Planetary Coral Reef Foundation Science Report
A total of twenty dives were completed, nine of which were Vitareef dives while the rest were observational dives.
PCRF also undertook a Vitareef Study at this site in April 2007.
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Papua New Guinea lies within the epicenter of marine biodiversity in the world due to its position between both the Pacific and Indian Oceans. Milne Bay Province is located at the southeast tip of New Guinea Island between the Solomon Sea and the Coral Sea. The bay is six miles long and 19 miles wide. Many volcanic peaks, coral islands and reefs are found in the region. Planktonic-rich water nurtures the marine life in the bay area as tidal currents flow in and out from both seas. The dive sites in the region boast a vast diversity of sea creatures, corals and multiple rare endemic species.
During WWII, a major battle took place in the region, The Battle of the Coral Sea, where Japanese troops suffered their first land defeat when attempting to take control of Milne Bay. Currently, many foreign companies are logging the forests in the Milne Bay Province region. Without the trees, many bare hills erode away and the sediment ultimately washes into bay waters.
Alotau is the provincial capital of the Milne Bay Province. It is a hub for islanders with a commercial centre. It has no road link to Port Moresby and, as a result, maintains a slower pace.
The reduced channel size and continuously growing mangroves are responsible for reduced water flow between the bay and the ocean and a greater degree of sedimentation within Port Stanley Bay. Inside the bay Uri Island’s fringing reef must now cope with these new conditions.
The Magic Spot dive site is located southeast of East Cape by Nuakata Island in the Raven Channel. Strong currents associated with tidal flows oftentimes exceed two knots and bring in both nutritious bay water and cool, oligotrophic oceanic water. Due to the reef’s position on the edge of the channel at the tip of Milne Bay, the marine life is vivacious.
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The Magic Spot is an open ocean reef with neither a central island nor lagoon, thus it is classified as a platform reef. The geological history is unknown but it is located in a region of unusually high seismic activity.
The reef crest is between four to ten meters deep with areas of coral rubble and other areas of rich coral growth. At the edge of the reef crest, the reef drops off as a steep slope until it gradually tapers off to a sand bottom in twenty-five meters of water.
Although no secci disk readings were taken over the course of the brief study, the visibility was estimated to vary between twenty and twenty five meters. The visibility was dependent on the dominant current. When the current was running out of the bay, the visibility was slightly poorer than when the current was running in from the ocean.
The currents varied throughout the day and were dependent upon the diurnal tide. We experienced two slack tides a day when the currents were almost motionless. As the tides changed, the currents picked up and rushed through Raven Channel and over the reef at speeds exceeding two knots.
Over the course of the study there was little fluctuation in water temperature. The water temperature ranged from 29.3-29.8 °C over the three-day period, but remained around 29.4°C. The mean, median, and mode temperature was 29.4°C. We believe that the currents in the area help keep the water cooler and temperature more constant than nearby areas that are not affected by currents.
The study site did not have a high occurrence of bleaching but it was observed in both the shallow and the deep zone. There was little difference between the percentage observed in the shallow zone compared to the deep zone. The overall figure for bleaching was 4.2%.
Bleaching was observed on 17 different genera within the study site. There was no genus that showed significant susceptibility to bleaching and the level of bleaching also varied widely on the colonies observed.
The significant currents most likely keep the water temperature slightly lower, and therefore this may help prevent high levels of bleaching occurring at this location.
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There were no sightings of the Crown of Thorns, Acanthaster planci, on any of the dives. However, across the Raven Channel at the Lighthouse reef there is a strong presence of Crown of Thorns. Feeding trails and tissue damage to coral colonies were evident and several Crown of Thorns were noted during one dive alone. Happily, also noted at Lighthouse reef was a most impressive, rare example of the Crown of Thorns’ predator, Triton’s Trumpet, Charonia tritonis, which measured 30cm in length and still contained the live animal.
White band disease was observed within the study site, primarily on table Acropora colonies but also seen on Porites colonies. The percentage calculated from this study site was 0.7% (check this figure). Although few colonies were seen to be affected by this disease, the impact on the individual coral colonies was dramatic, with up to 50% death observed.
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| Hawkfish on encrusting Acropora |
Red band disease was noted during Vitareef and observation dives. Although this is not a condition recorded within the Vitareef study it is important to include it here. Red band disease was present on Pachyseris and Hydnophora colonies. This is the first time that it has been encountered by Heraclitus crew. The number of colonies observed was minimal, approximately five in total, but the affect on the coral colonies was high with up to 30% death from this disease.
The reef flat consists of sand and patches of hard coral. These patches of reef possess the highest hard coral coverage observed (up to 30%). On the wall there is an overall hard coral coverage of about 15%. Around 30 metres the hard coral coverage was less than 5%.
The reef is diverse on the genus level. Acropora is the dominant genus in plate and encrusting growth forms. Few branching Acropora spp. were sighted. The majority of Acropora colonies observed were less than one meter in diameter. The genus Favia seemed to be the most affected by edge damage - a process which continuously decreases a colony’s size. The quantity of healthy coral colonies was significant.
The high soft coral coverage and extensive fields of leather coral (Sarcophyton spp.) mask a relatively low hard coral coverage especially on the reef top and crest.
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| Colony of branching Acropora | Colony of Montipora |
We dived this reef in December 2002 and we christened it ‘Magic Spot’ predominantly because of the incredible fish life that we witnessed on every dive. At times it was almost impossible to see the substrate because of the layers of fish clustered above it.
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Visiting here again in 2006, there was a definite shift in the marine life. Some of the fish species observed in 2002 were now absent, and the density of fish life was definitely lesser.
The most noticeable change was in the shark population. In 2002, we saw grey reef (Carcharhinus amblyrhynchos), black tip (Carcharhinus melanopterus), silvertip (Carcharhinus albimarginatus), nurse sharks (Ginglymostomatidae) and multiple white tip sharks (Triaenodon obesus), for example, five in one dive. In 2006, we saw only two white tips on one dive and one white tip on another. However, we did observe two epaulette sharks (Hemiscyllium ocellatum), each about 20 cm long on a night dive, hiding under corals.
Other large reef predators were also missing. We noted in 2002 the constant cruising of dogtooth tuna (Gymnosarda unicolor) including some very large specimens. We did not see any in 2006. Great barracuda (Sphyraena barracuda) which were a feature of 2002 dives was sighted only once in 2006 – a single fish. Huge Spanish mackerels (Scomberomorus commerson) used to pass in groups of five or more, but this time there was one sighting of a group of three large mackerels and another sighting of just one large mackerel.
We also noted previously many Napoleon wrasses (Cheilinus undulatus) but again, this time we saw just one or two. ‘Every jack in the book’ in 2002 was reduced to a school of 30 big-eye trevally (Caranx sexfasciatus) at the top of the reef in 2006.
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There was a resident giant grouper (Epinephelus lanceolatus) in 2002 which we did not come across in 2006 but we also did not particularly search for it.
In 2006 we also observed a devil ray (Mobula japonica), several eagle rays (Aetobatus narinari), a blue spotted stingray (Taeniura lymma) and a school of about 20 large bumphead parrotfish (Bolbometopon muricatum).
It is very possible that in 2002, we struck this reef at a particularly rich time. However, the visit in December 2002 and this visit in March 2006 are both in the same season – the north-west monsoon. Either this reef is in a different phase of productivity or there is a definite decline in the amount of larger fish on the reef. The absence of sharks is worrisome, but also not so surprising given that in Alotau, less than 35 miles away, there are two stores with signs saying ‘we buy shark fins / sea cucumbers / trochus shells’.
This summary covers the populations of invertebrates at the shallow and deep slopes and the reef tip at Magic Spot.
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| Cleaner shrimp on anemone |
Overall, this reef is bursting with invertebrate life, with all groups represented. Every inch of space on the reef is covered in a wide range of stunningly vibrant organisms, including sponges, corralimorpharians, anemones, ascidians, tunicates, echinoderms, molluscs, bryozoans, hydroids, and spectacularly beautiful soft corals. This rich diversity of invertebrate life creates an impression of great beauty and is indicative of the radiant health of the ecosystem.
There was evidence of snail feeding trails made by the corallivorous snail, Coralliophilia neritoidea, and sightings of the snails at the base of Acropora tables and on Porites heads. The presence of the highly valued and therefore usually rare trochus, Tectus niloticus was noted at a depth of 9 metres where one specimen 12 cm diameter was observed.
The reef shows good presence of Giant Clams, with Tridacna squamosa observed on every observational dive taken. Both juvenile clams and mature clams were sighted with measurements in length ranging from 5cm to 50cm.
Bio eroding snails, Dendropoma maxima, and bio eroding mussels, Lithophaga zittelliana were present but not prolific on the reef which is good news for the Scleractinia. Interestingly, the less common bio eroding snail, Serpulorbis grandis, was also noted on this reef, readily distinguishable from Dendropoma maxima by the elaborately mottled animal and by the fact that an operculum covering the shell opening is entirely absent. There was a healthy presence of the sea urchin genus Diadema throughout the area.
There was good presence of sea cucumbers (beche-de-mer), with several species noted including the high value species of Sandfish, Holothuria scabra and low value species of Pinkfish, Holothuria edulis and Flowerfish, Bohadshia graeffei.
There were many huge examples of the barrel sponge, Xestospongia testudinaria whose size indicates a maturity of age that may exceed one hundred years. Also noteworthy is the strong presence of the globose species of sponge, Coelocarteria singaporensis, bright yellow in colour with densely set long and finger like papillations.
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The reef has a very strong presence of beautiful soft corals; of particular note are the huge fields of Mushroom Leather Coral, Sarcophyton, Lobed Leather Coral, Lobophytum, and Palm Coral, Clavularia. Also firmly established on the reef are the Cauliflower soft coral, Lemnalia, Glomerate Tree Coral, Dendronephthya spongodes, and and Umbellate Tree Coral, Dendronephthya Morchellana.
All the large table corals and gorgonians are covered with beautiful Crinoids, feather stars, who apparently find them a perfect platform for filter feeding.
While there were no sightings of marine mammals at Magic Spot reef, the surrounding area of Raven Channel does have schools of dolphin. In the three days we were in the area we encountered one large pod of 40 to 50 spinner dolphins on our way back to the ship from Lighthouse reef in the Zodiac. The dolphins were bow riding and leaping out of the water in front of us. We turned back three times to where the pod was assembled, and let them bow ride again and again. After each bow ride several dolphins would spin and leap and twist through the air ahead of us. The encounter lasted approximately 15 minutes. The second sighting was of a small pod of Bottlenose dolphin, comprised of six adults, 20 meters off the bow of the Zodiac on our way to another dive site. They were with us for a few minutes, then disappeared.
Four hawksbill turtles and one green turtle were sighted in this area over the course of our twenty dives here. In one case, a male hawksbill turtle, about 70 cm carapace length, was observed feeding inside a crevice of a large coral head (Tubastrea) at about 7 meters depth, then later observed surfacing, taking two breaths, descending and swimming slowly away from the divers. In another case the tender of one of the dives, sitting in the zodiac tied to a mooring buoy, sighted a juvenile green turtle surfacing to take a breath about 10 meters away. All sea turtles sighted appeared to be in good health.
According to our Vitareef results, 17.9% of the conditions scored were invertebrate growth on coral. Many invertebrates that were growing on corals were sponges and tunicates. Many various corals including Faviids and Acropora spp. were either partially or fully overgrown by a particular encrusting sponge (possibly an Echinochalina species). Other invertebrates with no apparent negative effects were found on other coral genera.
Presently, the threats to the reef include invertebrate growth, biological predation, diver damage, and beche-de-mer fishing.
Of the coral conditions recorded, 8.6% were damage to tissue only. This code indicates that biological predation is occurring on the corals. Many of the Porites spp. had corallivorous snail scars, which accounted for most of the biological predation. No crown-of-thorn starfish were observed around the study site.
Another more substantial threat to the reef is the damage to coral tissue and skeleton. We observed many partially broken branching corals, such as Acropora spp. and Tubastrea micrantha. This condition was most likely caused by divers or beche-de-mer fishermen. Numerous live aboard dive boats visited this reef throughout the days we were there. The dive boats moor off on a buoy on the tip of the reef, which probably diminishes anchor damage, however the divers aboard these boats could be damaging these branching corals.
Another threat to the reef is the beche-de-mer (sea cucumber) fishery. Many local inhabitants of the neighboring islands fish for beche-de-mer on the reef. Numerous fishermen visited the boat during our stay. They use spears attached to heavy lead weights to catch the sea cucumbers. While snorkeling the surface, they spot the beche-de-mer and then drop the lead spear on the reef to catch them. The sea cucumbers are disappearing, and these lead weights might also cause structural damage to the corals.
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