Marine Biology

1. The Global Ocean: Earth's Dominant Feature and Life Support System

How inappropriate to call this planet Earth, when clearly it is Ocean.

Vast and interconnected. The Global Ocean covers 71% of Earth's surface, with an average depth of 3,682 meters. It contains 97% of the planet's water and is divided into five regional oceans: Pacific, Atlantic, Indian, Arctic, and Southern.

Life-sustaining role. The ocean produces half of the oxygen we breathe, stabilizes our climate, sustains coastal ecosystems, provides food, hosts diverse organisms for medicine and biotechnology, and supports recreation and tourism. Economists estimate the annual value of ocean services at US$2.5 trillion, with a total asset base of US$24 trillion.

Under threat. Human activities, including overfishing, habitat destruction, pollution, invasive species, and greenhouse gas emissions, are causing significant changes and damage to ocean ecosystems. This is eroding their ability to provide essential life support systems and services that sustain human well-being and prosperity.

2. Marine Microbes: Invisible Engines of Ocean Productivity

If one added up the weight of all the microbes in the oceans it would account for more than two-thirds of the total marine living biomass.

Microbial diversity. The marine microbiome consists of four main groups: bacteria, archaea, protists, and viruses. These microorganisms are astoundingly abundant, with bacteria occurring at concentrations of a billion or more per liter of seawater.

Primary production. Phytoplanktonic microbes in the sunlit surface layer of the oceans are responsible for almost all primary production in marine environments. Key players include:

• Cyanobacteria like Prochlorococcus
• Diatoms
• Dinoflagellates
• Coccolithophores

Efficient energy flow. Marine microbes form the base of the ocean food web, with energy moving through various pathways:

• Classic food chain: Phytoplankton → Zooplankton → Fish → Top predators
• Microbial loop: DOM/POM → Bacteria/Archaea → Protists → Zooplankton
• Viral loop: Rapid cycling between DOM/POM and microbes, mediated by phages

3. Coastal Ecosystems: Vital Habitats Under Human Pressure

Currently, roughly 44 per cent of the human population, or 3.4 billion people, crowd along the coast or live within 150 kilometres of a coast.

Diverse habitats. Coastal ecosystems include:

• Kelp beds
• Seagrass meadows
• Soft-bottom communities
• Estuaries and mangroves

Human impacts. These ecosystems face numerous threats:

• Pollution (industrial, agricultural, sewage, plastic)
• Overfishing
• Habitat destruction
• Invasive species
• Climate change effects (warming, acidification)

Conservation challenges. Efforts to protect coastal ecosystems include:

• Establishing marine protected areas
• Reducing pollution and plastic waste
• Implementing sustainable fishing practices
• Restoring damaged habitats
• Controlling invasive species

4. Polar Oceans: Unique Environments Facing Rapid Change

Clearly, the Arctic Ocean as we have known it is about to disappear with profound effects on its marine biology.

Arctic vs Antarctic. The polar oceans have distinct characteristics:

• Arctic: Landlocked, shallow shelves, seasonal ice cover
• Antarctic: Open to other oceans, steep continental shelf, seasonal sea ice

Sea ice ecosystems. Both polar regions have unique communities adapted to sea ice:

• Microbes living in brine channels
• Ice algae supporting higher trophic levels
• Specialized animals like polar bears (Arctic) and penguins (Antarctic)

Climate change impacts. Polar regions are warming faster than the global average, leading to:

• Rapid sea ice loss, especially in the Arctic
• Changes in primary production patterns
• Shifts in species distributions
• Potential for new commercial activities (fishing, shipping)

5. Coral Reefs: Diverse Ecosystems in Delicate Balance

These 'rainforests of the ocean' are very complex systems that are home to an incredible diversity of marine organisms—one-quarter to one-third of all marine species—with the number of different species on coral reefs globally totalling in the millions.

Symbiotic foundation. Coral reefs are built on the symbiotic relationship between corals and zooxanthellae:

• Corals provide shelter and nutrients to zooxanthellae
• Zooxanthellae provide up to 95% of corals' energy needs through photosynthesis

Ecosystem services. Coral reefs provide numerous benefits:

• Habitat for diverse marine life
• Food source for millions of people
• Coastal protection from storms
• Tourism and recreation opportunities

Threats and conservation. Coral reefs face multiple stressors:

• Ocean warming and acidification
• Pollution and sedimentation
• Overfishing and destructive fishing practices
• Coastal development

Conservation efforts focus on reducing local stressors and protecting reef systems through marine protected areas and sustainable management practices.

6. Ocean Circulation: Driving Climate and Marine Life

The Great Ocean Conveyor moves at much slower speeds than the wind-driven surface currents—a few centimetres per second—but it moves enormous volumes of water—more than a hundred times the flow of the Amazon River.

Surface currents. Wind-driven gyres in each ocean basin move water horizontally, transporting heat, nutrients, and organisms.

Thermohaline circulation. Deep ocean currents are driven by differences in temperature and salinity:

• Cold, dense water sinks at high latitudes
• Upwelling brings nutrients to the surface in certain regions
• The global conveyor belt connects all ocean basins over a ~1000-year cycle

Climate regulation. Ocean circulation plays a crucial role in:

• Distributing heat around the planet
• Absorbing and storing atmospheric CO2
• Influencing weather patterns and climate

Ecological impacts. Changes in ocean circulation due to climate change could have far-reaching effects on marine ecosystems and global climate patterns.

7. Human Impacts: Threats and Conservation Challenges for Marine Ecosystems

Unfortunately, human activities have been affecting the oceans for many years. It is now clear that overfishing, habitat destruction, pollution, the spread of exotic species, and the emission of climate-changing greenhouse gases are causing significant changes and damage to the oceans and the life forms living within them.

Major threats:

• Overfishing and destructive fishing practices
• Pollution (plastic, chemical, nutrient)
• Climate change (warming, acidification, deoxygenation)
• Habitat destruction (coastal development, bottom trawling)
• Invasive species

Conservation approaches:

• Establishing marine protected areas
• Implementing sustainable fishing practices
• Reducing pollution and plastic waste
• Mitigating climate change impacts
• Restoring damaged habitats
• Controlling invasive species

Future outlook. The health of marine ecosystems is crucial for human well-being and planetary stability. Addressing these challenges requires global cooperation, innovative solutions, and a shift towards sustainable use of ocean resources. The next few decades will be critical in determining the long-term fate of our oceans and the life they support.

Last updated: September 10, 2024