The Ecology and Oceanography of Harmful Algal Blooms

A National Research Agenda

Executive Summary

Over the last several decades, the United States has experienced an escalating and worrisome trend in the incidence of problems associated with harmful and toxic algae. Impacts of these phenomena include mass mortalities of wild and farmed fish and shellfish, human illness and death from contaminated shellfish or fish, death of marine mammals, seabirds, and other animals, and alteration of marine habitats or trophic structure through shading, overgrowth, or adverse effects on life history stages of fish and other marine organisms. Formerly only a few regions were affected by harmful algal blooms (HABs) in scattered locations, but now virtually every coastal state is threatened, in many cases over large geographic areas and by more than one harmful or toxic species.

It is still a matter of debate as to the causes behind this expansion, with possible explanations ranging from natural mechanisms of species dispersal to a host of human-related phenomena such as nutrient enrichment, climatic shifts, or transport of algal species via ship ballast water. Whatever the reasons, virtually all coastal regions of the U.S. are now subject to an unprecedented variety and frequency of HAB events. The U.S. is not alone in this respect, as nations throughout the world are faced with a bewildering array of toxic or harmful species and impacts and disturbing trends of increasing inci dence.

HAB events are characterized by the proliferation and occasional dominance of particular species of toxic or harmful algae. As with most phytoplankton blooms, this proliferation results from a combination of physical, chemical, and biological mechanisms and interactions that are, for the most part, poorly understood. Some HABs are unique, however, due to their production of toxins and the manner in which they affect co-occurring organisms and alter food-web function. As identified in Marine Biotoxins and Harmful Algae: A National Plan (Anderson et al., 1993), focused research into these ecological and oceanographic mechanisms is urgently needed. To achieve these ends, a workshop was co-sponsored by NSF and NOAA to develop a national research agenda to guide activities in the specific area of HAB ecology and oceanography.

The resulting program, called ECOHAB (ECology and Oceanography of Harmful Algal Blooms) provides a scientific framework designed to increase our understanding of the fundamental processes underlying the impacts and population dynamics of HABs. This involves a recognition of the many factors at the organismal level that determine how HAB species respond to, and potentially alter their environment, the manner in which HAB species affect or are affected by food-web and community interactions, and how the distribution, abundance, and impact of HAB species are regulated by the environment.

In its simplest form, the goal of the ECOHAB program is:

To develop an understanding of the population dynamics and trophic impacts of harmful algal species which can be used as a basis for minimizing their adverse effects on the economy, public health, and marine ecosystems.

The objective of the ECOHAB program is:

To investigate fundamental physical, biological, and chemical oceanographic questions critical to scientifically based management of fisheries resources, public health, and ecosystem health in regions threatened by toxic and harmful algae.

ECOHAB is thus a scientific program that addresses important societal issues through advances in fundamental or basic research. The research priorities identified at the workshop fell naturally into three main themes that represent the individual program elements of ECOHAB. The rationales, goals, and specific objectives and activities of each program element are listed below.

Program Element # 1

The Organisms

Rationale: The negative impacts of HABs reflect not only the growth and metabolism of individual algal cells, but the ecological selection of those cells within a diverse phytoplankton assemblage. Studies at the organismal level are essential if we are to understand the population dynamics of HABs and their toxic and/or harmful effects.

Goal: To determine the physiological, biochemical, genetic, and behavioral features and mechanisms of harmful algal species that influence their bloom dynamics, general ecology, and negative impacts.

Specific objectives:

· Develop methods to rapidly and accurately identify, enumerate, and physically separate HAB species from mixed phy toplankton assemblages.

· Identify the life history stages of major HAB species, determine what factors control transitions between those stages, and establish the role of the stages in bloom dynamics.

· Characterize the physiological responses and tolerances of HAB species to differing environmental conditions.

· Develop methods to permit in situ measurements of species-specific rates of growth, photosynthesis, and nutrient uptake,

and to assess the physiological condition of cells at different times and locations.

· Characterize the nutritional requirements, uptake and nutrient assimilatory characteristics of HAB species.

· Determine the functional role of toxins and/or exudates produced by HAB species.

· Define the genetic basis of toxin production, elucidate toxin biosynthetic pathways, and determine how toxin accumulation in cells is regulated.

· Investigate the mechanisms and importance of motility and other behaviors of HAB species.

Program Element # 2

Environmental Regulation of Blooms

Rationale: Concurrent with escalating influences of human activities on coastal ecosystems, the environmental and eco nomic impacts of HABs have increased over recent decades. It is therefore imperative to know if present trends of human activities and HABs will lead to unacceptable consequences, and if the means can be developed to mitigate negative impacts. The key to this knowledge is an understanding of the ecology and oceanography of HABs. An important facet of this complex topic is environmental regulation, that is, the influence of environmental factors on the population dynamics of harmful algal species and their competitors.

Goals: 1) Determine and parameterize the environmental factors that govern the initiation, growth, maintenance, dissipa tion and impacts of HABs; and 2) Formulate principles that explain similarities between ecosystems during HABs and under stand how those systems are unique with respect to the types of blooms that occur.

Specific objectives:

· Determine the extent to which HAB events reflect increases in growth rate versus physical transport, immigration, and accumulation. Determine whether there is a specific suite of physical factors with which known HABs are associated.

· Investigate physical and ecological processes that control the partitioning of nutrients within a system and the relationship between nutrient inputs and population dynamics of HAB species.

· Investigate whether there are specific physical, chemical, and biological regimes or processes that are associated with HAB events.

· Determine whether some ecosystems are more susceptible to HABs than others. If so, determine what makes them unique and whether they share characteristics that can be used to anticipate HAB events in other systems.

· Characterize HAB population dynamics, including the rate processes required in predictive models of bloom incidence.

Program Element # 3

Food-Webs and
Community Interactions

Rationale: The negative impacts of HABs are the result of complex interactions that begin at the phytoplankton community level and extend to upper trophic level compartments. Habitat physics, life cycles, community structures, growth and grazing processes all combine to regulate the dynamics of the HAB event. Therefore, studies on the impacts of trophic interactions in the selection and dynamics of HABs, and conversely, the impacts of HAB events on trophic structure, processes and interac tions are essential if we are to understand the ecology and oceanography of harmful algal blooms .

Goals: 1) Determine the impacts of trophic interactions on selection for, and dynamics of, HABs; and 2) determine the impacts of HABs on trophic structure, processes and interactions.

Specific objectives:

· Determine the extent to which bloom formation results from a breakdown of grazing or from harmful species outcompeting other phytoplankton for limiting resources.

· Determine whether biological controls (e.g., grazers, allelopathy, pathogens) are the cause of bloom termination.

· Investigate how HAB effects on the food-web are controlled by toxin dynamics, food-web routing of toxins, and the differential susceptibility of species at higher trophic levels. Determine whether chronic, sublethal impacts of HABs are more significant than acute (lethal) impacts.

· Determine if HAB impacts are controlled by the degree of temporal and spatial overlap between blooms and critical life cycle stages of target species.

· Determine whether high biomass (non-toxic) HABs adversely impact the food-web directly through reduced food quality, or indirectly through environmental effects.

Program Implementation

The diverse nature of HAB phenomena and the hydrodynamic and geographic variability associated with different out breaks throughout the U.S. pose a significant constraint to the development of a coordinated research initiative. Where other multi-investigator oceanographic research programs can concentrate field activities on one specific area of the ocean (e.g., GLOBEC on Georges Bank), no single ECOHAB study site could be identified that would permit all of the major biological and physical features that underly HAB phenomena to be investigated. Given this diversity, the ECOHAB program will rely on comparisons among large-scale, regional field programs, on laboratory and mesocosm studies by individual investigators or small groups, and on theoretical studies using new and existing models to provide realistic and testable simulations of HAB dynamics in different oceanographic systems. An integration of physical, chemical, and biological components is essential to all of these approaches.

The ECOHAB Research Agenda outlines research priorities that are intended to guide agencies in the efficient allocation of resources targeted to HAB issues, and to help them formulate new, multi-disciplinary HAB initiatives. The rate and extent of future progress will depend upon how the recommendations in this report are received and implemented. State and federal agencies should use this document to identify topics that they can support, and individual scientists should shape their specific research programs to meet the perceived needs of the HAB community.

Despite the focus on ecology and oceanography and the exclusion of many other aspects of HAB phenomena, the scope of the issues to be addressed by ECOHAB exceed the resources of any one agency or program. ECOHAB will be succesful only if a nationally coordinated interagency effort can be implemented to focus research personnel, facilities, and financial resources to the common goals outlined in this comprehensive national strategy. Nowhere else do the missions and goals of so many government agencies intersect and interact as in the coastal zone where HAB phenomena are prominent. Every effort must be made to keep the program flexible, efficient and responsive to the needs of the agencies that become partners in this endeavor. As soon as the participating agencies and programs are identified, a Steering Committee will be appointed to oversee program implementation. Where necessary, small working groups or sub-committees will be convened to address specific program needs. Once ECOHAB is underway and research programs begin to accumulate results, regional and national workshops will be convened to identify common mechanisms and processes underlying the diverse array of HAB phenomena and their impacts. One of the strengths of ECOHAB lies in this "comparative approach," but resources must be allocated to facilitate the scientific communication that is required for successful implementation.

Rationale and Benefits

The significant economic, public health and ecosystem impacts of HAB outbreaks are strong, practical motivations for a research program such as ECOHAB, made all the more pressing by the apparently escalating trend in their incidence. The direct benefits to society from a research program of this kind are many, and include management issues such as bloom detection and prediction, control or mitigation strategies, site selection criteria for aquaculture, and assessment of impacts from altered nutrient loading, dredging or other coastal zone activities. There are indirect benefits as well. For example, support of multidisciplinary field HAB programs can address specific, practical problems while providing new techniques and basic scientific information relevant to plankton ecology and oceanography in general. In this respect, one compelling aspect of the ECOHAB program derives from the need to study individual HAB species, rather than mixed planktonic assemblages. New autecological techniques must be developed, such as remote detection of bloom populations using satellites, swimming robots or moored instruments. Methods are needed to "tag" target species with molecular probes and then enumerate cells or separate them from co-occurring organisms, and techniques must be developed to estimate in situ growth rates or cell physiology. These are but a few examples of the areas where new technologies developed to meet the objectives of ECOHAB can benefit all of oceanography.