Aquatic Biomes

• Unit 1.3 covers aquatic biomes

Types of Aquatic Biomes

• Freshwater biomes have low salinity (less than 1% salt concentration)
• Marine biomes have higher salinity (around 3.5% salt concentration)

Freshwater Biomes

• Lakes and Ponds: Standing water systems with varying depth, nutrient levels, and oxygen availability
• They experience seasonal turnover, redistributing oxygen and nutrients
• Rivers and Streams: Flowing water systems that vary in speed and temperature based on location and elevation
• Fast-moving streams tend to be oxygen-rich
• Slow-moving rivers accumulate sediments and nutrients
• Wetlands: Saturated land areas like marshes, swamps, and bogs
• They provide critical ecosystem services such as flood control, water filtration, and biodiversity support

Marine Biomes

• Oceans cover approximately 70% of the Earth's surface
• They host vast biodiversity and regulate climate by absorbing heat and carbon dioxide
• Estuaries: Transitional zones between rivers and oceans with varying salinity levels
• They are highly productive ecosystems that support fish nurseries and act as natural water filters
• Coral Reefs: Among the most biodiverse ecosystems and provide habitat for marine species
• They are threatened by ocean acidification, climate change, and pollution

Key Abiotic Factors in Aquatic Biomes

• Salinity affects species composition and osmoregulation in aquatic organisms
• Depth influences sunlight penetration, temperature, and pressure, affecting photosynthesis and species distribution
• Water flow determines oxygen levels and nutrient distribution
• Temperature regulates metabolic rates and species adaptation
• Dissolved oxygen is higher in colder, turbulent waters, essential for aquatic life
• Nutrient availability varies with water movement and depth
• Upwelling zones bring nutrient-rich waters to the surface

Ecosystem Services Provided by Aquatic Biomes

• Water filtration: Wetlands and estuaries remove pollutants from water
• Habitat for biodiversity: Supports a wide range of aquatic organisms
• Carbon sequestration: Oceans and wetlands store carbon, helping mitigate climate change
• Climate regulation: Oceans moderate global temperatures by absorbing heat
• Food sources: Fisheries and aquaculture provide food for millions globally

Island Biogeography Theory

• Proposed by MacArthur & Wilson, stating species richness on islands is influenced by island size and distance from mainland

Island Size

• Larger islands support more species due to greater resources and habitat diversity

Distance from Mainland

• Closer islands have higher immigration rates and greater biodiversity

Effects of Isolation

• Endemic species: Unique species evolve due to geographic isolation
• Example: Galápagos finches
• Vulnerability to invasive species: Lack of natural predators makes native species susceptible to extinction
• Ecological interactions: Species often have specialized roles, making ecosystems fragile

Human Impacts on Island Ecosystems

• Habitat destruction: Deforestation, urbanization, and agriculture reduce native species' habitats
• Introduced species: Non-native predators disrupt island ecosystems
• Climate change effects: Rising sea levels threaten low-lying islands
• Overexploitation of resources: Hunting, fishing, and tourism strain fragile ecosystems

Consequences of Overfishing

• Population declines: Overharvesting reduces fish stocks, affecting food chains
• Trophic cascade: Loss of top predators disrupts entire ecosystems
• Example: Fewer sharks lead to an increase in their prey, causing imbalance
• Loss of biodiversity: Declining fish populations affect marine ecosystems and human livelihoods

Fishing Methods & Issues

• Bottom trawling: Large nets drag along the seafloor, destroying habitats and catching non-target species (bycatch)
• Longlining: Baited hooks catch large quantities of fish but also unintentionally capture endangered species
• Purse seining: Large nets encircle schools of fish, leading to overfishing
• Drift nets: Float freely, catching anything in their path, including dolphins and turtles

Sustainability Strategies

• Fishing quotas: Limits on catch sizes to prevent depletion
• Marine protected areas (MPAs): Restrict fishing in certain areas to allow populations to recover
• Gear modifications: Reduce bycatch (e.g., turtle excluder devices)
• Aquaculture: Farming fish instead of catching wild populations

Types of Aquaculture

• Open-net pens: Enclosures in coastal waters but pose risks of pollution and disease spread
• Recirculating aquaculture systems (RAS): Land-based systems that recycle water but are expensive
• Integrated multi-trophic aquaculture (IMTA): Multiple species farmed together to reduce waste

Environmental Concerns of Aquaculture

• Disease spread: High densities of fish increase disease transmission
• Antibiotic use: Can contribute to antibiotic-resistant bacteria
• Genetic contamination: Escape of farmed fish can disrupt wild populations
• Waste pollution: Excess feed and fish waste contribute to eutrophication

Sustainable Practices in Aquaculture

• Polyculture: Farming multiple species together to mimic natural ecosystems
• Offshore aquaculture: Reduces pollution near the shore
• Plant-based feeds: Reduces reliance on wild fish for feed
• Monitoring systems: Improve water quality and efficiency

Major Issues: Human Impacts on Aquatic Ecosystems

• Pollution includes oil spills (harm marine life, reduce oxygen, persist for decades), plastics (microplastics enter food chains), heavy metals (bioaccumulate), and agricultural runoff (eutrophication, dead zones)
• Climate Change Effects include ocean acidification (weakens coral reefs), rising sea levels (threatens habitats), and coral bleaching (warmer waters expel symbiotic algae)
• Overexploitation Includes unsustainable fishing (ecosystem collapse), habitat destruction (coastal development), and mineral/oil extraction (disrupts ecosystems)

Conservation Strategies

• Marine protected areas: Limit human activity to allow recovery
• Regulations: Fishing bans, pollution controls, and emissions reductions
• Ecosystem restoration: Coral reef restoration, wetland reforestation

Major Ocean Currents

• Gulf Stream warms the eastern US and Europe
• California Current brings cold waters to the US West Coast
• Antarctic Circumpolar Current encircles Antarctica, keeping it cold
• North Atlantic Drift warms Europe

Upwelling

• Brings nutrient-rich waters to the surface, supporting fisheries

El Niño & La Niña

• El Niño: Warmer Pacific waters cause disrupted fisheries, extreme weather
• La Niña: Cooler waters lead to stronger upwelling and intensified storms