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.