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Gersemia rubiformis - a soft coral found underwater at Race Rocks. Usually it is found at the depth of 8 to 10 meters with an amazing variety of many other invertebrates. Here, no invertebrate is found growing on its own, they always occur in association with other invertebrates.
Gersemia occurs in fairly big pink patches in rather greater depths in the ocean but there are some small patches of it along the North cliff of Race Rocks. The lumpy colonies it forms usually are 10 to 15 cm in diameter.
Gersemia grows at the shallow depth because of the availability of nutrients there. Emerging from the walls are small pale pink polyps
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A close-up picture of the polyps extended in feeding mode. |
Extended, the individual polyps stick out about 5 mm beyond the lump to which they belong. These polyps have small tentacles at the end. Each polyp has 8 of them, each with delicate branches which are able to catch masses of plankton for food. The vertical structure of the colony allows the polyps to be filter feeders and strain out plankton and other drifting organisms from the water column.
Embedded within the body wall of the polyp are millions of microscopic, photosynthetic organisms, known as zooxanthellae. They live symbiotically, provide food and fuel and absorb many of the waste products of the polyp. Without the zooxanthellae, the corals could not exist. It is the zooxanthellae that contains necessary chemicals for the adequate production of calcium carbonate, for reef forming types of corals. However Gersemia does not have a completely calcified skeleton, like that of reef-building corals of warmer seas. Zooxanthele are also responsible for providing much of the colour in corals, which usually range from cream through orange to deep pink elsewhere, but are consistently deep pink in Race Rocks.
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