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The Sink

Chapter 5 in: "Living with water: targeting quality in a dynamic world"
Roisin Nash
Ecological Consultancy Services Ltd., Dublin, Ireland

One third of the European Union population is estimated to live within 50 km of the coast. Unfortunately, human activities everywhere are depleting marine and coastal ecosystems in ways that are harmful and sometimes irreversible e.g. climate change, over fishing, and pollution. In the oceans, as on land, the scope of depletion and degradation has no precedent in human history.

Marine ecosystems provide many important functions at a global, national and regional level. The seas provide a unique set of goods and services to society and only can only continue to do so if the health of their ecosystems are not irreversibly changed. Different regions with equally different ecosystems can be distinguished:

- Estuaries are regions where the less dense freshwater from rivers float on seawater before mixing resulting in regular fluctuations in environmental conditions. Estuaries are inhabited by a variety of invertebrates and are vital nursery systems for fish and feeding grounds for birds.
- Coastal waters are commonly thought of as a place where the land meets the sea, e.g. a rocky or sandy shore. Coastal ecosystems are extremely productive and provide a range of economic and social benefits, such as fisheries and coastal protection.
- The open ocean (pelagic) environment extends from the tropics to the polar regions. Despite the enormous size of the open ocean, biomass is limited although the diversity is remarkably high. Animals and plants have adapted to living in open ocean in a variety of ways e.g. floatation devices of jellyfish allowing them to be carried by the current, the torpedo shape of fish to allow more efficient and quicker movement, vertical night migrations of deep sea animals to feed on the phytoplankton and to avoid predation.

Pollution
Water moves in an endless cycle from the air, to the land, to the oceans and then back again. All pollution, from air, land and freshwater sources, ultimately enters the ocean giving the ocean its colloquial name "the sink?. The types of pollution which typical have an effect on the seas and oceans include degradable wastes, fertilizers, plastics, thermal pollution, heavy metals, halogenated hydrocarbons (e.g. DDT) and radioactivity, to mention just a few. However, pollution is not the only factor that is a threat to the marine environment as a whole.

Resource overexploitation

- It has been estimated that every day between 1960 and 1995, a kilometre of European coastline was developed, causing permanent losses of valuable habitats, such as coastal wetlands, seagrass meadows and rocky shores.
- The dredging of billions cubic metres of sand and gravel, as a source of aggregate for the construction industry or to supplement land-based source, are altering valuable habitats and destroying the nurseries of numerous species far outside the excavation areas.
- In offshore waters, the increase in exploration and development of oil and gas activities over the last number of decades, even with improved technology, their construction and operational phases continue to threaten marine habitats, flora and fauna and water quality in the vicinity. The Deepwater Horizon oil spill (2010) in the Gulf of Mexico was one of the largest oils spills in the world and it is thought that a spill of this scale could take the ecosystem years and possibly decades to recover from such an infusion of oil and gas.
- the exponential growth in human population experienced in the last few decades has led to an overexploitation of coastal resources to meet growing demand for human goods and services in simple terms "harvesting the oceans". Fish stocks are important both as a component of marine biodiversity in their own right and as an integral part of marine food chains. It is in everyone's interest, and particularly that of the fishermen, to ensure that fish stocks are not depleted, and marine ecosystems are not disrupted.

Eutrophication
A wide range of chemical compounds can enter aquatic systems as nutrients and most are eventually carried by rivers into the oceans. Nutrient enrichment, can lead to a process known as eutrophication, an enhancement of plant productivity (algal bloom), reducing dissolved oxygen in the water and causing all organisms to die. Eutrophication is considered as one of the most serious ecological problems in the Baltic and Black Sea, resulting in the occurrence of reduced water transparency, surface scum and odours or even hypoxic dead zone's.

Aquaculture
Intensive aquaculture activities are particularly another important source of nutrients inputs to water bodies, which can lead to eutrophication. Constant deposition of large amounts of waste can create azoic zones devoid of macrobenthic organisms beneath cage farms. Besides these, the potential effect of chemicals used to disinfect the farm, control pests, predators and treat diseases or those derived from farm construction material and antifouling compounds used in treating net cages have to be considered. If top predators (which is typical) are grown in aquaculture, 10-100x their weight in smaller fish will be used to feed them. In this case, aquaculture contributes to overfishing of smaller species as well.

Biodiversity loss
It is estimated that every 20 minutes sees another species of plant or animal becoming extinct and during the same period 3,500 humans are born. A range of human activities are causing major impacts to natural environments producing changes in the number, abundance and the identity of species inhabiting these ecosystems. If a keystone species is affected, that plays a critical role in maintaining the structure of an ecological community, the loss of its presence can have a greater impact on the community than would be expected based on its relative abundance or total biomass. The results of a large scale collaborative project between marine ecology institutions across Europe, MarBEF, showed that in general changes in abundance of key species in coastal aereas were more important than changes in the absolute number of species.

Invasive species
The introduction of alien species in aquatic environments may cause disturbances leading to decline in ecological quality resulting from changes in biological, chemical and physical properties of aquatic ecosystems and thus can be viewed as a pollution agent which has been termed "biopollution". The EU funded project DAISIE has established an invasive species website in order to provide a "one-stop-shop" for information on biological invasions in Europe. Shipment has been responsible for carrying species around the globe, both within the ballast tanks and attached to their hulls. Ballast tanks "hitchhikers" include organisms burying in the tank sediment, such as Chinese mitten crab (Eriocheir sinensis), a species recently expanding its range in Europe.

Climate change
Climate change is expected to be one of the major environmental challenges of the 21st century, and its impacts are starting to be observed in the marine environment, one of which is increasing sea water temperatures. In waters from the Arctic southwards to the Mediterranean, research projects have recorded shifts in species distributions to northern and deeper waters, changes in the seasonal timing (phenology) of lifehistory events such as migration, reproduction, metamorphosis, and settlement, and how interactions among species (e. g., predation and competition) are changing.

Physical changes are even more scary: rises in temperature will be accompanied by changes in other abiotic conditions of seawater including acidity (pH), oxygen concentration, and in some areas, even the salt concentration itself (salinity); moreover the strength and direction of some ocean currents, on which nearly all marine species depend at some stage in their lives, could change due to climate changes.

The operation of Gulf Stream is responsible for the mild winters to the north-west Europe. In the north Atlantic, warm salty water from the Gulf of Mexico arrives, is cooled, become more dense and sink to the ocean floor. This body of water then moves towards the equator where it will warm slowly. To replace the sinking water in the arctic regions, water flows from the south to the north. At the end of the last Ice Age this warm gulf stream was reduced, or even shut-down completely. Temperatures in north-west Europe fell by 5C in just a few decades.

Another driver of global change is the increased concentration of CO2 in the atmosphere. This means that the CO2 concentration in the upper layers of the ocean also goes up. Oceans are at present CO2 sinks, and represent the largest active carbon sink on Earth. Although this may appear from the outside to be of positive benefit to the phytoplankton there is a less favourable side effect. Carbon dioxide dissolves into the seawater and combines with other elements to form chemical compounds with acidic properties and excessive amounts of CO2 resulting from human activities lead to acidification of the seas.

With the decreasing pH of seawater, several phytoplankton species that utilise calcium carbonate as construction material in their cell walls will have increasing difficulties to sequester it from the seawater, and to keep it in their cell walls. This process may thus lead to a reduction in the capacity for oceans to store CO2.

Actions
Research projects are working to address the many unanswered questions and increase our understanding of the current situation in relation to the consequences of biodiversity loss and water quality. By taking into consideration the results being produced through research, such as the development of new management tools, the EU can introduce legislation and monitoring programmes to help to reduce biodiversity loss and subsequently improve water quality throughout European waters.

Since International and European relations often work best within a framework of agreed legal instruments, considerable effort has been devoted to developing a series of conventions and other international and European instruments that promote the conservation of marine biological diversity and water quality. The challenge now is to ensure that the legislation in place is used effectively. In June 2008 the EU establishing a framework for community action in the field of marine environmental policy (Marine Strategy Framework Directive) which states that "it is evident that pressure on natural marine resources and the demand for marine ecological services are often too high and that the Community needs to reduce its impact on marine waters regardless of where their effects occur."