5.3.1. Introduct ion to Biofo uling
Biofouling refers to unwanted life growing attached to an
interface, such as between seawater and the surface of
The Ocean Cleanup Array. Biofouling can be separated into
two functional categories - microfouling and macrofouling
- but the size range is in fact a continuum that ranges from
micrometers, such as bacteria, to meters, such as kelp.
Many species considered macrofoulers may begin life as
microfoulers. Species vary enormously worldwide based
on factors such as season, geographic location, depth,
current speed, light, temperature, salinity, food availability,
surface type, surface texture, and presence of mates.
Some accumulations are highly biodiverse and others are
dominated by a single species. Some are temporary and
precondition the surface for the next wave of colonization,
while others are considered ‘mature’ and ‘stable’ communities.
Within an accumulation a bare patch can appear,
perhaps by the action of a storm or a predator. These
patches may become colonized by an entirely different
pattern of life than its surroundings. For the small number
of organisms that cause the greatest problems in industry
- typically shipping - a large amount of research exists.
Much less information is available for the larger population
of species and locations which do not cause issues,
The first phase of biofouling (after chemical conditioning
of the surface upon introduction to seawater) is the accumulation
of a biofilm. A biofilm is a microbial layer composed
of a variety of microscopic species enmeshed in a
slimy polysaccharide matrix. Marine bacteria, photosynthetic
microalgae and cyanobacteria are typical kinds of
organisms found here. They are the first to form because
of their ubiquity in the marine environment in addition to
their short generation time. A biofilm thickness ranges
from about 50 micrometers to about 2 millimeters, but
can be highly heterogeneous. Microbes in a biofilm are
able to create an environment very different to that of the
surrounding water. For instance, they may increase the
oxygen content (in the presence of photosynthesisers) to
300% saturation, but become anoxic in the dark and increase
the pH to 10. Biofilm formation can begin within
hours of a surface being introduced into the marine environment.
After the biofilm has formed, a succession of algal and
animal macrofoulers develops. The specific species comprising
the macrofouling community can be highly unpredictable,
as is their rate of arrival, spread and growth.
Most animal fouling species are fixed to the surface as
adults and therefore the larval stages are responsible for
the spread of fouling communities. Algal spores can be
only a few microns in size on arrival but grow and spread
to form large mats or fronds. Similarly, animal larvae tend
to be on the order of hundreds of microns, but can grow
to be very large.
Where it comes from and how it grows
There are various ways that marine fouling organisms reproduce
and spread. Some release their eggs and sperm
into the ocean where fertilization takes place. Others may
brood their larvae and release them locally. Some spread
clonally: one individual buds genetically identical sisters
and spreads out to colonize a surface. When larvae and
spores are released into the environment, most can only
survive for a very short period of time unless they find a
place to settle. The amount of time they can survive affects
how far they can travel - if carried by currents - to
colonize a new area. Algal dispersal tends to be limited
from meters to hundreds of meters, but for animal larvae
the range of dispersal potential spans many orders
of magnitude - from tens of meters to thousands of kilometers.
An example of this is seen in the islands of the
Pacific where groups with high dispersal potential are
better represented.
The attachment of only one individual organism can potentially
spread and colonize large areas. Sponges, corals,
ascidians, bryozoans and algae are examples of species
that commonly colonize a surface by clonal growth
or the release of larvae or gametes (eggs and sperm).
Coastal waters host fouling communities because there
are so many solid structures in a habitable zone. For
instance, the sea floor is shallower, manmade coastal
structures abound, rocks and the intertidal zone are all
solid surfaces that are easily encountered by marine organisms.