Planetary Coral Reef Foundation
Science Report
Sep 18th - Oct 7th, 2002
26.7° - 28.8°C
A bleaching event had begun on this site in January 2000. When we last studied this reef, we observed up to 30% of corals bleached in some areas - predominantly table Acropora colonies but the bleaching was noticeable to depths of 25 meters. Bleaching is now a minor impact on the reef (just over 5% of colonies analysed with Vitareef showed signs of bleaching), but the skeletons remain of the corals that bleached two years ago. Those that lost their zooxanthellae then were unable to recover and are now overgrown with both filamentous and macroalgae. Thankfully the event that began so suddenly never became an epidemic and only small scars remain on this reef.
None observed.
Very variable - from 10m upwards.
Only 2 observed during the entire study.
This reef spreads itself around the island called Sagharughombe Island. We nicknamed it One Tree Island two years ago because there was one large tree shooting up from this very small landmass (about 5 x 5 metres). Sadly, the tree has since gone and all that remains is the small rocky mount of the island itself. On nearby Kennedy Island, the sands have shifted causing a total change in island outline. This movement is also visible underwater - our memories of the sand patches on the reef did not match the present reality. There are parts where you can see sand smothering branching corals, especially on the upper slopes of the reef, just below the reef crest.
The reef runs in a strip from north west to south east. There is a 15 meter deep channel that partly separates it from the reef that surrounds the marker for the north east side of the channel between Sagharughombe and Kennedy Islands. But these two reefs are almost merged into one and for the purposes of our study, we covered both parts.
Fish: the fish life appears to be reasonably undisturbed on this reef, apart from the fact that we rarely saw sharks compared to two years ago when black tip reef sharks were a common sighting. But on the smaller scale of reef fish, there appeared to be little or no change in diversity and numbers. It is possible that the sharks have been fished out - the shark fin industry is part of the way of life here. But changes in the ecosystem balance have not manifested yet. Eagle rays were around for the first few days of the study, gathering in small schools and potentially preparing to mate - their behavior was very frisky. Groupers appeared to be collecting for spawning as well.
Corals: most corals are afflicted by some condition but rarely does it become so dominant that it kills the colony. There is plenty of filamentous algae and some macroalgae, very little bleaching. The shifting sands are causing a great deal of sedimentation but the currents appear to move the sands quickly so little of the coral is permanently damaged.
Following the western edge of the reef crest, it became very obvious that there is a protective shroud of closely packed massive Porites heads all along the upper edge of the reef slope, just below the crest. This seems to provide enough protection for more delicate and branching colonies (about 50% of which are Acropora) to grow safely on the reef flat. Beneath the rim of massive Porites, further down the slope, there is a great diversity of hard coral genus - Echiniopora, Pocillopora, Stylophora, Seriatopora, Cyphastrea, Astreopora, Favites, Favia, Montastrea, Pachyseris, Fungii, Diploastrea and many others.
There are many elephants ear sponges growing amongst the hard corals - this is the most dominant soft coral genus.
Invertebrates: there is a marked absence of sea urchins on this reef (as observed two years ago). Sea cucumbers are rather scarce too - several species of sea cucumber are highly prized and a source of fast income for the local Gilbertese communities. They appear to have cleared out a lot of species in the surrounding reefs. There is a reasonable diversity of invertebrates on this reef, especially sea stars. We were entranced by several large octopi during our time here.
The shape of Kennedy Island (the closest beach) has changed since two years ago. There appeared to be an increasing amount of litter on the beach. Two of our crew spent the night on Kennedy Island and unfortunately encountered rats, something we had not experienced two years ago.
The island is used by locals for weekend day trips, although during our visit this time there was very little traffic on the island due to bad weather. However, one Gilbertese fisherman was camping on the island under a plastic tarp, using this as a temporary home during the day while fishing for lobsters at night.
The two most noticeable changes to the reef at Sagharughombe Island are the cessation of the bleaching event that began two and a half years ago, and the absence of sharks from the reef.
Another major change in the area was the very few sightings of dolphins. Two years ago, we were treated almost daily to the passage of a large school of spinner dolphins. This time, we saw them only a couple of times. But we did have an encounter with six other cetaceans - three were roughtooth dolphins and the other three may have been false killer whales. They were in the area for two days, on the outer edge of the reef wall.
Logging is still an intensive industry in Kolombangarra, to the north east. A very large logging transport ship stopped in Gizo Harbour during our stay. Last time we were here, we visited the reefs around Kolombangarra, especially in Ringgi Cove and found them smothered from run off. But there is clearly a threat of logging spreading through other islands and causing wider damage.
