggs was much less than that assimilated by autotrophs.

MELIMEX, an experimental heavy metal pollution study: Effects of increased heavy metal loads on phytoplankton communities

Long-term impacts of increased metal loading (Hg, Cu, Cd, Zn and Pb) on phytoplankton communities of large limno-corrals (diameter 12 m, depth 10 m) were studied. Increased metal concentrations initially lowered phytoplankton biomass, as well as species number and photosynthetic activity of phytoplankton. They caused changes in metal speciation and shifts in phytoplankton community structure, favoring less susceptible species. Although adaptation was not sufficient to completely prevent the metal-induced depression of photosynthesis, due to depressed zooplankton grazing, at the end of the experiment even higher phytoplankton densities were observed in the metal-loaded corrals than in the control.