Intan Suci Nurhati, Ph.D.     
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Georgia Tech's Southern Line Islands Expedition

October 30 November 20, 2008
Field team: Intan Suci Nurhati, Jordan Watson & Branwen Williams


We conducted a three-week long scientific cruise expedition to visit three remote islands in the southern Line Islands chain of the Republic of Kiribati (Caroline, Malden and Flint Islands; 4-11S, 150-154W) aboard the R/V Bounty Bay in November 2008. The objectives of the expedition were to survey corals in these rarely visited islands and investigate the signature of anthropogenic forcing on tropical Pacific temperature and rainfall using coral -derived climate records. Coral surveys and cores retrieved from the expedition complement our previous work in the northern Line Islands (Palmyra, Fanning and Christmas Islands) (Cobb et al. 2003; Nurhati et al. 2009). Our Georgia Tech team of three scientists conducted coral survey on the leeward sides of each island via towing method, and retrieved the coral cores from ~10 m depth using underwater hydraulic dri lling equipment via SCUBA. We installed automatic temperature loggers at each island that are recording in situ temperature for the next three years at a 15 minutes interval. We hope to retrieve these devices on future trips organized by us or our collaborators. During the expedition, we also conducted land survey and collected fossilized coral deposits in hopes of extending the length of the climate record beyond the last century. Several gorgonian soft corals were also collected from ~40 m depth as an alternative archive for past climate changes. Along the cruise track, we conducted oceanographic measurements (sea-surface temperature and salinity) and collected seawater sampling at every one degree latitudes as well as at each island that will serve as calibrations for our coral-derived climate records.

We surveyed coral reefs on the leeward side of each island by towing two snorkelers behind a dinghy. The surveying method worked well in these islands where the reefs have fairly narrow (15 - 20m) coral flat areas to survey before they hit steep slopes. We were able to cover most of the leeward sides that were calm enough to survey, and possible to conduct underwater drilling if suitable (massive
Porites sp.) corals were found. At each island, we took many photographs of the reef and documented the species diversity, coral coverage, and overall coral health.



Caroline Island

Caroline Island (Fig.2) was the first island we visited during the cruise, where we spent two days conducting underwater coral survey and drilling. We approached the island from the south, and cruised along its leeward (west) side while observing and taking photographs of the island before anchored the boat on the northwest side of the island. The island has thick vegetations due to high mean rainfall of 1500 mm annually. The island is comprised of several islets, and has numerous fossilized coral deposits scattered in its tidal flats and lagoons. Red-algae covered reef formations surround the islets, which makes landing really difficult.

Caroline Island has a beautiful and healthy coral reef with high coral cover (>90%) and high biodiversity of corals and coral fishes, as well as high abundance of shark populations most notably the black-tip reef sharks (Fig.3). We retrieved two cores from a Porites lutea coral that provide 50 cm long cores each.


Malden Island

From Caroline Island, we continued our cruise northward towards Malden Island where we spent three days conducting underwater and land works. We approached Malden Island from the south, cruised along its leeward (west side), and anchored on the northwest side of the island where there is a wide extent of wide beach area that made landing relatively easy (Fig.4). The island is a tropical desert with a mean rainfall of 667 mm annually with vegetation mostly in the form of bushes, and a few coconut trees near the abandoned settlement compound.

Malden Island (Fig.5) has poor coral condition (50-70% coral cover), and low biodiversity of corals and coral fishes. The island is bathed by the colder equatorial upwelling seawater (27C), and is characterized by more energetic wave activity even on the leeward side of the island where our boat was anchored. We observed that coral coverage can vary appreciably from one area to another. While one area may have very low coral coverage and poor coral conditions, another area may be almost completely covered by Acropora sp., while yet another area has several massive colonies of plate morphology Porites corals. We retrieved two Porites sp. cores of 18-20 cm long with one of them has a replicate core. We also retrieved six soft corals from a depth of 60 m. We observed a vast community of soft corals in Malden at this depth.


During our land-based work, we observed massive fossilized corals scattered over a vast bushy area which may have been a dried lagoon, as well as dunes of coral rubbles that were washed onshore during strong storms. Branching and platy coral morphologies seem to be the dominant forms of both modern/living and fossilized corals in Malden Island. For our land work, we retrieved a 30 cm-long submassive fossilized coral that has a straight growth axis, and several pieces of coral rubble.  


Flint Island

On our southbound leg returning to Papeete, we approached Flint Island from the north and anchored on its northwest side (Fig.6). Similar to Caroline Island in latitude, Flint Island is also thickly vegetated with trees. It is a very narrow island with a narrow lagoon surrounding the island. Landing is also difficult; however, visitors may utilize the existing dynamited passage located in the northwest side.

Flint Island (Fig.7) has good coral condition with approximately >85% coral cover and fairly good biodiversity. The island has a large sea-turtle population (we counted 16 of them on our 1.5 hours survey transect). Despite good coral diversity, the coral colonies are uniformly small and the shark populations are not as abundant as those from Caroline Island. Flint was once a base of significant human activities associated with guano harvesting and coconut plantations, as well as fairly recent fishing activity. We retrieved two 55 cm-long cores from a same head of Porites solida, and another core of 30 cm-long drilled from a Porites lutea.





The absence of massive brain Porites corals that would provide a very long climate archive from these islands was surprising as well as alarming, given their relative abundance in the Northern Line Island chain. While it may be partly due to the oceanographic conditions (cooler sea-surface temperatures, stronger currents and wave activity), it might also be related to anthropogenic global warming and/or ocean acidification that have stressed these already marginal coral reef environments to the point of decreased diversity and coral colony size.