Coral Reefs Of Tuvalu
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The coral reefs of Tuvalu consist of three
reef A reef is a ridge or shoal of rock, coral, or similar relatively stable material lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic (non-living) processes such as deposition (geol ...
islands and six
atoll An atoll () is a ring-shaped island, including a coral rim that encircles a lagoon. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical parts of the oceans and seas where corals can develop. Most ...
s, containing approximately of reef platforms. The islands of the Tuvalu archipelago are spread out between the
latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...
of to 10° south and
longitude Longitude (, ) is a geographic coordinate that specifies the east- west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek lett ...
of 176° to 180°, west of the
International Date Line The International Date Line (IDL) is the line extending between the South and North Poles that is the boundary between one calendar day and the next. It passes through the Pacific Ocean, roughly following the 180.0° line of longitude and de ...
. The islands of
Tuvalu Tuvalu ( ) is an island country in the Polynesian subregion of Oceania in the Pacific Ocean, about midway between Hawaii and Australia. It lies east-northeast of the Santa Cruz Islands (which belong to the Solomon Islands), northeast of Van ...
are volcanic in origin. On the atolls, an annular reef rim surrounds the lagoon, and may include natural reef channels. The reef islands have a different structure to the atolls, and are described as reef platforms as they are smaller tabular reef platforms that do not have a salt-water
lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...
, although they may have a completely closed rim of dry land, with the remnants of a lagoon that has no direct connection to the open sea or that may be drying up.


Structure of the reefs of Tuvalu

The islands of the Tuvalu archipelago are very low-lying, with the highest elevation of above mean sea level on
Niulakita Niulakita is the southernmost island of Tuvalu, and also the name of the only village on this island. Niulakita has a population of 36 (2022 Census). The residents of Niulakita have moved to the island from Niutao. Niulakita is represented in ...
. The atolls and reef islands of Tuvalu have been formed from oceanic volcanos, with a coral reef growing around the shore of the volcano and then, over several million years, the volcano becomes extinct, eroded and subsided completely beneath the surface of the ocean. The reef and the small coral islets on top of it are all that is left of the original island, and a lagoon has taken the place of the former volcano. For the atoll to persist, the coral reef must be maintained at the sea surface, with coral growth matching any relative change in sea level (subsidence of the island or rising oceans). The boreholes on
Fongafale Fongafale (also spelled Fogale or Fagafale) is the largest and most populated of Funafuti's islets in Tuvalu. It is a long narrow sliver of land, 12 kilometres long and between 10 and 400 metres wide, with the South Pacific Ocean and reef on the ...
islet, at the site now called ''Darwin's Drill'', are the result of drilling conducted by the
Royal Society of London The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, r ...
for the purpose of investigating the
formation of coral reefs A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. C ...
to determine whether traces of shallow water organisms could be found at depth in the coral of Pacific atolls. This investigation followed the work on ''
The Structure and Distribution of Coral Reefs ''The Structure and Distribution of Coral Reefs, Being the first part of the geology of the voyage of the Beagle, under the command of Capt. Fitzroy, R.N. during the years 1832 to 1836'', was published in 1842 as Charles Darwin's first monogra ...
'' conducted by
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English Natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...
in the Pacific. Drilling occurred in 1896, 1897 and 1898. However, the geologic history of atolls is more complex than Darwin (1842) and Davis (1928) envisioned. The survey of Funafuti atoll published in 1970 described its structure as being:
Funafuti Funafuti is an atoll, comprising numerous islets, that serves as the capital of Tuvalu. As of the 2017 census, it has a population of 6,320 people. More people live in Funafuti than the rest of Tuvalu combined, with it containing approximately 6 ...
,
Nanumea Nanumea is the northwesternmost atoll in the Polynesian nation of Tuvalu, a group of nine coral atolls and islands spread over about of the Pacific Ocean just south of the equator and west of the International Date Line. Nanumea is with a po ...
, Nui,
Nukufetau Nukufetau is an atoll that is part of the nation of Tuvalu. The atoll was claimed by the US under the Guano Islands Act some time in the 19th century and was ceded in a treaty of friendship concluded in 1979 and coming into force in 1983. It h ...
,
Nukulaelae Nukulaelae is an atoll that is part of the nation of Tuvalu, and it has a population of 300 (2017 census). The largest settlement is Pepesala on Fangaua islet with a population of 341 people (2022 Census). It has the form of an oval and consist ...
and
Vaitupu Vaitupu is the largest atoll of the nation of Tuvalu. It is located at 7.48 degrees south and 178.83 degrees east. There are 1,077 people (2022 Census) living on with the main village being Asau. History Discovery and settlement The exa ...
are
atoll An atoll () is a ring-shaped island, including a coral rim that encircles a lagoon. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical parts of the oceans and seas where corals can develop. Most ...
s (sometimes known as a ''coral atolls''), which have a
coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in group ...
, which is a coral rim that encircles a
lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...
partially or completely, with
coral island A coral island is a type of island formed from coral detritus and associated organic material. It occurs in tropical and sub-tropical areas, typically as part of a coral reef which has grown to cover a far larger area under the sea. The term low ...
s or
islet An islet ( ) is generally a small island. Definitions vary, and are not precise, but some suggest that an islet is a very small, often unnamed, island with little or no vegetation to support human habitation. It may be made of rock, sand and/ ...
s (''motu'') on the rim.
Nanumanga Nanumanga or Nanumaga is a reef island and a district of the Oceanian island nation of Tuvalu. It has a surface area of about 3 km2 with a population of 391 (2022 census). History On 9 May 1824 a French government expedition under Captain ...
,
Niulakita Niulakita is the southernmost island of Tuvalu, and also the name of the only village on this island. Niulakita has a population of 36 (2022 Census). The residents of Niulakita have moved to the island from Niutao. Niulakita is represented in ...
and
Niutao Niutao is a reef island in the northern part of Tuvalu. It is one of the nine districts (islands) of Tuvalu. It is also one of the three districts that consist of only one island — not counting the three islets inside the closed lagoon. Niuta ...
have a
fringing reef A fringing reef is one of the three main types of coral reef. It is distinguished from the other main types, barrier reefs and atolls, in that it has either an entirely shallow backreef zone (lagoon) or none at all. If a fringing reef grows direc ...
in that they have either a shallow backreef zone (
lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') an ...
) or none at all. If a fringing reef grows directly from the shoreline, then the reef flat extends to the beach and there is no backreef. Although they have a completely closed rim of dry land, these reef islands can have the remnants of lagoons that has no connection to the open sea and are lakes, which are brackish to saline due to some connection with the ocean as the consequence of the porous nature of the limestone base of the islands. For example,
Niutao Niutao is a reef island in the northern part of Tuvalu. It is one of the nine districts (islands) of Tuvalu. It is also one of the three districts that consist of only one island — not counting the three islets inside the closed lagoon. Niuta ...
has two lakes, which are brackish to saline; and are the degraded lagoon as the result of coral debris filling the lagoon. Over a long period of time the reefs produce
coral sand Coral sand is a form of aragonite sand particles originating in tropical and sub-tropical marine environments primarily from bioerosion of limestone skeletal material of marine organisms. Often, this is due to corallivores, such as parrotfish ...
, which is a collection of
sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...
of particles from the
bioerosion Bioerosion describes the breakdown of hard ocean substrates – and less often terrestrial substrates – by living organisms. Marine bioerosion can be caused by mollusks, polychaete worms, phoronids, sponges, crustaceans, echinoids, ...
of
limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
skeletal material of marine
organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...
s. One example of this process is that of
Green humphead parrotfish The green humphead parrotfish (''Bolbometopon muricatum'') is the largest species of parrotfish, growing to lengths of and weighing up to . It is found on reefs in the Indian and Pacific Oceans, from the Red Sea in the west to Samoa in the ea ...
, ''taona'' (''Bulbometopon muricatum'') and other species of
parrot fish Parrotfish (named for their mouths, which resemble a parrot's beak) are a clade of fish placed in the tribe Scarini of the wrasse family (Labridae). Traditionally treated as their own family (Scaridae), genetic studies have found them to be dee ...
(''ulafi, laea, kamutu'') which bite off pieces of
coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...
, digest the living tissue, and excrete the
inorganic An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemistry''. Inor ...
component as sand. However, the term "coral" in ''coral sand'' is used loosely in this sense to mean limestone of recent biological origin; corals are not the dominant contributors of sand particles to most such deposits. Rather, remnant skeletal fragments of
foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...
, calcareous algae,
molluscs Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...
, and
crustacea Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...
ns can predominate. In Tuvalu the sand that has accumulated in lagoons or at the edges of the reefs, has been used for coastal protection and land reclamation projects. Over four decades, there had been a net increase in land area of all 101 Tuvaluan islands or islets of 73.5 ha (2.9%), although the changes are not uniform, with 74% increasing and 27% decreasing in size. The sea level at the Funafuti
tide gauge A tide gauge is a device for measuring the change in sea level relative to a vertical datum. It is also known as a mareograph, marigraph, and sea-level recorder. When applied to freshwater continental water body, water bodies, the instrument may ...
has risen at 3.9 mm per year, which is approximately twice the global average. The rising sea levels are identified as creating an increased transfer of wave energy across reef surfaces, which shifts sand, resulting in accretion to island shorelines.


State of the reefs of Tuvalu


Surveys of the reefs

The results of Job and Ceccarelli's 2010 survey were published as the ''Tuvalu Marine Life Scientific Report'' in 2012. showed that the mean hard coral cover of
Funafuti Funafuti is an atoll, comprising numerous islets, that serves as the capital of Tuvalu. As of the 2017 census, it has a population of 6,320 people. More people live in Funafuti than the rest of Tuvalu combined, with it containing approximately 6 ...
,
Nanumea Nanumea is the northwesternmost atoll in the Polynesian nation of Tuvalu, a group of nine coral atolls and islands spread over about of the Pacific Ocean just south of the equator and west of the International Date Line. Nanumea is with a po ...
and
Nukulaelae Nukulaelae is an atoll that is part of the nation of Tuvalu, and it has a population of 300 (2017 census). The largest settlement is Pepesala on Fangaua islet with a population of 341 people (2022 Census). It has the form of an oval and consist ...
were 15%, 11% and 6%, respectively. with Funafuti having a higher mean coral cover, which was attributed to better water flow through the large reef passes (''ava'') and greater habitat diversity due to it large size, however, the coral cover in Funafuti was highly variable, ranging from 0.1% to 58%, with a mean cover of 15% across all sites that were surveyed. Live coral cover (LCC) of hard coral was reported to be 19.5% across all reef habitats of Funafuti in 2004. The surveying of the LCC levels across Funafuti, Nanumea and Nukulaelae by Job and Ceccarelli in 2010 established an average of 20-30% LCC level across the three islands; as compared to 30-70% LCC levels across reefs in
Kiribati Kiribati, officially the Republic of Kiribati, is an island country in the Micronesia subregion of Oceania in the central Pacific Ocean. Its permanent population is over 119,000 as of the 2020 census, and more than half live on Tarawa. The st ...
, which is to the north-west of Tuvalu. The standard criteria for coral reef health define a LCC level of less than 24.5% as being low indicating that the reef habitats of Funafuti, Nanumea and Nukulaelae reefs are in poor health. Surveys conducted on
Funafuti Funafuti is an atoll, comprising numerous islets, that serves as the capital of Tuvalu. As of the 2017 census, it has a population of 6,320 people. More people live in Funafuti than the rest of Tuvalu combined, with it containing approximately 6 ...
,
Nanumea Nanumea is the northwesternmost atoll in the Polynesian nation of Tuvalu, a group of nine coral atolls and islands spread over about of the Pacific Ocean just south of the equator and west of the International Date Line. Nanumea is with a po ...
and
Nanumaga Nanumanga or Nanumaga is a reef island and a district of the Oceanian island nation of Tuvalu. It has a surface area of about 3 km2 with a population of 391 (2022 census). History On 9 May 1824 a French government expedition under Captain ...
, which were reported in 2020, focused on locations close the main settlements on those islands, as the surveys were in relation to proposals to carry out coastal protection and land reclamation projects. The results of the survey conducted on Nanumea established that there was a lower percentage of live coral cover at the existing boat ramp as compared to the reference site away from the village. The mean percentage LCC was assessed in terms of reef flat, reef crest and reef slope. The LCC levels for the reef flat at the boat channel site is 0%, at the reef crest was 1% and on the reef slope was 12.5%. At the reference site, LCC levels on the reef flat was also 0% with 10% on the reef crest and 8.5% on the reef slope. The distribution of coral cover at the
Nanumaga Nanumanga or Nanumaga is a reef island and a district of the Oceanian island nation of Tuvalu. It has a surface area of about 3 km2 with a population of 391 (2022 census). History On 9 May 1824 a French government expedition under Captain ...
boat channel showed an increasing percent of LCC levels with increasing distance from the shore across the reef flat, reef crest and reef slope. Only three corals of families (''
Merulinidae Merulinidae is a Family (biology), family of reef-building Scleractinia, stony corals. Characteristics All the genera in this family are colonial, reef-building corals. Skeletal structures are similar to those of Faviidae but are highly fused, w ...
'', ''
Pocilloporidae The Pocilloporidae are a family of stony corals in the order Scleractinia occurring in the Pacific and Indian Oceans. Description Pocilloporids are colonial and most species are reef-building. They are very variable in size and shape, some bein ...
'' and ''
Poritidae Poritidae is a family of stony corals. Members of the family are colonial hermatypic (reef-building) corals. They are variable in size and form but most are massive, laminar or ramose as well as branching and encrusting. The corallites are co ...
'') were recorded at the boat channel, while at the reference site, over seven families were recorded. No macroalgae (seaweed) was recorded at the boat channel site but was present at the reference site. Macroalgae species recorded included red filamentous and brown encrusting algae (''
Caulerpa racemosa ''Caulerpa racemosa'' is a species of edible Green algae, green alga, a seaweed in the family Caulerpaceae. It is commonly known as sea grapes (along with the related ''Caulerpa lentillifera'') and is found in many areas of shallow sea around the ...
'', ''
Halimeda ''Halimeda'' is a genus of green macroalgae. The algal body (thallus) is composed of calcified green segments. Calcium carbonate is deposited in its tissues, making it inedible to most herbivores. However one species, ''Halimeda tuna'', was desc ...
sp.'', ''
Dictyota ''Dictyota'' is a genus of brown seaweed in the family Dictyotaceae. Species are predominantly found in tropical and subtropical seas, and are known to contain numerous chemicals (diterpenes) which have potential medicinal value. As at the end ...
covernosa'' and ''Padina sp''.).
Nanumea Nanumea is the northwesternmost atoll in the Polynesian nation of Tuvalu, a group of nine coral atolls and islands spread over about of the Pacific Ocean just south of the equator and west of the International Date Line. Nanumea is with a po ...
has between 20 and 30% LCC levels and the results of the 2010 surveys by Job and Ceccarelli indicated that Nanumea has a higher percentage of live coral cover than Nanumaga. The survey did confirm that Nanumea has the highest and richest coral community of the three islands covered. The survey also supports the studies undertaken at other atolls, which, suggesting higher levels of nutrients in the water due to sewage increases the density of seaweed cover, which inhibits the growth of coral. No sewage treatment systems exist in Tuvalu so that sewage enters the ocean and lagoon directly or through seepage from the freshwater
lens A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...
as the result of sewage pits that leak into the watertable.
Crown-of-thorns starfish The crown-of-thorns starfish (frequently abbreviated to COTS), ''Acanthaster planci'', is a large starfish that preys upon hard, or stony, coral polyps (Scleractinia). The crown-of-thorns starfish receives its name from venomous thornlike spines ...
(''Acanthaster planci'') and other coral predators, such as the corallivorous snails ''
Drupella ''Drupella'' is a genus of sea snails, marine (ocean), marine gastropod mollusks in the family (biology), family Muricidae, the murex snails or rock snails. This genus was placed in the family Muricidae by Drivas & Jay, 1988 and by Richmond, 199 ...
spp.'', are found on the reefs of Tuvalu, although there has not been any indication of destructive outbreaks of those predators on the reefs. Giant clams ('' Tridacnidae'') have declined through the effects of increasing human populations, pollution,
habitat destruction Habitat destruction (also termed habitat loss or habitat reduction) occurs when a natural habitat is no longer able to support its native species. The organisms once living there have either moved elsewhere, or are dead, leading to a decrease ...
and harvesting. Coral reef invertebrates that are either edible or used in handicrafts exist at low densities, indicative of the high level of harvesting of those species. The
women of Tuvalu Women in Tuvalu continue to maintain a traditional Polynesia#Culture, Polynesian culture within a predominantly Christian society. Tuvaluan cultural identity is sustained through an individual's connection to their home island. In the traditio ...
use
Cypraeidae Cypraeidae, common name, commonly named the cowries ( cowry or cowrie), is a Taxonomy (biology), taxonomic family (biology), family of small to large sea snails. These are marine (ocean), marine gastropod mollusks in the superfamily Cypraeoidea, ...
(cowrie, ''pule'') such as '' Cypraea mauritiana'', ''C. arabica'', ''C. tigris'', ''C. depressa'', ''C. mapa'', ''C. carneola'', ''C. vitellus'', ''C. lynx'' and other shells harvested from the reefs in traditional handicrafts, which includes creating shell necklaces (''tui misa'' or ''tui pule'') and the decoration of mats, fans and wall hangings.


Impact of the main settlement on Funafuti atoll on the adjacent reef and lagoon

Funafuti Funafuti is an atoll, comprising numerous islets, that serves as the capital of Tuvalu. As of the 2017 census, it has a population of 6,320 people. More people live in Funafuti than the rest of Tuvalu combined, with it containing approximately 6 ...
is the largest atoll of the Tuvalu archipelago and comprises numerous islets around a central lagoon that is approximately (N–S) by (W-E), centred on 179°7'E and 8°30'S. There are a number of large reef passes (''ava'') through the reef, which results in flushing of the lagoon. A survey at the southern end of
Fongafale Fongafale (also spelled Fogale or Fagafale) is the largest and most populated of Funafuti's islets in Tuvalu. It is a long narrow sliver of land, 12 kilometres long and between 10 and 400 metres wide, with the South Pacific Ocean and reef on the ...
islet in 1999 & 2000 recorded that live coral cover was in the order of 50+% LCC levels on the reef slope, with '' Acropora robusta'' the dominant form. The 2007 baseline report for the Funafuti Atoll Coral Reef Restoration Project in the lagoon off Fongafale reported on the transplanting of common and locally abundant ''
Acropora ''Acropora'' is a genus of small polyp stony coral in the phylum Cnidaria. Some of its species are known as table coral, elkhorn coral, and staghorn coral. Over 149 species are described. ''Acropora'' species are some of the major reef corals ...
spp'' staghorn branching corals (principally '' Acropora robusta'' and ''Acropora formosa'', with a low number of '' Acropora grandis'' colonies) from the fringing reef out to open sandy areas, in which habitat a few similar naturally occurring coral patches were present. Another common species '' Acropora florida'', was also noted to be present on the fringing reef. The protected blue coral ''
Heliopora coerulea Blue coral (''Heliopora coerulea'') is a species of colonial coral. It is the only octocoral known to produce a massive skeleton. This skeleton is formed of aragonite, similar to that of scleractinia. Individual polyps live in tubes within the sk ...
'' was reported as being present in shallow habitats of Funafuti lagoon. The 2007 baseline report also recorded that the most common algae species included: ''
Asparagopsis taxiformis ''Asparagopsis taxiformis'' (red sea plume or limu kohu), formerly ''A. sanfordiana'', is a species of red algae, with cosmopolitan distribution in tropical to warm temperate waters. Researchers have demonstrated that feeding ruminants a diet c ...
''; ''
Caulerpa sertularioides ''Caulerpa sertularioides'', also known as green feather algae, is a species of seaweed in the ''Caulerpaceae'' family found in warm water environments. Description The seaweed has a pale to dark-green thallus that typically grows to outward to ...
''; ''
Caulerpa racemosa ''Caulerpa racemosa'' is a species of edible Green algae, green alga, a seaweed in the family Caulerpaceae. It is commonly known as sea grapes (along with the related ''Caulerpa lentillifera'') and is found in many areas of shallow sea around the ...
''; ''
Halimeda ''Halimeda'' is a genus of green macroalgae. The algal body (thallus) is composed of calcified green segments. Calcium carbonate is deposited in its tissues, making it inedible to most herbivores. However one species, ''Halimeda tuna'', was desc ...
cf gracilis''; ''
Dictyota ''Dictyota'' is a genus of brown seaweed in the family Dictyotaceae. Species are predominantly found in tropical and subtropical seas, and are known to contain numerous chemicals (diterpenes) which have potential medicinal value. As at the end ...
canaliculata''; '' Enteromorpha spp''; ''Microdictyon cf umbilicatum''; and ''Padina sanctae-crucis''. LCC levels appear to have been stable at an average of 20%–30% between 1997 and 2004 (Lovell et al., 2004), and was reported to be 19.5% across all reef habitats of Funafuti in 2004 (Sauni et al., 2008). The 2010 surveys by Job and Ceccarelli identify that the coral cover on the reefs of Funafuti are highly variable, ranging from 0.1% to 58% LCC levels, with a mean cover of 15% across all sites. The highest coral cover estimates were recorded on reef slopes off the islets of Tepuka (58%), Fualefeke (35%) and Fuafatu (34%).The coral cover on the reefs at Funafuti appears to have declined since 2004. The 2010 surveys by Job and Ceccarelli established that on islets to the south of the lagoon, coral cover was greater than 50% on the reef slope. In contrast, in the lagoon adjacent to Fogafale, 96% of the area has less than 1% LCC, and 3.7% has 1-5% LCC. The offshore reefs adjacent to Fogafale most (91%) have less than 1% LCC levels, with 5% of the reef with 1-5% LCC levels and 4% with 5-20% LCC level. On Funafuti atoll, the reef close to the main settlement on
Fongafale Fongafale (also spelled Fogale or Fagafale) is the largest and most populated of Funafuti's islets in Tuvalu. It is a long narrow sliver of land, 12 kilometres long and between 10 and 400 metres wide, with the South Pacific Ocean and reef on the ...
islet has been degraded, as compared to the results from previous surveys, with higher levels of algal cover in contrast to other areas of the Funafuti lagoon which have high percentages of live coral cover. Beginning in 2011, the non-native brown seaweed (''
Sargassum ''Sargassum'' is a genus of brown macroalgae ( seaweed) in the order Fucales of the Phaeophyceae class. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and ...
polycystum'') has rapidly spread in Funafuti lagoon especially adjacent to Fongafale. It has responded to nutrient enrichment in the lagoon in the vicinity of Fofafale and its dense coverage has reduced sunlight penetrating to the reef and it out competes corals and makes fishing difficult. It is suspected that it was introduced through ballast water, or on ships’ hulls or anchors. A survey in June 2014, recorded that LCC levels on the reef off Fongafale were dramatically lower than those recorded in previous surveys, with only around a 1% LCC level, consisting of a few clumps of ''
Pocillopora damicornis ''Pocillopora damicornis'', commonly known as the cauliflower coral or lace coral, is a species of stony coral in the family Pocilloporidae. It is native to tropical and subtropical parts of the Indian and Pacific Oceans. Description ''P. damic ...
'', '' Acropora hyacinthus'', ''
Acropora cytherea ''Acropora cytherea'' is a stony coral which forms horizontal table like structures. It occurs in the Indo-Pacific Ocean in areas with little wave action, favouring back reef environments from depth. Description ''Acropora cytherea'' is a col ...
'', '' Acropora florida'' and some '' Acropora robusta''. Most of the reef area was covered in turfing algae, with a mixture of ''
Halimeda ''Halimeda'' is a genus of green macroalgae. The algal body (thallus) is composed of calcified green segments. Calcium carbonate is deposited in its tissues, making it inedible to most herbivores. However one species, ''Halimeda tuna'', was desc ...
sp''., ''
Dictyota ''Dictyota'' is a genus of brown seaweed in the family Dictyotaceae. Species are predominantly found in tropical and subtropical seas, and are known to contain numerous chemicals (diterpenes) which have potential medicinal value. As at the end ...
covernosa'' and '' Hypnea''). The shallow waters were dominated by either '' Turbinaria'' or a turfing form of the ''
Sargassum ''Sargassum'' is a genus of brown macroalgae ( seaweed) in the order Fucales of the Phaeophyceae class. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and ...
''. The dramatic fall in LCC levels and the domination of the reef areas adjacent to Fogafale by varieties of algae is identified as the consequence of sewage from this densely populated islet. The consequence of this fall in LCC levels would be that production of corals and ''
Foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...
'' (that create sand) are reduced in the reef surrounding Fogafale, with a related reduction in natural breakwater functions of the reef and transportation of sand from the ocean to the lagoon.


Bleaching

In 2000, there was an average of 70%
bleaching Bleach is the generic name for any chemical product that is used industrially or domestically to remove color from (i.e. to whiten) fabric or fiber (in a process called bleaching) or to disinfect after cleaning. It often refers specifically t ...
of the Staghorn (''
Acropora ''Acropora'' is a genus of small polyp stony coral in the phylum Cnidaria. Some of its species are known as table coral, elkhorn coral, and staghorn coral. Over 149 species are described. ''Acropora'' species are some of the major reef corals ...
spp.'') corals in Funafuti lagoon, when water temperatures were 30.5 °C to 32 °C. The bleaching was a consequence of an increase in ocean temperatures that happened during the
El Niño EL, El or el may refer to: Arts and entertainment Fictional entities * El, a character from the manga series ''Shugo Chara!'' by Peach-Pit * Eleven (''Stranger Things'') (El), a fictional character in the TV series ''Stranger Things'' * El, fami ...
s that occurred between 1998 and 2001.
Bleaching Bleach is the generic name for any chemical product that is used industrially or domestically to remove color from (i.e. to whiten) fabric or fiber (in a process called bleaching) or to disinfect after cleaning. It often refers specifically t ...
is a process that expels the photosynthetic algae from the corals' "stomachs" or polyps. This algae is called
zooxanthellae Zooxanthellae (; zooxanthella) is a colloquial term for single-celled photosynthetic organisms that are able to live in symbiosis with diverse marine invertebrates including corals, jellyfish, demosponges, and nudibranchs. Most known zooxanthell ...
. It is vital to the reef's life because it provides the coral with nutrients; it is also responsible for the color. The process is called bleaching because when the algae is ejected from the coral reef the animal loses its pigment.
Zooxanthella Zooxanthellae (; zooxanthella) is a colloquial term for single-celled photosynthetic organisms that are able to live in symbiosis with diverse marine invertebrates including corals, jellyfish, demosponges, and nudibranchs. Most known zooxanthell ...
densities are continually changing; bleaching is an extreme example of what naturally happens. A reef restoration project has investigated reef restoration techniques; and researchers from Japan have investigated rebuilding the
coral reefs A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. ...
through the introduction of
foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...
. The project of the
Japan International Cooperation Agency The Japan International Cooperation Agency (), also known as JICA'','' is a governmental agency that delivers the bulk of Official Development Assistance (ODA) for the government of Japan. It is chartered with assisting economic and social gr ...
is designed to increase the resilience of the Tuvalu coast against
sea level rise The sea level has been rising from the end of the last ice age, which was around 20,000 years ago. Between 1901 and 2018, the average sea level rose by , with an increase of per year since the 1970s. This was faster than the sea level had e ...
, through ecosystem rehabilitation and regeneration and through support for sand production.


Marine protected areas

Locally Managed Marine Areas (LMMA) have been established on some of the islands by the community council, known as the ''
Falekaupule The Falekaupule on each of the Islands of Tuvalu is the traditional assembly of elders or ''te sina o fenua'' (literally: "grey-hairs of the land" in the Tuvaluan language). Under the Falekaupule Act (1997), the powers and functions of the ''Fale ...
'' (the traditional assembly of elders). Tuvalu has established ten LMMAs on eight of its nine islands. The rising population on Funafuti has resulted in an increased demand on fish stocks in Funafuti lagoon (''Te Namo''), although the creation of the Funafuti Conservation Area (FCA) has provided a fishing exclusion area to help sustain the fish population across the Funafuti lagoon. The FCA includes 20% of the reef area of Funafuti atoll. The FCA is located across the lagoon from the main island of Fongafale. The marine environment of the FCA includes reef, lagoon, channel and ocean; and are home to many species of fish, corals, algae and invertebrates. The results of the surveys by Job and Ceccarelli in 2010 found that coral cover was not significantly different inside and outside the FCA, however the LCC levels tended to be slightly higher outside the FCA, with mean values of 11% inside the FCA and 19% outside. Three species of giant clams ('' Tridacnidae'') have been identified in the Funafuti lagoon, mainly within the FCA: ''
Tridacna maxima The maxima clam (''Tridacna maxima''), also known as the small giant clam, is a species of bivalve mollusc found throughout the Indo-Pacific region.MolluscaBase eds. (2022). MolluscaBase. Tridacna maxima (Röding, 1798). Accessed through: World R ...
'' (the most abundant), ''
Tridacna squamosa ''Tridacna squamosa'', known commonly as the fluted giant clam and scaly clam, is a species of bivalve in the family Cardiidae.MolluscaBase eds. (2022). MolluscaBase. Tridacna squamosa Lamarck, 1819. Accessed through: World Register of Marine Sp ...
'' and ''
Tridacna derasa ''Tridacna derasa'', the southern giant clam or smooth giant clam, is a species of extremely large marine clam in the family Cardiidae. Description The southern giant clam is one of the largest of the "giant clams", reaching up to 60 cm in ...
''.
Nanumaga Nanumanga or Nanumaga is a reef island and a district of the Oceanian island nation of Tuvalu. It has a surface area of about 3 km2 with a population of 391 (2022 census). History On 9 May 1824 a French government expedition under Captain ...
has a LMMA, which encompasses the entire island. Spear fishing is also totally banned on the reef and, no fishing is allowed on the reef on the western side of the island, except handlining. The
Nanumea Nanumea is the northwesternmost atoll in the Polynesian nation of Tuvalu, a group of nine coral atolls and islands spread over about of the Pacific Ocean just south of the equator and west of the International Date Line. Nanumea is with a po ...
conservation area was established in 2006 as a no-fishing zone covering about 20% of the total reef area of Nanumea. The Nui conservation area covers the northern half of the lagoon; with a LMMA established over the remainder of the lagoon and reef.
Niutao Niutao is a reef island in the northern part of Tuvalu. It is one of the nine districts (islands) of Tuvalu. It is also one of the three districts that consist of only one island — not counting the three islets inside the closed lagoon. Niuta ...
has a LMMA encompassing all of the reef; with small conservation areas established over specific places on the reef.
Nukufetau Nukufetau is an atoll that is part of the nation of Tuvalu. The atoll was claimed by the US under the Guano Islands Act some time in the 19th century and was ceded in a treaty of friendship concluded in 1979 and coming into force in 1983. It h ...
has a LMMA encompassing most of the lagoon; with a conservation area established over the remainder of the lagoon. The
Nukulaelae Nukulaelae is an atoll that is part of the nation of Tuvalu, and it has a population of 300 (2017 census). The largest settlement is Pepesala on Fangaua islet with a population of 341 people (2022 Census). It has the form of an oval and consist ...
conservation area covers the eastern end of the lagoon; with a LMMA covering the rest of the lagoon. A baseline survey of marine life in the conservation zone was conducted by Job and Ceccarelli in 2010.
Vaitupu Vaitupu is the largest atoll of the nation of Tuvalu. It is located at 7.48 degrees south and 178.83 degrees east. There are 1,077 people (2022 Census) living on with the main village being Asau. History Discovery and settlement The exa ...
has a LMMA encompassing most of the larger lagoon; with conservation areas established over the remainder of the larger lagoon and the smaller lagoon at the north end of the island.


See also

*
Ocean acidification Ocean acidification is the ongoing decrease in the pH of the Earth's ocean. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. Carbon dioxide emissions from human activities are the primary cause of ...


References

{{DEFAULTSORT:Coral Reef Coral reefs Geography of Tuvalu