Environmental Engineering Reference
In-Depth Information
Benthic diatoms attach themselves to submerged surfaces by the secretion of either
mucilaginous materials or EPS [4, 24, 26]. They undergo primary and secondary
stages of adhesion. The primary reversible initial adhesion is an active process. This is
initiated either by chemical or physical cues. During this process the cells continuously
expend energy, use adhesion complexes to re-orient their position and move on the
surface in order to ind the most appropriate region for habitation [26, 27]. Secondary
adhesion provides permanent adhesion structures which includes pads, stalks, tubes
and ilms, that do not require the continuous burning of energy [26].
Protozoans can either be the sessile ilter feeding forms or motile predators of bacteria,
diatoms, other protozoa, and yeasts. These motile protozoans are not considered to
be true epibionts [4]. The proliferation of bacteria and diatoms in the bioilm leads
to an irregular distribution of microcolonies. With an increase in bioilm thickness,
sharp gradients of pH and dissolved oxygen are developed within the bioilm [28].
2.3 Macrofouling and the Effect of the Environment
Prominent events in marine biofouling are the colonisation of the surface by
macroscopic organisms. The macrofouling consists of both soft fouling and hard
fouling communities (
Figure 2.3
). Algae and invertebrates including anemones, soft
corals, hydroids, sponges, and tunicoids form the soft fouling community. Hydroids
comprise of invertebrates including barnacles, mussels and tubeworms [29]. Algal
spores usually pave the way for larval colonisation in the biofouling progress [4].
MICROFOULING
MACROFOULING
Tertiary foulers
2-3 week marine invertebrates
Secondary foulers
1 week algae and protozoa
Primary foulers
Conditioning film
1-24 h bacterial adhesion
1 min proteins, EPS binding
Substrate
Figure 2.3
Various stages in macrofouling
