Estuaries
General Characteristics
- Semi-enclosed areas where freshwater and seawater mix
- Sediment is organic-rich mud with high levels of anaerobic bacteria
- Salinity fluctuates dramatically (0 – 35 ppt) based on ratio of mixture, depth of estuary, and water circulationUnique among marine environments because it is regularly exposed to the air (emersion/immersion)
Salinity Adaptations
- Most organisms are euryhaline and can tolerate a wide range of salinities
- Soft-bodied organisms (molluscs, worms) are osmoconformers and allow their body fluids to change with the water
- Fish, crabs, others are osmoregulators and use active transport to pump out excess water and absorb more solutes
- Some plants have salt glands to remove excess salt or they accumulate large amounts of water to dilute salt
Open Water Estuaries
- Murky water restricts photosynthesis by phytoplankton
- Rich supply of fish and shellfish led to commercialization and urban development by humans
- Used as nurseries by many marine fish species
Mudflats
- Formed when bottoms of estuaries become exposed at low tide
- Similar to soft bottom intertidal zone –
- dominant primary producers are diatoms/bacteria
- animals are burrowing deposit and suspension feeders
Salt Marshes
- Grassy areas bordering estuary that are partially flooded at high tide
- Same environmental pressure as mudflats, but mud is held together by marsh plant roots
- Dominant plant is cordgrass, pickle weed – tolerant to salt and flooding during high tide
- Bacteria are crucial for decomposition of dead plant materials and nitrogen fixing to enrich sediment
- Animals include crabs, snails, mussels, fish, birds
Mangrove Forests
- Tropical equivalent of salt marshes (lots located in Florida and Indonesia)
- Mangrove trees are land plants adapted to intertidal environment – tolerance to immersion at high tide, adaptations to remove excess salt
- Crabs very common, mudskippers unique to Indonesian mangrove, lots of burrowing suspension and deposit feeders, birds and reptiles as predators
- Again, bacteria extremely important in breaking down detritus, but results in oxygen-deficient sediment
Random Pictures from our Gallery!