Corals of the genus Leptoseris can grow to ten millimeters a year, even at a depth of 111 meters. This unusually high growth rate for corals that depend on photosynthetic symbionts and live in low light conditions. As noted by the researchers in an article for the journal Coral Reefs, the main adaptation of this genus to the existence at depth may be a flat shape of the skeleton, which allows to gather more light and reduce the need for calcium.
The lives of many corals depend on tiny endosymbionts of algae, zooxanthellae, which provide the hosts with nutrients. However, these single-celled very capricious: they can only exist in a narrow temperature range and require a high level of illumination. This limits the distribution of photosynthetic corals narrow strip of shallow seas in the tropics and subtropics.
However, some MD photosynthetic corals (Scleractinia) normal at depths up to 100 meters, and individual colonies down to 165 meters. Unfortunately, due to the inaccessibility of these places on the biology of deep-water corals, little is known. It is assumed that due to the shortage of sunlight they grow very slowly, however, the existing assessment is very controversial. According to them, the growth rate of the coral Leptoseris fragilis at a depth of 90-120 metres does not exceed eight tenths of a millimeter per year, while close view of Leptoseris hawaiiensis every year adds eleven millimeters at a depth of 90 meters.
To clarify this question, a team of specialists under the leadership of Samuel Kang (Samuel E. Kahng) studied four colonies of corals of the genus Leptoseriscollected in 2004-2009 at the shores of the Hawaiian archipelago using special submersibles Pisces IV and V. the Point of collection was located at a depth from 70 to 111 meters.
The researchers assessed the growth rate of each colony by determining the age of individual sections of her skeleton by using uranium-thorium Dating. Comparing the age of different fragments with the distance between them, the authors calculated the average rate of growth of corals. It turned out that at a depth of 70 meters Leptoseris adds almost 25 millimeters per year. Below the rate of growth decreases, but even at 111 metres, it was ten millimetres per year. The figures coincide with the previous estimate obtained for the Hawaiian deep-sea corals.
Perhaps high growth rate of corals of the genus Leptoseris is that they enter into symbiosis with adapted to the depth of the zooxanthellae. However, the authors are inclined to a different explanation. Compared to shallow corals, the genus Leptoseris usually have thin and flattened skeletons. This reduces the need for calcium and to increase the area of the colony for the efficient collection of sunlight.
Due to global warming, more and more coral reefs are suffering from bleaching, which is caused by loss of symbionts. However, some of them not white, and acidic take on unusual colors. According to a recent study, this adaptation, which does not allow sunlight to penetrate deep into the tissue of the coral and increases the chances of the return of symbiotic algae.