Coral reefs Flashcards
(15 cards)
What is a thermocline?
A thermocline separates the cool water to the warm water.
The sunlight heats the surface water making it less dessert to therefore sits above the more dense cooler water. This means the water rapidly changes temperature with the depth (Thermocline).
How does the thermocline lock out nutrients from surface ocean water?
When marine life dies they mostly sink and decompose realising nitrogen, phosphorus and potassium these are used as fertilisers for plant growth.
Thermocline separates the cool nutrient rich to the warm nutrient poor water.
Therefore, the tropical water is usually warm but nutrient poor.
What is phytoplankton?
The marine environment is mostly microscopic plants called phytoplankton. They float on the surface water and photosynthesise to grow. However, they still need nutrients so the phytoplankton uses up any surface nutrients up rapidly. This nutrients is then not replaced if there is a stable thermocline.
What is zooplankton?
Zooplankton is animal plankton and feeds on phytoplankton and in turn gets eaten by larger critters and small fish.
However, with a lack of of the base in the food chain (phytoplankton) there are few zooplankton and few small fish. This condition in the tropical ocean results in a lack of life and low productivity in most areas.
What are coral reefs built from?
Due to the lack of life in the tropical waters coral reefs are built from a unique type of coral called hermatypic coral which can only exist in warm ocean water.
Hermatypic corals are a symbiotic combination of a coral animal and an organism called zooxanthellae. This relationship allows coral reefs to grow and exist for years and years allowing many other species to have a habitat.
What is a symbiotic relationship?
A symbiotic relationship is a mutually beneficial interaction between two different parts of the environment, such as between people and nature or between different natural systems.
What is zooxanthellae?
Zooxanthellae are:
Tiny algae that live in a symbiotic relationship inside the tissues of coral.
* The algae provide energy to the coral through photosynthesis.
* The coral provides protection and nutrients to the algae.
This relationship is essential for the survival of coral reefs and is a classic example of a symbiotic relationship in geography and biology.
How does a classic coral reef form and change?
They begin with a brand new tropical island which is produced by an oceanic hot spot or at a plate boundary. They gradually change through thousands of years from a fringing reef to a barrier reef to an atoll and then finally to an extinct reef as a seamount or guyot.
What is a new oceanic island and what happens with life forms overtime on the island?
The island will be entirely made of crustal material and with have no evidence of life forms. If there is no volcanic activity and the island cools there will be a succession of life forms from either flying, floating or swimming species. Over time a thriving community will be found on land as well as in the ocean.
What is a fringe reef?
A fringe reef forms along the shoreline of most tropical oceans. This is because the reef is made from animal coral (hermatypic) which can only survive in warm clear oceans and can survive in nutrient poor waters (These conditions are often found near new oceanic islands).
The coral animal reproduces sexually with a microscopic planktonic larval form that is abundant in tropical waters during coral reproduction.
Most of the larvae never grow to adults because there is no more space in the warm surface oceans on a solid surface. They need to attach to the solid surface so they wont move from the warm, sunlit, clear tropical waters but there is not normally space to do this but there is space on new islands.
So a coral reef forms along the edge of the island called a fringe reef - the first step in a “classical’ coral reef formation.
What is a barrier reef?
A barrier reef forms from the oceanic island slowly starting to sink into the earths crust.
Reasons for sinking:
- Absence of volcanic island building forces.
- Added weight from the coral reef.
- Erosion at the surface of the island.
The coral animals lay down lots of calcium carbonate in the form of their skeletons and if the conditions are good they can keep pace with the sinking island.
Their living tissues remain in the upper part of the reef in the warm, clear tropical water. The lower part is composed of the calcium carbonate skeletons left by the reef building corals. This upwards growth causes a lagoon of water between the top of the reef (that started as a fringing reef) and the sinking crustal island.
The lagoon gets filled with eroded material from the reef and the island which is a haven for marine forms that require protection from waves and storms.
What is an atoll reef?
An atoll reef occurs when the surface of the oceanic island sinks below the surface of the ocean but the coral continues to grow upwards. The atoll is usually circle shape but could be broken in places due to storms.
Eroded reef material could pile up on parts of the reef creating an area above the seal level. This is an island called a “cay” which may become stabilised enough to provide a permanent island for buildings. If the cay is not stable it could move across the reef or disappear.
What is a seamount or guyot?
These form when a coral reef can not keep up with the sinking island. Seamounts and guyots are below the surface of the ocean and can become a habitat for a large amount of species. Seamounts are rounded on top where as guyots are flat-topped. The flat occurs from when the waves planed unit down from its existence at the surface.
Why are coral reefs important?
- Biodiversity
- Seafood
- Tourism
- Coastal protection
What are some dangers to coral reefs?
- Overfishing, drag net fishing & blast fishing
- Tourism - Anchors destroying coral on tourist boats as well as locals wanting to eat local sea food leading to overfishing.
- Global warming - Rising sea levels and coral bleaching.
