encrusters

Encrusters are organisms that grow as crust-like coverings on hard substrates, forming a continuous or patchy veneer on surfaces such as rocks, shells, coral skeletons, or man-made structures. This encrusting growth form is common in marine environments and can involve organisms with calcareous or siliceous skeletons, as well as microbial or algal films. Encrusters typically attach at a single point or along partial margins and spread laterally to create a thin, planar layer rather than towering structures.

Major groups that function as encrusters include crustose coralline algae, encrusting bryozoans, certain sponges, barnacles, and some foraminiferans. Crustose coralline algae contribute calcium carbonate crusts that cement substrates together, while encrusting bryozoans form flat or irregular patches on shells or rock. Sponges and barnacles can produce pavement-like covers, and micro- or macroalgal films can create slimy to rigid encrustations. In some cases, microbial mats and diatoms also form encrusting layers on substrates.

Ecologically, encrusters are important as early colonizers that rapidly occupy available space, influence surface roughness, and modify habitat for other organisms. They compete for space with other sessile communities and can affect predation, sediment trapping, and abrasion on substrates. Encrusting organisms are also valuable indicators in paleoecology; their coverage, composition, and growth patterns help infer past environmental conditions such as water energy, clarity, depth, and substrate stability.

In research, encrustation is quantified by coverage area, species composition, and structural characteristics, supporting studies of marine succession, biogeography, and environmental reconstructions.