Estuarine Conditions - General Characteristics
Tidal mixing (salinity variations)
Productive ecosystems (high organic content, high biotic diversity, complex behavioral interconnections)
Often subject to algal blooms (red tides), due to organic input, high temperatures, and poor mixing within the estuary
Seagrass Communities
Highly productive habitat, dominated in New England by eelgrass, Zostera marina
Important habitat areas for important commercial fish and shellfish species
Extensive soft sediments at base of grasses where a rich biotic community thrives (see food chain)
Many restoration programs in place

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Tidal Mudflats
Soft muds, exposed at low tide, excellent habitat for burrowing animals
Molluscs, annelid worms, small arthropods
Productive community, heavily dependent on detritus food chain
Important habitat for commercial shellfish
Quahags, soft-shell clams, scallops
Salt Marshes
Dominated by grasses (Spartina alterniflora in Rhode Island), interspersed by tidal streams
May contain a mudflat area or salt pond (see photos)
Highly productive community, high biodiversity
Nursery area for many fish & shellfish
Complex food chain (detritus type)
Many restoration programs underway
Coastal Ponds
Shallow ponds, which may or may not be directly connected to the ocean
Ideal habitat for shellfish, especially oyster beds (lowered salinity blocks presence of oyster drill)
Rhode Island once a major producer of oysters for the East Coast)
Also called “salt ponds” (protected under the R.I. CZM Plan); SEE HANDOUT
Threatened by boating excesses
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Mangrove Swamps
Found in southern waters, dominated by mangrove trees (keystone species)
Creates ideal habitat for animal life (see photos)
Protection from wave action; high organic content
High biodiversity
Complex food chain
Rocky Intertidal Zone
Rocky intertidal zone exists between high and low tide (area below low tide line is called the subtidal zone)
Rock pools (also called tide pools) form between rocks
Challenges to Organisms
How to cling to rocks in strong wave action
How to withstand desiccation in summer low tides
How to deal with salinity variation in summer (increased) or in spring/fall storms (diluted)
Home to coelenterates (sea anemones), molluscs (snails, mussels), crustaceans (crabs, lobsters, gammarids, copepods), echinoderms (starfish, sea cucumbers)
Green, red, and brown algae common
Examples of Rock Pool Algae: Cladophora, Polysiphonia, Fucus, Ascophyllum
High diversity of species and interactions among the inhabitants, with elaborate food chains
Coral Reefs
Coral Reefs have very high biotic diversity, especially in tropical waters
Every kingdom represented, with dominance by the coral animals (coelenterates) and their symbiotic algae
Rich in fish life, occupying every possible niche on the reef
Complex food web, with many behavioral adaptations for sharing the reef
Coral reefs endangered throughout the world
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Summary
Estuarine environments have high biotic diversity, and are highly adaptable
Characterized by changing dynamics (salinity, tidal exchange, temperature)
Feature highly complex food webs and behavioral interconnections
Important support systems for coastal regions; support deep water fisheries
Glossary of terms
Seagrass Community
Tidal Mudflats
Coastal Ponds
Salt Ponds
Mangrove Swamps
Rock Pools
Coral reefs
Benthos
Productivity
Keystone species
Biotic diversity
Tidal mixing
Red tides
Toxic dinoflagellates
Phytoplankton
Zooplankton

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copyright
Gaytha A. Langlois, Ph.D., 2002
Bryant College, Smithfield, RI 02917
e-mail: langlois@bryant.edu
Last Updated: November 2002