Coral Reef Ecosystems - Learn and Act

What is Coral?


Corals are composed of thin plates, or layers, of calcium carbonate secreted over time by hundreds of soft bodied animals called coral polyps. Polyps range in size from a pinhead to a foot in length. Each polyp lives in a symbiotic relationship with a host zooxanthellae that gives the coral its color. Zooxanthellae take in carbon dioxide, process it through photosynthesis, and give off oxygen and other important nutrients that are then used by the host polyp. As in all photosynthesizing organisms, this means that corals must be exposed to a sufficient amount of sunlight. This confines most corals to shallow waters that are clean and clear.

There are two kinds of corals: hard and soft. Hard corals (Scleractinia), such as brain, star, staghorn, elkhorn and pillar corals have rigid exoskeletons, or corallites, that protect their soft delicate bodies. Soft corals (Gorgonians), such as sea fans, sea whips, and sea rods, sway with the currents and lack an exoskeleton.


What is a coral reef?

Coral reefs are one of the most biologically diverse ecosystems on earth, rivaled only by tropical rain forests. They are made up not only of hard and soft corals, but also sponges, crustaceans, mollusks, fish, sea turtles, sharks, dolphins and much more. Competition for resources such as food, space and sunlight are some of the primary factors in determining the abundances and diversity of organisms on a reef. Each component of a coral reef is dependent upon and interconnected with countless other plants, animals and organisms. This means that fluctuations in the abundance of one species can drastically alter both the diversity and abundances of others. While natural causes such as hurricanes and other large storm events can be the stimulus for such alterations, it is more commonly anthropological forces that effect these types of shifts in the ecosystem.

For example, overfishing of herbivorous fish often results in increased growth of algae and sea grasses. This generally results in an increase in other herbivorous marine life, such as sea urchins. Over time all ecosystems will naturally establish these types of balances between predators and prey and organisms in competition for similar resources. The question is how long those balances take to establish and what other reef relationships they affect.


What is the coral reef ecosystem?

The health, abundance and diversity of the organisms that make up a coral reef is directly linked to the surrounding terrestrial and marine environments. Mangrove forests and seagrass beds are two of the most important facets of the greater coral reef ecosystem. Mangroves are salt-tolerant trees that grow along tropical and sub-tropical coasts. Their complex root systems help stabilize the shore line, while filtering pollutants and producing nutrients. Their submerged roots and detritus provide nursery, breeding, and feeding grounds for invertebrates, fish, birds, and other marine life. Many of the animals raised in mangroves migrate to coral reefs for food, spawning and habitat.

Seagrasses are flowering plants that often form meadows between mangrove habitats and coral reefs. They form the foundation of many food webs, providing nutrients for everything from sea urchins and snails to sea turtles and manatees. Seagrass also provides protection and shelter for commercially valuable species such as stone crabs, snappers and lobsters. Additionally, they filter the water column, prevent seabed erosion, and release oxygen essential for most marine life.

The ecosystem services of mangroves and seagrass are vital to the long term health of coral reefs.

Source: http://reefrelief.org/


There is another very important element of the reef ecosystem that is often over looked: the land. Pollutants, nutrients and litter enter near shore waters through rivers, streams, underground seepage, waste water and storm water runnoff. Even areas hundreds of miles from the coast can effect the clarity and quality of water flowing to the reef. It does not matter how far removed a pollutant may seem, it all flows down stream and it can all impact our marine environment and our reefs.

Oysters - Here today gone tomorrow

The word oyster is used as a common name for a number of distinct groups of bivalve molluscs which live in marine or brackish habitats. A new, wide-ranging survey that compares the past and present condition of oyster reefs around the world finds that more than 90 percent of former reefs have been lost in most of the bays and ecoregions where the prized molluscs were formerly abundant. In many places, such as the Wadden Sea in Europe and Narragansett Bay, oysters are rated "functionally extinct," with fewer than 1 percent of their former reefs persisting. The declines are in most cases a result of over harvesting of wild populations and disease, often exacerbated by the introduction of non-native species. Oysters have fueled coastal economies for centuries, and were once astoundingly abundant in favored areas.

Some kinds of oyster are commonly consumed by humans, cooked or raw. Other kinds, such as pearl oysters, are not.


Oysters are filter feeders, drawing water in over their gills through the beating of cilia. Suspended plankton and particles are trapped in the mucus of a gill, and from there are transported to the mouth, where they are eaten, digested. Oysters feed most actively at temperatures above 50 °F. An oyster can filter up to 1.3 US gallon of water per hour. Chesapeake Bay's once flourishing oyster population historically filtered excess nutrients from the estuary's entire water volume every three to four days.

In the early 19th century, oysters were cheap and mainly eaten by the working class. Throughout the 19th century, oyster beds in New York harbor became the largest source of oysters worldwide. On any day in the late 19th century, six million oysters could be found on barges tied up along the city’s waterfront. Oysters were naturally quite popular in New York City, and helped initiate the city’s restaurant trade. New York’s oystermen became skilled cultivators of their beds, which provided employment for hundreds of workers and nutritious food for thousands. Eventually, rising demand exhausted many of the beds. To increase production, they introduced foreign species, which brought disease, when combined with effluent and increasing sedimentation from erosion, which destroyed most of the beds by the early 20th century.

Oysters’ popularity has put an ever-increasing demands on wild oyster stocks. This scarcity increased prices, converting them from their original role as working class food to their current status as an expensive delicacy.

The new survey is published in the February issue of BioScience, the journal of the American Institute of Biological Sciences. It was conducted by an international team led by Michael W. Beck of The Nature Conservancy and the University of California, Santa Cruz. Beck's team examined oyster reefs across 144 bays and 44 ecoregions. It also studied historical records as well as national catch statistics. The survey suggests that about 85 percent of reefs worldwide have now been lost. The BioScience authors rate the condition of oysters as "poor" overall.

Most of the world's harvest of native oysters comes from just five ecoregions in North America, but even there, the condition of reefs is "poor" or worse, except in the Gulf of Mexico. Oyster fisheries there are "probably the last opportunity to achieve large-scale oyster reef conservation and sustainable fisheries," Beck and his coauthors write.

Oysters provide important ecosystem services, such as water filtration, as well as food for people. The survey team argues for improved mapping efforts and the removal of incentives to over-exploitation. It also recommends that harvesting and further reef destruction should not be allowed wherever oysters are at less than 10 percent of their former abundance, unless it can be shown that these activities do not substantially affect reef recovery.

Source: http://www.enn.com/