Not all biofouling is equal. The distinction between hard fouling and soft fouling shapes which control methods work and how urgently cleaning is needed.
Hard foulers produce calcareous or rigid structures. Barnacles secrete cement and build conical shells of calcium carbonate. Calcareous tubeworms like Pomatoceros and Hydroides construct solid tubes. Encrusting bryozoans form stony sheets. Once established, these organisms grip surfaces tenaciously. Removing them typically requires mechanical scraping, high-pressure washing, or abrasive methods — and the process can damage net fibres and coatings. Browse the organisms database for detailed profiles of each species.
Soft foulers lack rigid skeletons. Hydroids form feathery colonies. Sea squirts are rubbery bags of tissue. Filamentous algae create tangled mats. Sponges spread as fleshy crusts. These organisms are easier to remove — air-drying, freshwater immersion, or gentle brushing often suffices — but they grow back faster and some species reproduce prolifically through budding or fragmentation.
The practical consequences differ. Hard fouling adds permanent structural weight that accumulates over a production cycle. A heavily barnacle-encrusted salmon cage net can weigh several tonnes more than a clean one, placing enormous strain on moorings and cage frames. Soft fouling is lighter per organism but reduces water flow more quickly because the flexible bodies of hydroids and tunicates drape across mesh openings.
Regional patterns vary. Colder northern waters tend toward mixed communities where hydroids and mussels dominate. Warm Mediterranean sites see more calcareous hard fouling — barnacles and tubeworms can encrust a net to near-total opacity within months. Fitridge and colleagues (Biofouling, 2012) compiled fouling community profiles across European aquaculture regions and found that the economic impact per kilogram of biomass was higher for hard foulers because of the greater cleaning effort required.
In practice: if your farm deals mostly with soft fouling, low-cost physical methods like air-drying and regular net changes go a long way. Hard fouling is a different problem. You either prevent it from settling in the first place — copper nets or silicone coatings — or accept that you need heavy mechanical cleaning to get cemented organisms off without shredding the nets.