Single-celled Dinoflagellates Research Articles

Quantitative comparison of phytoplankton community sampled using net and water collection methods in the southern Yellow Sea

Quantitative and precise observation of the phytoplankton is required for biogeochemical and environmental monitoring in coastal seas. However, phytoplankton data may vary greatly depending on the sampling methods. Net and water collection methods are widely adopted for obtaining marine phytoplankton in China; yet, exact differences and relationships between water- and net-collected phytoplankton communities remain poorly understood. Here, annual phytoplankton surveys in the southern Yellow Sea were conducted using these two sampling methods. Compared with water collection, net collection resulted in the loss of numerous noncolonial small-celled species, particularly cryptophytes and coccolithophores, and reduced phytoplankton depth-averaged abundance (DAA) by 1–2 orders of magnitude. However, through net collection, some scarce, large, or colonial species with low abundances were obtained, and the net-collected DAA distribution was highly consistent with the water-collected DAA distribution in each season. Moreover, DAAs of planktonic large-celled or long-chained dominant species, belonging to diatom, dinoflagellate, and cyanobacteria, were comparable in net- and water-collected samples. Regression analysis showed highly significant regression coefficients between net- and water-collected DAAs of phytoplankton, diatom, and diatom plus dinoflagellate, suggesting that net-collected data could be roughly derived from water-collected results. Non-metric multidimensional scaling and analysis of similarity indicated that phytoplankton community composition significantly differed between net- and water-collected samples. Similarity percentages confirmed that this difference was largely attributed to small-sized benthic and meroplanktonic diatoms, unidentified cryptophytes and coccolithophores, and single-celled dinoflagellates. Our results suggest that the sampling method profoundly influences phytoplankton analysis in terms of species information, abundance, dominant species, and community composition.

Kelp cultivation effectively improves water quality and regulates phytoplankton community in a turbid, highly eutrophic bay

Coastal eutrophication and its associated harmful algal blooms have emerged as one of the most severe environmental problems worldwide. Seaweed cultivation has been widely encouraged to control eutrophication and algal blooms. Among them, cultivated kelp (Saccharina japonica) dominates primarily by production and area. However, the responses of water quality and phytoplankton community to kelp farming remain unclear. Here, thirteen cruises were conducted in the kelp farms and control areas in the turbid, highly eutrophic Xiangshan Bay of the East China Sea from 2008 to 2015. Results indicated that kelp cultivation slightly increased dissolved oxygen and pH, but reduced dissolved inorganic nitrogen and phosphorus. We estimated that kelp harvesting would remove 297 t of nitrogen and 42 t of phosphorus from this bay annually. Because of decreased flow velocity, turbulence, and sediment resuspension, kelp farming greatly reduced suspended solids and increased transparency, resulting in increases in phytoplankton chlorophyll a and abundance. Additionally, kelp farming appreciably increased phytoplankton species number, Marglef richness, and Shannon–Wiener diversity indices by 51.6%, 40.1%, and 13.1%, respectively. Analysis of similarity and similarity percentages demonstrated that phytoplankton community composition differed significantly between the farm and control area, which was mostly attributed to long-chained diatoms and single-celled dinoflagellates. However, after the kelp harvesting, all measurements of water quality and phytoplankton biomass, diversity, and community composition exhibited no significant difference. Our study highlights that kelp cultivation alleviates eutrophication and acidification and enhances phytoplankton diversity, thus providing guidance for macroalgal aquaculture and remediation in eutrophic waters.

Comparative thermal performance of the reef-building coral Orbicella franksi at its latitudinal range limits

Temperature drives biological responses that scale from the cellular to ecosystem levels and thermal sensitivity will shape organismal functions and population dynamics as the world warms. Reef-building corals are sensitive to temperature due to their endosymbiotic relationship with single-celled dinoflagellates, with mass mortality events increasing in frequency and magnitude. The purpose of this study was to quantify the thermal sensitivity of important physiological functions of a Caribbean reef-building coral, Orbicella franksi, through the measurement of thermal performance curves (TPCs). We compared TPC metrics (thermal optimum, critical maximum, activation energy, deactivation energy, and rate at a standardized temperature) between two populations at the northern and southern extents of the geographic range of O. franksi. We further compared essential coral organismal processes (gross photosynthesis, respiration, and calcification) within a site to determine which function is most sensitive to thermal stress using a hierarchical Bayesian-modeling approach. We found evidence for differences in thermal performance, which could be due to thermal adaptation or acclimatization, with higher TPC metrics (thermal optimum and critical maximum) in warmer Panama, compared to cooler Bermuda. We also documented the hierarchy in thermal sensitivity of essential organismal functions within a population: respiration was less sensitive than photosynthesis, which was less sensitive than calcification. Understanding thermal performance of corals is essential for projecting coral reef futures, given that key biological functions necessary to sustain coral reef ecosystems are thermally mediated.

Expanding the population genetic perspective of cnidarian-Symbiodinium symbioses.

The modern synthesis was a seminal period in the biological sciences, establishing many of the core principles of evolutionary biology that we know today. Significant catalysts were the contributions of R.A. Fisher, J.B.S. Haldane and Sewall Wright (and others) developing the theoretical underpinning of population genetics, thus demonstrating adaptive evolution resulted from the interplay of forces such as natural selection and mutation within groups of individuals occupying the same space and time (i.e. a population). Given its importance, it is surprising that detailed population genetic data remain lacking for numerous organisms vital to many ecosystems. For example, the coral reef ecosystem is well recognized for its high biodiversity and productivity, numerous ecological services and significant economic and societal values (Moberg & Folke 1999;Cinner 2014). Many coral reef invertebrates form symbiotic relationships with single-celled dinoflagellates within the genus Symbiodinium Freudenthal (Taylor 1974), with hosts providing these (typically) intracellular symbionts with by-products of metabolism and in turn receiving photosynthetically fixed carbon capable of meeting hosts' respiratory demands (Falkowski et al. 1984; Muscatine et al. 1984). Unfortunately, the health and integrity of the coral reef ecosystem has been significantly and negatively impacted by onslaughts like anthropogenic eutrophication and disease in addition to global climate change, with increased incidences of 'bleaching' events (characterized as the loss of photosynthetic pigments from the algal cell or massive reduction of Symbiodinium density from hosts' tissue) and host mortality leading to staggering declines in geographic coverage (Bruno & Selig 2007) that have raised questions on the viability of this ecosystem as we know it (Bellwood et al. 2004; Parmesan 2006). One avenue towards anticipating the future of the coral reef ecosystem is by developing a broader and deeper understanding of the current genotypic diversity encompassed within and between populations of their keystone species, the scleractinian corals and dinoflagellate symbionts, as they potentially possess functional variation (either singularly or in combination) that may come under selection due to the ongoing and rapid environmental changes they are experiencing. However, such studies, especially for members of the genus Symbiodinium, are sparse. In this issue, Baums et al. (2014) provide a significant contribution by documenting the range-wide population genetics of Symbiodinium 'fitti' (Fig.1 ) in the context of complementary data from its host, the endangered Caribbean elkhorn coral Acropora palmata (Fig. 2). Notable results of this study include a single S. 'fitti' genotype typically dominates an individual A. palmata colony both spatially and temporally, gene flow among coral host populations is a magnitude higher to that of its symbiont populations, and the partners possess disparate patterns of genetic differentiation across the Greater Caribbean. The implications of such findings are discussed herein.

Distribution Patterns of Isomorphic Cold-Water Dinoflagellates (Scrippsiella/Woloszynskia Complex) Causing ‘red tides’ in the Baltic Sea

During the latest years medium-sized (15–30 μm), single-celled dinoflagellates have been reported to form blooms in the northern Baltic Proper and the Gulf of Finland in winter and spring. Recent studies (Kremp et al., 2003. Proceedings of the 7th International conference of Modern and Fossil Dinoflagellates, September 21–25, Nagasaki, Japan, 66 pp.) indicate that those blooms are caused by two isomorphic species – Scrippsiella hangoei (Schiller) Larsen, and a new species, tentatively belonging to the genus Woloszynskia. Until now there has been no report on how widely distributed these phytoplankton species are in the Baltic Sea. In this study, the occurrence of Scrippsiella/Woloszynskia complex in the entire Baltic Sea was investigated, by using monitoring data from 1997 to 2003. The species occurred in a salinity range from 2 to 8 PSU. Highest concentrations were observed at salinity 4.5–6.5 PSU. Maximum cell densities of Scrippsiella/Woloszynskia complex in the water column were mainly obtained in April or in the beginning of May by the water temperature 6 °C. Bloom formations in the Baltic Proper and in the Gulf of Finland may not only be explained by optimum temperature and salinity, but also with other factors e.g. high nutrient concentrations and good seeding conditions from the sediments.

Composition and biomass of plankton in spring on the Cape Hatteras shelf, with implications for carbon flux

The Ocean Margins Program, an interdisciplinary study focussed at Cape Hatteras, is evaluating whether this region is a net source or sink for carbon, while concurrently developing a mechanistic understanding of the production, cycling and fate of organic carbon. Preliminary to a large multi-ship field program in 1996–1997, the first of several short cruises surveyed Cape Hatteras in May 1993. High concentrations of chl a occurred across the shelf. Stations and depths at which chl a was highest also showed elevated concentrations of large phytoplankton, predominantly chained diatoms, but also single-celled dinoflagellates and obligately photosynthetic ciliates. These populations occurred in deeper waters, however, and their abundance was poorly correlated with proxies of community photosynthesis. Instead, small phototrophic nanoplankton, abundant in surface waters, were positively correlated with primary production. Carbon budgets indicated that inner shelf waters contained ca 50% more living POC than outer shelf waters. The relative importance of large phytoplankton and grazers decreased with distance offshore, and they were replaced by photosynthetic nanoplankton and microzooplankton. Even greater changes in living POC occurred in the alongshore direction due to the dramatic reductions in diatoms in southern waters. Estimated herbivory was ca 2–4 gC m −2 d −1. The ratio of heterotrophic : autotrophic POC increased from 38% in northern waters to 137% in southern waters, suggesting that phytoplankton was being converted into consumer carbon as shelf waters advected south. The dominant consumers at most stations were single-celled protozoan zooplankton and small copepods, whose fecal products remain in suspension in energetic shelf environments, suggesting that much of the non-diatomaceous POC was exported as shelf waters exited at Cape Hatteras.