Alexis Pasulka SIO 277 The deepest photosynthetic reef coral species The HMS Challenger Expedition served as a basis for understanding the distribution of reef corals During the expedition scientists collected 293 species of coral from 69 genera Because the Challenger had limited time at each reef station little or no information was recorded about the environmental conditions of each coral species collected Still the collection of reef corals on the Challenger provided a biogeographic comparison of reef coral species including species descriptions and depth ranges One of the most notable discoveries as a result of coral reef investigations on the Challenger Expedition was that photosynthetic reef building corals could live below 60 meters Although the mechanisms by which corals lived and grew were poorly understood at the time the discovery that corals could survive in deep waters stimulated further research in this realm The HMS Challenger collected three species of reef building corals from reefs off Honolulu HI at depths of 80 meters and one species from 140 meters The species were Porites lichen Montipora capitata Pocillopora nobilis now known as Pocillopora verrucosa and Domoseris regularis now known as Leptoseris scabra respectively All of these species are zooxanthellate scleractinian corals Veron 2000 meaning they have a symbiotic relationship with dinoflagellates known as zooxanthellae Lalli and Parsons 1997 These unicellular algae provide the coral polyps with food derived from photosynthesis while the coral provides the zooxanthellae with protection and compounds necessary for photosynthesis Lalli and Parsons 1997 Thurman and Trujillo 2004 In his report Sir John J Quelch 1886 recognized the limitations of the coral reef data set suggesting that certain observations and experiments on individual Reef Corals are sadly needed in order to bring to light the influences of local conditions upon their distribution Quelch 1886 Some of the types of measurements he suggested included the nature of the surface on which the corals grew temperature differences in the water column the presence or absence of direct sunlight the turbidity of the water and the position of the reef with regards to depth and distance from shore These types of observation would lead to a greater understanding of what factors limit coral reef distribution as well as the adaptations of certain species to live in a broad range of depths Shortly after the Challenger Vaughan 1907 collected four species of the genus Leptoseris from the waters off of Hawaii However since these corals were collected using dredge halls from depths of up to 312 fathoms the exact depth from which each coral was collected remained unknown Unfortunately research on understanding deep coral species and their adaptations remained difficult because of the constraints of dredging and SCUBA diving Dredging provided no information of the environmental conditions from which the corals were collected and SCUBA divers were unable to dive past safe depth limits about 30 meters The genus Leptoseris became of particular interest and provided an opportunity to investigate the physical and biological factors that controlled coral reefs because its lower depth limit extended past that of other zooxanthellate reef corals A study in the Indian Ocean revealed that L fragilis L hawaiensis and L incrustans were the only corals whose abundance increased with depth Bouchon 1981 This genus has been discovered Alexis Pasulka SIO 277 all over the world in clear oceanic waters Kahng and Maragos 2006 and sources within Leptoseris sp at 153 m near the Big Island of Hawaii L hawaiiensis at 165 m at Johnston Atoll Maragos and Jokiel 1986 and L fragilis at 145 m in the Gulf of Aqaba Reed 1985 L Hawaiiensis found at 165 in Johnson Atoll in the Pacific Maragos and Jokiel 1986 is the deepest known photosynthetic coral to date With the development of submersibles and remotely operated vehicles scientists had the ability to conduct more comprehensive deep sea coral reef surveys and began to investigate the mechanisms by which these corals survived in the deep It was discovered that the primary factor in determining morphophysiological features of coral colonies is light However temperature turbidity of the water column and the amount of suspended matter in the water are also important abiotic factors in determining colony shape and vertical distribution Titlyanov and Titlynova 2002 Scientists began to investigate adaptations that enabled Leptoseris species to live in low light environments It was discovered that L fragilis can survive in various light intensities because of a host lightharvesting system that enhances photosynthetic performance of its algal symbionts particularly in low light environments Fricke et al 1987 Schlichter and Fricke 1991 While the coral s optimum light conditions are at depths between 70 to 90 m the coralalgal photo adaptation enables L fragilis to survive as deep as 145 m in the Red Sea Fricke et al 1987 The distribution of Leptoseris sp in relation to other zooxanthellate corals and macroalgae provided insight into the notion that many biological and physical factors other than light can play an important role in coral reef distribution A comprehensive survey of the Au ua Channel in Hawaii Kahng and Kelley 2007 revealed that Porites Pocillopora and Montipora were present but rare at depths from 50 80 meters Kahng and Kelley 2007 However Leptoseris sp was rare in shallow water because of competition for space with abundant macroalgae Kahng and Kelley 2007 Rather Leptoseris sp dominated in areas of hard substrate between 60 120 meters most likely due to its light harvesting abilities It appeared that below 80 m this genus of coral benefited from the reduced macroalgae abundance and availability of hard substrate Its decline below 90 meters was attributed to daily temperature fluctuations 2 4oC and lack of available substrate Kahng and Kelley 2007 The lack of substrate at depths below 90 meters was a result of increasing competition for space because the relative abundance of azooxanthellate corals increased at these depths Kahng and Kelley 2007 concluded that light was not the dominant factor setting the lower depth boundary of Leptoseris sp in the Au ua Channel At the lower boundary of its depth range light limited colonies of Leptoseris sp appear small and stunted in growth up to a few cm in diameter Maragos and Jokiel 1986 Reed 1985