The United Nations declared 1998 the International Year of the Ocean. Activities during the past year have provided a renewed appreciation for the resources obtained from the ocean, the effects of human activities on the health of the ocean, and the importance of the ocean in regulating the world's climate. The more we learn about ocean processes and ocean life, the more we realize how critical the ocean will be for the future well-being of humankind. Human health is one of the areas strongly influenced by the ocean. There are negative impacts such as the spread of infectious diseases, coastal weather hazards, and harmful algal blooms, and positive impacts such as the use of marine organisms to develop new medical treatments and a better understanding of biological processes.
In recognition of the International Year of the Ocean, the National Research Council held a workshop on the Ocean's Role in Human Health in June, 1998. The workshop brought together members of the ocean sciences and biomedical communities to identify areas where improved understanding of marine processes and systems has the potential to reduce public health risks and enhance our existing biomedical capabilities. This document serves as an overview, based partly on discussions at the workshop, of the impacts of the ocean on human health with emphasis on (1) elucidating connections between the ocean and human health, (2) evaluating the present state of knowledge about these connections, and (3) suggesting how current and future efforts may be directed so that we can anticipate and respond to future health needs and threats.1
1 Because of the complex nature of both human health and ocean processes, and the limited scope of this study, the related issues of secondary effects of pollution and the contribution of the ocean to the world's food supply are not examined in this report.
Connections between the Ocean and Human Health
Marine Processes that Threaten Public Health
The ocean acts as a conduit for many human diseases. The distribution of viral, bacterial, and protozoal agents and algal toxins in marine habitats depends on the interplay of currents, tides, and human activities. The primary route of human exposure is through ingestion of contaminated seafood, but illness can also result from direct contact with seawater during recreational or occupational activities and from contact through aerosols (sea spray) containing toxins.
Disease-causing organisms can be spread by several different marine processes. Coastal and estuarine circulation patterns influence the frequency and geographic pattern of harmful algal blooms. Nutrient loading from heavy run-off also poses problems of anoxia and contributes to the proliferation of algae. Also, circulation of waters through estuaries and coastal areas plays a role in determining where and when the risks of contamination by human pathogens are highest. Pathogens from human or animal waste contaminate coastal and estuarine areas through freshwater runoff from sewers, rivers, and streams. Viruses (e.g., hepatitis A and poliovirus) and bacteria (E. coli and Salmonella) of fecal origin become concentrated in filter-feeding shellfish such as oysters and clams. Marine pathogenic bacteria (e.g., Vibrio cholera) and harmful algal species can invade new areas through the transport of organisms in the ballast water of ships. Thus shipping activities can introduce a disease from one part of the world into a new location causing ecological, economic, and human health problems. Harmful algal species can also be transported great distances by major ocean currents such as the Gulf Stream. Finally, international trade transmits algal toxins and pathogens through commerce in seafood.
In addition to these specific health threats from infectious and toxic organisms, there are both seasonal and periodic public health concerns that arise from severe weather and climate variability. Climate and weather are determined through interdependent atmospheric and oceanic processes. The world ocean functions as a huge reservoir of heat and moisture that fuels weather systems. These weather systems in turn affect the ocean by wind-driven mixing of surface and deep waters and by changes in sea level dependent on barometric pressure, winds, and melting of polar ice caps during warm periods.
The most vivid and direct impacts of the ocean on human health arise in coastal areas that are subject to tsunamis, storm surges, heavy rainfall and flooding, and severe winds. High water associated with torrential rains, storm surges, and tsunamis result in the highest mortality. However, lingering economic losses from damage caused by severe weather like a tropical storm can cause an overall decrease in public health in developing countries through increased poverty and the loss of housing, hospitals, and public sanitation systems.
The incidence and intensity of severe weather systems are affected by the recurring climatic patterns known as the El Niño / Southern Oscillation (ENSO)
and the North Atlantic Oscillation (NAO). These phenomena originate from shifts in the temperature and flow of ocean water masses and affect global weather systems, bringing droughts to some regions and torrential storms to others. In addition to the direct effects on coastal areas described above, these weather patterns can have impacts on inland areas through shifts in temperature and rainfall patterns which affect the density and distribution of disease-causing organisms.
The observed increase in global average temperature over the past century has generated concern that the world may be entering a period of global warming in excess of normal climatic variation (Nichols et al., 1995). Such a change in the heat balance of the ocean-atmosphere system could lead to dramatic effects on climate and local weather patterns. This has the potential to affect the frequency and severity of tropical storms and periodic events like ENSO (Gray, 1984; Gray et al., 1993; Gray et al., 1994; Landsea et al., 1994). Also, shifts in temperature and rainfall patterns influence the distribution of organisms that cause human diseases, including harmful algae, waterborne agents such as the pathogenic vibrios, and vectors of disease such as mosquitoes that carry malaria, dengue fever, and yellow fever. There may be public health effects due to unusual temperature extremes, air pollution, and the availability of fresh water and food.
Contributions of Marine Biodiversity to Biomedicine
In addition to recognizing the health problems associated with the ocean, this report describes how the ocean provides society with an essential biomedical resource through the rich diversity of marine organisms. Plants, animals, and microbes have provided either the source or the concept for more than half of the pharmaceuticals currently on the market. The emphasis has traditionally been on using terrestrial organisms, but despite continued and more sophisticated searches for new bioactive agents, there has been a decreasing return in molecular diversity, and hence new drug compounds. At the same time, many of the bacteria that cause life-threatening disease have become resistant to existing antibiotics, making the need for new drug discovery more urgent. Also, new bioactive agents are needed to overcome the limitations of our current arsenal of drugs for treating cancer and other diseases. Because the diversity of life at higher taxonomic levels is greater in the ocean than on land, marine organisms offer a promising source of novel compounds with therapeutic potential. A number of these compounds are already under investigation or development by the pharmaceutical industry for the treatment of diseases such as cancer. Nevertheless, there are significant challenges to be surmounted in collecting organisms from marine environments and uncovering new compounds with potential value as pharmaceuticals. Meeting these challenges will require cooperation and new programs that bring together scientists from both the oceanographic and biomedical communities.
Marine biodiversity also benefits medical research because scientists use marine organisms as models for basic research on biological and disease processes.
Marine organims are valued as experimental models for studies of essential molecular, cellular, and physiological processes. The diversity of oceanic life helps scientists investigate and understand the evolutionary basis of many fundamental processes such as the biochemical basis of learning and memory, the mechanics of cell division, and the physiology of salt tolerance in the kidney. Also, unique properties found in marine organisms facilitate the investigation of complex biological processes. For example, scientists have exploited the unusually large diameter of the giant axon in a squid neuron to study the electrophysiology of nerve impulses. In addition, marine animal models have provided insights into the origin of human diseases such as diabetes and cancer.
In this section we present three approaches to further our understanding of the ocean's role in human health that cross-cut the specific issues described in each chapter.
I. Information Resources for Improved Prediction and Prevention of Marine Public Health Disasters
Prediction and prevention of public health disasters precipitated by ocean phenomena depend on establishing an historical baseline of high quality observations. Predictions of marine events that affect health depend critically on the quality of the data used to develop and test models. To examine recurring and long term climate variations, observations need to be collected regularly over periods long enough to distinguish patterns. This requires an ongoing commitment to monitoring and analysis from both funding agencies and scientists. The advent of automated data gathering of physical and biological measurements has created the requirement for comprehensive, structured databases. Also, access to the databases must include query-driven retrieval systems. Through the establishment of baselines and documentation of trends, these systems will help researchers evaluate the implications of an ecological disturbance or a climatological event.
Priorities for Monitoring Programs
The following activities are important for gathering information needed to address the health issues discussed in this report:
1. Collection of baseline observations of physical ocean properties to monitor climate variation on a global scale.
Climate change represents not only a variation in global average temperature, but also a patchwork pattern of change in temperature, severity of storms, rainfall and drought, ocean circulation, and upwelling frequency. All of these changes will affect the ecosystems on which many human communities depend.
2. Measurement of oceanic (e.g., upper ocean heat content) and atmospheric (e.g., jet stream level winds, storm core dynamics) variables to improve tropical storm predictions.
Although disastrous events such as tropical storms cannot be prevented, improved predictions can help reduce the costs. It is estimated that the expense of evacuating a coastal area in the southern U.S. in preparation for a hurricane is approaching $1M per mile of coast (OFCM, 1997). Hence better predictions of the site of landfall could dramatically reduce the expense of the storm and the disruption of coastal communities.
3. Collection of an organized, ongoing compilation of health statistics, particularly in developing countries that lack extensive public health infrastructure, to allow retrospective analysis of the effects of oceanic events on human health.
Reduction and prevention of human health threats from oceanic phenomena requires determination of cause and effect, which is possible only by correlating oceanographic and atmospheric data with reliable reporting from the public health sector. First, it is important that infectious diseases and algal toxin poisonings by correctly diagnosed. Second, information on the frequency, location, and date of disease outbreaks needs to be accurately reported and made available to the international health community. Finally, the efficacy and comprehensiveness of disease surveillance programs need to be evaluated. Associations between environmental events such as El Niño and changes in human disease patterns will require an historical perspective. Participation by experts in many fields and by the appropriate international agencies will be needed to document, evaluate, and develop mitigation strategies. Professional societies in the disciplines of microbiology, meteorology, oceanography, parasitology, and epidemiology should be involved in the establishment of research priorities and methodological development.
4. Documentation of harmful algal blooms (HABs)
The reports of HABs have been increasing, with higher frequency of occurrence and greater geographic range of several species since the early 1970s. Accurate species identification is needed during a bloom to track species dispersal and identify toxin hazards. Increased monitoring of water conditions will allow comparisons before, during, and after an algal bloom to determine the physical, chemical, and biological factors that promote blooms of specific harmful algal species. Effective mitigation efforts will depend on the identification of the causes of the increasing incidence and geographic distribution of HABs.
II. New Technological Approaches to Help Reduce Risks to Human Health
New technologies offer greater opportunities to explore and understand the ocean and marine life. Satellite oceanography and molecular probes (to monitor both ocean chemistry and the contamination of coastal waters by pathogens or
algal toxins) provide more detailed information about marine environments than previous methods. Piloted and remotely operated submersible vehicles make it possible to study and retrieve new species from the underexplored ocean floor. Although great advances have been made in their development, implementation of these new technologies has not yet been fully realized.
Priorities for Implementation
Several of the technologies that could help address current and future health issues include:
1. Drifting and moored sensors (monitored by satellite), although not a new technology, need to be deployed more widely to accurately track ocean processes. Similarly, continued submersible development is needed to study and collect deep sea organisms.
2. Biological sensors will improve in situ measurements of biological processes in marien coastal waters and allow higher sensitivity measurements of water quality (including specific nutrients, oxygen, pH, species-specific monitoring of algae and bacteria).
3. DNA probes and antibody-based tests will provide more sensitive and specific detection of pathogens in marine waters as a supplement to the current standard, the coliform test, which acts as an indirect indicator of fecal pollution (i.e., sewage).
4. More accurate, cost-effective methods for detecting algal toxins in seafood, based on the molecular properties of the toxins.
III. Contributions of Marine Organisms to Medicine and Research
The diversity of life in the ocean has the potential to contribute to the development of effective new treatments of human diseases and a greater understanding of human biology. However, the level of effort expended to use this marine resource for biomedical applications has been modest compared to the potential benefits (NRC, 1994a).
Priorities for Marine Biomedical Research
Several of the promising areas for marine biomedical research include:
1. Exploration of marine biodiversity for discovery of new pharmaceutically-active compounds
The extent of marine biodiversity remains unknown because of both the relative inaccessibility of the habitats and, in the case of microorganisms, difficulty in culturing and classifying new species. Partnerships between industry and academia need to be encouraged to provide cross-disciplinary expertise and to offset the expense of investigating the potential value of marine species in the development of new therapeutics.
2. Understanding of the molecular mechanisms for natural marine toxin action on organisms.
There are three reasons for understanding the molecular mechanism of marine algal toxins: 1) to provide structural information needed to develop drugs that will interfere with the toxin's biological activity, 2) to develop less expensive methods for detecting toxins in contaminated seafood, and 3) to use toxins as tools for investigating the biochemistry of the nervous system.
3. Development of techniques to culture species with biomedical value.
One limitation on the use of marine organisms is their availability. Harvesting of species either for research or for extraction of a biologically active compound is expensive and may deplete the natural population. Aquaculture, cell culture, microbial fermentation, and recombinant DNA techniques can provide alternative sources of material for research and drug development.
4. Expansion of drug discovery efforts beyond anti-cancer compounds
Current programs have promoted drug discovery efforts for cancer therapy through the matching of compounds from non-traditional sources (such as marine organisms) with the screening and development potential of the pharmaceutical industry. Similar approaches would benefit drug discovery efforts for other disorders including neurodegenerative, cardiovascular, and infectious diseases.
5. Encourage training and research to expand our knowledge of marine organisms.
The use of marine organisms in biomedical research and in drug development depends on knowledge of marine biologythe natural history, taxonomy, physiology, molecular biology, and biochemistry of various species. As academic biology and other science departments become increasingly subdivided into specialized fields, it is important to encourage a multidisciplinary approach to exploring the diversity of life in the ocean and to provide opportunities for students and researchers to study organisms that are representative of marine diversity.
Pursuit of the priorities outlined above will promote the development of better strategies for reducing the health problems arising from marine natural hazards, climate change, and disease-causing organisms, and will support opportunities for using marine organisms to develop new treatments for human diseases.