Tonga - Vava'u

Spalding et al. (2001) describe Tonga as a double chain of islands spread over more than 800 km along the western edge of the convergent margin between the Indo-Australian and Pacific plates. The volcanic Tofua Arc forms the western chain, running from 'Ata to Niuafo'ou, and a trough some 1,800 m deep (the Tofua Trough) separates it from the eastern arc, where most islands are of reef origin, though blanketed in places by volcanic ash. The Vava'u group anchors the north of that eastern arc: it is dominated by the large island of Vava'u, with a broad spread of smaller islands and reefs off its southern side. Throughout the eastern islands, reefs are widespread and well developed, with fringing reefs around most shores and platform and barrier-type structures in most of the main groups. The atlas puts Tonga's national reef area at about 1,500 km². It also links eutrophication around Vava'u to untreated sewage and fertilizer runoff, mentions problems from causeway building, and notes that three proposed reserves in the group were surveyed in 1997. For Tonga as a whole, the same source records cyclone damage in 1995, 1997, 1999, and 2000, and a major bleaching event in 2000 after the reefs had largely escaped the 1998 bleaching.

No source in this set reports on Vava'u after 2001, so recent conditions come from regional overviews. Wilkinson (2006), drawing on the 2004 assessment of the Polynesia Mana network, which covers Tonga, described those reefs as largely healthy and among the least degraded anywhere because of their isolation, while warning that climate change, cyclones, and bleaching were the main worries and that sedimentation, overfishing, dredging, and nutrient pollution needed more attention near populous islands. For the Pacific region as a whole, Souter et al. (2021) report a fall in average hard coral cover from about 37% before 1998 to 31% in 2019, attribute most of the loss to bleaching, and note that most of the 15-year decline came between 2010–2014 and 2015–2019.

The 21 Vava'u stations, surveyed 22-28 September 2013 at maximum depths dived from 14 m (TOVA35) to 32.3 m (TOVA36), range from sheltered leeward lagoon reefs and channel entrances to fore reefs below uplifted coastal cliffs and a steep wall on a fore-reef pinnacle at TOVA49. Wide spurs separated by sand channels are the common framework, but the group also includes the massive Porites stand known as the Aquarium (TOVA35), a two-mouthed cave ringed by sea fans with black coral at a second cave entrance (TOVA37), and a north-shore terrace that drops near vertically onto spurs sloping past 35 m (TOVA38).

Dense branching and table Acropora dominate the shallow terraces, reaching 50-80% on the 3-8 m shallows of TOVA47 and 60-80% on the Treasure Island terrace at TOVA53; these are local patch values rather than site means. Deeper and on the spurs, massive Porites takes over, from colonies up to 5 m across at TOVA35 to mounding Porites lobata covering the spurs at Split Rock (TOVA36). Staghorn stands carrying damselfish algal lawns are a recurring feature, notably at Pete's Paradise (TOVA34), TOVA35, and TOVA46.

Transect cover ranged from 9.6% at TOVA50, where algae outweighed coral more than six to one, to 53% at TOVA44. Algae ranged from 25% at TOVA33 to 76% at TOVA49. The Coral Health Index (scale of zero to five; higher is healthier), scored at eight stations, was 4.24 at TOVA34, 3.71 at TOVA47, 3.46 at TOVA44, 3.10 at TOVA51, 2.20 at TOVA40, 3.00 at TOVA53, 2.49 at TOVA52, and 1.50 at TOVA35, a high-cover reef with large dead patches under damselfish lawns. Coral-eating snails were widespread (the TOVA39 survey notes record snails behind most of the mortality on about 20% of the Isopora, digitate Acropora, and Pocillopora), and Culcita were recorded at many stations. The expedition's field report describes localized crown-of-thorns outbreaks in the central lagoon, among stands of Pocillopora damicornis and around Treasure Island, where 25 starfish were collected (Bruckner 2014). Crown-of-thorns starfish appeared at TOVA40, TOVA44, and TOVA51, where five or six were massed together, and 15 were counted on a single bommie at the Japanese Coral Gardens (TOVA42). Anderson's sampling sheets record bleaching among the Pocillopora sampled at eight Vava'u stations (TOVA33, TOVA34, TOVA35, TOVA40, TOVA44, TOVA47, TOVA51, and TOVA52), among them all seven colonies 20-80% bleached at TOVA34 and four of eight 60-95% bleached at TOVA47.

Sightings include banded sea kraits at TOVA36 and TOVA37, giant clams at TOVA39, TOVA47, and TOVA49, and schooling fish along the TOVA49 wall.

ʻOku fakamatalaʻi ʻe Spalding et al. (2001) ʻa Tonga ko ha ongo laine motu ʻe ua ʻoku mafola ʻo laka hake ʻi he 800 km ʻi he kauʻā hihifo ʻo e feituʻu ʻoku fetaulaki ai ʻa e ongo papa ʻo e māmani (tectonic plates) Indo-Australian mo Pasifiki (Pacific). Ko e Tofua Arc moʻungaafi ʻa e laine ʻi he hihifo, ʻoku mafola mei 'Ata ki Niuafo'ou, pea ʻoku vaheʻi ia mei he laine ʻi he hahake ʻe ha luo ʻi he takele tahi ʻoku meimei loloto ʻaki ʻa e 1,800 m (ko e Tofua Trough); ko e lahi taha ʻo e ngaahi motu ʻi he laine hahake naʻe tupu mei he hakau, neongo kuo ʻufiʻufi ʻe he efuefu moʻungaafi ʻi ha ngaahi feituʻu. Ko e ʻotu motu Vava'u ʻa e taulaʻanga ʻo e potu tokelau ʻo e laine hahake ko ia: ʻoku puleʻi ia ʻe he motu lahi ko Vava'u, mo ha mafola lahi ʻo e ngaahi kiʻi motu mo e ngaahi hakau ʻi hono potu tonga. ʻI he ngaahi motu kotoa ʻi he hahake, ʻoku mafola mo tupu lelei ʻa e ngaahi hakau, mo e ngaahi hakau matafonua (fringing reefs) ʻi he lahi taha ʻo e ngaahi matātahi, pea mo e ngaahi hakau fakapapa (platform) mo e hakau fakaā (barrier-type) ʻi he lahi taha ʻo e ngaahi ʻotu motu lalahi. ʻOku fakafuofua ʻe he tohi fakafaʻahinga (atlas) ʻa e lahi ʻo e hakau ʻi Tonga kotoa ki he meimei 1,500 km². ʻOku toe fekauʻaki ai ʻa e fakatupu lahi fau ʻo e ngaahi meʻa fakatupu ʻi he vai (eutrophication) ʻi Vava'u mo e vai ʻuli (sewage) ʻoku teʻeki fakamaʻa mo e tafe mai ʻa e fakatupu ʻakau (fertilizer runoff), ʻoku ne lave ki he ngaahi palopalema mei he langa ʻo e ngaahi hala ʻi he tahi (causeways), pea ʻoku ne fakahā naʻe savea ʻi he 1997 ʻa e feituʻu tapu (reserves) ʻe tolu naʻe fokotuʻu atu ʻi he ʻotu motu. Ki Tonga kotoa, ʻoku lēkooti ʻe he maʻuʻanga tatau ʻa e maumau mei he ngaahi afā ʻi he 1995, 1997, 1999, mo e 2000, mo ha hinehina lahi ʻa e feo (coral bleaching) ʻi he 2000 hili hono hao lahi ʻa e ngaahi hakau mei he hinehina ʻo e 1998.

ʻOku ʻikai ha maʻuʻanga ʻi he kulupu ko ʻeni ʻoku ne lipooti ʻa Vava'u hili ʻa e 2001, ko ia ko e ngaahi tuʻunga ki mui ni ʻoku haʻu mei he ngaahi fakamatala fakavāhenga. Naʻe fakamatalaʻi ʻe Wilkinson (2006), ʻo makatuʻunga ʻi he vakavakaʻi ʻo e 2004 ʻo e kupenga (network) Polynesia Mana, ʻa ia ʻoku kau ai ʻa Tonga, ko e ngaahi hakau ko ia naʻe moʻui lelei lahi pea ʻi he ngaahi hakau siʻi taha hono maumau ʻi māmani koeʻuhi ko ʻenau mamaʻo, ka naʻa ne fakatokanga ko e feliuliuaki ʻo e ʻea (climate change), ngaahi afā, mo e hinehina ʻa e feo ko e ngaahi hohaʻa tefito, pea ʻoku fie maʻu ke tokangaʻi lahi ange ʻa e fakafonu ʻe he kelekele (sedimentation), toutai lahi fau, keli ʻo e takele tahi (dredging), mo e ʻuliʻi ʻaki ʻa e ngaahi meʻa fakatupu (nutrient pollution) ʻi he ngaahi motu ʻoku tokolahi ai ʻa e kakai. Ki he vāhenga Pasifiki kotoa, ʻoku lipooti ʻe Souter et al. (2021) ha holo ʻi he ʻavalisi ʻo e ʻufiʻufi ʻe he feo fefeka (hard coral cover) mei he meimei 37% ki muʻa ʻi he 1998 ki he 31% ʻi he 2019, ʻoku nau pehē ko e tupuʻanga ʻo e lahi taha ʻo e mole ko e hinehina ʻa e feo, pea ʻoku nau fakahā ko e lahi taha ʻo e holo ʻi he taʻu ʻe 15 naʻe hoko ia ʻi he vahaʻa ʻo e 2010–2014 mo e 2015–2019.

Ko e potu (stations) ʻe 21 ʻi Vavaʻu, naʻe savea ʻi he 22-28 Sepitema 2013 ʻi he loloto taha naʻe uku ki ai mei he 14 m (TOVA35) ki he 32.3 m (TOVA36), ʻoku kau ai ʻa e ngaahi hakau ʻi he namo (lagoon) ʻoku maluʻi mei he matangi mo e ngaahi hūʻanga ʻo e ngaahi hala vai, ʻo aʻu ki he tafaʻaki tuʻa ʻo e hakau (fore reefs) ʻi lalo ʻi he ngaahi mato matātahi kuo hiki hake, mo ha holisi (wall) tuʻu hangatonu ʻi ha tumutumu hakau (pinnacle) ʻi he tafaʻaki tuʻa ʻo e hakau ʻi TOVA49. Ko e fōtunga angamaheni ko e ngaahi spurs fālahi ʻoku vaheʻi ʻe ha ngaahi hala vai ʻoneʻone, ka ʻoku toe kau ʻi he kulupu ʻa e fuʻu tuʻunga lahi ʻo e Porites ʻoku ui ko e Aquarium (TOVA35), ha ʻana ʻoku ua hono ngutu ʻoku takatakaiʻi ʻe he ngaahi sea fans pea ʻoku ʻi ai ʻa e feo ʻuliʻuli (black coral) ʻi ha hūʻanga ʻana hono ua (TOVA37), mo ha tuʻunga ʻi he matātahi tokelau ʻoku tō hifo meimei hangatonu ki ha ngaahi spurs ʻoku hifo ʻo laka hake ʻi he 35 m (TOVA38).

Ko e Acropora fakavaʻavaʻa mo fakatēpile matolu ʻoku nau puleʻi ʻa e ngaahi tuʻunga mamaha, ʻo aʻu ki he 50-80% ʻi he mamaha ʻo e 3-8 m ʻi TOVA47 pea ki he 60-80% ʻi he tuʻunga ʻo Treasure Island ʻi TOVA53; ko e ngaahi mahuʻinga ʻeni ʻo ha ngaahi konga pē, ʻo ʻikai ko e averisi ʻo e potu. ʻI he loloto ange mo e ngaahi spurs, ʻoku puleʻi ia ʻe he Porites lalahi, mei he ngaahi kolonī ʻoku aʻu ki he 5 m hono fālahi ʻi TOVA35 ki he Porites lobata fakapuke ʻoku ʻufiʻufi ʻa e ngaahi spurs ʻi Split Rock (TOVA36). Ko e ngaahi tuʻunga staghorn ʻoku ʻi ai ʻa e ngaahi ngoue limu ʻa e ika damselfish ko ha meʻa ʻoku toutou hā, tautautefito ʻi Pete's Paradise (TOVA34), TOVA35 mo TOVA46.

Naʻe kehekehe ʻa e ʻufiʻufi ʻe he feo ʻi he transect mei he 9.6% ʻi TOVA50, ʻa ia naʻe laka hake ai ʻa e limu ʻi he liunga ono ʻo e feo, ki he 53% ʻi TOVA44. Naʻe kehekehe ʻa e limu mei he 25% ʻi TOVA33 ki he 76% ʻi TOVA49. Ko e Coral Health Index (sikēlī mei he noa ki he nima; ko e māʻolunga ange, ko e moʻui lelei ange ia), naʻe fakamaaka ʻi he potu ʻe valu, naʻe 4.24 ʻi TOVA34, 3.71 ʻi TOVA47, 3.46 ʻi TOVA44, 3.10 ʻi TOVA51, 2.20 ʻi TOVA40, 3.00 ʻi TOVA53, 2.49 ʻi TOVA52, mo e 1.50 ʻi TOVA35, ko ha hakau ʻoku lahi hono ʻufiʻufi ka ʻoku ʻi ai ha ngaahi konga mate lalahi ʻi lalo ʻi he ngaahi ngoue limu ʻa e damselfish. Naʻe mafola ʻa e ngaahi ʻelele kai feo (coral-eating snails) (ʻoku lēkooti ʻe he ngaahi nouti ʻo e savea ʻi TOVA39 ko e ʻelele naʻa nau fakatupu ʻa e lahi taha ʻo e mate ʻi he meimei 20% ʻo e Isopora, Acropora fakaʻuhiki mo e Pocillopora), pea naʻe lēkooti ʻa e Culcita ʻi he potu lahi. ʻOku fakamatalaʻi ʻe he lipooti ʻa e ʻekisipeteni ʻa e ngaahi kiʻi tupu lahi fakafeituʻu ʻo e ʻalamea (crown-of-thorns starfish) ʻi he loto namo, ʻi he lotolotonga ʻo e ngaahi tuʻunga Pocillopora damicornis pea takatakai ʻi Treasure Island, ʻa ia naʻe tānaki ai ʻa e ʻalamea ʻe 25 (Bruckner 2014). Naʻe hā ʻa e ʻalamea ʻi TOVA40, TOVA44 mo TOVA51, ʻa ia naʻe fakatahataha ai ha ʻalamea ʻe nima pe ono, pea naʻe lau ha ʻalamea ʻe 15 ʻi ha bommie pē ʻe taha ʻi he Japanese Coral Gardens (TOVA42). ʻOku lēkooti ʻe he ngaahi pepa sampling ʻa Anderson ʻa e hinehina (bleaching) ʻi he Pocillopora naʻa ne toʻo ʻi he potu ʻe valu ʻi Vavaʻu (TOVA33, TOVA34, TOVA35, TOVA40, TOVA44, TOVA47, TOVA51 mo TOVA52), kau ai ʻa e feo kotoa ʻe fitu naʻe hinehina ʻaki ʻa e 20-80% ʻi TOVA34 mo e feo ʻe fā ʻi he valu naʻe hinehina ʻaki ʻa e 60-95% ʻi TOVA47.

Ko e ngaahi meʻa naʻe sio ki ai ʻoku kau ai ʻa e ngata tahi (banded sea kraits) ʻi TOVA36 mo TOVA37, vasuva lalahi (giant clams) ʻi TOVA39, TOVA47 mo TOVA49, mo e ngaahi kulupu ika ʻi he tafaʻaki ʻo e holisi (wall) ʻi TOVA49.