Tonga - Ha'apai (TOHA05)

Setting

A leeward lagoonal pinnacle reef in Tonga's Ha'apai group (the survey team's field report and the Living Oceans Foundation habitat map; see Notes). Anderson dived this station on 12 September 2013 during the Khaled bin Sultan Living Oceans Foundation's Global Reef Expedition to Tonga and sampled one Pocillopora colony for coral-health work (sampling sheet).

General benthic features

Acropora was the most common coral genus on this station's transects (12% of the benthos), followed by Montipora (9.5%), Coelastrea (2.5%), Favites (1.8%), Goniastrea (1.5%), Platygyra (1.3%), Leptoria (1.0%), and Echinopora, Isopora, and Pocillopora (0.8% each). Alongside the hard coral already reported for this site, the same transects recorded 30% crustose coralline algae, 3.0% turf, 2.8% macroalgae, 4.8% erect algae, and 0.3% cyanobacteria (40% algae in all). Non-living substrate came to 55% pavement, 2.5% dead coral, 7.3% rubble, and 1.0% sand.

Coral cover

• Reference: Khaled bin Sultan Living Oceans Foundation, Global Reef Expedition (in situ transect)
• The expedition's benthic transects recorded 35% 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 35 ± 4.9% SE (n = 4 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 six crown-of-thorns starfish and two Culcita cushion stars (Khaled bin Sultan Living Oceans Foundation expedition site notes, 2013; regional summary in Bruckner 2014). The Living Oceans Foundation transects here recorded 0.3% cyanobacteria and no recently dead coral.

Fish and other fauna

Paired fish transects recorded about 16 fish species per transect and about 1.3 kg per 100 m2 of biomass.

Comparisons with other data

The closest Reef Check site, Kito si'I, is 3.0 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 separate station, not a survey of this station).

Dive record

Anderson's dive: in at 15:15 for 62 minutes, to a maximum depth of 17.4 m on the dive computer (the team dive log gives 37 ft, 11.3 m, for the same dive). At 16:08, at 11 m, Anderson sampled one Pocillopora colony (sample T9.3), which the sheet describes as 'not 100% sure of identity, small, short stubby branches, healthy appearance', with 0% bleached, in calm water with about 25 m visibility. No photographs survive from this dive.

Other notes

Field terms: the survey team's field report opens 'Leeward patch reef'; Anderson's sampling sheet (LOF fellowship 2016 workbook) gives 'leeward', 'lagoonal', 'patch reef'; the 933-site table lists a 'protected' patch reef inside the lagoon. The Living Oceans Foundation habitat map places the pin inside 'lagoonal pinnacle reefs - calcareous red-algal conglomerate', so the reef type printed above is the map's and the aspect is the field report's.

Survey team's site notes: Leeward patch reef. The shallow part of the reef consists of large mounds that slope steeply from 4-5 m to 15 m ending in sand/rubble channel. A second reef extends seaward. These are wide spurs that slope from the sand channel up to 12 m, then gradually to 15, then drop fairly steeply to 25-30 m. The shallows have a high cover of branching acroporids, small table acroporids, thickets of bottlebrush acropora, Pocillopora, small Montastrea, and Goniastrea; coral cover is about 30%. There is also 30-40% cover soft corals. On the edges of the mounds, near the base are larger plating corals intermixed with soft corals and small branching corals. The seaward spurs are fairly high relief (up to 1 m) with lots of framework, depressions, and a rugose matrix of skeletons with holes and crevices. Between 10-15% dead colonies were seen. Much of the complex framework is also long dead, but numerous corals have colonized the skeletons. At 15 m the reef is dominated by bottlebrush Acropora, small table acroporids, and some staghorn coral with small to medium Goniastrea, Massive and encrusting Montipora, and moderate numbers of Platygyra, Leptoria, Lobophyllia, Acanthastrea, Cyphastrea, Montastrea, and Coscinaraea. Most of which are 20-30 cm diameter. The reef had numerous recently eaten corals, especially bottlebrush Acropora. Low cover (2.0–3.0%) macroalgae, predominantly Tydemania, and 5.0% cyanobacteria (a by-eye estimate; the transects recorded 0.3%).