Although algal blooms, including those considered toxic or harmful, can be natural phenomena, the nature of the global problem of harmful algal blooms (HABs) has expanded both in extent and its public perception over the last several decades. Of concern, especially for resource managers, is the potential relationship between HABs and the accelerated eutrophication of coastal waters from human activities. We address current insights into the relationships between HABs and eutrophication, focusing on sources of nutrients, known effects of nutrient loading and reduction, new understanding of pathways of nutrient acquisition among HAB species, and relationships between nutrients and toxic algae. Through specific, regional, and global examples of these various relationships, we offer both an assessment of the state of understanding, and the uncertainties that require future research efforts. The sources of nutrients poten- tially stimulating algal blooms include sewage, atmospheric deposition, groundwater flow, as well as agricultural and aquaculture runoff and discharge. On a global basis, strong correlations have been demonstrated between total phos- phorus inputs and phytoplankton production in freshwaters, and between total nitrogen input and phytoplankton pro- duction in estuarine and marine waters. There are also numerous examples in geographic regions ranging from the largest and second largest U.S. mainland estuaries (Chesapeake Bay and the Albemarle-Pamlico Estuarine System), to the Inland Sea of Japan, the Black Sea, and Chinese coastal waters, where increases in nutrient loading have been linked with the development of large biomass blooms, leading to anoxia and even toxic or harmful impacts on fisheries re- sources, ecosystems, and human health or recreation. Many of these regions have witnessed reductions in phytoplankton biomass (as chlorophyll a) or HAB incidence when nutrient controls were put in place. Shifts in species composition have often been attributed to changes in nutrient supply ratios, primarily N:P or N:Si. Recently this concept has been extended to include organic forms of nutrients, and an elevation in the ratio of dissolved organic carbon to dissolved organic nitrogen (DOC:DON) has been observed during several recent blooms. The physiological strategies by which different groups of species acquire their nutrients have become better understood, and alternate modes of nutrition such as heterotrophy and mixotrophy are now recognized as common among HAB species. Despite our increased un- derstanding of the pathways by which nutrients are delivered to ecosystems and the pathways by which they are assimilated differentially by different groups of species, the relationships between nutrient delivery and the development of blooms and their potential toxicity or harmfulness remain poorly understood. Many factors such as algal species presence/ abundance, degree of flushing or water exchange, weather conditions, and presence and abundance of grazers contribute to the success of a given species at a given point in time. Similar nutrient loads do not have the same impact in different environments or in the same environment at different points in time. Eutrophication is one of several mechanisms by which harmful algae appear to be increasing in extent and duration in many locations. Although important, it is not the only explanation for blooms or toxic outbreaks. Nutrient enrichment has been strongly linked to stimulation of some harmful species, but for others it has not been an apparent contributing factor. The overall effect of nutrient over- enrichment on harmful algal species is clearly species specific.

/pdf/harmful-algal-blooms-and-eutrophication-nutrient-sources-4ujytujxjq.pdf

Harmful Algal Blooms and Eutrophication: Nutrient Sources, Composition, and Consequences

Communities of microscopic plant life, or phytoplankton, dominate the Earth's aquatic ecosystems. This important new book by Colin Reynolds covers the adaptations, physiology and population dynamics of phytoplankton communities in lakes and rivers and oceans. It provides basic information on composition, morphology and physiology of the main phyletic groups represented in marine and freshwater systems and in addition reviews recent advances in community ecology, developing an appreciation of assembly processes, co-existence and competition, disturbance and diversity. Although focussed on one group of organisms, the book develops many concepts relevant to ecology in the broadest sense, and as such will appeal to graduate students and researchers in ecology, limnology and oceanography.

/pdf/the-ecology-of-phytoplankton-4ev70n3jsq.pdf

The Ecology of Phytoplankton

http://www.jlakes.org/news/hal-200812-sdarticle.pdf

Eutrophication and harmful algal blooms: A scientific consensus

Marine plankton support global biological and geochemical processes. Surveys of their biodiversity have hitherto been geographically restricted and have not accounted for the full range of plankton size. We assessed eukaryotic diversity from 334 size-fractionated photic-zone plankton communities collected across tropical and temperate oceans during the circumglobal Tara Oceans expedition. We analyzed 18S ribosomal DNA sequences across the intermediate plankton-size spectrum from the smallest unicellular eukaryotes (protists, >0.8 micrometers) to small animals of a few millimeters. Eukaryotic ribosomal diversity saturated at ~150,000 operational taxonomic units, about one-third of which could not be assigned to known eukaryotic groups. Diversity emerged at all taxonomic levels, both within the groups comprising the ~11,200 cataloged morphospecies of eukaryotic plankton and among twice as many other deep-branching lineages of unappreciated importance in plankton ecology studies. Most eukaryotic plankton biodiversity belonged to heterotrophic protistan groups, particularly those known to be parasites or symbiotic hosts.

/pdf/eukaryotic-plankton-diversity-in-the-sunlit-ocean-pxea35iar7.pdf

Eukaryotic plankton diversity in the sunlit ocean

Over 100 gigatons of terrestrial plant biomass are produced globally each year. Ninety percent of this biomass escapes herbivory and enters the dead organic matter pool, thus supporting complex detritus-based food webs that determine the critical balance between carbon mineralization and sequestration. How will changes in biodiversity affect this vital component of ecosystem functioning? Based on our analysis of concepts and experiments of leaf decomposition in forest floors and streams, we suggest that changes in species diversity within and across trophic levels can significantly alter decomposition. This happens through various mechanisms that are broadly similar in forest floors and streams. Differences in diversity effects between these systems relate to divergent habitat conditions and evolutionary trajectories of aquatic and terrestrial decomposers.

Diversity meets decomposition

Planktonic members of most algal groups are known to harbor intracellular symbionts, including viruses, bacteria, fungi, and protozoa. Among the dinoflagellates, viral and bacterial associations were recognized a quarter century ago, yet their impact on host populations remains largely unresolved. By contrast, fungal and protozoan infections of dinoflagellates are well documented and generally viewed as playing major roles in host population dynamics. Our understanding of fungal parasites is largely based on studies for freshwater diatoms and dinoflagellates, although fungal infections are known for some marine phytoplankton. In freshwater systems, fungal chytrids have been linked to mass mortalities of host organisms, suppression or retardation of phytoplankton blooms, and selective effects on species composition leading to successional changes in plankton communities. Parasitic dinoflagellates of the genus Amoebophrya and the newly described Perkinsozoa, Parvilucifera infectans, are widely distributed in coastal waters of the world where they commonly infect photosynthetic and heterotrophic dinoflagellates. Recent work indicates that these parasites can have significant impacts on host physiology, behavior, and bloom dynamics. Thus, parasitism needs to be carefully considered in developing concepts about plankton dynamics and the flow of material in marine food webs.

https://bioone.org/journals/the-journal-of-eukaryotic-microbiology/volume-51/issue-2/j.1550-7408.2004.tb00539.x/Parasites-and-Phytoplankton-with-Special-Emphasis-on-Dinoflagellate-Infections1/10.1111/j.1550-7408.2004.tb00539.x.pdf

Parasites and phytoplankton, with special emphasis on dinoflagellate infections.

This paper presents results of field and laboratory studies on mixotrophy in the estuarine dinoflagellate Gyrodinium galatheanum (Braarud) Taylor. We tested the hypotheses that this primarily photosynthetic organism becomes phagotrophic when faced with suboptimal light and/or nutrient environments. In Chesapeake Bay, incidence of feeding of this species on cryptophytes is positively correlated with prey density and concentrations of nitrate and nitrite, but negatively correlated with depth, salinity, and phosphate concentration. Feeding in natural assemblages and cultures increased hyperbolically with light intensity. The stoichiometric proportions of dissolved inorganic P and N (DIP:DIN) at the stations where G. galatheanum was present were far below the optimal growth P:N (1:10). Incidence of feeding was negatively related to the ratio of DIP to DIN, suggesting that P limitation may have induced feeding. Addition of nitrate, or addition of both nitrate and phosphate, inhibited feeding in a natural population, indicating that N limitation may also induce feeding. Ingestion of the cryptophyte, Storeatula major, by cultured G. galatheanum was higher in media low in nitrate or phosphate or both, but moderate rates of feeding occurred in nutrient-replete cultures. When cells were grown in media with varying concentrations of nitrate and phosphate, N deficiency resulted in greater cellular N and Chl a losses than did P deficiency, but P deficiency stimulated feeding more than N deficiency. Both N and P deficiency, or P:N ratios that deviated greatly from 1:10, result in an increase of cellular carbon content and an increase in propensity to feed. Our results suggest that feeding in G. galatheanum is partly a strategy for supplementing major nutrients (N and P) that are needed for photosynthetic carbon assimilation. Feeding in G. galatheanum may also be a strategy for supplementing C metabolism or acquiring trace organic growth factors, since feeding occurs, although at a reduced rate, in nutrient-replete cultures.

Mixotrophy in gyrodinium galatheanum (DINOPHYCEAE): grazing responses to light intensity and inorganic nutrients*

Several genera of marine dinoflagellates contain species that have evolved parasitic life styles. Dinoflagellate infections have been reported for a wide range of host organisms including sarcodines. ciliates, free-living dinoflagellates, various invertebrates, and a few vertebrates. Some dinoflagellates even parasitize other parasitic dinoflagellates. Most species are obligately parasitic and rely on heterotrophy as their sole means of nutrition; however, some are mixotrophic, as they possess chloroplasts during part or all of their life cycle. Many are ectoparasites that use highly specialized structures to attach to their host and feed, while others are intracellular parasites that feed by osmotrophy. Parasitic dinoflagellates often have adverse effects on their host that can lead to reproductive castration or death. The ecological importance of parasitic dinoflagellates is particularly evident during epidemic outbreaks that cause mass mortality of host organisms. Species that infect fish can pose threats to aquaculture. while other species can make commercially important crustacea unpalatable. In the planktonic realm, parasitic dinoflagellates influence the structure and function of the microbial food web. They compete with copepods and other grazers by utilizing ciliates as hosts and can stimulate rapid recycling of nutrients by causing the decline of toxic and non-toxic red tides.

Parasitic life styles of marine dinoflagellates

Amoebophrya ceratii (Koeppen) Cachon is an obligate parasite of dinoflagellates and may represent a species complex. However, little is known about the biology and host range of different strains of Amoebophrya Cachon. Here, we determined parasite generation time and dinospore infectivity, survival, and ability to infect nonprimary hosts for strains of Amoebophrya from Akashiwo sanguinea (Hirasaka) G. Hansen et Moestrup, Gymnodinium instriatum (Freudenthal et Lee) Coats comb. nov., and Karlodinium micrum (Lead-beater et Dodge) J. Larsen. Akashiwo sanguinea was readily infected, with parasite prevalence reaching 100% in dinospore:host inoculations above a 10:1 ratio. Parasitism also approached 100% in G. instriatum, but only when inoculations exceeded a 40:1 ratio. Karlodinium micrum appeared partially resistant to infection, as parasite prevalence saturated at 92%. Parasite generation time differed markedly among Amoebophrya strains. Survival and infectivity of dinospores decreased over time, with strains from G. instriatum and A. sanguinea unable to initiate infections after 2 and 5 days, respectively. By contrast, dinospores from Amoebophrya parasitizing K. micrum remained infective for up to 11 days. Akashiwo sanguinea and G. instriatum were not infected when exposed to dinospores from nonprimary Amoebophrya strains. Karlodinium micrum, however, was attacked by dinospores of Amoebophrya from the other two host species, but infections failed to reach maturity. Observed differences in host-parasite biology support the hypothesis that Amoebophrya ceratii represents a complex of host-specific species. Results also suggest that Amoebophrya strains have evolved somewhat divergent survival strategies that may encompass sexuality, heterotrophy during the "free-living" dinospore stage, and dormancy.

Parasitism of photosynthetic dinoflagellates by three strains of Amoebophrya (Dinophyta): parasite survival, infectivity, generation time, and host specificity

.Gymnodinium sanguineum, Gyrodinium uncatenum, and Ceratium furca are large phototrophic dinoflagellates that commonly form red tides in the mesohaline portion of Chesapeake Bay during the summer. Examination of protargol-stained specimens revealed that these dinoflagellates also feed heterotrophically as indicated by the presence of food vacuoles containing partially digested prey. Ingested prey were generally identified as nanociliates (≥20 μm) belonging to the oligotrich genera Strobilidium and Strombidium; occasionally other small ciliates (e.g. Balanion sp. and Mesodinium sp.), dinoflagellates, and diatoms were observed in early stages of digestion. the percentage of these mixotrophs that had ingested prey was usually less than 20%, but approached 30% in some samples. Occurrence of food vacuoles in Gymno. sanguineum was positively correlated with ≤20 μm oligotrichous ciliate density; limited data for Gyro. uncatenum suggests a similar relationship, but C. furca feeding was not related to nanociliate densities.

D. Wayne Coats

Papers

Parasites and phytoplankton, with special emphasis on dinoflagellate infections.

Mixotrophy in gyrodinium galatheanum (DINOPHYCEAE): grazing responses to light intensity and inorganic nutrients*

Parasitic life styles of marine dinoflagellates

Parasitism of photosynthetic dinoflagellates by three strains of Amoebophrya (Dinophyta): parasite survival, infectivity, generation time, and host specificity

Spatial and Temporal Aspects of Mixotrophy In Chesapeake Bay Dinoflagellates