7. Intertidal life

The intertidal region of the Global Ocean is a thin strip of shoreline lying between the high and low tide marks; it is completely submerged by seawater at the highest high tides and completely uncovered at the lowest low tides. The intertidal region is occupied almost exclusively by marine organisms that have adapted to live in a very stressful physical environment influenced by exposure to air, temperature extremes, wind, and the pounding of waves. This region is home to a diverse and interesting marine community that is easy to study and enjoy due to its accessibility. It is also a place where people routinely harvest seafood, and is prone to a wide range of human impacts.

4. Polar marine biology

Flourishing marine biological systems are present in the extreme environments of the Arctic and Antarctic polar regions of the planet. Both these regions are characterized by constantly cold sea temperatures, ice-covered oceans, and extreme seasonal fluctuations in light levels, but ‘Polar marine biology’ explains how they have evolved strikingly different and unique marine ecosystems. The Arctic Ocean is largely landlocked while the Southern Ocean surrounds the Antarctic continental land mass and is in open contact with the Atlantic, Indian, and Pacific oceans. The impact of human-induced climate change is also discussed, which will affect the Arctic and Antarctic food webs in profound ways.

5. Marine life in the tropics

The tropical marine environment encompasses those parts of the Global Ocean where the surface waters are consistently warm throughout the year, rarely falling below 20°C. Coral reefs embody the archetypal image of a tropical marine environment and are globally significant natural systems in terms of their beauty, biological diversity, productivity, and economic significance. ‘Marine life in the tropics’ explains the physical requirements, biology, and productivity of coral reefs. It discusses the physical and biological disturbances on coral reefs that can cause their destruction along with the local-, regional-, and global-scale human impacts on coral reefs before considering the future of coral reefs.

2. Marine biological processes

Roughly half of the planet’s primary production—the synthesis of organic matter by chlorophyll-bearing organisms using light energy from the sun—is produced within the Global Ocean. The primary producers in the oceans are phytoplanktonic microbes suspended in the sunlit surface layer. These energy-fixing microorganisms form the basis of the marine food web, the network of pathways through which food energy is transferred to all the other organisms in the marine system including other microbes, zooplankton, fish, marine mammals, and, ultimately, humans. ‘Marine biological processes’ outlines the four main groups of marine microbes—bacteria, archaea, protists, and viruses—and discusses the factors affecting marine primary productivity.

Introduction

The oceans cover 71 per cent of our planet’s surface, create a vast globally connected fluid living space, and support a diverse array of life forms. The Introduction outlines the ocean environment’s role in providing essential services for human survival and well-being. They produce half of the oxygen we breath; stabilize our climate; sustain ecosystems that protect our coasts; provide us with abundant healthy food and with natural products for medicine and biotechnology; and support many forms of recreation and tourism. But all of this is under threat due to human activity. Action is required to create a more sustainable relationship with our oceans so that they can be restored and protected for future generations.

9. The future of our oceans

Current marine ecosystems have profoundly changed since the pre-industrial era and the pace of change has accelerated greatly over the past four decades. What will be the state of our oceans in 2050? Are we capable of plotting a new course and reversing many of the most severe impacts we have had on the oceans so far? ‘The future of our oceans’ explains that recent studies have shown that no ocean wilderness remains anywhere on the planet since the impacts of climate change and human activities are so widespread and unmanageable. The challenge now is to find ways to stabilize and prevent the further degradation of marine ecosystems and embark on a path of ocean restoration.

8. Food from the oceans

Humans have been harvesting food from the oceans for millennia. This would have begun as small-scale subsistence fishing in coastal waters, but with more experience and as population numbers increased, it evolved into a wide-ranging commercial enterprise. Now fishing the oceans takes place globally at an industrial scale and provides the human population with its last significant source of wild food. ‘Food from the oceans’ considers the historical expansion of seafood harvesting; commercial fishing methods and their effects; commercially exploited marine species; trends in the global seafood catch; and the role of marine protected areas in the management and future of marine fisheries.

6. Deep-ocean biology

The deep ocean is currently defined as the water column and ocean bottom greater than 500 metres, which is the depth at which seasonal variation in temperature and salinity and the influence of sunlight is minimal. This habitat encompasses roughly 90 per cent of the ocean’s volume yet this vast region is the least investigated and understood environment on the planet. ‘Deep-ocean biology’ explains that there are many issues for the existence of life in the deep ocean: lack of light, extreme pressure, scarcity of food, and temperature. However, deep-ocean animals have adapted to their surroundings. The diversity of deep-ocean benthic animals is described along with the unique ecosystems found around hydrothermal vents and seamounts.

3. Life in the coastal ocean

The coastal regions of the Global Ocean comprise a narrow strip of ocean extending from the shoreline to the edge of the continental shelf. This coastal ocean environment accounts for only about 7 per cent of the area of the Global Ocean, but it is of huge importance to human society. Roughly 44 per cent of the human population lives within 150 kilometres of a coast, meaning that the coastal ocean is heavily impacted by human activities. ‘Life in the coastal ocean’ describes the kelp bed habitats, the seagrass meadows, and soft-bottom communities, before considering the impact of harmful phytoplankton blooms, biological invasions, and the increase in plastic debris in our oceans.

1. The oceanic environment

The Global Ocean constitutes about 97 per cent of all the water that exists on our planet. It is divided into five regional oceans: the Pacific, Atlantic, Indian, Arctic, and Southern oceans. ‘The oceanic environment’ looks at the structural features of the oceans, the composition of the water, the temperature, the light sources, water pressure, gases, and the living environment they contain. It also discusses the movement of the water throughout the oceans: at the surface in a series of five enormous, roughly circular, wind-driven current systems, or gyres, and at deeper levels, which transports oxygen, nutrients, and heat throughout the oceans, moderating the global climate.