The environmental cost of seafloor damage

Editorial from Thematic Issue of Science for Environment Policy: Seafloor damage,

by Prof. Phil Weaver National Oceanography Centre, UK; Director, Seascape Consultants Ltd, UK

Damage to the seafloor, due to a range of human activities, including fisheries, sand and gravel extraction and navigational dredging, has affected large areas of the seabed for over a century. Recent reports by EU Member States estimate that, in some parts of Europe, over 75% of their waters have been physically damaged. This damage has destroyed critical marine habitats and led to significant biodiversity loss.
The European Commission’s work in implementing the 2008 Marine Strategy Framework Directive (MSFD), in which EU Member States are required to achieve ‘good environmental status’ (GES) by 2020, combined with the EU’s ‘Blue Growth’ strategy, should improve the quality of our marine waters. One specific aim of the MSFD is to improve the quality of the seafloor and its habitats throughout European waters.
However, our history of engagement with the oceans suggests that economic growth has often brought high environmental costs, with many areas suffering the effects of overfishing and destructive fishing practices, as well as growing amounts of marine pollution, including plastic waste. To add to these pressures, marine life will need to adapt to climate change and adjust to increased acidification of the oceans in the coming years, as well as cope with new industries, such as deep-sea mining of high-grade ores. Now, however, is the time to get our marine management right, by combining the drive for new exploitation (‘Blue Growth’) with a better and more sympathetic approach to environmental protection. This ‘ecosystem-based’ approach to management of human activities and uses of our seas is an integral part of the MSFD and vital for the achievement of GES. Improving the quality of the environment brings many benefits to our society, through the provision of ecosystem goods and services.
We are developing a better appreciation of how we have affected the marine environment. Let us hope that in this latest drive to exploit the ocean we take seriously the term ‘sustainable’ and interpret it to mean ‘sustaining ecosystems’, by harvesting and exploiting at rates and with methods that will achieve this.
This Thematic Issue of Science for Environment Policy presents key pieces of research looking at physical damage to the seafloor, which explore topics such as the impacts of seafloor trawling and of dumping dredged material; the potential effects of seafloor mining and how we might develop guidelines for this new industry; the impacts of wind farms; and new tools to map sensitivity to fishing and other human influences. It focuses on physical damage to the seafloor, a key topic to be addressed by the MSFD, as other forms of environmental impact, such as chemical contamination and nutrient enrichment, already well known issues that are addressed by a number of policies.
The first article, ‘Animal forests of the sea need better protection‘, examines the physical destruction of ecosystems based on structural species, such as corals and sponges, together with additional new pressures, such as climate change and ocean acidification. The example of the destruction of the North American cod fishing industry is given, where the combination of overfishing and habitat destruction led to a complete collapse of the fish stocks in the late 1980s. The fishery was closed in 1992 and has shown little sign of recovery since.
The article, ‘Estimating the true extent of damage to exploited seafloor ecosystems’, presents a study in which researchers attempted to reconstruct the history of shellfish beds on the east coast of Scotland, UK. These were vastly more extensive in the early 1800s, with landings (the fish catch which is brought ashore) for oysters falling by 99% during the 19th century, and by a similar amount for queen scallops during the 20th century when the industry had switched to fishing these. Impacts from bottom trawling (fishing at or close to the seafloor) are known to have significant negative effects on seabed communities and more evidence of this is provided in the article, ‘Impacts of seabed trawling extend further than thought‘. This presents research that showed that the sediment plumes stirred up by the impact of a trawl can travel deeper into the sea for considerable distances and smother unfished habitats, thus expanding the area affected by the fishery.
Fishermen have their favourite spots on the seabed and visit these regularly. Thus, in some areas, the seabed has been completely altered by the fishing activity. Based on a UK study, the article ‘Reductions in fishing activity in marginal areas could substantially reduce the footprint and impact of seabed fishing‘, describes three case studies where core, well-used fishing grounds are surrounded by occasionally fished margins. The research found that excluding these marginal areas, which contained only 10% of fishing activity, approximately halved the total area of fishing grounds. Such a management approach to bottom fisheries offers the potential to significantly reduce the environmental impacts of fisheries on the seafloor, whilst safe-guarding the core fishing grounds, and providing more space for other uses of the sea, such as wind farms.
Three articles in this issue discuss new methods for providing seabed information. The article ‘New tool to map seafloor sensitivity to fishing‘ describes a means of assessing the sensitivity of a variety of habitats to a range of fishing impacts and intensity. Of the 31 habitats assessed by a study, 23 were sensitive to some form of fishing practice. A new way of mapping seabed habitats using a variety of physical parameters is reported in the article ‘New method for mapping seafloor ecosystems‘. The method works better for natural ecosystems rather than those already affected. The third method, described in ‘Assessing human-driven damage to seafloor habitats‘, has been used in a Baltic Sea example to test a scoring method. Using this method, researchers found that only 37% of habitats here had good environmental status, with oxygen deficiency, trawling and shipping causing the highest impacts on the habitats.
The last set of articles addresses other uses of our seas which, although often having a smaller spatial footprint on the seafloor, are nevertheless important aspects concerning seafloor quality.
One of the new pressures on marine ecosystems will be deep-sea mining, which is covered in two articles. The first article relates to ‘How the environmental impacts of deep-sea mining are assessed‘, concentrating on massive sulphide deposits that are formed at mid-ocean ridges in hydrothermal vents (volcanic openings on the seafloor which release mineral-rich water). Potentially these can destroy rare and complex ecosystems that exploit methane and sulphides in the vent fluids. The article outlines the key features of hydrothermal vent ecosystems and discusses the issues that would need to be taken into account during an environmental impact assessment of deep-sea mining, including studies which identify future research areas and an ecological risk assessment. The second article ‘New guidelines for the protection of unique deep-sea ecosystems‘, discusses the protection of hydrothermal vent ecosystems, by creating effective seafloor reserves based on the precautionary approach which take multiple impacts, such as fishing and mining, into account. This article stresses the need for engagement of all stakeholders in the process of protecting these important ecosystems.
The article ‘What are the impacts of depositing dredged sediment on the seafloor‘ demonstrates how dumping dredged material not only has an impact on the seabed, but also the functioning of the whole ecosystem, reducing the amount of food available to animals such as fish. Such impacts are not currently accounted for in environmental impact studies.
Finally, ‘Offshore wind farm foundations could substantially alter seafloor ecosystems of the North Sea‘ reveals how planned wind turbines in the German Bight could become colonised by a range of invertebrates, including mussels. Although these could radically change the local ecosystem, they may also develop into a sustainable fishery.
While this Thematic Issue shows how difficult it may be to attain good environmental status for many areas of the seabed, a wide range of research is identifying the scale of the problem and the activities that have caused the greatest impact. Given the extent of damage in some parts of Europe’s seas, restoration of the seafloor to good status is likely to be one of the most challenging policy issues for Member States to address in the next few years.