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September 16, 2008: The Motu trip
To get to Motu Tiahura, we hopped on the station boats and proceeded through Cook's Bay Pass out to the open ocean. We skirted the forereef, venturing back into the lagoon at Opunahu Pass. We could see the motu in the distance, but before getting there, the boats pulled into the sand shallows of the lagoon, where we got quite a treat. We were surrounded by more than a dozen Pink Whiprays, a large stingray species common in the South Pacific. We hopped out of the boats and enjoyed a quick snorkel with these beauties, which were not at all shy. Apparently, local tour guides feed the rays to encourage them to congregate for tourists. Although we did not engage in any ray feeding, the rays were clearly looking for food from us by mouthing our hands and approaching the boats. In the nearby channel we could see Black-tipped reef sharks lurking just out of reach. Soon we bid goodbye to the rays and headed on to the motu.
Upon our arrival, Frank Murphy, Ph.D., who is the associate director of Gump Station, gave us a fascinating introductory lecture on the geology of the motus around Moorea. Moorea is the third youngest island in the Society Islands, an archipelago of volcanic islands. As such, it is a high island, with towering peaks that once composed a volcanic caldera. Unlike its sister island, Tahiti, Moorea is fully framed by a lagoon and barrier coral reef. Motus form on the barrier reef when large storms (the sort that only hit once in a millennium) tear up the forereef (the part of the reef submerged by open ocean) and deposit huge amounts of coral rubble inside the reef. The rubble forms a rock barrier that eventually gets cemented together by reef-building organisms. Subsequent smaller storms deposit more coral rubble that degrades into sand, forming the upper layer of the motu.
Motu Tiahura seemed like a desert island paradise to me, but in reality it is a very harsh environment where it is hard for terrestrial plants and animals to make a living. The sandy soil holds a lens of freshwater, but not many nutrients. Winds buffet the small islands and the sun beats down incessantly during the dry season. Most of the motus are separated from the mainland by deep channels. Only a subset of the Moorean flora and fauna survive in these harsh environments, and some of the species found on the motus are endemic to these habitats.
We circumnavigated the motu, snorkeling in the pristine patch reef that surrounds it, exploring the Pemphis acidula habitat on land, and poking under rocks in the sand flats, where we found many brittle stars, crabs, gobies, sea cucumbers, and even a sea hare (a type of sea slug). I did not find any P. litoralis, but I was also so intent on every new marine invertebrate discovery, that I didn't look very hard. We ate our lunches on the beach, took one last swim, and then it was time to get back on the boats and return to Gump Station. Tomorrow, I'll tell you more about my own research, but for now I'm feeling a bit sunburnt and more than a little tired from the day's motu adventures.
Regrettably, we must take leave of Molly and the isle of Moorea … but let's jump ahead three years and catch up with Molly and her research in this 2011 blog entry.
Moorea image courtesy of the Image Science & Analysis Laboratory, NASA Johnson Space Center, photo number ISS007-E-14619, http://eol.jsc.nasa.gov; pink whiptail rays photo by Albert Park; all other photos by Molly Wright.
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