Coral Reef Fish & Habitats

Noteworthy

The area of Amaala reef habitat in our target depth range of less than 20m is much smaller than at TRS (1,077 Ha compared to nearly 7,000 Ha at TRS), as most of the Amaala waters are deeper.

Therefore, our baseline survey effort at Amaala was limited to 69 sites compared to the 280 we surveyed last year for the TRS baseline. The team also re-surveyed 82 TRS baseline sites as part of our ongoing monitoring there.

Although smaller in area than TRS, Amaala reef habitats still contain many impressive reefs, with Amaala coral cover averaging 21.5% and the highest cover at any site being 57.2%.

Fish biomass at Amaala varied between 32.2 g/m2 and 240.3 g/m2 and was very similar overall between Amaala and TRS (Amaala averaged 93.7 g/m2; TRS, 91.8 g/m2).

In total, 193 fish species were recorded during the 69 Amaala surveys, with the most diverse families being wrasse (36 species) and damselfish (24 species).

Notable fish species sighted at Amaala include both of the two endangered reef fish species known to be present in our area: Sky Emperor (L. mahsena) seen at four sites in 2022, and Humphead wrasse (Cheilinus undulatus) seen at eight sites. The Amaala survey team also recorded the presence of four species listed as vulnerable: Bumphead parrotfish (Bolbometopon muricatum); Harlequin filefish (Oxymonacanthus halli) and two species of Coral grouper (Plectropomus areolatus and P. marisrubri)

Compared to TRS, reef sharks were more frequently seen this year at Amaala (12 of 69 sites) than at TRS (six of 82 sites). All the sharks seen during in-water surveys by the coral reef team this year were White-tip reef sharks (Triaenodon obesus). However, a number of other shark species were observed at other times this year (see megafauna section for details).

Methods

Our approach for the TRS baseline in 2021 and now TRS and Amaala in 2022 is to conduct highly comprehensive surveys of fish and habitats at representative sites across all coral reef habitats in our target domain of complex reef areas less than 20m deep. Those reef areas were classified into seven habitat types at TRS, but only five of those habitat types are found at Amaala. The TRS baseline included a total of 280 sites. Because the reef area at Amaala is much smaller than at TRS, the Amaala baseline comprised 69 sites. As with TRS, in the Amaala baseline the survey effort was greatest in habitats where we expected highest coral cover, fish biomass, or diversity, and in the habitats that are most comparable across the Red Sea Zone and beyond - reef walls and slopes.

At each site, the survey team recorded the number, size and species of all fishes observed within standard 50m-by-5m transects and took 50 benthic planar photographs at a standard distance (1m) above the reef. Accurate records of location, depth, and survey bearings at each site were made to ensure the same sections of reef can be subsequently resurveyed, greatly improving the ability to precisely measure and assess changes over time.

Our intention is to resurvey all the baseline sites every five years, but a subset of ‘core’ sites will be surveyed annually. In 2022, we surveyed 82 such core sites at TRS. Revisiting the core sites allows us to track change from year to year and thereby rapidly identify any indications of changing state.

Table: Habitat classification used for survey design

Results

In general, coral cover at Amaala tended to be relatively high on many of the nearshore wall and slope sites and on the exposed offshore side of An Numan Island. Areas of lower coral cover included the sheltered inshore side of An Numan and sites in the cluster of offshore slope and patch reefs in the southern part of Amaala. Fish biomass varied considerably among sites, but there were no clear spatial patterns across the Amaala reefs we surveyed.

Note: We only included areas where we could realistically survey at least 100m of near continuous reef. There are extensive additional habitats within Amaala where corals and associated fishes are present, but those are typically patchy, sparsely populated or too deep for divers to feasibly survey.

At Amaala, fish biomass tended to be highest at reef crest sites, but there were not large differences in fish biomass among other habitats. By far the lowest fish biomass habitat at TRS in both 2021 and 2022 was at the offshore algal, possibly due to lower habitat complexity and diversity there.

Overall, and within habitat types, reef fish biomass was similar between Amaala and TRS. However, Amaala reef wall sites tended to have lower biomass than TRS walls. That difference was possibly due to impacts of shoreline fishing at Amaala. Unlike Amaala, most of the TRS reef wall sites are far offshore and only accessible by boat.

Coral cover per habitat type was also very similar between Amaala and TRS, generally being higher in shallow habitats such as reef crest and reef top habitats at both locations. The re-surveys of core monitoring sites at TRS (at 82 of the 280 sites surveyed for the 2021 baseline) showed only small changes in coral cover or fish biomass between years.

Reef Fish Aggregation Sites

Fish spawning aggregations are impressive natural events in which large numbers of fish gather at one place, typically to engage in mass spawning events. However, due to their predictability in time and space, and the large numbers of mature fish involved, spawning aggregations are vulnerable to over-exploitation.

We are learning more about the timing and location of these events in order to protect these fishes better at a critical stage in their lifecycle. Knowledge of the timing and location of these events also provides opportunities for visitors to experience what can be spectacular sights. Since our team began surveys in late 2020, we have documented several such aggregations.

Table: Details on known reef fish spawning aggregations

Species Location Timing Description

Lethrinidae Pinnacle back of Waqadi Early June

Crescent-tail bigeye (Priacanthus hamrur) South of Breem Mid July

Blackspot snapper (L. ehrenbergii)

Pinnacle offshore of Sheybarah Mid/late July

Reported aggregation by boat captains and fishermen. Sandbar and tiger sharks seen in the area at this time

School of hundreds of fish. Low on the reef wall in around 20-30m of water

Two-spot snapper (Lutjanus bohar)

Pinnacle offshore of Sheybarah Mid/late July

Thousands of snappers swimming back and forth across the reef

Pre-spawning behavior of 20/30 snappers

Mangrove snapper (L. argentimaculatus)

Pinnacle offshore of Sheybarah Mid/late July

Two-spot snapper (Lutjanus bohar) Waqadi wall

Bumphead parrotfish (B. muricatum)

Early September

A small school of around 20/30 snappers showing pre-spawning behavior

A school of around 100 snappers swimming together up and down the reef wall

Reef wall at Ghawar

Late September

Group of around 100 fish aggregated in shallow water