Biological Algae Control

The control of problematic species of algae is probably the most troublesome hurdle for new and veteran reef aquarists alike. We covered the topic quite thoroughly in Volume One, but we have some additional information to offer here, some in the captions and some in the text.

Dinoflagellates have coated the surface of this gorgonian,

Pseudopterogorgia elisabethae, preventing it from opening. Such blooms can smother and kill gorgonians and other soft corals. These blooms can persist for several weeks but usually die back spontaneously. It is a good idea to swish the algae off of gorgonians to prevent it from injuring them. As we mentioned in volume one, the use ot kalkwasser and protein skimming is effective in curbing the growth of dinoflagellates. J. Sprung

Black band disease is caused by a cyanobacteria, Phormidium coral-lyticum. It smothers the coral tissue as it grows. This gorgonian, Pseudopterogorgia sp. is unable to ward off the growth of Phormidium, and is losing tissue as a result. Without intervention the gorgonian will be completely consumed within a few weeks. Stopping the progress of this disease is quite simple: Siphon the algae off with a small diameter hose and lightly brush the exposed area to remove the remaining filaments of Phormidium. A brief dip in freshwater of about 30 seconds duration is also effective in killing the remaining filaments. After replacing the specimen in the aquarium, direct a billowing water current over it to encourage the tissue to grow back over the exposed skeleton.

The green alga Bjyopsis is a chronic nuisance in many reef aquaria, though normally it only appears during the first six months after the aquarium is set up and gradually disappears. We discussed this problem alga in volume one, and offered some recommendations for controlling it, including the use of a sea slug, Tridcicbici crispata.

Another sea slug, Elysia ornata (Ophistobranchia, Elysidae) feeds on Bryopsis only, and other species in the genus are likely to also eat Bryopsis. The Mexican lettuce slug, Elysia diomedea, which looks like Tridachia crispata, is another possibility for the control of Bjyopsis. In our experience the slugs do eat Bryiopsis, but they are not very7 effective at controlling it when the algae is blooming throughout

Elysia sp. J. Sprung

Clump Slugs

Elysia sp. feeding on a clump of Bryopsis. J. Sprung

Natural Algae Control Clump Slugs

the tank. The slugs do not graze the algae like other herbivores do. They actually suck the juices out of the plant, leaving it mostly intact. One would probably need many of them to effect any significant control through this form of herbivory. Other genera of sea slugs worth investigating for their ability to eat green algae, possibly Bryopsis, include Berthelinia, Polybranchia, Stiliger; and Cyerce. The beautiful black and yellow species, Cyerce nigricans would certainly be a welcome addition to any aquarium, and it feeds on turf algae. To offer another alternative, we have seen long spine sea urchins, Diadema spp. graze Bryopsis, but usually they avoid it. The Pacific collector urchin, Tripneustes gratilla, also removes Bryopsis, but strips off coralline algae too, and it cannot remove Bryopsis from crevices or the interstices within dead coral heads.

Small hermit crabs of the genus Paguritta are sometimes encountered in newly imported Pontes colonies. Occupying old worm tubes, they use their large feathery antennae to strain the passing water for planktonic food. Photo taken at the New York Aquarium for Wildlife Conservation. Such creatures are a real treasure to have in the aquarium as they offer a rare glimpse of the diversity of life on a coral reef. J. C. Delbeek

The mystery of the sudden appearance and disappearance of Biyopsis seems worth noting to solve the problem of its existence in an aquarium. What we have noticed is that the availability of nitrite in the water seems to be an important limiting factor. When there is some available nitrite (sometimes below the level that common test kits can measure) this alga blooms. When the nitrite level is reduced, one can observe a marked decline in the presence of Biyopsis.

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