We have seen many coral reefs. Some of these are algae staple because they are rich in nutrients. However, in such a situation we observed a coral reef dominated by Sponges. Physical and other parameters of the water indicate that it should also be an algae-dominated reef rather than a sponge-dominated coral reef. We can't understand why this happened.
Generally when are together coral reefs and sponges, there is a relation between both of them and this relation is through a food web.The coral reef are formed for cnidaria,specially sea anemones (Actiniaria),Scleractinia, Pennatulacea, and another order. They have specials cells called nematocysts,and it are extroused for catching food through water current and this current too can to move food to sponges and it through cells known koanocysts can to get food too.So between both of them there is a beneficiuos.
Spores of algae need firm substratum to settle & when it starts growing into germling, it's possible that they may be devoured by various marine animals.
If sponges have overtaken a patch of substratum, then spores don't have space to grow, neither it can grow on sponges.
It's also possible that the spore releasing season might have been shifted by a period of time, and in the meantime, the sponges could have overtaken the space.
Another possibility is extreme adverse conditions (Physico-chemical) faced by germlings, wherein they all fail to grow further.
There could have been wanton destruction of the 2X stage, leading to almost nil production of X spores, leaving the substratum free to be taken over by sponges.
Sponges are typical filter-feeding organisms that engage in intense competition for space with corals across the globe. If the nutrient levels are high, corals are no doubt in poor position. It could favour both macroalgae as well as sponges.
Are there no macroalgae at all on those coral reefs? If yes, several factors could be responsible depending on which sponge species are there (some species are very aggressive in invasions). One strong possibility (very practical) is that some highly aggressive sponge species invaded a very vulnerable, weak coral reef completely not leaving any possibility for algal spores to develop and thereafter outcompete the sponges. More information on which sponge and coral species are involved could answer this better.
Interesting!
Suman
Thank you all for your valuable comments. As I have seen in many coral reef areas, as nutrition increases, algae diversity increases and coral declines. Under similar environmental conditions, sponges dominate only in rare cases. As you have mentioned that some species of sponges are very aggressive and they inhibit the further development of algal spores due to allopathic effects. If this is true, then these species of sponges should dominate all of the above environment rather than algae. However, it is not, so in my opinion and you have also indicated that it may be a result of specific sponge and coral interactions at that location.
Regards,
Shyam
It may be related to the luminosity in the location. Sponges may be in advantage on low light environments.
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