The Coastal Ecosystem in Tuvalu and Geo-ecological Acknowledgements Management against SATREPS ( JICA-JST), Japan Sea-Level Rise Department of Environment, Tuvalu Department of Fisheries, Tuvalu Department of Land and Survey, Tuvalu Photos and illustration by Hajime KAYANNE, Takashi HOSONO, Akihiro KAWADA in Akihiro KAWADA Foram Sand Project Fumiko MATSUDATE (April 2009 – March 2014) Hajime KAYANNE Paeniu LOPATI Saki HARII Takashi HOSONO PART PAGE 01 Atolls and coral reefs ........................................................................................ 04 02 Islands formed by the skeletons of marine animals ............................. 05 03 Coral and foraminifer ....................................................................................... 06 04 Marine animals and the ecosystem ............................................................. 07 05 Big drought in 2011 and resilience of the coastal ecosystem ........... 08 06 After the collapse of the coastal ecosystem ........................................... 09 07 Is Tuvalu sinking? ............................................................................................... 10 08 Obstacles to the island formation process .............................................. 11 09 Geo-Ecological management of islands ................................................... 13 10 Application to other atoll island countries .............................................. 14 11 Our island is alive ............................................................................................... 15 Islands formed by Atolls and coral reefs 01 02 marine animals Atolls are ring-shaped coral reefs tiated by deep drilling at the Eniwetak Atoll Tuvalu is a chain of atoll islands coral reef. The debris of coral skeletons standing in mid-ocean and surrounding a just after WWII, which penetrated into vol- several hundred meters wide with eleva- are tossed up to form the ocean-side storm shallow lagoon. They are the final stage canic rocks 1267 m below the sea surface tions ranging from one to four meters. The ridge. Forams are protozoa, which live on of coral reef evolution: a newly born vol- that were overlaid by coral reef limestone. islands of Tuvalu are formed on a rigid the reef flat by attaching to turf algae and canic island is first fringed with coral reefs Today, the initial volcanic island and its framework of coral reefs, which have been that precipitate calcareous shells of one to constructed by piling up the skeletons of two millimetres in size. The major part of (fringing reef). As the island subsides, the subsidence are explained by plate tectonics hermatypic corals. Corals are cnidarian an- the island body (the lagoon-side ridge and coral reef grows upward to form a barrier in which a volcanic island is formed at a imal relatives of jellyfish and sea anemone the central depression) is formed by the reef separated from the island by a shallow hot spot and then travels and subsides with that precipitate calcium carbonate skele- shells of the forams (foram sand). lagoon. Finally, the island subsides well a plate. tons. They pile up to form coral reefs that Coral and foram are the two major beneath sea level to form an atoll. This hy- Approximately 500 atolls exist in provide a foundation for the island and act players that construct the islands in con- pothesis was proposed by Charles Darwin the world, with 400 located in the Pacific as a natural breakwater. However, coral junction with several other calcifying or- in 1842 during the survey of the HMS Bea- Ocean. Tuvalu consists of 9 atolls. They are reefs never accumulate above low water ganisms, such as molluscs, calcareous red gle and then tested by deep drilling at the aligned from southeast to northwest, corre- level. and green algae, and sea urchins. There- Funafuti Atoll in 1896-1898, which failed sponding to plate motion. Tuvaluan atolls Those islands above high water fore, island formation is governed by both to reach the volcanic basement but recov- have travelled from the southwest. Islands level serving as habitable land for humans physical and ecological processes. The sus- ered more than 300 m of shallow coral reef on the atolls are formed by unconsolidat- have been formed by coral debris and for- tainability of the national land of Tuvalu sediments, implying subsidence. Darwin’s ed coral gravel and foraminifera sand over aminifera (foram) sand tossed up onto the depends fully on coral and foram. subsidence theory was eventually substan- several thousand years. a b c a. Beach sand in FUAKEA Island. b. Coral community in the lagoon of FUNAMANU Island. c. Foraminifer population in TENGAKO Island (TH). 04 Foram Sand Project Foram Sand Project 05 Marine animals and Corals and foraminifers 03 04 the ecosystem Corals and foraminifers belong to a quite different phylogenetic groups. How- ever, their nutrient acquisition methods Corals and foraminifers can be are similar. Coral and foraminifer contain found in littoral and sublittoral zones symbiotic algae within their bodies. They utilize sunlight and allow their symbiotic in Tuvalu. They utilize sunlight in algae to photosynthesize. Then, they ac- shallow areas to acquire nutrients. quire nutrients from the photosynthetic products of the symbiotic algae. They also eat plankton from the water column using tentacles by the coral and pseudopods by However, they need more to sur- more than these three factors to survive. the foraminifers. vive than only sunlight and nutrients. Corals Coral easily die in polluted environments, also need a hard substrate for attachment, can become bleached or be covered with al- and foraminifers also need macroalgae for gae. Foraminifers also die and can become attachment. In addition, they still require bleached under some conditions. b a. Surface and inside of a foraminifer (Baculogypsina sphaerulata). Orange color inside the foraminifer is a symbiotic diatom (TH). b. Foraminifer (Amphistegina lessonii) attached to a glass microscope slide. The arrow indicates a pseudopod (TH). c. Corals (SH) d. Tentacles and symbiotic algae (SH). c d Coastal ecosystem in the reef of FUAFATU Island (TH). 06 Foram Sand Project Foram Sand Project 07 Big drought in 2011 and resilience After the collapse of the 05 of the coastal ecosystem 06 coastal ecosystem The big drought occurred in 2011, and its negative effects have mostly subsided. The dry breadfruit trees have returned to life. Many water tanks donated from foreign coun- We can easily understand the tries will not be used until the next drought. However, that prolonged drought caused sig- damage that the coral community nificant problems that affected many lives. At experienced after the collapse of the the same time, we also recognize the degrada- coastal ecosystem and the loss of tion of the ecosystem in our sea. One example a is the black-coloured algae that were unnat- resilience when the following pictures urally overgrown in the lagoon. Coastal eco- are compared. systems that have low resilience are supposed to easily change their forms in response to small external forces. Sometime after the rain returned, the ecosystems appeared to recover their former forms, and therefore, the current a b ecosystem exhibits some resilience. However, the drastic changes in the coastal ecosystem b during the big drought clearly reflect strong a. Landing of water tanks donated as relief anthropogenic stress and weak resilience in supplies from foreign countries (TH). the coastal ecosystem. b. Lagoon beach of the island covered with spoiled algae (FM). c c d a. Table coral in a healthy coast of the Funafuti Atoll. b. Dead table coral in the lagoon of Fongafale Island. c. Branching coral in a healthy coast of the Funafuti Atoll. c. Black cyanobacteria-covered branching coral in the lagoon of Fongafale Island during the drought (PL). d. Dead branching coral in the lagoon of Fongafale Island. (HK). 08 Foram Sand Project Foram Sand Project 09 Obstacles to the Is Tuvalu sinking? 07 08 island formation process During the spring high tide (King The islands of Tuvalu were first The major site of foraminifera sand pro- tide), the inland areas of Fongafale Island formed by coral reefs. They still act as duction is the ocean-side reef flat, and this become inundated with seawater. Such in- a natural breakwater in front of both the sand is first delivered to the lagoon through undation has been occurring more frequent- ocean-side and lagoon-side coasts. Corals the channels between the islands and then ly. Local people argue that they have never also provide sand and gravel. However, transported along the lagoon-side coast by experienced such inundation before and coral reefs have never grown above low the longshore current. that it is therefore caused by rising sea lev- exists. The spring high tide reaches 1.2 m, water level, and the islands above high wa- A healthy ecosystem with living els induced by global warming. and thus the central depression is naturally ter level were formed by gravel and sand coral and foraminifera is fundamental to is- The landform of Fongafale Is- inundated by spring-tide water. from the calcareous skeletons of organisms. land formation, and sand production, trans- land consists of a coral reef, a storm ridge, An old geologic map revealed that The major body of the island was formed portation and sedimentation is the key pro- a central depression, and a lagoon-side the central depression was formerly cov- by the sand of foraminifera, coral, calcar- cess in island formation. Fongafale