Estuaries and Coral Reefs

Tahir A. Baig

Estuary An estuary is a partially enclosed body of water along the coast where

freshwater from rivers and streams meets and mixes with salt water from

the ocean. Estuaries and the lands surrounding them are places of transition

from land to sea and freshwater to salt water. Although influenced by the

tides, they are protected from the full force of ocean waves, winds, and

storms by such land forms as barrier islands or peninsulas.

An estuary may also be called a bay, lagoon, sound, or slough.

Water continually circulates into and out of an estuary. Tides create the

largest flow of saltwater, while river mouths create the largest flow of

freshwater.

Estuarine environments are among the most productive on earth, creating

more organic matter each year than comparably-sized areas of forest,

grassland, or agricultural land. The tidal, sheltered waters of estuaries also

support unique communities of plants and animals especially adapted for life

at the margin of the sea

Thousands of species of birds, mammals, fish, and other wildlife depend on

estuarine habitats as places to live, feed, and reproduce And many marine

organisms, including most commercially-important species of fish, depend

on estuaries at some point during their development. Because they are

biologically productive, estuaries provide ideal areas for migratory birds to

rest and re-fuel during their long journeys. Because many species of fish

and wildlife rely on the sheltered waters of estuaries as protected

spawning places, estuaries are often called the "nurseries of the sea.

Estuaries have important commercial value and their resources provide

economic benefits for tourism, fisheries, and recreational activities. The

protected coastal waters of estuaries also support important public

infrastructure, serving as harbors and ports vital for shipping and 

transportation.

Estuaries also perform other valuable services. Water draining from uplands

carries sediments, nutrients, and other pollutants to estuaries. As the water

flows through wetlands such as swamps and salt marshes, much of the

sediments and pollutants are filtered out. This filtration process creates

cleaner and clearer water, which benefits both people and marine life.

Wetland plants and soils also act as natural buffers between the land and

ocean, absorbing flood waters and dissipating storm surges. This protects

upland habitat as well as valuable real estate from storm and flood damage.

Salt marsh grasses and other estuarine plants also help prevent erosion and

stabilize shorelines.

Over half the U.S. population lives in coastal areas, including along the

shores of estuaries. Coastal watershed counties provided 69 million jobs and

contributed $7.9 trillion to the Gross Domestic Product in 2007 (National

Ocean Economics Program, 2009).

What happens on the land affects the quality of the water and health of the organisms that live in an estuary if a river or stream flows through an agricultural area, it picks up

fertilizer, manure, and pesticides from farming operations that run off the land after a rainstorm.

As it passes urbanized and suburbanized areas, it gathers fertilizers or pet waste that wash off lawns, untreated sewage from failing septic tanks, wastewater discharges from industrial facilities, sediment from construction sites, and runoff from impervious surfaces like parking lots.

Estuary of the Klamath river in Noortern California River Exe estuary

 River Nith estuary Amazon Estuary

Types of Estuaries There are four different kinds of estuaries, each created a different way:

1) coastal plain estuaries; 2) tectonic estuaries; 3) bar-built estuaries; and 4) fjord estuaries.

Coastal plain estuaries (1) are created when sea levels rise and fill in an existing river valley. The Chesapeake Bay, on the East Coast of the United States, is a coastal plain estuary. 

Tectonic estuary :Tectonic activity, the shifting together and rifting apart of the Earth's crust, creates tectonic estuaries (2). California's San Francisco Bay is a tectonic estuary. 

Bar-built estuaries; When a lagoon or bay is protected from the ocean by a sandbar or barrier island, it is called a bar-built estuary (3).

The Outer Banks, a series of narrow barrier islands in North Carolina and Virginia, create sandy, bar-built estuaries.

Fjord estuaries are a type of estuary created by glaciers. Fjord estuaries occur when glaciers carve out a deep, steep valley. Glaciers retreat and the ocean rushes into fill the narrow, deep depression. Puget Sound is a series of fjord estuaries in the U.S. state of Washington.

Coral Reefs A coral polyp is a tubular saclike animal with a central mouth

surrounded by a ring of tentacles. The end opposite the tentacles,

called the base, is attached to the substrate.

Depending on the species, coral polyps may measure less than an inch

to several inches in diameter (a few millimeters to several centimeters).

One of the largest corals, Fungia (mushroom coral), is a solitary coral

that can extend 10 in. (25 cm) in diameter.

Colonial coral polyps are much smaller and average 0.04 to 0.12 in. (1-3

mm) in diameter.  Coral colonies also vary in size. Some corals form

only small colonies. Others may form colonies several feet (a few

meters) high. Star coral (Montastrea annularis) colonies reach an

average height of 10 to 13 ft. (3-4m).

Staghorn Corals

Mushroom Corals

Maze Corals

Florescent Corals

Black Corals

Spiral Corals

Pillar Corals

Brain Corals

Table Corals

Tiny coral polyps build the massive structure of the reef. There are 4 main types of coral reef: fringing reef; barrier reef; atoll; and

patch reef. As reefs mature, they can develop from fringing reefs to barrier reefs to

atolls Coral reefs are underwater rock outcrops covered by a thin layer of living

coral polyps. These outcrops can be huge, sometimes over a kilometer (1 km = 0.7 miles) thick and hundreds of kilometers in length. But the coral polyps that build these massive structures form a layer only a few millimeters thick (1 mm = approximately 1/32").

Reef-building coral polyps live in a protective shell made from calcium carbonate (CaCO3), and as they divide and grow they form colonies. These colonies form the basic structure of the reef, helped by other organisms, like coralline algae. Building a reef is a slow process because the coral that form reefs grow about 0.3 - 2 cm (5/16 -13/16") each year. It is estimated that coral polyps need about 10 000 years to form a reef, and 100 000 to 30 million years to build a fully mature reef.

In medicine, chemical compounds from corals are used for cancer, AIDS, pain, and other uses. Coral skeletons, e.g. Isididae (Bamboo coral) are also used for bone grafting humans

 The 4 kinds of reef Polyps are only able to build a reef with the help of single-celled

zooxanthellae algae. Polyps provide zooxanthellae with nutrients and

shelter, and receive food in return. Zooxanthellae algae require sunlight

for photosynthesis, and coral reefs usually begin to form in clear, shallow

waters near land because water gradually filters out sunlight with depth.

This relationship with land is used to categorize the different types of coral

reef. 4 main types of reef exist:

A fringing reef forms along the shoreline of most new tropical islands.

This is because the reef building coral animal is one of the few marine

organisms that can survive in the warm, nutrient-poor surface tropical

waters. In fact, the reef building coral (hermatypic) can only survive in

warm, clear ocean waters (such as would be common around a new

oceanic island).

The coral animal reproduces sexually with a microscopic planktonic larval

form that is abundant in tropical waters during coral reproduction. Most of

these larvae never grow to adults because there is no place for them to exist

in the warm surface ocean waters on a solid surface.

They need to attach to a solid surface that will stay in the warm, sunlit, clear

tropical water and most places are already taken … but not on a new island.

So a coral reef forms along the edge of this new island, right next to the

island and is called a fringing reef - the first step in 'classical' coral reef

formation.

A barrier reef It  forms as the oceanic island begins to sink into Earth's crust due to the absence of volcanic

island building forces, the added weight of the coral reef, and erosion at the surface of the island.

As the island sinks, the coral reef continues to grow upward. The coral animals lay down

tremendous amounts of calcium carbonate (in part due to their symbiotic zooxanthellae) in the

form of their skeletons (called corallites). If conditions are good they can usually keep pace with

the sinking island.

Their living tissue remains in the upper part of the reef in the warm, clear, tropical water. The

lower part of the reef is composed of the calcium carbonate skeletons left by the reef building coral.

This upward growth creates a lagoon of water between

the

top of the reef (that started as a fringing reef) and the

sinking

crustal island. The lagoon fills in with eroded material

from both

the reef and the island and is a haven for marine forms

that

require protection from waves and storms.

This barrier reef is generally not a complete circle as it

may

be broken, here and there, by storms.

An atoll forms when the oceanic island sinks below the surface of the

ocean but the coral reef continues to grow upward. The atoll is usually

circular in shape but a broken circle (due to the history of storms). Eroded

reef material may pile up on parts of the reef, creating an area above sea

level, an island called a 'cay.' caye or key, is a small, low-elevation, sandy

island on the surface of a coral reef. Cays may become stabilized enough

(often through plants) to provide a permanent island for buildings. Cays

may also be unstable and move across the reef or disappear.

Patch Reef

These outcrops of coral usually lie within a lagoon.

Atoll showing the island below sea level and a lagoon in the center of the reef.

Heron Island, Australia

How to make an atoll Fringing reefs, barrier reefs and atolls are thought to represent

stages in coral reef formation. Charles Darwin first proposed this theory of coral reef formation in 1842.

Step 1: A fringing reef forms first, and starts growing in the shallow waters close to a tropical island.

Step 2: Over time, the island subsides and the reef grows outwards, and the distance between the land and the reef increases. The fringing reef develops into a barrier reef.

Step 3: If the island completely subsides, all that is left is the reef. The reef retains the approximate shape of the island it grew around, forming a ring enclosing a lagoon. Darwin speculated that underneath each lagoon should be a bed rock base – the remains of the original island. Subsequent drilling into atolls proved this prediction true

Aerial view of the stages of coral reefs (fringing, barrier, atoll).

Importance of corals and coral reefs.

1. Corals remove and recycle carbon dioxide. Excessive amounts of

this gas contribute to global warming.

2. Reefs shelter land from harsh ocean storms and floods.

3. Reefs provide resources for fisheries. Food items include fishes,

crustaceans, and molluscs.

4. Coral reefs attract millions of tourists every year.

5. The coral reef is an intricate ecosystem and contains a diverse

collection of organisms. Without the reef, these organisms would die.

6. Some evidence suggests that the coral reef could potentially

provide important medicines, including anti-cancer drugs and a

compound that blocks ultraviolet rays.

Importance of corals and coral reefs.

7. Coral skeletons are being used as bone substitutes in

reconstructive bone surgery. The pores and channels in certain

corals resemble those found in human bone. Bone tissue and

blood vessels gradually spread into the coral graft. Eventually,

bone replaces most of the coral implant.

8. The coral reef provides a living laboratory. Both students and

scientists can study the interrelationships of organisms and their

environment.