Size matters: Microherbivores make a big impact in coral aquaculture

Reef restoration activities and the ornamental trade are increasing the demand for sexually propagated corals. One challenge faced in scaling up the aquaculture production of corals is high mortality as a result of fouling organisms overgrowing coral spat, with manual removal of algae and other fouling organisms being costly and time consuming. Here we test the use of microherbivore grazers as a potential biocontrol method for fouling in coral aquaculture and compare their effectiveness to manual cleaning by an aquarist. Recruits of six coral species (Acropora millepora, Acropora kenti, Goniastrea retiformis, Porites lobata, Dipsastraea speciosa and Lobophyllia corymbosa) were reared for 112 days with aquarist cleaning, or co-cultured with gastropods (Calthalotia strigata or Turbo haynesi), sea urchins (Tripneustes gratilla or Echinomentra mathaei), the hermit crab Clibanarius cf. taeniatus or under a control treatment with no grazers. Corals grown in the aquarist cleaning treatment displayed high survival and growth, though similar responses were observed for most coral species grown with C. strigata or T. gratilla, likely due to minimal damage via overgrazing and the promotion of relatively short turf algal communities in these treatments. However, effort required, measured as average cleaning time, was 2–3 times greater in the aquarist treatment compared to C. strigata or T. gratilla treatments. Survival of coral recruits housed with C. cf. taeniatus, E. mathaei or T. haynesi were variable, likely due to the dominance of long, filamentous turf algae in tanks with E. mathaei, and physical disturbance to recruits by C. cf. taeniatus and T. haynesi. Our results demonstrate microherbivores have potential for application in aquaculture to promote production, while also reducing labour costs.