6.4 Marine Ecosystems and Biodiversity

Marine ecosystems are diverse and complex, ranging from coral reefs to deep-sea vents. These environments support a wide array of life, each adapted to unique conditions. Understanding marine biodiversity is crucial for appreciating the ocean's role in Earth's systems.

Marine organisms have evolved fascinating adaptations to thrive in challenging environments. From osmoregulation to bioluminescence, these traits enable survival in extreme conditions. Species interactions and keystone species play vital roles in shaping marine communities and maintaining ecosystem balance.

Major Marine Ecosystems

Coral Reefs and Kelp Forests

Top images from around the web for Coral Reefs and Kelp Forests

• 

  Frontiers | Coral Reefs of the High Seas: Hidden Biodiversity Hotspots in Need of Protection ... View original

  Is this image relevant?

• 

  File:Coral Reef.jpg - Wikipedia View original

  Is this image relevant?

• 

  File:The Coral Reef at the Andaman Islands.jpg - Wikimedia Commons View original

  Is this image relevant?

• 

  Frontiers | Coral Reefs of the High Seas: Hidden Biodiversity Hotspots in Need of Protection ... View original

  Is this image relevant?

• 

  File:Coral Reef.jpg - Wikipedia View original

  Is this image relevant?

1 of 3

Top images from around the web for Coral Reefs and Kelp Forests

• 

  Frontiers | Coral Reefs of the High Seas: Hidden Biodiversity Hotspots in Need of Protection ... View original

  Is this image relevant?

• 

  File:Coral Reef.jpg - Wikipedia View original

  Is this image relevant?

• 

  File:The Coral Reef at the Andaman Islands.jpg - Wikimedia Commons View original

  Is this image relevant?

• 

  Frontiers | Coral Reefs of the High Seas: Hidden Biodiversity Hotspots in Need of Protection ... View original

  Is this image relevant?

• 

  File:Coral Reef.jpg - Wikipedia View original

  Is this image relevant?

1 of 3

• Coral reefs are shallow, warm-water ecosystems dominated by reef-building corals that create complex habitats supporting high biodiversity
  • Found in tropical and subtropical regions with clear, nutrient-poor waters (Caribbean Sea, Great Barrier Reef)
  • Corals secrete calcium carbonate skeletons that form the foundation of the reef structure
  • Provide shelter, food, and nursery grounds for a wide variety of fish, invertebrates, and other marine life
• Kelp forests are temperate, coastal ecosystems characterized by dense stands of large, brown algae (kelp) that provide shelter and food for diverse marine life
  • Occur in cool, nutrient-rich waters along rocky coastlines (California, Australia, South Africa)
  • Giant kelp (Macrocystis pyrifera) can grow up to 2 feet per day and reach heights of 100 feet or more
  • Support a complex food web, including sea otters, sea urchins, fish, and invertebrates

Deep-Sea Communities and Other Marine Ecosystems

• Deep-sea communities, such as hydrothermal vents and cold seeps, exist in the aphotic zone and rely on chemosynthetic primary production by microorganisms
  • Hydrothermal vents occur along mid-ocean ridges where superheated, mineral-rich water escapes from the seafloor
  • Cold seeps are found on continental margins where methane and other hydrocarbons seep from the sediment
  • Chemosynthetic bacteria form the base of the food web, supporting unique assemblages of organisms (giant tube worms, clams, crabs)
• Other major marine ecosystems include estuaries, salt marshes, mangrove forests, seagrass beds, and the open ocean (pelagic zone)
  • Estuaries are transitional zones where rivers meet the sea, characterized by varying salinity and high productivity (Chesapeake Bay, Amazon River estuary)
  • Salt marshes and mangrove forests are coastal wetlands that provide critical habitat for juvenile fish and protect shorelines from erosion and storms
  • Seagrass beds are submerged meadows that stabilize sediments, store carbon, and serve as nurseries for many marine species
• Each marine ecosystem has unique physical and chemical characteristics, such as temperature, light availability, and nutrient levels, that shape its community structure and function
  • Temperature influences metabolic rates, species distributions, and ecosystem productivity
  • Light availability determines the depth of the photic zone and the vertical distribution of photosynthetic organisms
  • Nutrient levels (nitrogen, phosphorus, iron) control primary productivity and the abundance of phytoplankton and macroalgae

Adaptations of Marine Organisms

Morphological and Physiological Adaptations

• Marine organisms have evolved adaptations to cope with the challenges of their environments, such as high salinity, pressure, and limited light
  • Osmoregulation mechanisms help maintain water balance in cells and tissues (salt glands in seabirds, specialized kidneys in marine mammals)
  • Pressure-resistant proteins and membranes allow deep-sea organisms to function under extreme hydrostatic pressure
  • Bioluminescence, the production of light by living organisms, is common in deep-sea species for communication, camouflage, and attracting prey (anglerfish, vampire squid)
• Adaptations can be morphological (e.g., streamlined body shapes for efficient swimming), physiological (e.g., osmoregulation to maintain water balance), or behavioral (e.g., vertical migration to follow food sources)
  • Streamlined body shapes reduce drag and improve swimming efficiency in fast-moving predators (sharks, dolphins, tuna)
  • Countershading, a color pattern with a dark back and light belly, helps fish blend in with the background when viewed from above or below
  • Vertical migration allows zooplankton to feed near the surface at night and avoid predators by descending to darker depths during the day

Species Interactions and Keystone Species

• Species interactions, such as predation, competition, and symbiosis, play crucial roles in shaping marine communities and ecosystem dynamics
  • Predation can control the abundance and distribution of prey species, leading to trophic cascades that affect the entire ecosystem
  • Competition for limited resources, such as food and space, can drive niche partitioning and species coexistence
  • Symbiotic relationships, including mutualism, commensalism, and parasitism, involve close associations between two or more species
• Examples of symbiotic relationships include the mutualism between coral polyps and zooxanthellae, and the commensalism between clownfish and sea anemones
  • Coral polyps provide shelter and nutrients for zooxanthellae, while the algae supply the coral with oxygen and remove waste products
  • Clownfish gain protection from predators by living among the stinging tentacles of sea anemones, while the anemones benefit from the clownfish's nitrogen-rich waste
• Keystone species, such as sea otters in kelp forests and parrotfish in coral reefs, have disproportionately large impacts on their ecosystems through trophic cascades and habitat modification
  • Sea otters prey on sea urchins, which can overgraze kelp forests if left unchecked, leading to the formation of urchin barrens
  • Parrotfish consume algae that compete with coral for space, helping to maintain the balance between coral and algal cover on reefs

Marine Biodiversity and Threats

Importance and Value of Marine Biodiversity

• Marine biodiversity encompasses the variety of life in the ocean, including genetic diversity, species diversity, and ecosystem diversity
  • Genetic diversity refers to the variation in genes within a species, which enables adaptation to changing environmental conditions
  • Species diversity is the number and relative abundance of different species in an ecosystem
  • Ecosystem diversity describes the variety of habitats, communities, and ecological processes in the marine environment
• High biodiversity enhances ecosystem resilience, productivity, and the provision of ecosystem services, such as fisheries, coastal protection, and carbon sequestration
  • Greater species diversity can buffer ecosystems against environmental perturbations and species loss
  • Diverse ecosystems are often more productive due to niche complementarity and the efficient use of resources
  • Marine ecosystems provide valuable services, such as food production, shoreline stabilization, and the regulation of climate and biogeochemical cycles

Major Threats to Marine Biodiversity

• Major threats to marine biodiversity include overfishing, habitat destruction, pollution, climate change, and invasive species
  • Overfishing can lead to the collapse of fish stocks, trophic cascades, and shifts in community structure
    • Excessive removal of top predators can release prey populations from predation pressure, leading to ecosystem imbalances
    • Bycatch, the unintentional capture of non-target species, can threaten vulnerable populations such as sea turtles, sharks, and seabirds
  • Habitat destruction, such as the degradation of coral reefs and coastal development, reduces the availability of critical habitats for marine organisms
    • Coral reefs are threatened by ocean acidification, rising sea temperatures, pollution, and physical damage from fishing gear and anchors
    • Coastal development, such as dredging, land reclamation, and the construction of seawalls, can destroy wetlands, mangroves, and other important habitats
  • Pollution, including plastic debris, oil spills, and nutrient runoff, can have toxic effects on marine life and cause eutrophication and hypoxia
    • Plastic debris can entangle or be ingested by marine animals, leading to injury, starvation, and death
    • Nutrient runoff from agricultural and urban areas can stimulate harmful algal blooms and create oxygen-depleted "dead zones"
  • Climate change impacts, such as ocean acidification and rising sea temperatures, can disrupt the physiology and behavior of marine organisms and alter ecosystem functioning
    • Ocean acidification, caused by the absorption of atmospheric carbon dioxide, can impair the ability of calcifying organisms (corals, mollusks) to build their shells and skeletons
    • Rising sea temperatures can cause coral bleaching, the expulsion of symbiotic algae from coral tissues, leading to coral mortality and reef degradation
  • Invasive species, introduced through shipping, aquaculture, and the aquarium trade, can outcompete native species and disrupt ecosystem balance
    • The lionfish, native to the Indo-Pacific, has become a major threat to coral reef ecosystems in the Caribbean and western Atlantic
    • The European green crab has altered coastal habitats and displaced native species in North America, Australia, and South Africa

Primary Productivity in Marine Food Webs

Primary Productivity and Energy Transfer

• Primary productivity in marine ecosystems is driven by photosynthesis by phytoplankton and macroalgae in the photic zone, and chemosynthesis by microorganisms in deep-sea environments
  • Phytoplankton, microscopic algae that drift with currents, are responsible for approximately 50% of global primary production
  • Macroalgae, such as kelp and seaweeds, are important primary producers in coastal ecosystems
  • Chemosynthetic bacteria use chemical energy from hydrogen sulfide or methane to fix carbon dioxide into organic compounds
• The rate of primary productivity varies across marine ecosystems, depending on factors such as nutrient availability, light penetration, and water column stability
  • Upwelling zones, where deep, nutrient-rich waters are brought to the surface, support high primary productivity (Peruvian upwelling, California Current)
  • Oligotrophic regions, such as the open ocean gyres, have low nutrient concentrations and lower primary productivity
• Energy is transferred through marine food webs via trophic levels, from primary producers to primary consumers (herbivores), secondary consumers (carnivores), and higher-level predators
  • Phytoplankton are consumed by zooplankton, small crustaceans, and filter-feeding organisms (copepods, krill, bivalves)
  • Zooplankton and other primary consumers are eaten by small fish, jellyfish, and larger invertebrates
  • Small fish and invertebrates are preyed upon by larger fish, seabirds, and marine mammals
• The efficiency of energy transfer between trophic levels is typically low (around 10%), limiting the number of trophic levels in marine food webs
  • Much of the energy consumed by organisms is lost through respiration, heat, and undigested materials
  • The low efficiency of energy transfer constrains the biomass and abundance of organisms at higher trophic levels

Trophic Cascades and the Microbial Loop

• The concept of trophic cascades illustrates how changes in the abundance of predators can indirectly affect the abundance and distribution of organisms at lower trophic levels
  • In the North Pacific, the removal of sea otters by fur traders in the 18th and 19th centuries led to an increase in sea urchin populations and the destruction of kelp forests
  • The reintroduction of sea otters has helped to restore kelp forests by controlling sea urchin numbers and allowing kelp to regrow
• The microbial loop, involving the cycling of dissolved organic matter by bacteria and their consumption by protists and zooplankton, plays a significant role in marine food web dynamics and nutrient recycling
  • Bacteria consume dissolved organic matter released by phytoplankton, zooplankton, and other organisms
  • Protists, such as ciliates and flagellates, graze on bacteria and are in turn consumed by larger zooplankton
  • The microbial loop transfers energy and nutrients from the dissolved organic pool back into the classical food chain, increasing the efficiency of nutrient recycling and energy flow in marine ecosystems