11.3 Estuarine ecosystems and salt marshes

Estuaries and salt marshes are dynamic coastal ecosystems where freshwater meets the sea. These unique environments support diverse life and provide crucial services like water filtration and storm protection. They're also vital nurseries for many marine species, including commercially important fish and shellfish.

These ecosystems face threats from pollution, development, and climate change. Understanding the factors influencing their productivity and the services they provide is key to protecting them. Conservation efforts focus on habitat restoration, pollution reduction, and public education to safeguard these valuable coastal areas.

Estuarine Ecosystems

Characteristics of estuaries and salt marshes

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• Estuaries are semi-enclosed coastal bodies of water where freshwater from rivers and streams mixes with saltwater from the ocean creating brackish water environments (Chesapeake Bay, San Francisco Bay)
  • Varying salinity levels create unique habitats supporting diverse flora and fauna adapted to these conditions
  • Serve as transition zones between terrestrial, freshwater, and marine environments facilitating nutrient exchange and species migration
• Salt marshes are coastal wetlands regularly flooded by tidal waters creating salt-tolerant vegetation communities (cordgrass, pickleweed)
  • Provide essential habitat for numerous species of birds (herons, egrets), fish (mummichogs, striped bass), and invertebrates (fiddler crabs, ribbed mussels)
  • Act as nursery grounds for commercially important fish and shellfish species supporting coastal fisheries
• Ecological importance lies in high productivity due to nutrient input from rivers and tidal flushing supporting complex food webs
  • Offer valuable ecosystem services including water filtration, coastal protection from erosion and storms, and carbon sequestration in sediments

Estuaries as marine nurseries

• Sheltered, nutrient-rich environments serve as nursery grounds for many marine species providing protection from predators and abundant food sources for juvenile organisms
  • Examples of species relying on estuaries as nurseries:
    1. Fish: salmon, striped bass, herring, flounder
    2. Shellfish: oysters, clams, shrimp
• Crucial role in life cycles of commercially important species with juveniles spending time in estuaries before migrating to open ocean as adults
  • Healthy estuarine habitats maintain sustainable populations supporting commercial and recreational fisheries dependent on their productivity

Factors Influencing Estuarine Ecosystems and Salt Marsh Services

Factors in estuarine ecosystem productivity

• Nutrient input from rivers and coastal runoff stimulates primary production by providing nitrogen and phosphorus
  • Excess nutrients can lead to eutrophication and harmful algal blooms (red tides) disrupting ecosystem balance
• Salinity gradients create distinct habitats within estuaries inhabited by organisms adapted to specific salinity ranges contributing to diversity
  • Freshwater species near river mouths transition to saltwater species near ocean outlets
• Tidal flushing distributes nutrients, oxygen, and sediments throughout the estuary while removing waste products maintaining water quality
  • Tidal currents also transport planktonic larvae facilitating dispersal and connectivity between populations
• Other influential factors include water temperature, dissolved oxygen levels, and sediment type and distribution impacting species composition and ecosystem functions

Ecosystem services of salt marshes

• Coastal protection by salt marsh vegetation dissipating wave energy and stabilizing shorelines
  • Reduces erosion and buffers coastal communities from storm surges and flooding preventing property damage
• Nutrient cycling through natural filtration removing excess nutrients (nitrogen, phosphorus) and pollutants from water
  • Microbial communities in sediment break down organic matter recycling nutrients back into the system
• Carbon sequestration by efficiently capturing and storing atmospheric carbon dioxide in accumulating organic matter in sediments
  • Creates long-term carbon sinks playing a significant role in mitigating impacts of climate change (sea level rise, ocean acidification)

Threats to estuarine environments

• Habitat destruction from coastal development (dredging, filling, construction) directly destroying estuarine habitats
  • Upstream activities (dam construction, water diversion) alter freshwater input and sediment delivery impacting ecosystem dynamics
• Pollution from industrial, agricultural, and urban runoff introduces harmful substances (heavy metals, pesticides, excess nutrients)
  • Oil spills and marine debris pose direct threats to estuarine flora and fauna health and survival
• Climate change impacts include sea level rise submerging and eliminating salt marsh habitats
  • Changing temperature, precipitation patterns, and ocean acidification shift species distributions and disrupt ecosystem functioning
• Conservation and management strategies involve:
  1. Habitat restoration and creation projects compensating for lost or degraded estuarine habitats
  2. Improved land-use practices and regulations reducing pollution and minimizing habitat destruction
  3. Establishing marine protected areas and reserves safeguarding critical estuarine ecosystems
  4. Monitoring programs assessing health and trends of estuarine habitats and species
  5. Public education and outreach promoting awareness and stewardship of estuarine ecosystems