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 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.







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


The Variety of Coral Reefs

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


Tropical Coral Reefs



A Critical Situation


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.



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


Large Estuaries


The Amazing Mangrove Forest




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.




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.



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.


“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.


  1. what is the approximate number of species in a marine ecosystem?



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