Can small grazers replace hand-cleaning in coral culture?

Can small grazers control fouling without creating a new problem for young corals? Neil and colleagues compared five invertebrate grazers with hand-cleaning and an ungrazed control. Some grazer–coral pairings preserved survival or growth while sharply reducing cleaning time, but the useful pairing depended on the coral.

Study at a glance: a 2024 experiment at the Australian Institute of Marine Science followed 6,146 newly settled recruits from six coral species across 28 independently maintained tanks for 112 days.

The tank—not each recruit—carried the treatment.

Four separate tanks represented each husbandry regime. That replication supports tank-level comparisons even though many recruits shared each tray.

“Grazer treatment” bundled several differences. Each taxon brought its own body size, behavior and survival pattern, and the hermit-crab tanks began with 15 animals while the other grazer tanks began with 30. The experiment identifies useful whole husbandry regimes; it does not isolate grazer size, density or identity as a single cause.

What remains unresolved?

Strengths: The design used four tanks per regime, an ungrazed control, a practical hand-cleaning comparison, six coral species and repeated measurements through 112 days. Survival, growth, fouling and labour were assessed together instead of treating any one endpoint as sufficient.

Limits: Grazer taxa were tested at one starting density each, and the densities were not standardized by biomass or grazing capacity. Grazer abundance changed during the study; C. strigata ranged from 4 to 58 animals among tanks by day 112. One Calthalotia tank also developed a Dictyota outbreak. These details make the result informative for regime selection but weak for a simple “more grazers is better” rule.

The experiment used recently settled Great Barrier Reef corals in one flow-through facility. It did not establish how the same taxa would behave in recirculating systems, with older colonies, or under different fouling communities.

What this means

Reef Cloverson interpretation: Biological algae control should be treated as a matched husbandry decision, not as a generic cleanup crew. The useful unit is a specific grazer, at a documented density and life stage, paired with a specific coral size and measured against manual care.

The clearest next experiment would separate grazer density from grazer identity. That would test whether a promising pairing has a workable dose range before it is scaled.

Could we replicate this?

Published protocol: The manipulated variable was one of seven tank-level husbandry regimes. The no-grazer tanks provided the biological control; hand-cleaned trays provided the operational comparison. Each regime had four 50-L tanks, and one 77-plug tray was assigned to each tank. Tanks were randomly positioned in temperature-stabilizing water baths, while treatment allocation was described as assignment rather than a fully specified randomization procedure. The study ran for 112 days at 27.5 °C under an eight-hour light period, with flow-through seawater, internal circulation and daily planktonic feeding.

Proposed smaller pilot—not performed in the paper: Ask whether one legally sourced, aquarium-appropriate grazer can reduce plug fouling without slowing survival or growth. Compare that grazer regime with manual plug cleaning and a no-grazer condition. The independent unit must be the separately maintained aquarium; multiple plugs or recruits inside one aquarium are subsamples. Keep starting grazer density, body-size range and replacement rules explicit, and distribute coral genotypes or families across treatments.

Essential equipment includes independently maintained tanks, stable temperature and light, matched circulation, conditioned settlement plugs, repeatable imaging, and a way to record cleaning minutes and fouling cover. A smaller pilot could test workflow, grazer survival and a large system-specific response. It could not identify a universal grazer, reproduce the National Sea Simulator’s flow-through conditions, or establish performance for coral species not tested.

Practical constraint: the original grazers and corals were sourced under Australian facility and collection arrangements. Any adaptation must use legally obtained organisms suited to the local system; the paper does not establish access, permits or compatibility in the United States.

Methods: How they did it

National Sea Simulator, Queensland · six coral species · 6,146 recruits at day 0 · 28 tanks · four tanks per regime · 112 days.

Funding source

The paper acknowledges support from the Reef Restoration and Adaptation Program, funded through a partnership between the Australian Government Reef Trust and the Great Barrier Reef Foundation. Rachel C. Neil also reports an Australian Government Research Training Program Stipend, the Joyce and George Vaughan Bequest Scholarship and AIMS@JCU funding. No grant or contract numbers are stated. National Sea Simulator staff and the RRAP CAD-1 team provided separate technical and operational support, and James Cook University facilitated open-access publication. Read the paper’s acknowledgments and funding details ↗

Sources

Neil et al. (2024) · Aquaculture 581, 740402 · Primary paper

James Cook University · Publication record and licensed full text

Australian Institute of Marine Science · Study data record