bio 207 chapter 12: estuaries - where rivers meet the sea

estuaries

semi-enclosed areas where fresh water and seawater meet and mix, most productive environments on Earth, most affected by humans

other names for estuaries

lagoons, sloughs, bays

seas with restricted circulation

the Baltic and Black seas, classified as estuaries

estuary origins

sea level rose because of ice melting at the end of the last ice age (18,000 years ago), the sea invaded lowlands and river mouths

drowned river valleys/coastal plain estuaries

most common type of estuary formed when rising sea levels flooded existing river valleys
locations: Chesapeake Bay, mouth of Delaware River, St. Lawrence river in eastern Canada and River Thames in England

bar built estuary

the accumulation of sediments along the coast builds up sand bars and barrier islands acting as a wall between the oceans and freshwater from rivers
locations: Gulf coast of Texas, Outer Banks and Hatteras Barrier islands of North Carolina, North Sea coast of the Netherlands and Germany

tectonic estuaries

created when land sank or subsided as a the result of movements of the Earth’s crust
location: San Francisco Bay in California

fjord

retreating glaciers cut deep, spectacular valleys along the coast, the valleys were partially submerged when sea level rose and rivers flowed into them
locations: southeastern Alaska, British Columbia, Norway, southwestern Chile, South Island of New Zealand

broad, well developed estuaries

common in regions with flat coastal plains and wide continental shelves (passive margins), Atlantic coast of North America

estuary restriction

steep coasts and narrow continental shelves of the Pacific coast of North America and other active margins, have narrow river mouths along the steep coast

salinity

fluctuates dramatically and varies with depth

salt wedge

move back and forth with the daily tides, wedge-shaped intrusion of salt water underneath freshwater

negative estuaries

salinity in the estuary is higher than in the adjacent ocean, like Laguna Madre, Texas coast

substrate

sand settles out in upper reaches, muddy particles are carried further, often anoxic

mud

silt and clay, rich in organic material

respiration by bacteria

uses up oxygen from the water between sediment particles resulting in anoxic sediments

water temperature

vary especially when water levels are low

water clarity

very poor due to suspended sediments and particles from rivers, making it more difficult for photoautotrophs

primary production

result of flowering plants in the salt marsh

euryhaline

tolerate a wide range of salinities, can live anywhere in the ecosystem

stenohaline

tolerate a narrow range of salinities, limited to upper or lower ends and rarely penetrate estuary proper, brackish water or intermediate salinity

estuary proper

the middle of the estuary

osmoconformers

maintain osmotic balance by allowing body fluids to change with the salinity of the water, many mollusks and some polychaete worms

osmoregulators

keep the salt concentration of body fluids the same regardless of the water salinity, many fish, crabs, other mollusks and polychaete worms

osmoregulation in low salinity

when the salinity of the water is lower than the salinity of the blood, they get rid of excess water and take in solutes via active transport by gills, kidneys

anadromous fish

migrate from sea to spawn in freshwater, salmon

catadromous fish

migrate from fresh water to spawn in the sea, freshwater eels

Spartina

cordgrasses, salt marsh plants and mangroves, excrete excess salt via salt glands in leaves

succulents

pickleweed (Salicornia), accumulate large amount of water to dilute salts they take up

adapting to mud

nothing to hold onto, less drastic salinty fluctuations, low oxygen levels

nothing to hold onto

animals burrow or live in tubes beneath sediment surface and inhabitants are stationary or slow moving

low oxygen

organsims pump in oxygen-rich water and possess hemoglobin which has high affinity for oxygen

open water characteristics

murky water, rich variety of fish and shellfish, migrations

marine commercial catch in Gulf of Mexico

90% of catch is of species that depend on estuaries at some point in their lives

fish variety

many are juveniles, breed at sea and use estuaries as nurseries, menhaden, anchovies, mullets, croakers, flatfish

mudflats

the bottoms of estuaries that become exposed at low tide, extensive where there is a large tidal range with a gently sloping bottom

mudflat characteristics

similar to muddy shores, primary producers (green and red algae, benthic diatoms) flourish, bacteria and archaea abundant, many infauna and few epifauna, more deposit than suspension feeders

mudflat bacteria and archaea

decompose organic matter brought in by rivers and tides, produce H2S when oxygen is gone that is used by chemosynthetic/sulfur fixing bacteria

mudflat meiofauna

protozoans, nematodes, minute animals

mudflat infauna

polychaetes and bivalves

mudflat epifauna

amphipods, snails, shrimp, some crabs

salt marshes

estuaries in temperate/subarctic regions that are bordered by extensive grassy areas that extend inland from mudflats, flooded at high tide and grouped with freshwater marshes as wetlands

salt marsh characteristics

develop long sheltered open coasts, disturbance from wave action is minimal allowing for accumulation of muddy sediments, replaced by mangroves, Atlantic and Gulf coasts, mud held together by marsh plant roots, few hard grasses

salt marsh species

decay bacteria (nitrogen fixing), diatoms, filamentous green algae and cyanobacteria, same species as in mudflats

mangrove forests

AKA mangals, not limited to estuaries but are the tropical equivalent of salt marshes, 75% of sheltered tropical shores were littered, Indo-West Pacific has most, red, black and white trees

mangroves

flowering land plant adapted to live on the intertidal zone, get rid of salts taken in by roots via salt glands on leaves

pneumatophores

vertical root extensions of some mangrove trees assisting in gas exchamge

mangrove forest species

same as mudflats and salt marshes, seaweeds, sponges, oysters, sea anemones, barnacles, sea squirts, attached to roots, insects (bees), bats, birds, snakes and lizards, frogs, fish, crabs

seagrass beds

found in estuaries if water clarity permits, must be better than an estuary

oyster reefs

congregations of oysters, platform on which dozens of other species can grow

salt marsh food web

producers: cordgrasses and pickleweed
carnivores: fish, birds

open water and muddy bottom food web

producers: phytoplankton and diatoms, seaweeds
carnivores: fish, birds

mangrove forest food web

producers: mangroves
carnivores: fish, birds