“The quality and occurrence of habitats and the distribution and abundance of species are in line with prevailing physiographic, geographic and climatic conditions.”
Biological diversity, or biodiversity, describes the variety of life on earth, and this diversity operates at various scales, from genes, species to entire ecosystems. Biodiversity therefore refers to all life-forms and their behaviours, the environments or habitats in which they live, and the complex system of relationships between organisms, such as food webs and competition for resources.
A rich ecosystem has many available habitat niches, and many different organisms, which fill those niches. Such a system containing a wide variety of life-forms generally is more resilient to environmental change than one with either a more restricted range of species or where the species present have a narrower range of lifestyles. As conditions change, some organisms are less able to survive and reproduce, but others readily take their place. Similarly, species which have a high genetic variability within populations are more resistant to environmental stress than those with a more restricted range of genetic combinations.
The range of marine biological life is hard to imagine. Some marine organisms can live in extremely cold environments, such as in sub-zero waters in polar regions, or within sea-ice, whereas others live in extremely hot habitats, such as hydrothermal vents, where cracks in the earth's crust cause geothermal heating of bottom seawater, up to 400°C. Some organisms live in shallow waters, where there is high exposure to sunlight, whereas others thrive in the deep sea, where there is no light at all.
We often see underwater images showing extremely colourful coral reefs, fish and invertebrates. However, marine life starts with tiny bacteria, viruses and single-celled plants, or plankton, which convert energy from the sun and transform it into food for other small animals in the water column.
Plankton are preyed upon by larger animals, such as small fish and other invertebrates. These in turn constitute the food of mammals, large fish, such as sharks, and reptiles, such as sea turtles.
With Descriptor 1, the Marine Directive aims to ensure that biodiversity is "maintained", that is, kept in line with the natural state appropriate to the area in question, and also corresponding to the large-scale, on going climatic changes, which we are unable to regulate.
Oceans cover more than 70% of the earth's surface, and therefore marine biodiversity is an essential part of the global system. Marine ecosystem services include:
Much debate surrounds the concept of biodiversity, and perceptions of its decline. What is good biodiversity? Is more biodiversity always better? What do we mean by increase or decrease in biodiversity? Changes in numbers of species, ecological niches, individual tolerances? The key to maintaining a good ecological state of biodiversity to first understand what the natural state is for the various parts of our seas, and then to determine whether the current status is equivalent to or degraded, relative to natural conditions.
Generally, the more diverse a system is, the more resilient it is to pressures. However, the physical environments within European Seas differ greatly, from the enclosed Black Sea to the low-salinity Baltic Sea; the more open, sandy-bottomed North Sea to the warm, almost tide-less Mediterranean, to the Atlantic, extending almost from pole to pole, and covering some of the world's deepest marine areas. As a result, biodiversity is far from the same across all seas, and pressures also differ from one sea to another. This makes international environmental legislation particularly challenging. However, large-scale, long-term management is important precisely because biodiversity is a global concern, and organisms do not respect national boundaries.
Biodiversity is influenced by a wide range of external environmental pressures. Some pressures are very direct, and their impacts are easy to observe, whereas others are far less obvious and therefore more difficult to understand. For example, fisheries and shipping directly influence populations of fish and marine mammals, and sediment extraction causes localised habitat destruction. However biodiversity is also affected by the on going rise in sea temperatures across many of the world's oceans, combined with ocean acidification, although the mechanisms involved and the possible consequences are still the topic of current research.
The Marine Directive defines a series of qualitative descriptors of Good Environmental Status (GES). A range of specific pressures are treated within these separate descriptors but most also impact biodiversity in some way.
The key pressures on marine biodiversity are fisheries and physical damage to the sea floor. Fisheries directly impact biodiversity in two main ways. Firstly, fishing removes a considerable biomass of fish from the ecosystem, both target species as well as unwanted by-catch. Secondly, bottom trawling causes extensive physical damage to the sea floor. Maintaining both biodiversity and a sustainable fisheries industry requires efficient stock assessment and management. In addition, developing less destructive fishing gear reduces the physical impacts. Ensuring that populations of all commercially exploited fish and shellfish are within safe biological limits is the goal of Descriptor 3.
Physical damage to the marine environment, in particular to the seafloor, can create disturbances in the structure and composition of seabed habitats and in the species composition of the communities associated with these habitats. The animal communities living on and in the sea floor perform a variety of functions, which keep the sediments oxygenated and productive, in a similar manner to garden earthworms. Changes in species composition can disturb this oxygenation, and change the role of the sea floor within the ecosystem. Furthermore, the bottom fauna, or benthos, is a major food source for larger invertebrates, fish and mammals, and therefore damage to the sea floor has implications for the food web. Descriptor 6 therefore states that sea-floor integrity shall be at a level that ensures that the structure and functions of the ecosystems are safeguarded and benthic ecosystems, in particular, are not adversely affected.
Invasive species can directly outcompete local populations, and in some cases cause large-scale changes in food-web structure. Descriptor 2 aims to ensure that non-indigenous species introduced by human activities, such as ballast water or hull fouling, are at levels that do not adversely alter the ecosystems.
The conditions of the seawater, such as the temperature and salinity, in which marine organisms live, play a major role in structuring the biodiversity. The objective of Descriptor 7 is that the permanent alteration of hydrographical conditions does not severely affect marine ecosystems.
Eutrophication is caused by an enrichment of water bodies with inorganic nutrients, leading to an overdevelopment of algal blooms, the decomposition of which uses up oxygen. This can cause depletion of oxygen within the sediments and the water, such that many species die out of the system. Descriptor 5 tackles the adverse effects of human-induced eutrophication.
Since the industrial age, human activities have introduced a wide range of contaminants into the environment, and some of these have major impacts on both humans and other animals throughout the ecosystem. Some contaminants are deposited locally, whereas many are released into the atmosphere, and are transported across the globe. Descriptor 8 aims to ensure that concentrations of contaminants are at levels not giving rise to pollution effects and Descriptor 9 states that contaminants in fish and other seafood for human consumption must not exceed internationally accepted levels.
Marine litter poses a threat to biodiversity because animals such as mammals, fish and seabirds can ingest objects that are not excreted, such that they accumulate in the stomach and intestines. Locally, surface currents can cause marine litter to form large drifting piles and the extent of litter washed up along the shores can be considerable. Descriptor 10 aims to ensure that the properties and quantities of marine litter do not cause harm to the coastal and marine environment.Finally, energy, such as heat or noise, can change the occurrence and behaviour of a wide range of organisms. The objective of Descriptor 11 is that the introduction of energy, including underwater noise, is at levels that do not adversely affect the marine environment.
Monitoring biodiversity levels
A knowledge-based monitoring strategy is recommended for Descriptor 1, where the specific pressures applicable to each area are considered, and an appropriate monitoring strategy devised. Targets for acceptable status, or “Good Environmental Status”, are set according to the background conditions relevant to each area. For example, in an area where industrial activities are present, which potentially affect the sea floor (such as petroleum extraction), the most appropriate monitoring strategy would focus on sea-floor biodiversity at the EU scale.
The overall aim of the Marine Directive is to achieve a sustainable balance between human needs and the natural environment across the European seas. Monitoring all aspects of biodiversity across all the European seas is neither possible nor an acceptable use of resources. A starting hypothesis is adopted, where we assume that in the absence of pressures, both the environment and marine biodiversity in particular will be in a favourable state. An efficient monitoring strategy for biodiversity may therefore be to:
Repeated monitoring allows us to follow progress and adjust remedial actions accordingly.
Marine Protected Areas (MPAs)
One important measure taken by Member States is the establishment of a network of Marine Protected Areas (MPAs). MPAs are designated areas of our oceans, seas and coasts where species and habitats are protected (through legal or other effective means) from activities that are damaging or that cause disturbance to the environment. Activities, which do not have a significant impact on wildlife may be permitted, but other activities such as fishing may be restricted in certain areas, or modified to avoid disturbance to wildlife. In some marine protected areas, such as in the Arctic, human presence is not permitted at all.
Therefore, in addition to providing valuable information on background conditions, MPAs have a further role in creating protected and pressure-free havens for particularly valuable, vulnerable or otherwise threatened organisms to exist and reproduce.
Article 13(4) of the Directive requires Member States to include in their programmes of measures the establishment of MPAs, thus contributing to one of the key objectives of the Convention on Biological Diversity: the creation of a global network of marine protected areas (see “International Cooperation” for more information on the Convention on Biological Diversity). MPAs, as defined under the Marine directive, should include Special Areas of Conservation designated under the Habitats Directive (Directive 92/43/EEC) and Special Protection Areas designated under the Birds Directive (Directive 2009/147/EC), both part of the Natura 2000 network (see Interaction with other Policies for more information on these Directives).