Marine Ecosystem

Marine Ecosystem

Marine Ecosystem

Marine ecosystems are a part of the largest aquatic system on the planet, covering over 70% of the Earth’s surface. The habitats that make up this vast system range from the productive nearshore regions to the barren ocean floor.

Marine EcosystemMarine ecosystems are home to a host of different species ranging from tiny planktonic organisms that comprise the base of the marine food web (i.e., phytoplankton and zooplankton) to large marine mammals like the whales, manatees, and seals. In addition, many fish species reside in marine ecosystems including flounder, scup, sea bass, monkfish, squid, mackerel, butterfish, and spiny dogfish. Birds are also plentiful including shorebirds, gulls, wading birds, and terns. Some marine animals are also endangered including whales, turtles, etc. In summary, many animal species rely on marine ecosystems for both food and shelter from predators.

Marine ecosystems contain several unique qualities that set them apart from other aquatic ecosystems, the key factor being the presence of dissolved compounds in seawater, particularly salts. This total gram weight of dissolved substances (salts) in one kg of seawater is referred to as salinity. In general 85% of the dissolved substances are Sodium (Na) and Chlorine (Cl) in seawater. On average seawater has a salinity of 35 parts per thousand grams (ppt) of water. These dissolved compounds give seawater its distinctive “salty” taste, affect species composition of particular marine habitats, and prevent oceans from freezing during the winter. Daily changes in factors such as weather, currents, and seasons as well as variations in climate and location will cause salinity levels to vary among different marine ecosystems.


The emerging science of Marine Conservation Biology aims to address the rapidly deteriorating state of marine life by applying science to marine conservation. This exciting new field was born following the First Symposium on Marine Conservation Biology held during the 1997 annual meeting of the Society for Conservation Biology.

Marine Conservation Biology, like Conservation Biology, is a multi-disciplinary approach to providing the data needed to prevent the loss of marine biodiversity. Data on the threats to the marine environment are urgently needed to inform policymakers and other stakeholders on the most critical problems that need to be addressed. The study of marine conservation biology facilitates the cross-pollination of a number of disciplines in marine science including marine biology, ecology, ichthyology, oceanography, biological oceanography, and others so that scientific data can be used to help solve problems effectively and sustainably.

The list of marine species listed as threatened or in danger of extinction grows longer every year. The world’s coral reefs, home to the greatest biodiversity of marine fishes, are deteriorating due to destructive fishing practices and bleaching. Mercury levels in many commercially fished species are at an all time high. Dead zones and algae blooms are increasing in both size and number.

Global Marine Biological Diversity: A Strategy for Building Conservation into Decision Making

In 1989, the Center for Marine Conservation (now The Ocean Conservancy) joined a large group of international organizations in developing a Global Biodiversity Strategy (World Resources Institute et al. 1992). This companion volume, the work of 106 authors – marine biologists, oceanographers, economists, lawyers, government officials, environmentalists, and others – has been called the most comprehensive book on marine conservation. It presents, for the first time, basic principles of marine conservation for decision makers in governments, industries, and conservation organizations and for marine resource managers, students, and all others concerned with protecting our vital ocean resources.


Until recently, humankind seemed to view the ocean as a source of infinite resources. Its vast size and depth and unexplored frontiers made the ocean appear invulnerable to overexploitation. The truth is that the populations of many species are decreasing at an unsustainable rate, and the number of species listed as endangered from marine life families such as whales, dolphins, manatees and dugongs, salmon, seabirds, sea turtles, and sharks to name a few, are on the rise. The threats to marine species are difficult to perceive because marine animals are not as visible as animals on land. But unfortunately, marine creatures are equally, if not more, vulnerable to problems such as habitat destruction and overexploitation. Shallow water animals that breathe air, like turtles, manatees, dugongs, and whales are often hit by boats and caught in fishing gear. Species such as turtles that lay their eggs on land often lose their nurseries due to coastal development. Animals that have taken millions of years to evolve, that are invaluable to all ecosystems, have and continue to vanish from places where they once flourished.

The Endangered Species Act

The Endangered Species Preservation Act of 1966 was established in the U.S. to protect species facing possible extinction, but it only covers native species and the extent to which they are protected is extremely limited. In 1969, the Departments of the Interior, Agriculture, and Defense passed the Endangered Species Conservation Act to prevent mass extinctions of certain species. The use of endangered species by humans for food, fur, and other commercial uses was outlawed by this act and by the Marine Mammal Protection Act of 1972. In 1973, the Convention on International Trade in Endangered Species (CITES) of Wild Fauna and Flora was implemented to cut back on the trade of plants and animals in trouble. The 1973 Endangered Species Act is one of the most significant environmental laws in America and defines endangered or threatened species, puts plants and invertebrates under protection, requires federal agencies to start programs to conserve important habitats, creates a wide umbrella of laws against hunting for endangered species, and matches contributions from individual states towards the project. The United States Fish and Wildlife Service (FWS) and the National Marine Fisheries Service (NMFS) are responsible for the enforcement of the Endangered Species Act.

Marine mammals

Marine mammals close to becoming an endangered species are categorized under threatened. These include: Eastern Stock of the Steller sea lion, Guadalupe fur seal, and the California sea otter.

Pinnipeds are seals, sea lions or walruses but are taxonomically relatives of bears, dogs, raccoons, otters or weasels. The families under pinnipedia include Phocidae, Otariidae and Odobenidae which are earless seals, fur seals or sea lions, and walrus respectively. The main reason for the loss of many pinnipeds is the amount of commercial fishing that took place from the 1700’s up to the 1900’s. Other reasons include the development of coastline and lack of fish due to overfishing.

Marine invertebrates

Marine invertebrates and plants are currently listed under the “candidates or species of concern” category in the Endangered Species Act due to a lack of information or time. These include Brachiopods, Corals, Mollusks, and various plant life. Brachiopods are invertebrates that live on the seafloor and feed through a filter appendage. They are attached to objects in the ocean and resemble a clam. Brachiopods reached the peak of their numbers in the Paleozoic era and were reduced greatly during the Permo-Triassic mass extinction. The two classes or types of brachiopods are the Inarticulata and the Articulata. Reasons for decline in number of brachiopods include habitat destruction, overfishing, pollution and sediment accumulation, general vulnerability to stress, and small numbers.

Marine Plants

Most marine plants include types of seagrass, types of mangroves and types of algae. Mangroves and seagrasses are flowering plants and use pollen to reproduce. They are often found close to the coast. Algae can be anything from tiny phytoplankton to huge seaweeds. So far, Johnson’s seagrass is listed as threatened, although many other plants should be on the list. Plants are mostly lost when humans change the habitat, natural events change the environment or oxygen is used up by organisms thriving in nutrient-enriched areas (also often caused by humans).

Sea Turtles

Sea turtles are another animal threatened by extinction in the oceans. With aerodynamic bodies, oversized flippers and the ability to breathe air, these unique animals live in tropical or subtropical oceans all over the planet. The United States is visited by six of the seven types of sea turtles including the green, hawksbill, Kemp’s ridley, leatherback, loggerhead and the olive ridley. Sea turtles rely on undisturbed beaches to lay eggs and can travel huge distances to feed or nest.

Marine and anadromous fish

Marine and anadromous (born in freshwater first) fish are also under protection by the NOAA. Anadromous fish start out in freshwater, go to saltwater and then return to freshwater. Marine fish spend their entire lives in saltwater. Most fish listed under the Endangered Species Act are Pacific salmonids and have been listed as Evolutionary Significant Units. Other types of fish listed are Atlantic salmon, shortnose sturgeon, smalltooth.


The Importance of Coral Reefs

Coral reefs are a precious resource in the ocean because of their beauty and biodiversity. Coral reefs provide shelter for a wide variety of marine life, they provide humans with recreation, they are a valuable source of organisms for potential medicines, they create sand for beaches, and serve as a buffer for shorelines. Coral reefs are built by millions of coral polyps, small colonial animals resembling overturned jellyfish that use excess carbon dioxide in the water from the atmosphere and turn it into limestone.

The Variety of Coral Reefs

Coral reefs can be found in both shallow and deep waters and are classified into 3 categories:

In 1999, a deep coral reef 60 m below the surface was discovered by the United States Geological Survey (USGS) Center for Coastal and Wetland Studies near Pulley Ridge, an underwater barrier island west of the Dry Tortugas National Park off the southern coast of Florida. The Pulley Ridge reef absorbs more light by increasing surface area and growing flat rather than the usual vertical growth seen in shallower coral reefs. Other deep water reefs include the Darwin Mounds and the Mingulay reef complex. More is known about shallow water coral reefs in tropical zones than deep-water reefs discovered recently, however much research into these unique ecosystems is being conducted.

Tropical Coral Reefs

Tropical Coral reefs are biotic reefs formed in tropical waters by live organisms such as calcareous algae (including red algae) and corals. In contrast, abiotic reefs are formed by the deposit of sand and other materials in shallow water. Organisms responsible for building tropical (biotic) coral reefs can only grow at 20-28°C, so although coral reefs live in all oceans, most are found between the Tropic of Capricorn and the Tropic of Cancer. The best growing habitat for coral reefs is a clear-water photic zone less than 50 m deep where light shines down and microscopic algae can best provide photosynthesis for the corals.

The wide array of coral reef forms includes the Apron reef, the Fringing reef, the Barrier reef, the Patch reef, the Ribbon reef, the Table reef and the Atoll reef. The Apron and Fringe reef both reach down and out from the shore point or peninsula although the Apron reef is typically not as steep as the Fringe reef. Barrier reefs, like the Great Barrier Reef, are separated from the shore by lagoons. An Atoll reef surrounds a lagoon in a circular or uninterrupted fashion and is different from the others because there is no island in the middle.

A Critical Situation

Coral reefs are extremely sensitive to changes in light, temperature (bleaching), overfishing, damaging fishing practices, pollution, and excess sediment from development and erosion. Reefs in Southeast Asia are most at risk of damage due to these factors. Human activity is one of the greatest threats to coral reefs, particularly the destruction of mangrove forests that naturally absorb sediment and nutrients that can suffocate coral reefs with silt and algae blooms.

Cyanide fishing in the Indonesian and Philippine coral reefs of South Asia stuns and injures valuable fish. Although 85% of the world’s aquarium fish are captured with this destructive method, they suffer a 90% mortality rate usually several weeks after they have been poisoned by cyanide. Unfortunately, fishermen in developing countries depend on reef fish for income to provide for their families; however illegal fishing practices and overfishing is depleting fish stocks in these areas rapidly threatening the livelihood of these local populations. Fishermen hit the coral reefs with crowbars to shake out stunned fish and they also even fish with dynamite, which often destroys every living thing on the reef. Many reefs once teeming with life are now wastelands that even the most vigorous conservation efforts can’t begin to restore.

The effects of El Niño during 1998 and 2004 are an example of the natural factors that influence the growth of coral reefs. During this El Niño, sea temperatures rose and the many coral reefs were bleached or obliterated. Coral bleaching occurs when the single-celled algae vital for coral reef survival and known as symbiotic zooxanthellae are rejected from the coral, soft corals, some sponges and even Tridacna clams. The pigment containing organisms are lost as temperature or stress level due to increased light reaches intolerable levels. As temperatures return to normal, some reefs can recover within several weeks or months. However, equilibrium may not be restored due to global warming and the bleaching effect exposes corals to white and black band diseases. There is some evidence that global warming may actually add to the productivity of an ecosystem through an increase in carbon dioxide and higher temperatures, though the validity of this evidence remains to be seen.


Salt Marshes, estuaries, and mangrove forests are unique ecosystems in semi-sheltered areas near the Ocean coastline. These areas often serve as nursing grounds where young marine life is protected during development.


A salt marsh is a marshy area found near estuaries and sounds. The water in salt marshes varies from completely saturated with salt to freshwater. Estuaries are partly sheltered areas found near river mouths where fresh water mixes with seawater. Both salt marshes and estuaries are affected by high and low tides. Mangrove forests are found in the intertidal zone of tropical coastlines and estuaries, commonly in the tropical coastal areas of Australia, Africa, North and South America between 32-degree north and 38 degrees south. Mangrove forests are made up out different types of mangrove trees and a wide variety of plants. The mangrove tree is a tree with roots and leaves that filter salt and other materials. Different mangrove species are adapted to serve different functions depending on their location. Mangroves are so good at expelling salt, that in some species the water in the roots is fit to drink.

The Salt Marsh

Many salt marshes are located in the southern United States, particularly in South Carolina with more than 344,500 acres, which is more marshland than any other state on the Atlantic coast. Marine life in salt marshes is incredibly diverse and abundant. Salt marsh species rely on the decay of marsh plants to supply a steady source of food in the form organic material, or detritus, resulting from the decomposition of plants and animals. Most marsh plants flourish in the spring and summer, growing taller and more abundant. In the fall they begin to decay and are distributed within the same marsh, or into other marshes and mudflats where they become the first level of the food chain. Microscopic organisms like bacteria, small algae, and fungi help decompose the detritus resulting from salt marsh plants. These microorganisms and the remaining decomposing plant material become an ideal source of food for bottom-dwellers in salt marshes like worms, fishes, crabs, and shrimps. The cycle continues when the feces of the bottom-dwellers is cleaned up by microorganisms. Anything left over is great fertilizer for the next spring, when the marsh plants fill the marsh with green lush leaves.

Large Estuaries

The largest estuary in the United States is the Chesapeake Bay, located off of the Atlantic Ocean bordered by Virginia and Maryland, although the watershed covers 165,800 km in the District of Columbia and New York, Pennsylvania, Delaware, Maryland, West Virginia, and Virgina. Over 150 streams and rivers drain into the 304 km long Chesapeake Bay. Like many other estuaries, the Bay was once a valley with a river running through it, until the sea level rose or the Chesapeake Bay impact crater was formed by the bolide impact event towards the end of the Eocene period about 35.5 million years ago. At its narrowest section, the Chesapeake Bay estuary is only 6.9 km wide. The Bay is extremely shallow. A person of average height could probably walk across the 2,800 km of the bay. The average depth of the Bay is less than 9 meters.

The Amazing Mangrove Forest

A crucial component of the coastal ecosystem and a powerful form of erosion control, mangrove trees provide shelter and nutrients to their ecosystems. Like salt marshes, these shallow, nutrient rich areas provide shelter to young fish, shrimps, crabs and mollusks where they can live safely and develop. Hundreds of birds species migrate and nest in mangrove forests such as those found in Belize that provide a home to over 500 species of birds. Other animals that inhabit mangrove forests include manatees, sea turtles, fishing cats, monitor lizards and mud-skipper fish. Not only do mangrove trees directly support countless food webs, they are also indirectly responsible for the survival of the most primary planktonic and epiphytic algal food chains, which in turn provide carbon for the mangrove tree. Mangroves protect coastlines from storm damage, wave effects, and erosion. Erosion is avoided when mangroves take on the force of the waves and help replace lost sediment by catching suspended particles in their root system while simultaneously keeping that same silt from covering (and damaging) coral reefs and sea grass beds.



A beach is defined as an accumulation of sediment-usually sand or gravel-that occupies a portion of the coast. The active beach, the area of loose sediment subject to transport by wind, waves, and currents, is divided into three regions: the backshore, the foreshore, and the offshore . The active beach is backed by the coastal upland, which can be a dune, a cliff, a soil embankment, a fossil berm, or an engineering structure such as a seawall or a revetment. Common geomorphic features of the beach include berms, scarps, and offshore sand bars .

Sand Dunes

Dunes are accumulations of wind-blown sand. Although some dunes are bare, most are vegetated with coastal plants, which help stabilize the dune . Vegetation traps wind-blown sand and then grows up through the new sand accumulation. This process is repeated to build larger dunes. The thick root system of native plants slows coastal erosion during high-wave events and helps trap wave- and wind-deposited sand during post-event recovery. Many dunes are host to burial sites and are legitimate environmental systems that support specific ecosystems. Because of their cultural and environmental sensitivity, many dunes are worthy of all due protection.

Coral Reef Ecosystems

Coral reefs are also important components of the beach system. Reefs are natural breakwaters; they absorb much of the incoming wave energy and help protect the shoreline from wave attack. Without the wave buffering and sand production that coral reefs provide, rates of coastal erosion and beach loss would be significantly higher.

Furthermore, coral reefs provide habitat for a rich diversity of marine life . Several reef organisms build their skeletons and shells out of calcium carbonate. When these organisms die, their skeletal remains are transported to the beach or are cemented into the framework of the reef. Most of the light-colored sand on beaches derives from coral reefs.


Preliminary examination of a report on shoreline changes from 1949 to 1989 suggests that 62% of the sandy shoreline studied on Maui is eroding at an average rate of 1.25 ft/yr , and as much as 30% of Maui’s shoreline has experienced beach loss or significant narrowing . Based on field and photographic observations, nearly all of this beach degradation is in front of or adjacent to shoreline armoring such as seawalls and revetments.

Typically, these armoring structures are erected when coastal erosion threatens beachfront development. Armoring the shoreline usually halts coastal erosion and protects property and structures, but on shorelines undergoing long-term retreat, it often leads to beach loss . The impact that armoring has on the adjoining beach creates a conflict between the rights of coastal property owners to protect their land and the rights of the public to utilize the beach resource.

Coastal Erosion

Sea-level rise, wave and current impacts, and sediment deficiencies drive coastal erosion . Sea-level rise, currently averaging about 2.5 cm/decade on Maui, causes the littoral system to shift landward by eroding the upland area-usually a coastal dune or the coastal plain. This natural process, known as coastal erosion, has occurred for millennia as sea level has risen nearly 110 meters since the last ice age. The retreat of the shoreline-and associated loss of coastal lands-is the natural response of the beach to rising sea levels and has been the underlying premise of coastal engineering theory for over thirty years . The influx of sediment released to the active beach by erosion of the coastal upland helps maintain beach width.

Certain human activities create significant sediment deficiencies and aggravate coastal erosion. These include sand mining, dune alteration (e.g., dune grading and building on dunes), construction of shoreline structures such as seawalls, revetments, and groins, degradation of coral reefs, and construction of harbors and navigational channels.

Sand mining on the beach removes sediment from the beach system leading to beach narrowing and deflation. Up until the early 1970’s, large volumes of sand were mined from beaches around Maui to provide cement aggregate for construction and lime for sugar cane processing.

Beach Loss

Armoring shorelines undergoing long-term retreat with structures such as revetments and seawalls halts coastal erosion, but refocuses the erosion onto the beach in front of the structure. This causes beach narrowing, a decrease in the usable beach width, and beach loss, the volumetric loss of sand from the active beach . Coastal armoring often aggravates erosion along downdrift properties by decreasing the supply of sediment to downdrift areas.

The site-specific history of coastal processes for a particular beach segment must be assessed to help guide the most effective beach management practices. Certain management tools-beach nourishment and dune restoration, for example-can counteract coastal erosion and beach loss. Other management tools-such as requiring sufficient building setbacks and wiser construction codes-can delay or prevent the need to armor the shoreline to protect beachfront development. Hence, coastal erosion does not necessarily present a conflict between coastal property owners and the public. It can be mitigated through effective beach management strategies.

Reef degradation

Harbor and navigational channel construction compromise the reef’s wave buffering capacity. If a portion of the reef is dredged during harbor and channel construction, larger waves can reach the shoreline and accelerate erosion.

Many other human activities degrade water quality and harm coral reef ecosystems. Since most carbonate sand ultimately derives from the coral reef ecosystem, poor water quality reduces the amount of sand produced by the reef and delivered to the beach. Impacts to water quality caused by human activities include: siltation, nutrient loading, and urban runoff. In addition, over-fishing can deplete the reef ecosystem of certain species of fish and upset the ecological balance necessary for healthy coral reef ecosystems, and introduced species have disrupted the preexisting food web, which also disrupts the reef ecosystem. Finally, anchoring on reefs causes physical damage to coral, as does standing on or touching these sensitive creatures.

In some cases, coastal erosion can have adverse effects on water quality and harm the reef. The erosion of dirt embankments or coastlines that have been artificially filled releases fine sediments to the nearshore waters. Furthermore, the significant increase in drainage outlets for recent developments and concrete channelization for flood protection have both had significant impacts on near-shore water quality and sediment loads.


Sustainable tourism encompasses the responsible use of natural resources for recreation. This includes eco-friendly boating, scuba-diving, fishing, and tourism.

Ecotourism is defined as leisure travel that provides tourists with an educational and adventurous experience visiting complex and fascinating ecosystems and their associated cultures and traditions. The concept of ecotourism began in the late 1980’s and increased in popularity in 2002 during the United Nations “International Year of Ecotourism.” According to environmental and other organizations, ecotourism should have a minimal impact on both the environment and the culture. Ecotourism should inform tourists about what’s needed to sustain the environment they’re visiting, and should also help local populations understand the importance and value of their home. Ecotourism can also help foster a sense of environmental stewardship by encouraging travelers to be mindful of wasting resources and polluting the environment. Ecotourism can also help local economies by generating revenue and jobs, which further encourages the local population to preserve its environment.

A good ecotourism operation will strive to support the community and encourage travelers to be culturally sensitive by training and employing local people and by purchasing local supplies and services to further stimulate the economy. Increasingly, national governments such as Costa Rica and Australia are supporting the ecotourism trade for its benefit to both their country and their visitors. Tourist regions in many countries now rely on ecotourism as the primary source of revenue.

The education and good practices taught by ecotourism may also help foster sustainable development in a world increasingly faced by destructive practices such as clear-cutting forests and poor land-use policies that destroy habitats. Good ecotourism should ideally support criteria such as:

Although the overall concept and intent of sustainable tourism is positive, the industry is not without its critics largely due to companies who abuse the concept of ecotourism to take advantage of the wealth generated by the interest in ecotourism. Some ecotourism operators have been accused of masking their environmentally destructive practices by marketing their businesses as ecotourism.

With time, the standards for good ecotourism will be established and both travelers and the industry will be aware of what constitutes an ecologically and culturally sensitive operation.


Temperature and density share an inverse relationship. As temperature increases, the space between water molecules—also known as density, decreases. If the temperature of a liquid decreases the density will increase. At a temperature of 0°C with zero movement, water freezes and is at peak density.

Salinity and density share a positive relationship. As density increases, the amount of salts in the water—also known as salinity, increases. Various events can contribute to change in the density of seawater.

Salinity can decrease from the melting of polar ice or increase from the freezing of polar ice. Evaporation increases salinity and density while the addition of freshwater decreases salinity and density.

Seawater is saturated with salts at 35 ppt and at 4°C the salinity causes the density to actually be 1.0278 g/cm3. This slightly heavier density is another contributing factor to upwelling as it causes the water molecules to roll over each other.

Temperatures range from -2°C to 28°C in most cases but are hotter near hydrothermal vents or closer to land. Salinity is usually 35 ppt (parts per thousand), but can range from 28-41 ppt and is highest in the northern Red Sea.

During the summer, the phytoplankton absorb most of the dissolved inorganic nutrients from the surface waters and are consumed by the zooplankton, decreasing the rate of photosynthesis. Vertical mixing ceases and phytoplankton, which remain in the upper layers, become nutrient-limited. The cycle starts all over in the fall when the surface water cools, churning the deeper, nutrient-rich waters into the depleted surface waters. Nutrients become available again and the phytoplankton blooms in great quantity during the spring after the intense winter mixing. Fall and summer are the least plentiful months due to the less active summer waters.


What does the future hold for the ocean and marine life…? We hope to see a healthy ocean free of pollution and teeming with life. Clean beaches. Magnificently colored coral reefs crowded with a multitude of fish, octopuses, squid, and sharks. Ocean waters free of excess carbon dioxide which allows for healthy acidity levels so that clams and snails can build their shells and corals can continue to grow… an ocean filled with the proper numbers of schools of tuna, cod, grouper, snappers, mackerel… pods of whales and dolphins free of the threat of harpoons and nets…. The future ocean has few dead zones with waters restored to their healthy oxygen-rich state… in balance once again. Mangroves and estuaries restored providing the much needed marine life nurseries with happy manatees and dugongs… beaches filled with the nests of sea turtles and coastlines crowded with hatchlings as they find their way back to the sea each year.

The application of sound science and aggressive conservation will ensure that this is truly what the future holds. Increased understanding of the ocean and marine life and educating the planet will help cultivate a sea ethic and ensure a sustainable future for the ocean.

“Never doubt that a small group of thoughtful, committed citizens can change the world; indeed, it’s the only thing that ever has.” – Margaret Mead

“If we have a hope of really understanding our place in nature and of carving out a place for ourselves that is sustainable, it’s primarily because of the new level of communication. It used to be, ‘What you don’t have in your mind, you have on your shelf.’ But now we have the Web.” – Sylvia Earle.

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