The biodiversity of the world's oceans directly supports many of the services and industries reviewed in Parts III, IV, and V, and may be affected by how the various social and economic benefits are used. To ensure the ongoing availability of those benefits to current and future generations, and to maintain healthy oceans, it is essential that the uses made of the ocean are sustainable, both individually and in the aggregate. In Part VI we examine ocean biodiversity from several perspectives, and when trends are apparent, link those trends to their main drivers. From this multi-perspective investigation of biodiversity trends, we obtain the third part of the information to be integrated in this first Assessment. This information may contribute importantly to improving global ocean literacy worldwide, and informing policies and selection of management measures from local to global scales.

The Convention on Biological Diversity1 (CBD 1992) emphasizes that “biodiversity” exists on many scales: from genetic diversity within populations, through diversity of populations of the same species, the diversity of species in ecosystems, to the diversity of habitats within geographic areas. The diversity at all of these scales reveals patterns and structures that are crucial to the functioning of ecosystem processes and the delivery of ecosystem functions. However, in-depth analyses of patterns and trends, linking them to all drivers that underlie them and their ecological, social, and economic consequences are not feasible for the entire ocean, at even one of these scales.

Therefore Part VI presents overviews of these biodiversity features first spatially, and then followed by more focused examinations of key species groups and habitats. From these overviews, it is possible to present an analysis that integrates how global ocean biodiversity is changing as a result of the impacts of humanity's uses of the ocean, with the ability of the ocean to sustain itself, and humanity's uses of it into the future.

Chapters 34 and 35 present the main global patterns of diversity of populations, species, and habitats.

Physical, chemical, and ecological characteristics Seamounts

Seamounts are predominantly submerged volcanoes, mostly extinct, rising hundreds to thousands of metres above the surrounding seafloor. Some also arise through tectonic uplift. The conventional geological definition includes only features greater than 1000 m in height, with the term “knoll” often used to refer to features 100 – 1000 m in height (Yesson et al., 2011). However, seamounts and knolls do not appear to differ much ecologically, and human activity, such as fishing, focuses on both. We therefore include here all such features with heights > 100 m.

Only 6.5 per cent of the deep seafloor has been mapped, so the global number of seamounts must be estimated, usually from a combination of satellite altimetry and multibeam data as well as extrapolation based on size-frequency relationships of seamounts for smaller features. Estimates have varied widely as a result of differences in methodologies as well as changes in the resolution of data. Yesson et al. (2011) identified 33,452 seamount and guyot features > 1000 m in height and 138,412 knolls (100 – 1000 m), whereas Harris et al. (2014) identified 10,234 seamount and guyot features, based on a stricter definition that restricted seamounts to conical forms. Estimates of total abundance range to >100,000 seamounts and to 25 million for features > 100 m in height (Smith 1991; Wessel et al., 2010). At least half are in the Pacific, with progressively fewer in the Atlantic, Indian, Southern, and Arctic Oceans. Identified seamounts cover approximately 4.7 per cent of the ocean floor, with identified knolls covering an additional 16.3 per cent, in totalan area approximately the size of Africa and Asia combined, about three-fold larger than all continental shelf areas in the world's oceans (Etnoyer et al., 2010; Yesson et al., 2011).

Seamounts can influence local ocean circulation, amplifying and rectifying flows, including tidal currents, particularly near seamount summits, enhancing vertical mixing, and creating retention cells known as Taylor columns or cones over some seamounts. These effects depend on many factors, including the size (height and diameter) of the seamount relative to the water depth, its latitude, and the character of the flow around the seamount (White et al., 2007).

Introduction – the regulatory system

The disposal at sea of waste generated on land and loaded on board vessels for dumping is the object of long-standing global, and (in many areas) regional, systems of regulation. (These systems also cover, for completeness, dumping from aircraft and waste (other than operational discharges) from fixed installations in the sea). Such dumping must be distinguished from discharges into rivers and directly from land into the sea and emissions to air from land-based activities discussed in Chapter 20 (Land-based inputs).

When concerns about the environment developed in the 1960s, growing constraints on the land disposal of waste and discharges into rivers led to pressures to find new routes for waste disposal. Concerns about these pressures led to action in several forums. Several United Nations specialized agencies set up the Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP1 – later altered to “Marine Environmental Protection”).

The preparatory committee for the 1972 Stockholm Conference on the Human Environment, set up by the United Nations General Assembly, established an intergovernmental working group on marine pollution. At the national level, several countries started developing approaches to control such dumping. The United States of America put forward proposals for an international agreement on the subject. Spurred from the national level by an attempt by the vessel Stella Maris to dump 650 tons of chlorinated waste, several countries started developing approaches to control such dumping. States adjoining the North-East Atlantic adopted an international convention regulating dumping in that area in Oslo, Norway, on 15 February 1972 (OSPAR, 1982; IMO, 1991).

Later that year, the Stockholm Conference adopted a set of principles for international environmental law and called, among other things, for an international instrument to control dumping of waste at sea. The United Kingdom, in consultation with the United Nations Secretariat, organized a further conference in London, and the Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter 1972 (the 1972 London Convention) was signed on 13 November 1972 in London, Mexico City and Moscow (ICG, 1982, IMO, 2014f).

Introduction

The North Atlantic is characterized by relatively wide continental shelves, particularly in its northerly portions, with steep slopes to the abyssal plain1. The width of the shelf decreases towards the south, with typical boundary current systems, characterized by strong seasonal upwelling, off the Iberian Peninsula and northwest Africa. Two chains of volcanic islands, the Azores and the Canaries, are located in the east central North Atlantic, and a large number of islands of volcanic origin, many with associated warm water coral reefs, are found in the southwest portion of the North Atlantic. In the far north of the region is the world's largest island, Greenland, primarily of Precambrian origin, whereas Iceland and the Faroe Islands are of more recent volcanic origin. All have rugged coastlines with rich faunas.

The biota of the North Atlantic is strongly influenced by both the warm Gulf Stream flowing north-eastward from the Gulf of Mexico and the Caribbean to northwest Europe, and the cold, fresh Labrador Current flowing south from the Canadian Archipelago and Greenland to the northeast coast of the United States. Major oceanographic and associated biotic regime shifts have been documented in the North Atlantic, but not with the frequency or scale of the North Pacific.

Around the coasts of the North Atlantic are a number of semi-enclosed seas. These seas have distinct oceanographic and bathymetric regimes, and ecosystems with many characteristics determined by local-scale processes and pressures. Hence each of these semi-enclosed seas, including the Black Sea, Mediterranean Sea, Baltic Sea (and similar coastal estuaries of the United States), the Caribbean Sea, and the Gulf of Mexico, receive some individual consideration in this assessment. Within the North Atlantic, there are several habitat types of special importance for biodiversity, such as seagrass beds and cold- and warm-water corals. Since these are important where they are found on the globe, they are treated in an integrated manner, respectively, in chapters 47, 42-43, rather than separately.

Coastal areas of the Northeast Atlantic have been settled in and used for several millennia. Commercial fisheries, both coastal and, as technology developed, offshore, have exploited fish and shellfish resources for centuries as well (Garcia et al., 2014), with periods of widespread overfishing in the twentieth century.

Introduction

Marine environments encompass some of the most diverse ecosystems on Earth. For example, marine habitats harbour 28 animal phyla and 13 of these are endemic to marine systems. In contrast, terrestrial environments contain 11 animal phyla, of which only one is endemic. The relative strength and importance of drivers of broad-scale diversity patterns vary among taxa and habitats, though in the upper ocean the temperature appears to be consistently linked to biodiversity across taxa (Tittensor et al. 2010). These drivers of pattern have inspired efforts to describe biogeographical provinces (e.g. the recent effort by Spalding et al., 2013)) that divide the ocean into distinct regions characterized by distinct biogeochemical and physical combinations). Biogeographers such as Briggs (1974) examined broad-scale pattern in marine environments in historical treatises and although many of the patterns described therein hold true today, the volume and diversity of data available to address the question have increased substantially in recent decades. We therefore focus our chapter on more recent analyses that build on those early perspectives. The International Census of Marine Life programme that ran from 2000-2010 provided significant new data and analyses of such patterns that continue to emerge today (McIntyre, 2011; Snelgrove, 2010). Indeed, many of our co-authors were part of that initiative and that influence is evident in the summary below. In the few years since that programme ended, some new perspectives have emerged which we include where space permits, noting that we cannot be exhaustive in coverage and also that the large data sets necessary to infer broad-scale patterns do not accumulate quickly.

Not surprisingly, the different scales, at which many organisms live, from ambits of microns for microbes to ocean basins for migratory fishes and marine mammals, along with variation in the drivers and patterns of diversity, render a single analysis impossible. In order to assess gradients in marine biodiversity we use a taxonomic framework for some groups of organisms and a habitat framework for others.

Introduction

Marine mammals occupy a wide range of marine and some freshwater habitats around the world. They have been used by humans for millennia for food and to obtain other products. Marine mammals consist of cetaceans (whales, dolphins and porpoises), pinnipeds (seals, sea lions and walruses), sirenians (dugongs and manatees), mustelids (sea otters and marine otters) and the polar bear – 130 or more species in total, including several that range into fresh water and some that exclusively occupy rivers and lakes. Human interactions, both direct and indirect, have negatively affected most marine mammal species at least to some degree. Historically, industrial harvesting greatly reduced the abundance of many populations. Although the intensity of such exploitation has declined in recent decades for many species, humans continue to use certain species of marine mammals in some places for food, skins, fur, ivory and increasingly as bait for fisheries. In addition, human activities continue to reduce the availability and quality of marine mammal habitats and cause substantial numbers of marine mammals to die incidentally as a result of entanglement or entrapment in fishing gear and from being struck by vessels. Mitigation of ongoing and future threats to marine mammals from human activities requires improved knowledge of those human activities and of the animals’ ecology, behaviour and habitat use.

Changes in Biological Diversity

Globally, certain species of marine mammals have become extinct over the last several centuries, i.e., Steller's sea cow, the Japanese sea lion, the Caribbean monk seal. The Yangtze River dolphin (baiji) is also likely to have become extinct although there has been one unconfirmed sighting in 2005. In addition, many populations have been reduced to remnant status, such that they no longer play a significant role in the ecosystem, i.e., they are functionally extinct. For example, right whales have essentially disappeared from the eastern North Atlantic, and walruses are gone from their former strongholds in south-eastern Canada (Gulf of St. Lawrence and Sable Island). The loss of marine mammal diversity due to actual and functional extinctions has had significant effects on marine ecosystems at varying scales from local to ocean-basin-wide (Estes et al., 2006).

Magnitude of changes

Besides the above-mentioned extinctions and extirpations, the numerical abundance (and biomass) of many other marine mammal populations has been greatly reduced.

Introduction

The movement of materials from land to sea is an inevitable part of the hydrological cycle and of all geological processes. Nevertheless, human activities have both concentrated and increased these flows as a result of the creation of large human settlements, the development of industrial processes and the intensification of agriculture. Until the 1960s, many took the view that the oceans were capable of assimilating everything that humans wanted to discharge into the oceans. In the 1960s, this view came to be seen as out-dated (UNESCO, 1968). Following the 1972 Stockholm Conference on the Human Environment, many steps were taken to address issues of marine pollution. During the preparations for the United Nations Conference on Environment and Development (“the first Earth Summit”), held in Rio de Janeiro, Brazil, in 1992, there was general agreement that, in spite of what had been done, a major initiative was needed to address the problems of landbased inputs to the oceans. As a result, Agenda 21 (the non-binding action plan from the 1992 Earth Summit) invited the United Nations Environment Programme (“UNEP”) to convene an intergovernmental meeting on protection of the marine environment from land-based activities (Agenda 21, 1992). In October 1995, the Global Programme of Action for the Protection of the Marine Environment from Land-Based Activities (GPA) was adopted in Washington, DC. First among the priorities of this Programme was improving the management of waste-water: this concerned not only waste-water containing human wastes, but also waste-water from industrial processes. In addition, a wide range of other source categories also creating problems for the marine environment was identified (UNEP, 1995). The Programme reflected the experience of over twenty years’ work by governments, both individually and through regional seas organizations, to address these problems. Subsequent intergovernmental reviews of the implementation of the GPA show that progress is being made in many parts of the world, but only slowly.

In evaluating the impacts of contamination on the marine environment, there are significant difficulties in comparing the situations in different areas. For many aspects of contamination, evaluating the levels of contamination requires chemical analysis of the amounts of the contaminants in samples of water, biota and/or sediments. Unless there is careful control of the sampling methods and analytical techniques in all the cases to be compared, it is difficult to achieve scientifically and statistically valid comparisons.

Introduction

The ocean provides countless ecosystem services. The Millennium Ecosystem Assessment describes ecosystem services as “the benefits people obtain from ecosystems” (MEA, 2005). Some of the ecosystem services from the ocean are delivered without human intervention – though they can be affected or disrupted by such intervention. Examples of these are the regulating and supporting ecosystem services (as described in Chapter 3), such as distribution of heat around the planet, the functioning of the hydrological cycle and the absorption of carbon dioxide as part of the carbon cycle. Other ecosystem services are obtained as a result of human activity to acquire the benefits. Most of these are provisioning ecosystem services (as also described in Chapter 3). The obvious example of such acquired ecosystem services is the food provided by capture fisheries, where humans take from the ocean significant amounts of the protein required for human diets. As demonstrated in Part IV and Part V and in Chapter 54, if the human activities are not carefully managed to maintain ecosystem structure and function, the acquisition of such ecosystem services can result in damage to the marine environment and reduction or loss of ecosystem services. Important issues arise for the institutions of ocean governance at global, regional, national and local levels in balancing the benefits of acquiring these services against the disbenefits (referred to by some as detriments) caused by over-exploitation and in preventing or mitigating those disbenefits.

Very different aspects of the concept of value are brought into play by these different kinds of ecosystem services. For most of the ecosystem services obtained from the ocean by human effort, there are global or local markets for the products obtained. Market valuations are therefore possible, although in some cases questions arise whether such a market value captures all the facets of the value to humans. For example, the value of fish in the sea in maintaining biodiversity and ecosystem functions may be more than the market value of the fish if they were caught and sold for consumption. Or, on a lesser scale, the value of their activities to recreational sea anglers may well be more than the market value of the fish (if any) that they catch. For ecosystem services that do not involve human effort to benefit from them, there is no market, and it is a question of producing a valuation in other ways.

Biodiversity itself

Biodiversity has natural patterns globally, at all levels from phytoplankton to top predators, including fish, marine reptiles, seabirds, and marine mammals. Main factors that underlie these patterns include depth and proximity to coastline, latitude, habitat complexity and primary productivity, temperature and substrate (Chapter 34). These patterns occur on many scales from meters to full ocean basins; the mosaic structure of seafloor benthic biodiversity is often particularly strong. Some types of species are particularly widespread and/or have specialized life history characteristics, making them even more vulnerable to threats and pressures than most other species. They receive special attention in both characterizing the factors that determine their patterns of distribution and in assessing their trends and the associated pressures.

Chapter 35 highlights that although many such patterns are well documented, the ocean's diversity of species, communities and habitats is far from completely sampled. As research continues, new species, new patterns of distribution, and new relationships between components of biodiversity and natural and anthropogenic drivers are being discovered. The incompleteness of our knowledge of biodiversity and the factors that affect it means that decision-making about potential impacts will be subject to high uncertainty, and the application of precaution is appropriate. Nevertheless, as documented below, a central message from Part VI is that detrimental trends in biodiversity on many scales can be at least mitigated, and sometimes eliminated, even when knowledge is incomplete, if the available knowledge is enough to use in choosing appropriate measures and the capacity for implementation of the measures is available.

Biodiversity hotspots

Although nearly all parts of the ocean support marine life, biodiversity hotspots exist where the number of species and the abundance and/ or concentration of biota are consistently high relative to adjacent areas. Some are sub-regional, like the coral triangle in the Pacific (Chapter 36D.2.3) and coral reefs in the Caribbean (Chapter 43), cold-water corals in the Mediterranean Sea (Chapter 36A) the deep seas (Chapter 36F) and the Sargasso Sea (Chapter 51). Some are more local and associated with specific physical conditions, such as biodiversity-rich habitat types. This Assessment has several chapters on these types of special habitats, such as hydrothermal vents (Chapter 45), cold-water (Chapter 42) and warm-water (chapter 43) corals, seamounts and related deep-sea habitats (chapter 51), and the sea-ice zone (Chapter 46), that highlight some of the main factors making an area richer in biodiversity than adjacent areas.

Introduction

Let us consider how dependent on the ocean we are. The ocean is vast: it covers seven tenths of the planet, is on average about 4,000 metres deep and contains 1.3 billion cubic kilometres of water (97 per cent of all the water on the surface of the Earth). There are, however, 7 billion people on Earth. This means that each one of us has just one fifth of a cubic kilometre of ocean as our portion to provide us with all the services that we get from the ocean. That small, one fifth of a cubic kilometre portion generates half of the annual production of the oxygen that each of us breathes, and all of the sea fish and other seafood that each of us eats. It is the ultimate source of all the freshwater that each of us will drink in our lifetimes.

The ocean is a highway for ships that carry the goods that we produce and consume. The seabed and the strata beneath it hold minerals and oil and gas deposits that we increasingly need to use. Submarine cables across the ocean floor carry 90 per cent of the electronic traffic of communications, financial transactions and information exchange. Our energy supply will increasingly rely on sea-based wind turbines and wave and tidal power from the ocean. Large numbers of us take our holidays by the sea. The seabed is a rich repository for archaeology.

That one fifth of a cubic kilometre also suffers from the sewage, garbage, spilled oil and industrial waste which we collectively allow to go into the ocean every day. Demands on the ocean continue to rise together with the world's population. By the year 2050, it is estimated that there will be 10 billion people on Earth. Our portion, or our children's portion, of the ocean will then have shrunk to one eighth of a cubic kilometre. That reduced portion will still have to provide each of us with oxygen, food and water, while still suffering from the pollution and waste that we allow to enter the ocean.

The ocean is also home to a rich diversity of animals, plants, seaweeds and microbes, from the largest animal on the planet (the blue whale) to plankton and bacteria that can only be seen with powerful microscopes.

Definition

Fish stock propagation, more commonly known as fisheries enhancement, is a set of management approaches involving the use of aquaculture technologies to enhance or restore fisheries in natural ecosystems (Lorenzen, 2008). “Aquaculture technologies” include culture under controlled conditions and subsequent release of aquatic organisms, provision of artificial habitat, feeding, fertilization, and predator control. ”Fisheries” refers to the harvesting of aquatic organisms as a common pool resource, and “natural ecosystems” are ecosystems not primarily controlled by humans, whether truly natural or modified by human activity. This places enhancements in an intermediate position between capture fisheries and aquaculture in terms of technical and management control (Anderson, 2002).

The present chapter focuses primarily on enhancements involving releases of cultured organisms, the most common form of enhancements often described by terms such as ‘propagation’, ‘stock enhancement’, ‘sea ranching’ or ‘aquaculture-based enhancement’.

Enhancements in marine resource management

Enhancements are developed when fisheries management stakeholders or agencies take a proactive, interventionist approach towards achieving management objectives by employing aquaculture technologies instead of relying solely on the protection of natural resources and processes. Enhancement approaches may be used effectively or ineffectively in resource management. To understand how enhancement initiatives can give rise to such different outcomes, it is important to consider not only the technical intervention but the management context in which the initiative has arisen, including ecological and socioeconomic factors as well as the governance arrangements (Lorenzen, 2008).

Effective enhancements

Enhancement approaches may be employed towards different ends commonly referred to as sea ranching, stock enhancement and restocking (Bell et al. 2008). Sea ranching entails releasing cultured organisms to maintain stocks that do not recruit naturally in the focal ecosystem. This may involve stocks that once recruited naturally but no longer do so due to loss of critical habitat, or it may involve creation of fisheries for desired “new” species for which the focal system provides a habitat suitable for adult stages but not for spawning or for juveniles.

Inventory

Hydrothermal vents and cold seeps constitute energy hotspots on the seafloor that sustain some of the most unusual ecosystems on Earth. Occurring in diverse geological settings, these environments share high concentrations of reduced chemicals (e.g., methane, sulphide, hydrogen, iron II) that drive primary production by chemosynthetic microbes (Orcutt et al. 2011). Their biota are characterized by a high level of endemism with common specific lineages at the family, genus and even species level, as well as the prevalence of symbioses between invertebrates and bacteria (Dubilier et al., 2008; Kiel, 2009).

Hydrothermal vents are located at mid-ocean ridges, volcanic arcs and back-arc spreading centres or on volcanic hotspots (e.g., Hawaiian archipelago), where magmatic heat sources drive the hydrothermal circulation. Venting systems can also be located well away from spreading centres, where they are driven by exothermic, mineral-fluid reactions (Kelley, 2005) or remanent lithospheric heat (Wheat et al., 2004). Of the 521 vent fields known (as of 2009), 245 are visually confirmed, the other being inferred active by other cues such as tracer anomalies (e.g. temperature, particles, dissolved manganese or methane) in the water column (Beaulieu et al., 2013) (Figure 45.1).

Sediment-hosted seeps occur at both passive continental margins and subduction zones, where they are often supported by subsurface hydrocarbon reservoirs. The migration of hydrocarbon-rich seep fluids is driven by a variety of geophysical processes, such as plate subduction, salt diapirism, gravity compression or the dissociation of methane hydrates. The systematic survey of continental margins has revealed an increasing number of cold seeps worldwide (Foucher et al., 2009; Talukder, 2012). However, no recent global inventory of cold seeps is available.

Both vent and seep ecosystems are made up of a mosaic of habitats covering wide ranges of potential physico-chemical constraints for organisms (e.g., in temperature, salinity, pH, and oxygen, CO2, hydrogen sulphide, ammonia and other inorganic volatiles, hydrocarbon and metal contents) (Fisher et al., 2007; Levin and Sibuet, 2012; Takai and Nakamura, 2010). Some regions (e.g., Mariana Arc or Costa Rica margin) host both types of ecosystems, forming a continuum of habitats that supports species with affinities for vents or seeps (Watanabe et al., 2010; Levin et al., 2012). Habitats indirectly related to hydrothermal venting include inactive sulphide deposits and hydrothermal sediments (German and Von Damm, 2004).