Definition  Estuaries: semi-enclosed areas where fresh water and seawater mix and meet  Most productive environments on earth  Most affected by humans  Many cities are built along them  Ex. New York City

About Them  Salt-marsh grasses and mangroves thrive along the shore  Many worms, clams, and shrimps burrow in the muddy bottom of estuaries  Snails and crabs crawl along the shore  Fish swim in the plankton-rich water

Seagrass Mangrove

About Estuaries  Scattered along the shores of all the oceans  Can be called lagoons or bays  Share a mixing of fresh water with the sea in a partially enclosed section of the coast

Lagoon Bay

Types of Estuaries  Coastal plain: formed when the sea invaded lowland and river mouths  Most common type  Found at the mouths of rivers  Ex. Chesapeake Bay, mouth of the Delaware River

 Bar-built: accumulation of sediment along the coast that builds up  Sand bars and barrier islands formed  Act as a wall between the ocean and fresh water from rivers  Ex. Outer Banks in North Carolina

 Broad well-developed estuaries are common features of passive margins  Flat coastal plains  Wide continental shelves  What about passive margins makes it a good place for estuaries?

Physical Characteristics  Salinity- fluctuates dramatically from place to place  Also changes from time to time  Dense seawater stays on bottom  Less dense freshwater from rivers stays on top  Salt wedge: a layer of denser, saltier seawater that flows along the bottom of estuaries

Physical Factors cont.  Substrate- sand or soft mud  Mud contains a rich amount of organic materials and detritus  Allows for plants to take root  Water temperature- varies because of shallow depths and large surface area  Marine organisms must be even better adapted to adjust to these even more extreme temperature changes  Clarity- large amounts of suspended sediment reduce water clarity  What happens when clarity is reduced?

Dealing with Excess Salinity  Marine organisms need to maintain proper salt and water balance in their cells  Greatest challenge for marine organisms  Many organisms pump excess salt out of their bodies  Grasses and salt-marsh plants have high salt tolerance  Succulents: fleshy plants that accumulate large amounts of water in leaves to dilute salt

Cordgrass have special glands in their leaves that excrete excess salts

Pickle weed are succulents that accumulate large amounts of water in leaves

Adapting to Mud  Most animals either burrow or live in permanent tubes beneath sediment surface  Clams extend siphons through mud to get water for food and oxygen  Organisms tend to be stationary or slow- moving

Types of Estuarine Communities

 Estuarine communities consist of few species  Few species represented by many individuals of that species  Plankton, fish, and birds come in and leave with the tide  Plankton: tiny organisms that drift in the water

Open Water  Murky water restricts light going through water  Little photosynthesis able to occur  Plankton are flushed in and out with the tides  Cities located along them  Provides rich supply of fish and shellfish  Fish and shrimp use it as a nursery for their young  Take advantage of abundant food and safety from predators

 Variety of fish  Breed out at sea and then use estuaries as nurseries  Many species of flat fish  Anchovies, mullets, croakers  Few fish species spend their lives in an estuary  Killifish is only exception

Anchovies

Mullets

Killifish

Mudflats  Estuaries where bottom becomes exposed at low tide  Organisms must deal with desiccation, wide variations in temperature, and predators  Large tidal ranges and a gently sloping bottom  Organisms must be able to handle regular changes in salinity

 Few hardy seaweeds that manage to grow on shells  Green algae  Sea lettuce  Red alga  Abundance of bacteria  decompose huge amounts of organic matter brought in by rivers and tides

Green algae Sea lettuce

 Dominant animals- infauna  Very few Epifauna  Feeding: feed on detritus  Deposit and suspension feeders  Can be filter feeders  Suspension feeders have difficulty  filtering mechanisms tend to become clogged with sediment  Animals are important for commercial use  humans eat them

Animals in Mudflats  Quahog or hard clam  Soft-shelled clam  Razor clam  Bent-nosed clam

 Ghost shrimp  Mud shrimp  Fiddler crab

Birds and Fish  Fishes and birds are most important predators in mudflats  Fish swim in at high tide  Birds gather at low tide  Estuaries are important stopovers for migratory birds  Bird’s bill length determines which type of burrowing animal it eats

 Sandpipers- rely on bills probing sand as they walk around  Plovers- use eyesight to detect slight movements on mud  Herons and egrets- catch fish and shrimps

Salt Marsh  Estuaries that are bordered by grassy areas and extend inland from mudflats  Become flooded at high tide  Wetland: collective group of salt marshes  Develop along sheltered open coasts  Develop as long as wave action is minimal  allows sediment to accumulate  Tidal creeks, freshwater streams, and shallow pools cut through marshes

 Salt marsh communities dominated by few hardy grasses and other salt-tolerant land plants  Cordgrasses most common  Found where seaward limit of marsh meets the mudflats  Help stabilize soil by decreasing effects of wave action  Pickle weeds are also found

 Animals:  Nematodes  Crabs  Ribbed mussel  Killifish  Juvenile silversides  Birds feed and nest in salt marshes  Ospreys and raccoons are common visitors

Nematode- roundworm Ribbed mussel Silverside

Mangrove Forests  Mangrove: flowering land plants adapted to live in the intertidal zone  Mangals: trees and shrubs that form dense forests  Found in tropical and subtropical regions  Commonly found along the coast of Florida and in the along the coast of islands in the Gulf of Mexico

 Red mangrove- most common species of mangrove along the shores of southern Florida  Lives right along shore  Easily identified by its propped up roots  act as silts

 Many animals live among the mangroves  Crabs feed on abundant leaf litter that accumulates from trees  Mudskippers- burrow in the mud and spend most of their time out of water skipping over mud and crawling up mangrove roots to catch insects and crabs  Sponges attach to roots of mangroves  Birds make homes on the branches and feed on fishes and crabs  Snakes, frogs, lizards, and bats also live among them

Feeding Interactions

 Detritus is the main food source  Distinctive feature- most of the animals feed on dead organic matter  Few herbivores graze on salt-marsh plants  What is an herbivore?  Outwelling: surplus of detritus in exported to open ocean  Serves a valuable source of food and nutrients to other ecosystems

The End!