Ecology of Estuaries

Definition of an estuary

• An estuary can be defined as a “semi-enclosed coastal body of water which has a free connection with the open sea and within which sea water is measurably diluted with fresh water from a river, stream, or from groundwater”

Florida Estuary – Gulf of Mexico

Florida Bay

Florida Bay Mangroves

Estuary Map of Florida

• Importance of estuaries• Physical conditions• Habitats• Biological characteristics• Threats to estuaries

Why estuaries are important

• Productivity• Nursery areas• Filtration• Spawning sites• Migration routes• Resting and feeding areas

productivity

• High levels of nutrients• Shallow and tidal- lots of solar radiation for

primary production• Warmer than surrounding ocean during the

summer

Nursery Areas• High productivity - lots of food; high growth• Reduced predation – low mortality• Gag Grouper will only spend about a year in the

estuary before moving offshore to spawn• Redfish stay in the estuary for several years but

spawn offshore• Snook go offshore to spawn but then come back

to the estuary• Spotted sea trout live their entire life in the

estuary

Gag Grouper(Charlotte Harbor, FL)

Red Drum fingerling(Charlotte Harbor, FL)

Young Permit(Charlotte Harbor, FL)

Snook fingerling(Charlotte Harbor, FL)

Filter for nutrients and toxicants

• Outflowing groundwater and rivers pass through estuaries on the way to the ocean

• Plants, animals, and sediments take up nutrients and toxicants

• Keeps these chemicals out of the ocean (good) but concentrates them in estuaries (bad)

Shrimp reproducton• Other species such as the shrimp spawn

offshore– The larvae then move toward inshore waters,

changing form by molting as they progress through various stages of development

– As young shrimp, they burrow into the sea floor at the mouth of the estuary as the tide goes out

– They then ride into the estuary on the incoming tide where they then develop into adults.

– When mature, the shrimp migrate offshore and the cycle begins all over again

Shrimp Reproduction

Migration routes

• Many species migrate through estuaries to reach spawning/feeding grounds

Resting and feeding areas

• Long distance migratory species (birds)• Atlantic flyway

The oyster; an importantFlorida estuarine animal

The American OysterCrassostrea virginica

• Oysters are the most widely studied and best known of all the marine and estuarine invertebrates

• While the oyster is greatly appreciated when showing up on the dining room table, few realize the ecological importance of this mollusc

• An estuary can be defined as a “semi-enclosed coastal body of water which has a free connection with the open sea and within which sea water is measurably diluted with fresh water from land drainage”

The ecological position of the oysterwithin the estuarine community

• Because the American oyster extends over a wide latitude from 20 degree’s N to 54 degree’s N, the ecological conditions under which it lives are not uniform

• The present description applies primarily to populations of oysters and associated organisms in the intertidal zone of the Southeastern United States

The Oyster – a reef builder

• In many parts of the southeast, the oyster builds massive, discrete reefs in the intertidal zone

• They are especially prominent in northeastern Florida, especially the Appalachicola region

• Oysters are considered the “keystone” species (i.e., indispensable) when reefs are present.

The Oyster is the quintessential estuarine animal

• It can tolerate a wide range of salinity, temperature, turbidity, and low oxygen conditions

• Under high salinity, for example, the oyster simply closes

• Therefore, the oyster is well adapted to the wide range of water quality that occur normally within estuaries and are therefore euryhaline

• Salinity’s tolerated by the oyster range from 5 to 32 0/00; i.e., from almost freshwater to full strength sea water

Who (or what) eats or kills oysters(besides humans)

• The oyster drill (Urosalpinx cinerea_• The oyster “Leech” – a flatworm (Stylochus

ellipticus)• The moon snail (Polinices)• Two diseases – MSX and “Dermo”

Oyster cluster

Mangrove Oyster Reef

Doing laundry on an oyster skiff

Tonging oysters

Physical Conditions

• Physical configuration• Mixing of fresh and seawater• Tidal fluctuations• Resulting abiotic variation• Adaptations to abiotic conditons

Physical configuration

• Partially enclosed body of water where rivers meet oceans • Type of estuary based on geology

– Coastal plain – flooded river valley; Chesapeake Bay, Delaware Bay

– Delta – sediments deposited at mouth by river; Mississippi River Delta

– Fjords – dug out by advancing glaciers, form when glacier retreats– Bar-built estuary – created by sandbars at the mouth of the river

- Charlotte Harbor, FL– Salt-marsh estuary – no river thus high salinity. Atlantic coast of

Florida from Cape Canaveral North

Mixing of Fresh and Seawater

• Freshwater mixes with seawater to create brackish water

• Creates salinity gradients from ocean to mouth of river– Salinity gradients change depending on rainfall

and tidal flushing– Tides: high tide pushes saltwater in

Mixing of Fresh and Seawater

• Variable salinity requires animals to be euryhaline (tolerant to high and low salinities); contrast with coral reefs which are stenohaline– Limits diversity of organisms in estuaries– Sets pattern of distribution within estuaries

Mixing of Fresh and Seawater

• Estuaries can also be classified by how thoroughly the fresh and salt water mixes vertically– Salt-wedge: freshwater rides over dense saltwater

wedge at the mouth of the river; requires a high freshwater input (Delaware River, Mississippi River)

– Slightly stratified – like salt-wedge but with more mixing

– Vertically mixed – no vertical stratification (Florida?)

Mixing of fresh and seawater

Resulting abiotic variation

• Salinity• Oxygen• Submergence• temperature

Eutrophication

Loss of seagrass from reduction of light (sedimentation)

Invasive species inTampa Bay

• 55 known plant and animal invaders in Tampa Bay

• Asian green mussel has rapidly spread; probably arrived via ballast water of ships

• Brazilian pepper• Chinese water lettuce• Asian swamp eel• Marine toad