3. What are the different kinds of coastal ecosystems?

What is a ecosystem?

An ecosystem is a natural unit consisting of all plants, animals and micro-organisms (biotic factors) in an area functioning together with all of the physical (abiotic) factors of the environment.
An ecosystem is a unit of interdependent organisms which share the same habitat. Ecosystems usually form a number of food webs which show the interdependence of the organisms within the ecosystem.
The main idea is that living organisms interact with every other element in their local environment.

Lange ecosystems such as desserts or rainforest or tundra are also know as biomes. 2.3A_Biomes_map.jpg

What does each biome share? The same kind of climate and other physical conditions such as rocks and soil. This means that the same kind of plants and animals thrive there. We will return to look at biomes if we do the ecosystems and rural environment.2.3B_Marine_eco.png

However, for the moment we will look at the kind ecosystems – smaller than biomes – that are found around the coast.
The beach is that portion of the coast that is exposed between high tide and low tide and is called the inter-tidal zone. This is exposed to very harsh and varied conditions. Within 24 hours it could be covered twice by waves and subject to their pounding and uncovered twice to receive either strong hot sun or frosty air. These animals and plants need many adaptations to survive. For example most seaweeds that get regular exposure have a covering of mucilage that prevents them desiccating (drying out) when the tide is out. The higher up the beach the seaweeds are found the greater their exposure and the more resistant they are to this problem.

Sandy beaches and rocky bays have a very different conditions – more or less exposure to winds and beach movement (longshore drift), more or less stable ground (rock does not move around much) and more or less inter-tidal pools (sand/shingle dries out quickly).

Rocky shores are superb places for exploration - there is so much to see! Rockpools provide a glimpse into the underwater world, while ledges, crevices and overhangs provide surfaces for animals and seaweeds to cling to. When the tide returns, the shore becomes part of the sea once more.

Why do rock shores have zones?
Different kinds of animal and seaweed are found on different parts of the shore. As a result of the tides, and of varying conditions over the shore, all shores and beaches can be divided into zones which have specific characteristics and communities. They are all affected by wave action, availability of light, desiccation due to exposure to air, the type of rock surface (substrate), aspect, and by other life on the shore through competition and grazing.

2.3C_Sea_slater.pngSplash zone: This zone is only occasionally inundated by seawater. This makes it a harsh place for anything alive to survive here. Plants include rock samphire, thrift and sea campion and low-growing encrusting lichens. The sea slater (type of woodlouse) is common here, but it is a nocturnal (night - time) feeder that hides away from predators during the day.
Upper shore: Here life is well adapted to the vigorous conditions of exposure, wave activity and wide fluctuations in salinity and temperature. The most abundant seaweed is the channelled wrack. The few animal species that are adapted to live within this zone tend to have a protective outer shell or are permanently attached to the rock surface. The acorn barnacle is permanently cemented to the rock surface and can close its “trap door” when exposed to air. Limpets remain firmly attached to a rock surface when the tide is out; when submerged the limpet becomes active, leaving its “home spot” to feed. The shore crab is able to control its own salt levels so can live quite happily under the stressful conditions of the upper shore.
Middle shore: This zone displays a greater diversity of species because it is an area that does not suffer such long periods of exposure to air and variation in physical factors as the upper shore. Bladder wrack. serrated wrack and knotted wrack are common. Look for wandering periwinkles, dogwhelks and limpets.
Lower shore: This zone is the most prolific because the rocks and pools are exposed and cut off from the sea for only short periods, allowing many more soft - bodied animals and large seaweeds to survive. Seaweeds include familiar tangle weed, sugar kelp and thongweed and many red-pigmented species. Many larger animals such as crabs and lobsters may be hiding amongst rocks and crevices, whilst fish such as butterfish and even wrasse which have been trapped pools may be found. Starfish. brittlestars and anemones can be seen.
(thanks to Marine conservation society http://www.mcsuk.org/marineworld/habitats/rocky+shores for the inspiration)

There are other ecosystems you may come across, for example salt marshes and sand dunes, all of which have their own issues and problems.
However there are 2 ecosystems that occur regularly in environmental articles as they are giving rise to concern in many different parts of the world. They are mangrove swamps and coral reefs.


Where are the coral reefs?

Coral reefs are located in three primary regions located between 20 degrees N and 20 degrees S of the equator: the Indo-Pacific, the Western Atlantic, and the Red Sea. The Indo-Pacific region stretches from southeast Asia through Polynesia and Australia, eastward across the Indian Ocean to Africa. This is the largest and richest assemblage of reefs in terms of coral and fish species present. The Western Atlantic region stretches from Florida to Brazil, including Bermuda, the Bahamas, the Caribbean, Belize and the Gulf of Mexico. The Red Sea is the smallest of the three regions, located between Africa and Saudi Arabia. It is considered a separate region because of the high number of coral reef life found only in this area.
Based upon geographic distribution, 60% of the world's reefs are found in the Indian Ocean and Red Sea, 25% are located in the Pacific Ocean, and 15% in the Caribbean.

What do coral reefs need?
  • They require quite specific conditions in order to thrive. None are found in areas where the water temperature drops much below 18°C (64°F) for more than a few days.
  • Apart from temperature, corals also require clear waters. This is partly because they need sunlight to support the algae that live within their tissues. They are also very sensitive to particles of mud or sediment settling on them, which means that corals rarely grow close to rivers or other sources of sediment. In the sea, light is filtered out by depth, so reef-building corals can only grow in relatively shallow water. Even in the clearest oceans few reef-building corals grow below a depth of 80 to 100 m (260 to 328 ft).
  • Although corals need nutrients, they cannot thrive in areas where there are large amounts of nutrients. Typically, microscopic organisms in the plankton, or seaweeds (macroalgae), grow to excess in nutrient-rich water and smother the corals, blocking out the light.
  • Waves can often be seen crashing onto coral reefs. Being supported by limestone skeletons, corals can survive in very tough conditions. However, in the strongest storms many corals will be smashed to pieces. In the short term this can be damaging, but many of the broken pieces will continue to grow. New corals will arrive from other areas, so the reef can recover, often within a few years.
Two other groups of plants are often associated with coral reefs. Mangroves (much more about that below) are trees and shrubs that grow in the intertidal zone between the land and the sea, while seagrasses are the only true plants that live completely submerged in the sea. Both mangroves and seagrasses are particularly abundant and diverse in tropical waters. Many reef animals move between these ecosystems during their lives. The mangroves and seagrasses are also important for filtering and holding sediments and thus keeping the water over the coral reefs clearer.

What are coral reefs?
Colourful and full of life, coral reefs support a great diversity of life. They require shallow seas with suitable conditions: temperature, wave exposure and water quality. Coral reefs are built from the limestone remains of coral skeletons and coralline algae - but corals are not restricted to the tropics. They thrive in temperate seas, in the cold blackness of the deep oceans and even under polar ice. But in the absence of warm water and symbiotic algae they are unable to grow into reefs.

How are they built?
2.3E_Coral_polyp.pngThe basic ‘unit’ of a coral is the polyp - a small anemone-like animal. The branching, massive. plate-like or encrusting corals that build reefs are colonies of hundreds or thousands of polyps held together by soft tissue and the calcareous skeleton they secrete. Symbiosis is the condtion of 2 or more organisms living together for their mutal benefit. Symbiotic brown algae (zooxanthellae) living within the tissues of corals are fundamental to reef building. They live within the tissues of the coral and work together. Coral grows up to 3 times as fast with their help.
They work together in the following way to convert nutrients:
1. Coral polyps capture food using their stinging tentacles.
2. The digest their prey and create waste.
3. The algae convert the nutrients in the coral's waste products into food.
4. The algae give some of this food to the polyp.
5. Polyps consume this food and create more waste.
6. Repeat!!

The algae give the corals their characteristic greenish colour. A change of environmental conditions such as higher temperatures or a change in salinity but also disease can cause the polyps to expel the algae. The coral becomes totally white (= coral bleaching). If the coral regains some algae it might survive, but bleaching can be irreversible and then the coral dies.

Why are they important?
  • Thousands of fish species and tens of thousands of invertebrates and algae combine on coral reefs to produce the highest biodiversity of all shallow water marine ecosystems. This is why they are so important. Destroy them and we loose much more than just the coral.
  • Coral reefs act as natural self-repairing breakwaters, protecting adjacent land from storm-driven waves and reducing coastal erosion.
  • They are rich fishing grounds for molluscs, crabs, lobsters, fish and other edible species. Many people depend on reef produce for their everyday needs.
  • Reefs provide exotic non-food products such as shells for decoration and live fish and invertebrates for the aquatic trade.
  • Certain reef organisms contain compounds with important pharmaceutical properties which can be used to develop sunscreens and powerful drugs. Some types of coral skeleton can be used as bone graft substitutes, for example to repair bones damaged by cancer. They are not rejected and are proving highly successful.

What are the different types of reef?
Coral reefs are divided into four main types: fringing reef, platform reefs, barrier reefs and atolls.
Go to this link for a video explaining these: http://videos.howstuffworks.com/hsw/12605-coral-reef-biomes-types-of-coral-reefs-video.htm

2.3F_Fringe_reef.pngFringing reefs are relatively young. They can develop in shallow waters along the coast of tropical islands or continents. The corals grow upwards to sea level or just below and outwards towards the open ocean. Fringing reefs are generally narrow platforms a short distance from shore and don't contain a substantial lagoon.
Platform reefs usually lie in sheltered seas and quite far offshore. They are flat-topped with small and very shallow lagoons.

2.3H_Barrier_reef.pngA coral reef growing parallel to the coastline and separated from it by a lagoon is called a barrier reef. The lagoon may develop beyond the fringing reef and the land. As the reef continues to grow further and further offshore it eventually reaches the edge of the continental shelf. Barrier reefs can also originate offshore if the depth of the seabed out there is shallow enough to allow corals to grow.
The most famous barrier reef is the Great Barrier Reef in Australia. It stretches over 2300 km and covers over 200'000 km2. It lies between 24 and 240 km from the main continent.

Atolls are rings of reef, often encircling an island (sand and coral rubble). They typically have a shallow, sandy, sheltered lagoon in the middle. Access to the open sea beyond is through a number of channels. These provide fresh and colder water for the lagoons. Corals atolls are on the top of submarine mountains. These mountains are remnants of volcanos. Once there were fringing reefs around the volcano. As it slowly submerged the corals continued to grow up to the surface of the water. What remained after the volcano became invisible is a ring of coral reefs surrounded by deep ocean. However some atolls were probably formed by rising sea levels rather by the sinking of islands.
A fringing reef surrounding an active volcano - subsidence of the seafloor or rising sea levels
A shrinking of the island - an atoll results when the island has disappeared


What are mangroves?
2.3P_Mangrove_pic.pngMangroves (generally) are trees and shrubs that grow in saline (brackish) coastal habitats in the tropics and subtropics. The word is used to refer to the habitat and entire plant assemblage or mangal . They are found in intertidal zones along estuaries and marine shorelines. They face problems of frequent emersions, a saline environment that tress and shrubs generally cannot survive and a lack of oxygen. Different plants have different ways of dealing with these problems
How do mangroves survive?
Avoiding the salt: some plants contain a waxy covering to their roots which prevent it entering. Others deposit the salt in dying leaves that soon drop off (a bit like putting the rubbish out on the pavement to be taken away)
Lack of oxygen: their long knobbly roots take in air when they can through little pores.
Getting nutrient: because salt water is low in oxygen, bacteria survive well and release phosphates

Where do you find mangroves?
What do they need?
2.3N_Mangrove_diag.pngTropical or semi tropical environment where the shore is soft and muddy enough for them to take root. The shoreline needs to be undisturbed for them to do well.

Why are mangroves important?
People used to think of mangroves as noxious impenetrable swamps full of diseases, and they were destroyed as a public health measure, but now we know better!
  • They provide a habitat and protection for many fish and other sea animals, especially when young. Where they are permanently underwater, they are home to algae, barnacles, oysters, sponges which need some hard to hang on to ( the mud will not do this). Shrimps and mud lobsters use the muddy bottom as their home. The survival of some types of fish depend on mangroves.
  • Mangrove trees grow well in their special conditions and they produce a lot of leaves and other organic matter. The leaves fall in the water, where they rot and provide food for microbes and many tiny animals. This rich food is not only eaten in the mangrove swamp, but much of it may be carried out into the lagoon or to coral reefs and other coastal fisheries areas, where it helps to feed the fish. The areas near mangroves are thus often very important for fishing.
  • They slow the water flow and so encourage any sediments to be deposited, thus keeping the sea water clear. Often these sediments contain toxins, heavy metal etc and so they provide a sink for them and prevent them contaminating the sea water.
  • They protect the coast from erosion, storm surges (especially during hurricanes), and tsunamis. Their massive root system is efficient at dissipating wave energy.
  • Mangroves also build land which can be very important on islands where land is so limited. Mud and sediment are often washed down rivers and streams. The water spreads out into the mangroves, and the sediment settles to the bottom where it is trapped by the mangrove roots. As the bottom gets shallower, the mangroves can grow further out, while those on the inside eventually find themselves on dry land, where they are replaced by land plants. In this way the mangrove forest advances slowly outward, leaving land behind.
  • Mangroves are an important source of food and materials for many coastal people. Crabs, clams, oysters, fish and other food are often collected there. Even the mangrove fruits are sometimes eaten. Mangrove wood is often collected as firewood, and it can also be used for building. The bark has tannin which has craft and medicinal uses.
  • Even in the city, mangroves can be important. The city wastes run off and pollute the nearby coastal waters. When the wastes from all the people run into a mangrove swamp, they can be taken up and used by the plants and animals in the swamp. In a way the swamp filters the water, leaving clean water to go out the other side. As long as there is not too much waste for the mangroves, and no poisonous wastes from industries, the mangroves are an excellent waste treatment system, and much cheaper than a sewage treatment plant.
Mangroves, Corals and seagrass interdependence
Seagrass is so called because it looks like grass and grows under the sea. They are the only flowering plants that can. They produce seed as a result of pollen being transferred from the male organ to the female. They occur in many places in the world but only form ’meadows’ – large areas – in the warmer places – another reason for the term grass.
Tropical seagrasses are important in their interactions with mangroves and coral reefs. All these systems exert a stabilizing effect on the environment, resulting in important physical and biological support for the other communities (Amesbury and Francis 1988).
Barrier reefs protect coastlines, and the lagoon formed between the reef and the mainland is protected from waves, allowing mangrove and seagrass communities to develop. Mangroves and seagrasses trap sediment and slow water movement, causing suspended sediment to fall out. They stabilize salinity levels in the coastal zone and act as buffers or sinks for nutrient concentrations in terrestrial run-of This trapping of sediment benefits coral by reducing sediment loads in the water.
Coral-reef-associated species spawn and/or grow up in a sheltered sea grass or mangrove environment.
Coral reefs serve as a shelter for fishes during storms.

Links to visit


http://www.stanford.edu/group/microdocs/index.html is where the second video came from - there are many more there - it will also help with the case study we do in Unit 2.4 on managing a coral ecosystem in Fiji