3.2 Marine biodiversity patterns and distribution

Marine biodiversity patterns are shaped by various factors, creating a complex tapestry of life in the oceans. Latitude, depth, and habitat complexity play crucial roles, influencing species distributions and creating hotspots of diversity in tropical regions and shallow waters.

Understanding these patterns is vital for conservation efforts and sustainable use of marine resources. From coral reefs teeming with life to the unique adaptations of deep-sea creatures, marine biodiversity supports ecosystem functioning, enhances resilience, and provides invaluable benefits to humans.

Factors Influencing Marine Biodiversity Patterns

Factors in marine biodiversity patterns

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• Latitudinal gradient
  • Biodiversity decreases moving from equator to poles due to changes in temperature, solar radiation, and productivity
  • Tropical regions (coral reefs) have highest diversity while polar regions (Arctic Ocean) have lowest
• Depth gradient
  • Biodiversity varies with water depth, highest in shallow, sunlit areas (coral reefs) and decreases in deeper zones
  • Bathyal zone has lower diversity but increases again in abyssal zone with unique deep-sea species
• Habitat complexity
  • Structurally complex habitats (coral reefs, kelp forests, seagrass beds) support higher biodiversity by providing diverse niches and resources
  • Simple habitats (sandy bottoms, open ocean) have lower diversity due to fewer microhabitats and resources
• Other factors
  • Temperature, salinity, and nutrients influence species distributions based on physiological tolerances
  • Ocean currents and upwelling zones affect nutrient and larval transport, impacting local biodiversity
  • Evolutionary history and geological events (Isthmus of Panama) shape regional species pools and endemism

Marine biodiversity hotspots vs coldspots

• Biodiversity hotspots
  • Exceptionally high species richness and endemism, often in tropical regions (Coral Triangle, Caribbean Sea)
  • Associated with coral reefs and other complex habitats but threatened by human activities (overfishing, pollution, climate change)
  • Examples: Great Barrier Reef, Indo-Pacific, Gulf of Guinea
• Biodiversity coldspots
  • Relatively low species richness and endemism, often in polar and deep-sea regions (Arctic Ocean, Southern Ocean)
  • Harsh environmental conditions (low temperature, limited sunlight) and low primary productivity
  • Support unique species adapted to extreme conditions (ice algae, deep-sea vents)

Shaping of marine species distributions

• Dispersal
  • Movement of individuals or propagules (larvae, seeds) enables colonization of new habitats and gene flow
  • Influenced by ocean currents, larval duration, and adult mobility (fish vs sessile organisms)
  • Long-distance dispersal events can connect distant populations and shape biogeographic patterns
• Isolation
  • Separation of populations by physical or ecological barriers leads to reduced gene flow and potential speciation
  • Examples: isolated islands (Galapagos), deep-sea trenches, semi-enclosed seas (Red Sea)
  • Promotes endemism and unique evolutionary trajectories in isolated regions
• Environmental gradients
  • Gradual changes in abiotic factors (temperature, salinity, depth) shape species distributions based on physiological tolerances
  • Leads to zonation patterns and distinct community assemblages (intertidal zones, deep-sea layers)
  • Species replacements and adaptations occur along these gradients (cold-adapted vs warm-adapted species)

Importance of marine biodiversity

• Ecosystem functioning
  • Biodiversity supports ecosystem processes (primary production, nutrient cycling, carbon sequestration)
  • Higher diversity leads to increased productivity and stability through complementary resource use
  • Examples: diverse algal communities fix more carbon, seagrass beds stabilize sediments
• Resilience
  • Higher biodiversity enhances ecosystem resilience to disturbances through functional redundancy and complementarity
  • Diverse systems better equipped to adapt to environmental changes (climate change, invasive species)
  • Examples: coral reefs with higher diversity recover faster from bleaching events
• Importance for humans
  • Marine biodiversity provides valuable resources (food, medicine, raw materials)
  • Supports livelihoods and economies through fisheries, tourism, and other industries (aquaculture, biotechnology)
  • Offers cultural, recreational, and aesthetic benefits (diving, beach visits, traditional practices)