Islands 101: Geography & Ecosystems


For those of us relatively new to island conservation, picking up on all the island lingo can be tricky. What is an atoll? (And how do you say it?) How do you know if a species is endemic or just indigenous? And why are mangroves so important?

To answer these and other questions, I've compiled an island cheat-sheet. Read on for the first post in Seacology U's Islands 101 lecture series!

Island Geography

While some island features, such as mountains and beaches, are well-known, others might be less familiar to land-lubbers.

Archipelago An archipelago is a cluster of small islands. There are hundreds of archipelagos around the world; the largest, Indonesia, has been the site of many Seacology projects. Archipelagos are often formed when underwater volcanic activity causes magma to create rock formations that eventually reach the water's surface. 

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Atoll: An atoll is an island of coral that encircles a lagoon partially or completely. Many of the islands where Seacology works are atolls, such as Manihiki Atoll in the Cook Islands.  Like other island types, atolls are formed from the subsidence of an ocean volcano. Corals grow around an underwater mountain or volcano, gradually building upwards toward the water surface, while the mountain sinks. Eventually, the layers of dead coral become islands surrounding a lagoon.  And it's normally pronounced A-toll, as in "Yay, toll for this island is free!"  You can see an example of an atoll in the picture to the left, and find more information on them here

Lagoon: Though not exclusive to islands, lagoons form in atolls and near other island features. Lagoons are shallow pools, with either salty or brackish water, that are separated from the ocean by thin barriers, such as sandbanks or coral. While many beautiful creatures can be found in lagoons, Seacology's projects, such as our work in the Cook Islands, focus protecting highly productive lagoon ecosystems from exploitation or development.

Island Ecosystems

Although islands host a wide range of environments, Seacology's work often focuses on certain critical ecosystems.

Coral Reefs: Coral reefs are complex and highly biodiverse marine ecosystems. They are built on corals, an animal whose calcium carbonate exoskeleton forms a strong foundation for other underwater plants and animals. Reefs are usually found in shallow tropical waters, although some deep water reefs exist. They are highly sensitive to climate change, since increased carbon dioxide in the oceans (from released greenhouse gases) prevents the coral from properly forming the exoskeleton, which causes harm to the entire ecosystem. With the many threats to coral reefs today, Seacology has frequently funded coral protection projects, such as one Kimbe Bay, Papua New Guinea. You can learn more about ocean acidification here

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Mangrove: Mangrove can refer to a specific type of tree; usually, however, the term "mangrove" indicates the wetland ecosystem that mangrove trees foster. Adapted to thrive in salt water wetlands, mangrove swamps (also called mangrove forests) are found on tropical coastlines around the world. The large roots of mangrove trees keep the trees anchored through regular tidal changes in water level, while other adaptations allow them to access oxygen, release excess salt, and bear seeds that will grow even in the harsh wetland climate. (You can see these unique roots in the picture at right, courtesy of Wikimedia Commons.) Like other wetland ecosystems, mangroves are critical because of their ability to filter contaminants and protect coasts from erosion. They also serve as fish nurseries, providing important habitat for many young fish. Mangroves are currently threatened by coastal development, overfishing, harvesting of trees, and climate change. Seacology and many other organizations are encouraging mangrove restoration projects that will renew these fragile ecosystems and protect their islands. 

Rainforest: Most people associate rainforest with the Amazon or Congo, the world's largest tropical rainforests. But much of the world's rainforests can also be found on islands--Indonesia alone has 10% of the remaining tropical rainforest. Since rainforests are the most biodiverse terrestrial ecosystem in the world, preserving them is critical to the health of the planet. Seacology has funded many projects protecting rainforests in Indonesia and on other islands. 



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This page contains a single entry by Carynne McIver published on February 4, 2010 4:05 PM.

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