In January 2003, the US Environmental Protection Agency sponsored a "roundtable discussion" to develop a consensus on the relationship between eutrophication and harmful algal blooms (HABs), specifically targeting those relationships for which management actions may be appropriate. Academic, federal, and state agency representatives were in attendance. The following seven statements were unanimously adopted by attendees based on review and analysis of current as well as pertinent previous data: 1) Degraded water quality from increased nutrient pollution promotes the development and persistence of many HABs and is one of the reasons for their expansion in the U.S. and the world; 2) The composition -not just the total quantity -of the nutrient pool impacts HABs; 3) High biomass blooms must have exogenous nutrients to be sustained; 4) Both chronic and episodic nutrient delivery promote HAB development; 5) Recently developed tools and techniques are already improving the detection of some HABs, and emerging technologies are rapidly advancing toward operational status for the prediction of HABs and their toxins; 6) Experimental studies are critical to further the understanding of the role of nutrients in HAB expression, and will strengthen prediction and mitigation of HABs; and 7) Management of nutrient inputs to the watershed can lead to significant reduction in HABs. Supporting evidence and pertinent examples for each consensus statement is provided herein.

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Blooms of autotrophic algae and some heterotrophic protists are increasingly frequent in coastal waters around the world and are collectively grouped as harmful algal blooms (HABs). Blooms of these organisms are attributed to two primary factors: natural processes such as circulation, upwelling relaxation, and river flow; and, anthropogenic loadings leading to eutrophication. Unfortunately, the latter is commonly assumed to be the primary cause of all blooms, which is not the case in many instances. Moreover, although it is generally acknowledged that occurrences of these phenomena are increasing throughout the world's oceans, the reasons for this apparent increase remain debated and include not only eutrophication but increased observation efforts in coastal zones of the world. There is a rapidly advancing monitoring effort resulting from the perception of increased impacts from these HABs, manifested as expanding routine coastal monitoring programs, rapid development and deployment of new detection methods for individual species, toxins, and toxicities, and expansion of coastal modeling activities towards observational forecasts of bloom landfall and eventually bloom prediction. Together, these many efforts will provide resource managers with the tools needed to develop effective strategies for the management and mitigation of HABs and their frequently devastating impacts on the coastal environment.

Cyanobacteria blooms in marine waters are limited to only a few taxa with Trichodesmhm, Richelia, Nod&aria, and Aphanizomenon being most commonly observed. Nonhetcrocystous, nitrogen-fixing Trichodesmium spp. are found throughout low and mid-latitude oceans and seas of the Atlantic, Pacific, and Indian Oceans, and this genus is thought to be a major contributor to new nitrogen influx into these nitrogen-poor systems. Hcterocystous, nitrogenfixing Richelia and other cyanobacteria form unique symbioses with the centric diatoms, Rhizosolenia and Hemiaulus, in the North Pacific, Caribbean, and North Atlantic. Hcterocystous, diazotrophic, toxic Nodularia spumigena is restricted to brackish waters of the Baltic Sea and a coastal estuary of southern Australia and often arises from elcvatcd phosphorus input accompanying anthropogenic activities or vertical mixing processes. The nontoxic nitrogcn-fixing Aphanizomenon$os-uquae is also common in the Baltic, often co-occuning with Nodularia in the Baltic and Gulf of Finland but more often found in lower salinity areas of the region. Although each taxon responds to its environment uniquely, it appears that bloom production in the three free-living cyanobactcria largely supports an active microbial food web through dissolved organic compound flux to hetcrotrophic bacterial communities and their grazers.Blooms of cyanobacteria are common to freshwater systems throughout the world, and although less frequently observed, can dominate carbon and nutrient flux in some saline waters. The few taxa that are observed in marine environments at bloom levels often dominate nutrient-poor surface waters over large geographic areas and variable time scales, with nitrogen fixation contributing a significant fraction of new nitrogen inputs to these systems. These halo-tolerant taxa include oceanic Trichodesmium spp., symbiotic taxa such as Rich&a intracellularis, as well as coastal varieties of Nodularia and Aphanizomenon. Trichodesmium, Noduluria, and Aphanizomenon also pose other problems as each can produce toxins creating health hazards for livestock, canine, and human populations (Francis 1878; SatB et al. 1963; Edler et al. 1985; Nehring 1993; Tenson 1995).The purpose of this review is to provide a general summary of the physiology, ecology, and toxicology of the most common cyanobacteria forming blooms in coastal and pelagic environments and includes those taxa that grow in brackish media (therefore eliminating several common forms such as Microcystis). It is by no means comprehensive; the reader should also consult other sources (e.g.

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Abstract. As three-dimensional (3-D) aquatic ecosystem models are used more frequently for operational water quality forecasts and ecological management decisions, it is important to understand the relative strengths and limitations of existing 3-D models of varying spatial resolution and biogeochemical complexity. To this end, 2-year simulations of the Chesapeake Bay from eight hydrodynamic-oxygen models have been statistically compared to each other and to historical monitoring data. Results show that although models have difficulty resolving the variables typically thought to be the main drivers of dissolved oxygen variability (stratification, nutrients, and chlorophyll), all eight models have significant skill in reproducing the mean and seasonal variability of dissolved oxygen. In addition, models with constant net respiration rates independent of nutrient supply and temperature reproduced observed dissolved oxygen concentrations about as well as much more complex, nutrient-dependent biogeochemical models. This finding has significant ramifications for short-term hypoxia forecasts in the Chesapeake Bay, which may be possible with very simple oxygen parameterizations, in contrast to the more complex full biogeochemical models required for scenario-based forecasting. However, models have difficulty simulating correct density and oxygen mixed layer depths, which are important ecologically in terms of habitat compression. Observations indicate a much stronger correlation between the depths of the top of the pycnocline and oxycline than between their maximum vertical gradients, highlighting the importance of the mixing depth in defining the region of aerobic habitat in the Chesapeake Bay when low-oxygen bottom waters are present. Improvement in hypoxia simulations will thus depend more on the ability of models to reproduce the correct mean and variability of the depth of the physically driven surface mixed layer than the precise magnitude of the vertical density gradient.