cultch

Cultch is substrate material placed on the seabed to provide a hard surface for the attachment and growth of shellfish larvae, especially oyster spat, and other sessile marine organisms. In shellfish aquaculture, cultch improves recruitment by supplying a settlement surface beyond the natural seabed, helping to initiate and enhance populations.

Materials used as cultch include both natural and artificial options. Natural cultch consists of shells, fragments of shells, rock, or limestone. Artificial cultch comprises concrete blocks, ceramic tiles, or specially designed reef-like modules. The choice of material depends on local conditions such as depth, currents, substrate type, and the target species, with attention to roughness, porosity, durability, and environmental safety.

Cultch is deployed in designated plots or on gear such as spat collectors or lines used in grow-out operations. It is left in place for a period sufficient for larvae to settle, grow, and become more robust, after which the juveniles may be transferred to grow-out systems or the cultch may remain as part of a reef-like habitat. In some cases, cultch is retrieved or replaced as management objectives evolve.

Environmental and management considerations include avoiding contaminants or invasive species from non-local materials, assessing potential ecological impacts on local habitats, and complying with regulations governing placement and removal. Best practices emphasize material suitability, site selection, and monitoring of recruitment and ecological effects.

See also: shellfish aquaculture, spat collection, reef restoration.