Tonga - Vava'u (TOVA46)

Setting

Barrier reef on the leeward side at the southwestern end of the reef system. This is a very gently sloping system of wide spurs and wide sand patches and channels with little rubble.

General benthic features

The frames show the crest and flank of a wide, gently sloping spur, with open white sand immediately alongside it. Image 1 and Image 6 both catch the boundary directly: a coral-covered ridge running diagonally across the frame and falling away to a broad, clean sand channel with no coral on it at all.

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This wide-spur-and-sand-channel arrangement is consistent with the surveyors' account of a gently sloping system of wide spurs and wide sand patches, but relief and depth zonation are not readable from these frames and no such claim is made from them. Image 8, Image 2, Image 3, and Image 4 look along and over the crest under open blue water, with sand visible beyond the reef in Image 4. Image 3 is the only frame with real vertical structure in it — a dark undercut running beneath the crest.

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Where the camera is over the reef the community is branching- and plating-dominated. The recurring elements across all eight frames are corymbose and digitate Acropora in tan, mauve, and lavender; tabular and plating Acropora, several of them broad and low; olive- and yellow-green foliose and encrusting colonies; small tan knobby and digitate heads; and pale gray-cream colonies of several growth forms scattered through. Image 5 is the densest benthic frame — a close mosaic of green tabular plates, olive-green foliose colonies, mauve branching thickets and, filling the lower frame, a large pale gray-white convoluted foliose colony.

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Image 7 is a bushy mauve-brown Acropora stand filling the frame with green tabular plates above it and pale rubble showing in the gaps between colonies. Image 4 carries a distinctly blue-lavender branching Acropora that is the most conspicuous single colony in the set.

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The sand channels beside the spur, plainly visible in Image 1 and Image 6, carry no coral. The shallow areas (8-12 m) have up to 1.5 m relief, but relatively low cover dominated by faviids, small acroporids, Pocillopora, and Stylophora. At 12-15 m there is very little relief – largely a flat-topped reef with little coral and 40-50% soft corals. At 15-25 m the spurs are 2-3 m above the surrounding sand with large patches of staghorn corals (most partially dead with dense turf algae and damselfish), soft corals, scattered large table acroporids (up to 2 m, 10% dead), Isopora, Goniastrea, Montipora plates, Stylophora colonies (most with partial mortality and snails), Favia stelligera, Coscinaraea, and Porites 1-2 m in diameter. Found one very large Porites (3 m × 2 m) at the edge of the spur in the sand (15 m) and one very large (2 m) Montipora plate. The reef has 10-15% cover Halimeda, good CCA (30%) throughout all depths and 20% turf (except in damselfish algal lawns).

Coral cover

• Reference: Khaled bin Sultan Living Oceans Foundation, Global Reef Expedition (in situ transect)
• 19%, from the Khaled bin Sultan Living Oceans Foundation's in situ transect survey (Global Reef Expedition site data); the photographs illustrate the site.
• Transect mean 19 ± 1.8% SE (n = 5 transects; Living Oceans Foundation per-transect benthic data); the headline above is this all-transect mean.

Stressors

On condition the frames say less than they appear to. Pale gray-cream colonies appear in Image 2, Image 3, Image 6, and Image 5, and pale rubble and bare patches show between colonies in Image 7 and along the crest in Image 1 and Image 4. At this range those cannot be separated from one another — pale but normally pigmented tissue, older dead skeleton crusted with coralline algae, and recent whitening all read much the same in a wide frame lit by ambient light. They are reported as seen and diagnosed no further, and no bleaching or mortality percentage should be read off this set. Equally, the surveyors' specific observations — partial mortality with turf algae on the staghorn stands, snails on Stylophora, the very large Porites and Montipora plate, the three Culcita — are neither confirmed nor contradicted by these eight frames. The 2013 survey notes for this site record snails on most of the Stylophora colonies and three Culcita cushion stars (Khaled bin Sultan Living Oceans Foundation expedition site notes, 2013; regional summary in Bruckner 2014). Typical recent thermal stress: mean annual maximum of 8.1°C-weeks (Degree Heating Weeks, 2021-2025, NOAA CRW; Southern Tonga virtual station). The Living Oceans Foundation transects here recorded 2.9% cyanobacteria and no recently dead coral.

Fish and other fauna

Faunally the set is quiet and consistent: loose schools of dark surgeonfishes and unicornfishes over the crest and the adjacent sand in Image 1, Image 2, Image 3, Image 6, and Image 4, with scattered damselfishes among the corals. Low numbers of sea cucumbers found.

Comparisons with other data

TOVA46 (Vava'u) was surveyed on 26 September 2013 during the Khaled bin Sultan Living Oceans Foundation Global Reef Expedition.

Other notes

Eight habitat frames survive from TOVA46 (Vava'u, 26 Sep 2013), all of them genuine wide or mid-range reef views, with no apparatus, tag, or dive-computer frames among them. There are no sampled-colony frames.

Anderson recorded none of the target Pocillopora ('no Pdam') here. That is Anderson's field determination and it stands as recorded; it is also why this site produced habitat photography and no colony sampling. No quadrat, transect line, or scale reference appears anywhere, so no colony dimension in this set is measured.