Estuaries Partially enclosed coastal areas where freshwater mixes with seawater Aka: Saltmarshes, lagoons, mudflats, sloughs, coastal wetlands Highly productive environments –Important role in many marine species life history

4 basic types: Drowned river valleys –Coastal plain estuaries –Rising sea level (melting of last ice age) encroached lowlands –E.g. Chesapeake Bay Bar-built –Sedimentation partially blocks sea –E.g. Batiquitos Lagoon; San Eligo Lagoon Tectonic –Coast lands subside via plate movements –E.g. San Francisco Bay Fjords –Glacier-carved estuaries –Very deep, up to 1000s ft deeper than neighboring sea –E.g. parts of Norway, Alaska, New Zealand…

Water mixing Broad range of salinity Incoming seawater is more dense than freshwater influx –Salt wedge is affected by tides –& fluctuates seasonally Low freshwater influx, partial blocking, and high evaporation can increase salinity –Negative estuaries

Salinity Adaptations Tolerate wide range –Euryhaline Narrow range –Stenohaline species Brackish adapted –Intermediate salinity Osmotic regulation –Osmoconformers Internal fluctuations with environment (blue) –Osmoregulators Maintain constant internal concentration via active transport (red) –Both…

Productivity & protection Lots of nutrients –Freshwater influx –Tidal flushing Carries plankton –Sustains lots of consumers Coastal fishes, flatfishes, crustaceans, mollusks, worms… –Nurseries Anadromous fishes (spawn in freshwater) –Salmon, smelts, shad Catadromous fishes (spawn at sea) –Freshwater eels

Why so productive? ↑ 1 o production ↑ nutrients –Tides & rivers Recycling –Decomposition Breaking down detritus →DOM (dissolved organic matter) –Nitrogen fixation Producers can use the organics

Birds and estuaries Breeding, feeding and nesting grounds Key stopover point on the Pacific Flyway for over 370 species of migratory and native birds –E.g. Tijuana River Estuary –Most of our local lagoons Diverse species & resources –Willet, godwits, dowitchers, plovers, & sandpipers –Oyster catchers, herons, egrets –Ducks, terns, & gulls