Tonga - Ha'apai (TOHA11)

Setting

A leeward fore reef slope in Tonga's Ha'apai group (Living Oceans Foundation habitat map; see Notes). The expedition team surveyed this station on 15 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 (church)').

General benthic features

Acropora was the most common coral genus on this station's transects (22% of the benthos), followed by Pocillopora (9.3%), Montipora (3.4%), Pavona (2.6%), Leptoria (2.0%), and Montastrea (1.4%). Alongside the hard coral already reported for this site, the same transects recorded 21% crustose coralline algae, 1.8% turf, and 4.3% macroalgae. Non-living substrate came to 42% pavement, 7.9% dead coral, and 1.0% rubble.

Coral cover

• Reference: Khaled bin Sultan Living Oceans Foundation, Global Reef Expedition (in situ transect)
• The expedition's benthic transects recorded 50% 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 50 ± 6.8% SE (n = 5 transects; Living Oceans Foundation per-transect benthic data); the headline above is this all-transect mean.

Stressors

The Living Oceans Foundation transects here recorded no cyanobacteria and no recently dead coral, and they carry no bleaching, disease, or crown-of-thorns starfish field. The survey team's site notes for this station, which Anderson did not dive, describe cyanobacteria as low, with small patches at 5.0% cover at 15 m. Island-level context, not an observation at this station: the Living Oceans Foundation Tonga field report notes considerable partial coral mortality at many Ha'apai locations, attributed to damselfish algal lawns, Culcita sea stars, and Drupella snails.

Fish and other fauna

Paired fish transects recorded about 19 fish species per transect and about 2.8 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 42.4 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: Anderson's sampling sheet (LOF fellowship 2016 workbook) gives 'lagoonal', 'patch reef' with no aspect, and the survey team's field report gives none; the 933-site table lists an 'intermediate' patch reef outside the lagoon. The Living Oceans Foundation habitat map places the pin 9 m from 'shallow fore reef slope' (within about 65 m, the distance within which a mapped reef is taken as the station's own reef); the slope faces west-northwest, 165-180 degrees off the prevailing trade winds, which makes it leeward. Trade-wind reference: east-southeast trades, about 120 degrees (under 60 degrees off = windward, over 120 = leeward, between = side-on). The depth printed is the team dive log's maximum for this station (47 ft, 14.3 m), not a dive of Anderson's. No photographs exist for this station.

Survey team's site notes: Reef has a terrace consisting of a gently sloping scoured hardground in shallows (3-6 m) with large areas covered in turf. This drops to a rubble field in 10 m, and then a second terrace that extends seaward for about 50-100 m at 6 m depth, sloping very gradually to 10 m, then a vertical drop from 12-40 m. The reef has large very wide spurs with narrow deep grooves. Shallows have high cover (40% at 5 m, increasing to 80% at 10-15 m) dominated by small to medium Acropora, both staghorn and tabular growth forms with some digitate colonies, along with small to medium Astreopora, Pocillopora, and other species. There is a slight build-up from 10 – 15 m with a high abundance of branching, bottlebrush, and table acroporids, large plating corals on the top of the slope, including Porites, Coscinaraea, Echinophyllia, and Mycedium, some 3-4 m diameter. At 20 m, there is a dominance of Pocillopora, Pavona varians, Stylophora, and many large Favites and Montipora plates and crusts. Cover drops at 25-30 m to 25-30% with a dominance of Pachyseris, Montipora, Leptoseris, Mycedium, Echinopora, Echinophyllia, and other plating corals. There is also 40% Caulerpa, mostly on the outer horizontal faces of the wall, with corals on the vertical and near vertical areas. Soft coral is most abundant at 5 m (20%), declining to 10% at 10 m and 5.0% from 15-20 m. There is very little soft coral from 25 m (2.0%) to 30 m (0). Very good CCA cover throughout the reef (30-40% cover). Cyanobacteria low with small patches at 5.0% cover at 15 m.