Tonga - Ha'apai (TOHA20)

Setting

A lagoonal reef in Tonga's Ha'apai group, side-on from its position on the southwest side of the Ha'apai island group relative to the prevailing southeast trade winds (the survey team's field report calls it leeward; see Notes). The expedition team surveyed this station on 17 September 2013 during the Khaled bin Sultan Living Oceans Foundation's Global Reef Expedition to Tonga (station records and team dive log); Anderson was on the expedition but did not dive this station (sampling sheet: 'did not dive').

General benthic features

Acropora was the most common coral genus on this station's transects (8.7% of the benthos), followed by Montipora (4.4%), Pocillopora (2.2%), Goniastrea (2.0%), Leptoria (1.5%), and Porites (1.2%). Alongside the hard coral already reported for this site, the same transects recorded 24% crustose coralline algae, 12% turf, 3.9% macroalgae, 3.9% erect algae, and 0.5% cyanobacteria (45% algae in all). Non-living substrate came to 54% pavement, 7.3% dead coral, 4.2% rubble, and 8.6% sand.

Coral cover

• Reference: Khaled bin Sultan Living Oceans Foundation, Global Reef Expedition (in situ transect)
• The expedition's benthic transects recorded 26% hard coral cover (LOF-GRE in situ transects; mean of all of this station's own transects) — a diver transect measurement, not a photographic or computer vision estimate.
• Transect mean 26 ± 2.1% SE (n = 5 transects; Living Oceans Foundation per-transect benthic data); the headline above is this all-transect mean.

Stressors

The 2013 survey notes for this site record four crown-of-thorns starfish, three Culcita cushion stars, Drupella snails, and snail damage on about 5% of the Acropora (Khaled bin Sultan Living Oceans Foundation expedition site notes, 2013; regional summary in Bruckner 2014). The Living Oceans Foundation transects here recorded 0.5% cyanobacteria and no recently dead coral.

Fish and other fauna

Paired fish transects recorded about 11 fish species per transect and about 1.5 kg per 100 m2 of biomass.

Comparisons with other data

No Reef Check station lies within 5 km of this station. The closest Reef Check site, Kito si'I, is 35.6 km away; its only survey date, 15 August 2002, recorded 18% hard coral (mean of 2 surveys, 3 m and 10 m; Reef Check data, a different reef, not a survey of this station).

Other notes

Field terms: the survey team's field report opens 'Leeward lagoonal reef in SPA (outside of MPA)'; Anderson's sampling sheet (LOF fellowship 2016 workbook) gives 'leeward', 'lagoonal', 'fringing reef'; the 933-site table lists a 'protected' fringing reef on the fore reef, outside the lagoon. The Living Oceans Foundation habitat map places the pin on 'deep fore reef slope', facing south to south-southeast, about 47-62 degrees off the prevailing trade winds. Trade-wind reference: east-southeast trades, about 120 degrees (under 60 degrees off = windward, over 120 = leeward, between = side-on). The aspect shown, 'side-on', comes from the station's GPS position on the southwest side of the Ha'apai island group relative to the prevailing southeast trade winds (about 100° off the upwind direction; the reef-edge reading agrees), which takes precedence over slope facing, lagoon shelter, imagery, and field labels. The depth printed is the team dive log's maximum for this station (48 ft, 14.6 m), not a dive of Anderson's. No photographs exist for this station.

Survey team's site notes: Leeward lagoonal reef in SPA (outside of MPA). Shallow reef (2-5 m) dominated by large Lobophytum and Sinularia colonies (60% cover) with some table, thick tabular, branching, digitate acroporids, and small massive corals. Many of the acroporids had snail damage (5%) and white syndrome on staghorns and tabular acroporids. Corals with mortality also had numerous damselfish. Occasional 1-2 m patches of reef framework with thick CCA. From 5-10 m deep mixed reef framework interspersed with patches of sand. In places the framework was up to 1 m tall with scattered corals and 20-30% cover soft corals. Corals included small to medium faviids (20-30 cm; Favia, Goniastrea, Favites, Platygyra), tabular and branching acroporids (most < 50 cm), and fewer Pocillopora, Seriatopora, Stylophora, Lobophyllia, Astreopora, Euphyllia, and other species. 10-15 m were low relief spurs, up to 50 cm tall with some larger patches of framework and dead boulders with 5.0-10% live coral, 30-40% dead coral, and 10% soft corals; more than 50% of the benthos sand with scattered rubble. Below 15 m 5.0% live coral, 5.0% soft corals mostly Lobophytum. Corals include isolated medium sized massive Porites (up to 1 m), Montipora crusts, faviids, small acroporids, and increasing numbers of plating corals including Mycedium, Echinopora, Pachyseris, Merulina, and Goniopora, most of which were less than 1 m. Coral ends at 20 m in sand. The sand with small corals, dead coral, and some rubble slopes moderately steeply deeper. Many of the corals had partial mortality. No macroalgae; CCA on rocks to 15 m; turf mostly in damselfish territories. Moderate abundance of sea cucumbers (3 spp.) in sand and adjacent to corals; low numbers of giant clams; white syndrome on acroporids. Few fish.