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?

• ↑ 1o 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