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1.1 Level and type of fouling 
As mentioned above, level and type of biofouling can introduce varying levels of biosecurity risk. 
It increases with the level of biofouling. Biofouling can be divided in soft- and hard- and micro- and 
macrofouling (table 2). The biofouling level increases here from the left to the right. 
Table 2: Examples of biofouling types (BIMCO 2021). 
Soft biofouling 
Micro 
Macro 
Slime 
Soft corals 
Sponges 
Hydroids 
Anemones 
Algae 
Kard calcareous biofoulina 
Macro 
Barnacles 
Mussels 
Tube worms 
Bryozoa 
Oysters 
Tunicates 
The process of biofouling attaching to a ship starts immediately upon the ship has entered the 
water no matter a newly applied AFC or a recent cleaning (Flemming 2002). Therefore, all ships 
show some level of fouling starting with slime layer, the microfouling/biofilm. Table 3 shows a level 
of fouling (LOF) scale divided in “low”, “medium” and “high” based on the ranking system by Floerl 
et al. 2005. 
The speed and intensity of biofouling growth on the hull depend on certain factors that were 
presented above. Additionally, the location and design of niche areas are of high importance 
regarding the degree of fouling since they often represent sheltered areas, where species 
attachment and growth is easier than at the exposed areas of the hull. 
Macrofouling contains a higher level of species introduction since the spectrum of species can be 
more distinctive and may be harder to remove (Department of the Environment and MPI 2015). 
Even non-sessile species like mobile crustaceans might use macrofouling as habitat. 
Currently, the IMO Biofouling Guidelines are under revision. The ranking of the biofouling level is 
one central part of this revision process and it is still under discussion. When taking this proposal