It is fully possible that octocorals employ a combination of some or all of the above feeding mechanisms, with varying degrees of importance for each (see polytrophic feeding described earlier). Further research is needed in this area and it is likely that in the next few years we will know much more about the diets and nutritional requirements of octocorals.
The growth rates of soft corals are poorly documented in the scientific literature. We know by observing them in our aquaria that many soft corals are capable of extremely rapid growth. Our experience, however, does not mean that the same growth rates occur naturally on the reefs, though we believe that the growth in our aquaria should not be very different from that in the natural setting. Fabricius (1995) studied Sinularia and Sarcophyton species on Australia's Great Barrier Reef. She found average radial growth rates of only 0.5 to 1.5 cm per year! In aquaria many Sinularia species grow in excess of 1 cm per month, but not all of them do, so one can not generalize about the growth rate of different members of the same genus. The growth rate also decreases as colonies approach certain size limits (Fabricius, 1995). In the wild she found that juvenile Sarcophyton may increase in size 28% per year while large colonies increase only 6% per year. In our aquariums Sarcophyton species can grow much faster, increasing in size about 25% per month, though they do so often in spurts followed by periods in which the size does not change much. Other studies have shown that when stony corals are decimated by Crown-of-Thorns sea stars, soft corals (Sarcophyton, Lobophytum and Sinularia mainly) can rapidly move in and cover significant areas of reef (Benayahu, 1995). Therefore it may be possible that these corals show accelerated growth rates when colonizing new areas, but then slow as they age or grow beyond a certain size. Dendronephthya spp, can also quickly colonize new areas. In the Red Sea D. hemprichi have been know to cover man-made structures down to 240 ft 80 m) growing to 12 in. (30 cm) in height in only a few months (in Fabricius et ah, 1995b). Growth rates of young colonies of D. hemprichi can be greater than 8% of biomass per day (K.E. Fabricius, unpubl. data). This suggests that when their requirements are thoroughly understood at last, it may be possible to propagate Dendronephthya species in captivity.
Growth series in Pseudopterogorgia americana in John Haydock's aquarium, Ontario Canada. J. C. Delbeek mm
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