Figueiredo, Joana

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Reef tanks, publicaquariums andaquaculture facilitiesare commonly invadedby pest organisms, such as the glass-anemone (Aiptasiapallida), the fireworm (Hermodice carunculata) and thebubble algae (Valonia spp. and Ventricaria ventricosa). In aneffort to minimize or eliminate the impacts and spread of pestorganisms in reef tanks and public aquariums, a wide rangeof control techniques have been established including: (1)physical removal; (2) chemical treatments and (3) bio-control.Ornamental crabs of the genus Mithraculus (Decapoda:Brachyura: Majidae) are utilized in reef aquaria to controlnuisance algae, particularly bubble algae (Valonia spp. andVentricaria ventricosa). Bubble algae are greenish, grapelikeclusters of small (usually less than 1 cm in diameter), single-cell, fluid-filled spheres. Often living on the surfaces ofsponges, soft corals, coral rock and other algae, these greenalgae cover hard substrates and corals, blocking light tozooxanthellae and may cause coral bleaching and death.Emerald crab Mithraculus sculptus have modified,spooned-shaped chelae to feed on both fleshy andfilamentous algae. However, they are able to consume a widevariety of animal feeds such as frozen and formulated food.Actually, in aquaria, their bubble algal consumption reducessignificantly when pellets are also supplied, but it did notreduce when offered mysids. So, in case of infestation withbubble alga, using mysids as aquaria food may render M.sculptus as efficient bubble alga bio-controllers; the use ofpellets is not advised.M. sculptus of both sexes might be considered equallyefficient has controllers. Since larger crabs can consumegreater quantities of bubble algae and are able to exploit awider size range of bubble algae, they may be consideredmore efficient bio-controllers. While less efficient, smallercrabs may be effective in controlling algae in areas difficult toaccess, such as crevices.Emerald crabs actively feed on bubble alga Ventricariaventricosa; they grab bubble alga with the chelae, burst it, andthen proceed to eat the cell membrane. As the crab tears thealgal cell apart, the cell liquid that contains juvenilecytoplasmatic spheres is released into the water, whichmight contribute to algal dispersal and consequently algalinfestation. However, by taking into account that: (1) bubblealgae juveniles may be removed and eliminated by tankfiltration, (2) fish are fed few times a day while crabs arecontinuous foragers and (3) the greatest amount of food isconsumed by fish while still in the water column (in this wayinaccessible to crabs), we suggest the bio-control efficiencyof M. sculptus could be improved by increasing density ofcrabs, along with not providing food in excess and using aneffective filtration (mechanic filtration, skimmers and U. V.sterilizer to trap bubble algal juvenile cytoplasmatic spheres).Joana FigueiredoLaboratório Marítimo da Guia, Faculdade de Ciências da Universidade de Lisboa, Av. N. S. do Cabo,939, 2750-374 Cascais, PortugalE-mail: joana_figueiredo@portugalmail.ptJMBA Global Marine Environment 7Also Published in JMBAFigueiredo, J., Narciso, L., Turingan, R. & Lin, J. Efficiency of usingemerald crabs Mithraculus sculptus to control bubble algaVentricaria ventricosa (sin Valonia ventricosa) in aquaria habitats.JMBA 88, 95–102Emerald crabs keep bubble algae under control

Emerald Crabs Keep Bubble Algae Under Control

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