Diatoms are single-celled photosynthetic algae enclosed in a two-part silica frustule, typically 10–200 micrometres across. Within hours of any surface being submerged in seawater, a conditioning film of dissolved organic molecules adsorbs to it, followed by bacterial colonisation and then diatom settlement. Common genera on aquaculture equipment include Navicula, Nitzschia, Cocconeis, and Amphora. Together they form the brown-green slime visible on nets and ropes within the first week of deployment — a layer found in every European marine region, from the Baltic to the Black Sea.
Diatom biofilm itself causes minimal structural damage. It adds negligible weight and only marginally increases drag. But its real significance lies in what it enables: the biofilm changes surface chemistry and releases biochemical cues (peptides, fatty acids) that barnacle cyprids, mussel spat, and hydroid larvae use to identify suitable settlement sites. Research consistently shows that surfaces with a mature diatom biofilm accumulate macrofouling 2–5 times faster than clean surfaces. In practical terms, every day a biofilm is left unchecked shortens the window before heavy fouling arrives.
Silicone foul-release coatings reduce diatom adhesion by creating an ultra-smooth, low-energy surface — diatoms still land but detach under even mild water flow. Copper-based anti-fouling coatings suppress diatom growth chemically. Regular early-season cleaning, before macrofoulers establish, is the most cost-effective mechanical approach — see our FAQ on cleaning frequency for guidance. Understanding the biofilm stage is the foundation of any fouling management plan. Browse the full fouling succession, from biofilm through heavy macrofouling, in the organisms database.
Control Methods
Anti-fouling coatings Silicone foul-release surfaces Regular cleaning