Marine Environment and Human Health: An Overview

J. ICARUS ALLEN

ABSTRACT

The marine environment currently provides many beneficial goods and services to mankind but also poses a risk to the health of coastal populations. For example, toxic algal bloom events, microbial pathogens and pollutants all act to negatively impact human health mediated by the marine environment. At the same time, regular contact with the natural environment results in many health benefits, including increased fitness and reduced levels of stress. The marine environment is under pressure from land-derived contaminants and climate change, of which the socioeconomic consequences and the implications for human health and wellbeing are not well understood. The scientific challenge is to understand and predict the consequences of environmental changes and exploitation of natural resources upon our coastal ecosystems and upon society, including human health. Addressing this challenge requires the integration of a wide range of disciplines, from physical oceanography and marine biology, to molecular biology and epidemiology.

1 Introduction

Oceans and coastal seas form a vital part of the environment, currently providing many beneficial goods and services to mankind but also posing a risk to coastal populations. They provide a source of natural resources and are a magnet for human habitation. The marine environment's natural grandeur is a source of artistic inspiration, and yet mankind often allows it to be a sink for society's waste. Increasingly, the fragile balance of marine environments is being disrupted by the impacts of climate change and human activities. Interactions between the marine environment and humans are highly significant, diverse and complex. At the same time, the marine environment is strongly affected by the wider global environment (ocean, atmosphere and land) and is sensitive to climate change. Interactions between the atmosphere and the oceans play a significant role in the regulation of climate and weather, which in turn interact with marine environments.

Mankind benefits from the marine environment in many ways. It provides direct tangible benefits, including protein sources and economic activity associated with fisheries and aquaculture. In addition, there are the economic benefits associated with, for example, tourism, renewable energy and recreational activities. Marine ecosystems are a major source of biodiversity and a focal point for biogeochemical cycling. They play a pivotal role in the water cycle and the global biogeochemical cycling of carbon and nitrogen. Other benefits are less obvious and harder to quantify. For example, regular contact with the natural environment results in many benefits, including increased physical activity and therefore fitness, reduced levels of stress, stronger communities and an increased awareness of the value of the natural environment.

Human utilisation of the marine environment also has many negative impacts, with fisheries, industries, agriculture and aquaculture along the world's coastlines contributing to significant physical, chemical and ecological impacts on the surrounding seas. Human activity gives rise to significant inputs of pollutants and pathogens (e.g. nanoparticles, radionuclides, bacteria, viruses, nutrients and mixtures of chemical waste), in addition to natural sources (e.g. sea birds, marine mammals) to the surrounding seas. Pathogens impact directly on human health through recreational activity: for example, bathing and via shellfish into the human food chain. Both of these areas are subject to stringent regulation. Other pollutants and toxins will impact directly on marine organisms, leading to a degradation of ecosystem function and the goods and services provided in terms of carbon and macronutrient cycling, which in turn will impact on fisheries, the recreation value of the marine environment and general human wellbeing. The direct accumulation of pollutants and toxins in human food sources (e.g. shellfish) provides pathways for impact on human health. Climate change may exacerbate these effects. Seawater temperature rise may encourage the migration of Vibrio cholera and other marine bacteria, such as toxigenic Vibrios and Pseudomonads, into coastal waters. Increased run-off will also add nutrients to coastal waters, which, together with higher light intensities and temperatures, may increase the growth of toxic algal and cyanobacterial blooms. Flooding associated with sea-level rise and increased storminess may remobilise pollutants from sediments.

The impact/costs of marine environmental degradation are highly dependent on the activities and distribution of the human population and the extent/ types of waste water management and environmental regulation. It is therefore important to work towards understanding the pathways and mechanisms through which environmental hazards work and hence be able to communicate these risks to the population at large. Rapid development and unsustainable consumption of natural resources has led to an increasing complexity of environmental health hazards. For example, when an individual person living with poor sanitary conditions in an undeveloped situation consumes seafood contaminated with microbial pathogens, the effects are often apparent. The affected individual will get sick in a short time. In this case the link between cause and effect is relatively easy to measure and, crucially, to communicate. However, if the seafood is contaminated with low levels of persistent organic chemicals which may interfere with human physiology and/or reproduction, the situation is less clear cut. The links between cause and effects are much harder to demonstrate, quantify and communicate. The societal perception of risk presents another great challenge. For example, in the 1950s and 1960s there was a groundswell of public opinion that the UK's bathing waters posed a risk to human health. This was largely attributed to the discharge of untreated sewage into coastal waters. Although the supporting epidemiological evidence for a health risk was not strong, there was an overwhelming belief that swimming in dilute sewage was not healthy.

Climate change is arguably the greatest challenge facing mankind in the twenty first century. In addition to the aforementioned issues, our framework needs to take account of the potential for climate-induced changes in the marine environment.

Resulting from natural variability and anthropogenically induced changes, climate change can only be understood through improved knowledge of the coupling and feedback mechanisms between dynamic processes in the Earth system, as well as the interaction with the anthroposphere. These processes, feedback mechanisms and interactions, in turn, can have unprecedented and dramatic impacts on the marine environment and its ecology and directly on human health.

Marine ecosystems and biodiversity are already under pressure from pollution and overfishing. The marine dimensions of global climate change, such as ocean warming, sea-level rise and changes to ocean chemistry driven in part by atmospheric greenhouse gas concentrations, will influence the marine environment and its impacts on human health. Warmer temperatures and acidification will lead to changes in species reproduction, feeding and, with associated changes in distributions of marine organisms, more frequent algae blooms and shifts in plankton communities. Phytoplankton is a key component of the marine ecosystem, fixing atmospheric carbon and providing the primary food source for the zooplankton, and together they form the base of the oceanic food chain. Larger invertebrates, fish and mammals depend on plankton for their survival. Changing conditions can lead to shifts in the traditional ranges of marine species, resulting in latitudinal shifts in fisheries. In addition, coastal and offshore waters and a range of sensitive marine habitats, such as coral reefs, are likely to be vulnerable to changes in sea-level rise and ocean acidification. Increasing temperature may also influence pollution impacts. For example, it has been shown that warming around the Faroe Islands will facilitate the methylation of mercury, resulting in an estimated 3–5% increase in the mercury content of cod for a 1 °C rise in seawater temperature. Combinations of such changes will impact on fisheries and aquaculture and will require adaptive measures in order to exploit opportunities and to minimise negative impacts.

The World Health Organisation estimated that over the last 30 years 150 000 lives per year are lost due to anthropogenic climate change impacts on temperature and precipitation. Climatic variations and extreme weather events have profound impacts on infectious disease. The impact of climate change on water quality and quantity is also expected to increase the risk of contamination of public water supplies. Both extreme rainfall and droughts can increase the total microbial loads in freshwater and have implications for disease outbreaks and water quality in estuaries and coastal seas. In particular, infectious agents such as viruses, bacteria and protozoa do not have thermostatic mechanisms, and reproduction and survival rates are strongly affected by fluctuations in temperature. For example, cholera has been shown to vary with climatic fluctuations and sea surface temperatures associated with El Nino Southern Oscillation and many foodborne infectious diseases are sensitive to higher than average temperatures. Finally, coastal tourism will also be affected as a consequence of accelerated coastal erosion and changes in the marine environment and marine water quality, with less fish and more frequent jellyfish and algae blooms.

Although there is clear evidence that climate change will have a significant impact on water quantity and quality, further research is needed in order to ensure that proper decisions on adaptation can be taken. There is a need to improve understanding and modelling of climate changes related to the hydrological cycle and of the water-related impacts of climate change on human health, including their socio-economic dimensions, as well as a need to develop better tools to facilitate integrated appraisals of adaptation and mitigation options across multiple water-dependent sectors. A key issue is that there are large uncertainties in the relationship between atmospheric composition and the resulting climate change. It is highly likely that global climate change will increasingly impact in an all-pervading manner all the connections between the oceans and human health. The diverse and complex issues discussed above require an interdisciplinary and holistic approach to impacts assessments as climatic and societal pressures change in the future.

The scientific challenge is to understand and predict the consequences of environmental changes and exploitation of natural resources upon our coastal ecosystems and upon society, including human health. Addressing this challenge requires the integration of a wide range of disciplines from physical oceanography and marine biology, to molecular biology and epidemiology. Over recent years, this requirement has been increasingly recognised and marine environment and human health is a growing area of interdisciplinary science. By interdisciplinary, I mean the process of answering a question, solving a problem, or addressing a topic that is too broad or complex to be dealt with adequately by a single discipline or profession. This is distinct from a multidisciplinary approach, the act of joining together two or more disciplines without integration. The philosophy should be to engage researchers from multiple disciplines in creating and applying new knowledge, working together as equal stakeholders to address a common challenge. The overall objective of this chapter is to provide an introduction to the current state of research in the marine environment and human health subject area, with an emphasis on interdisciplinary science and the cross-cutting role of modelling and forecasting. Only by integrating a range of scientific disciplines can we hope to understand the present and potential future effects of oceanic and coastal processes and biota on human health and wellbeing, taking account of emerging scientific issues and relevant policy drivers and identifying gaps and synergies in current capability.

2 Conceptual Framework

Management of the marine environment and its consequences for human health requires an understanding of the complex interactions within it. The way in which marine environmental processes and functions interrelate is complex and clearly confounded by their interaction with anthropogenic factors. The potential effects that these may have in terms of human health and wellbeing add a further level of complexity. At the policy level, there is an international consensus, embodied in the EU Marine Strategy Framework Directive, for example, that management of marine resources, in particular management of fisheries, should be conducted on an ecosystem basis. The adoption of an ecosystem-based approach to managing the seas is a step towards addressing these complexities in terms of environmental state. The central tenet of such an approach is the holistic assessment of impacts of human activities on the marine ecosystem and the development of integrated management measures. This requirement is usually translated to mean that, in making management decisions, attributes of the marine ecosystem, such as health, vigour and resilience, should be protected.

As previously stated, the field of the marine environment and human health embraces a wide range of disciplines, from physical oceanography and marine biology to molecular biology and epidemiology, and requires a holistic or 'ecosystem' approach to address it. In order to provide a conceptual framework with which to describe the interaction between the marine environment and human health, I will draw on the Driver–Pressure–State–Impact–Response Model (DPSIR) (see Figure 1). DPSIR was developed for constructing environmental indicators for policy development and implementation of the ecosystem approach to management. Within this model:

• Drivers: these describe large-scale, socio-economic conditions and sectoral trends such as population growth, patterns in coastal and watershed land use and land cover, and growth and development in watershed industry sectors.

• Pressures: these are the stresses that human activities place on the marine ecosystem, such as anthropogenic climate change, fisheries, aquaculture, wastewater management, the introduction of industrial contaminants and fertiliser use in the coastal watershed which have the ability to directly affect the quality of marine environments.

• State: this is essentially the condition of the environment. Indicators of state should describe observable changes in coastal environmental dynamics.

• Impacts: these are, for the purpose of this chapter, the effects of environmental state on human health. For example, measured consequences for human health linked to environmental condition such as marine-vectored disease, infections from recreational bathing waters, or exposure to contaminants and toxins via fish and shellfish.

• Response: this refers to the response of society to the impact of environmental state on human health. It is the institutional response to changes in the system (primarily driven by changes in state and impact indicators).

Coastal and shelf seas are susceptible to a number of large-scale, socioeconomic conditions and drivers. It is estimated that over 60% of the world's people live within 100 km of the coast and that this proportion is set to rise as coastal population densities increase. In addition, the world population is expected to increase from about 6 billion to in excess of 8 billion by 2025. Coastal communities are very often heavily reliant on the marine environment for food and raw materials. The dominant driver is population growth, resulting in increased demand for food (fisheries and aquaculture), changes in land use (living space, industry, waste water) and leisure activities (tourism).