Studies on the Marine Fouling Alga Ulothrix flacca (Dillwyn) Thuret

I 
 
Abstract 
 
 
 Marine biofouling is a worldwide problem which costs billions of pounds each 
year in purchasing and applying the antifouling products in order to clean the fouled 
surfaces and to repair the damages caused by fouling organisms. Recent immersion 
panel trials and examination of the fouling literature have revealed the marine green 
macroalga Ulothrix flacca to be a major pioneering fouling organism on toxic 
surfaces. Despite its importance, virtually nothing is known about this alga in a 
fouling context. The present study addressed this issue and attempted to provide a 
better understanding of its biology, its fouling role and aspects of its resistance to 
current antifouling biocides and heavy metals. 
 The toxicity of biocides and heavy metals was tested only on the vegetative 
growth of U.flacca, because spore production could not be carried out. In order to 
produce vegetative material, investigation of the effects of light quality on the life 
cycle of U.flacca was carried out. White (control), blue, green, red and yellow lights 
were used, and only yellow light has been found to be the one to block spore 
production while producing a vegetative growth in the same quantity as the control. 
Then, all the bioassays were carried out under yellow light. 
 The biocides investigated were Irgarol 1051
©
, Preventol A6
©
 and Sea-Nine 
211
©
 and the heavy metals were copper, cadmium and zinc. Laboratory studies, 
using varying concentrations of the toxins, gave EC
50
 values after 1 and 2 weeks of 
204 µg.L
-1
 for Irgarol,1 µg.L
-1
 for Preventol, 903 µg.L
-1
 for Sea-Nine. This order of 
toxicity, Preventol>Irgarol>Sea-Nine was not found after 3 weeks of treatment 
where Irgarol showed a better efficacy. Concerning the heavy metals, laboratory 
studies showed EC
50
 values after one week of 2213µg.L
-1
 for copper, 2906µg.L
-1
 for 
cadmium, 4903µg.L
-1
 for zinc. After one week of treatment, Preventol is far more 
efficient than any other toxin used.  
 The scanning electron microscopy studies looked at the different stages of the 
life cycle of U.flacca focusing on the attachment mechanisms, which enable its 
strong adhesion to the surface. The result of these studies showed the high tolerance 
of U.flacca to common toxins and the results could lead to further research in order 
to find alternative antifouling products with a lower environmental cost.
Chapter 1    Introduction 
1 
 
 
 
 
 
 
 
 
 
 
 
Chapter 1 
 
Introduction
Chapter 1    Introduction 
2 
1.1  Marine Biofouling 
 
 Marine biofouling is a worldwide problem. It has been defined as: “The 
growth of unwanted organisms on the surfaces of man-made structures submersed in 
the sea, which has economic consequences.” (WHOI, 1952). The fouling organisms 
may be fixed or floating on artificial surfaces submerged in seawater, intertidal or 
subtidal, and can be located in coastal waters or offshore (Fletcher, 1988; cited in 
Braithwaite, 2003), on structures such as ship’s hulls, wharfs, fish cages and netting. 
Some studies showed that the fouling organisms can be fixed on all materials 
including metal, plastic, wood and rope (Berk et al., 2001; Stachowitsch et al., 
2002).  
 The main effect on these submerged structures is the addition of weight, 
which can cause a disruption of structural activity, such as the emergence of rust, and 
more generally the acceleration of corrosion, and then even the formation of holes on 
it if it is not treated. Offshore oil platforms, can be affected in the same way. Indeed, 
now it is known it is very important to design a minimum area on the platforms, 
where fouling organisms can be fixed, because it has been shown that fouling 
organisms rapidly colonise the submerged portions of these structures (Gunn et al., 
1984), and then cause a decrease of the structural integrity. It also has been shown 
that biofouling on mariculture equipment is a great and costly problem (Fletcher, 
1995; Hodson et al., 1997; Solberg et al., 2002). 
 
1.1.1 The Fouling Community 
The fouling community consists of organisms which cover the submerged 
structures. In the fouling community, firstly 2000 fouling species were reported 
(Woods Hole, 1951; cited in Braithwaite, 2003), and later other sources showed 4000 
fouling organisms (Crisp, 1973; cited in Braithwaite, 2003). Algae, bacteria, diatoms, 
barnacles, fungi, sponges, corals, bryozoans, mussels, amphipods, isopods, fish and 
arthropods are the most important species of all the biofouling organisms (Relini et 
al., 1994). Most of these organisms spend their larval stages drifting on the ocean 
currents as part of the plankton. Eventually they mature and attach themselves to 
solid objects where they will remain the rest of their adult lives. These organisms, as 
many and different as they are, have some important characteristics in common.
Chapter 1    Introduction 
3 
 Firstly, the composition depends on the nature of the place where they are 
(Callow, 1996), with both quantitative and qualitative aspects. The fouling 
community varies as well with a wide seasonal distribution, and is a dynamic process 
(Callow, 1996). All benthic organisms are potential foulers. Fouling organisms have 
to be locally abundant, with an extended period of reproduction and a rapid growth 
rate (Moss, 1976). Indeed, it is obvious that a large abundance of organisms with a 
rapid growth rate and long periods of reproduction assist the persistence of these 
organisms. These characteristics mean that there are already difficulties in 
controlling them; plus, these organisms are physiologically hardy, resistant to 
antifoulants (Woods et al., 1988) and have efficient and rapid attachment 
mechanisms. Additionally, the water flow, the salinity or the nutrient supply can 
increase or decrease the composition of this community (Callow, 1996). It has been 
shown as well that fouling varies in intensity and diversity following the composition 
of the benthos (Holm et al., 2000), and that fouling organisms are more intense in 
coastal waters where the conditions are better for greater species diversity. It is also 
more of a problem in tropical than temperate regions (Bennett, 1996), where the 
temperature is higher. With all these specificities, it can be said that the fouling 
organisms are in some ways perfect parasites for the immersed structures.   
 The conditioning of a fouling community on an immersed surface is 
methodical, and each phase is conditioned by the phase which takes place before (fig 
1.1; fig 1.2). Firstly, when a new surface is immersed, there is the adsorption of 
inorganic material and macromolecules on it. Then there is the formation of a 
primary film, composed of dissolved organic material (Gunn et al., 1984). This is the 
first stage for the settlement of the microfouling organisms, which are slime 
components, including diatoms (fig 1.3), bacteria, blue-green algae and 
dinoflagellate algae (Scott et al., 1996). Studies have shown that these organisms are 
mainly bacteria; indeed, cell densities of 2
18
.cm
-2
 have been observed after only 4 
hours of immersion (Dempsey, 1981).
Chapter 1    Introduction 
4 
 
 
Figure 1.1 The composition of Marine Fouling Community  
(Davis and Williamson, 1995; cited in Candries, 2000). 
 
 
 Typically, this primary layer reaches a thickness of 100-600µm (Woods et al., 
1988). For adherence, bacteria and diatoms use an excretion of EPS (extracellular 
polymeric substance), a sticky polysaccharide, and then with the division of cells, 
there is a rapid increase in the colony (Callow, 1996; Callow and Fletcher, 1994). 
After the settlement of this microfouling layer, there is the development of a 
macrofouling community which will overgrow the microfouling community (Fig 
1.4).  
 This community is composed of organisms which are permanently attached to 
a substrate. Among all the macrofouling organisms, macroalgae, such as Ulothrix, 
are the most important group responsible for ship fouling (Fletcher, 1980; Fletcher, 
1988; Evans, 1981). There is a lot of algal species from the three main groups 
(Chlorophyta, Phaeophyta, Rhodophyta).
Chapter 1    Introduction 
5 
 
Figure 1.2 Dynamic chart representing the sequence of events involved in the 
settlement of a fouling community. 
 
 
 
Figure 1.3 View on the electronic microscopic microfouling including diatoms 
(Amphora) (University Of Birmingham).
Chapter 1    Introduction 
6 
 
Figure 1.4 Example of the diversity of the macrofouling community. 
 
 Algae seem to be physiologically more tolerant than the animals to the 
antifouling paints and they often dominate the fouling communities (Evans, 1981; 
Fletcher, 1976). They are physiologically very hardy and have a strong regeneration 
after scrubbing. Another factor which favours the domination of algae in the 
macrofouling community is that spore settlement on the ships’ hulls takes only a few 
minutes, and it takes less time than the settlement of animal larvae. Additionally, 
fouling algae can settle and grow in strong water currents (Houghton et al., 1973) 
and they can live in places where there is not a lot of light, such as the undersides of 
ships’ keels (Fletcher, 1988). The green alga Enteromorpha is the most important 
macroalga found on ships’ hull (Callow and Callow, 2000). Another very good 
fouler is the filamentous green alga Ulothrix flacca (Braithwaite, 2003). 
 
1.1.2 The Effects and Problems of Marine Fouling 
1.1.2.1 Ships and submersed Structures 
 The effect of fouling on ships is most important, and the one for which all the 
efforts are focused to resolve this problem. Basically, when the antifouling organisms 
accumulate on the ship’s hull, an enormous increase in the mass of bio-organisms is 
seen, which reduces the capacity and the operational efficiency of the vessel. 
Additionally, this addition of weight causes a diminution of the speed. Indeed, the 
hulls of the ships are normally smooth and made for moving as easy as possible 
through sea water and to sail as fast as possible; with fouling organisms, the increase 
of roughness generates an increase of the frictional resistance, and then a decrease of 
the maximum speed. Shipping companies want to maintain the maximum speed for
Chapter 1    Introduction 
7 
financial reasons, so it involves an increase in fuel consumption. The fouling 
organisms’ composition varies spatially on the hulls (Lewthwaite et al., 1984); these 
variations can be attributed to the variation of environmental factors such as light or 
predation, but also change with the action of the sea water on the hull (Gunn et al., 
1984). The roughness on the hull also generates an increase in noise made by the 
ship, and then the “acoustic signature” is not the same as it would be if there were no 
organisms present. Coastal ships are subject to more fouling. This is the same 
problem for the sonar domes which are placed under the boat, and send out an 
acoustic pulse in water for measuring distances in terms of the time for the echo of 
the pulse to return. Indeed, fouling results in degradation of the performances and the 
signal received is not the real one. This causes problems, especially for military 
submarines. 
 The hulls of the boats become also more and more rusty because of corrosion, 
and finally holes can appear if nothing is done. Also, navigation buoys are rapidly 
damaged by the corrosion caused by the fouling organisms. For seawater piping 
systems in coastal power stations, fouling is also a major problem, reducing tunnel 
diameter and then causing restricted water flow. Oceanographic and geological 
instruments are also damaged by fouling, blocking rotors and other mechanisms for 
the dynamic high-tech materials, or coating the windows of optical instruments or on 
the solar cells which generate energy for the functioning of all these instruments. 
Submersed structures for which fouling is a big problem include the off-shore 
platforms. Indeed, the biofouling increases the weight which has a negative impact 
on the static conditions and induces corrosion.  
 
1.1.2.2 Mariculture 
Mariculture is the cultivation of marine organisms for food, either in their 
natural environment, or in seawater in ponds or raceways. An example of the latter is 
the farming of marine fish, prawns, or oysters in saltwater ponds (Cook et al., 2006). 
Mariculture is the aquaculture branch specializing in sea organisms. In these cultures, 
there is the release of a lot of dissolved inorganic nutrients and particles, because of 
faecal material or even uneaten food. All these inorganic nutrients are thus present in 
the environment and can cause the settlement of other organisms. Firstly, the 
community will be quite rich in species, but later the species will rarefy and finally 
only the adapted species for the environment will remain (
Chapter 1    Introduction 
8 
1978; cited in Braithwaite, 2003). However this has never received much attention 
from scientists and the information on this community is rare. As seen previously, 
the fouling community is composed of micro and macro organisms.  
Some recent studies showed that the nutrient enrichment of the water column 
adjacent to caged mariculture enhances growth of macro organisms such as mussels 
(Cook and Black, 2003; cited in Braithwaite, 2003) and macroalgae (Chung et al., 
2002; cited in Braithwaite, 2003). For example, the culture of macroalgae in the 
proximity of fish cages showed an increase of nitrogen assimilation, and then an 
increase in growth rates.  
These fouling macroalgae can also change the pH of the water, and this is 
another problem, especially for good development and the growth of the culture 
itself. For the culture of crustaceans or shells, the use of multi-filament netting 
material is applied, but unfortunately, this is an ideal substrate for fouling organisms 
(Fig 1.5-B). Fouling is particularly a problem in cage mariculture, increasing the 
weight of the nets and occluding the net mesh in size. This is a problem as it prevents 
sea water flowing through the cage (Fig 1.5-B) and, there is less oxygen for the 
organism in culture and finally, their development will be impaired and possibly a 
high percentage of the population will die (Champ, 2000).  
 
       A              B  
Figure 1.5 Effects of fouling on mariculture:  A: On a basket; B: On the nets.
Chapter 1    Introduction 
9 
1.1.2.3 Economical Effects: The Cost of Fouling 
 Every year in the World, huge sums of money are spent fighting fouling and 
trying to find solutions to the problem. Governments and industry spend more than 
£9.8 billion annually to prevent and control marine biofouling. The most important 
cost is on ships. As seen before, the presence of fouling organisms adds weight to the 
ships and to reach the maximum speed, they need to increase the fuel consumption. 
This over-consumption of fuel has two aspects; one ecological, because more fuel 
consumed means more CO
2
 emissions; and another, economical, because more fuel 
means also more money. Fouled ship hulls burn 40% more fuel at an additional, 
annual global cost of £13 million. Apart from these costs linked to the increase of the 
fuel consummation, there are other problems on the ships such as paint removal and 
the need for repainting. The total global market for antifouling coatings for ship and 
pleasure craft is approximately £1.2 billion per annum. For the oil platforms, 8% of 
the lifetime cost is for antifouling measures. Other structures affected by fouling, 
which is very costly per year, are heat exchangers used to transfer heat from a fluid 
on one side of a barrier to a fluid on the other side without bringing the fluids into 
direct contact. Despite significant technical progress in the design and construction 
of heat exchangers in the last two decades, the problem of fouling on heat exchanger 
surfaces is still one of the major unresolved issues. Fouling in heat recovery and 
transfer equipment costs U.S. industry $5 billion per year (Watts and Levine, 1984; 
cited in Braithwaite, 2003). Control of fouling of water intakes, piping systems and 
heat exchangers in desalinization and power plants, costs over £26 billion per year. 
Also for the seawater piping systems, the cost of the control of fouling on 
membranes used in wastewater and desalinisation systems is over £1.4 billion per 
year. For other submersed structures such as oceanographic and geologic instruments 
and buoys, the cost is always really important. For mariculture, fouling organisms 
can be considered as parasites which prevent the normal development and the growth 
of the cultures. So fouling necessitates frequent and costly cleaning of nets. This 
contributes to an increase in costs up to 25%. Fouling of aquaculture systems in fish 
farms costs an average producer £70,000 per year (University of Connecticut Team 
Benthos website).
Chapter 1    Introduction 
10 
1.2  Ulothrix flacca as a Fouling Alga 
1.2.1 Taxonomic Background and Fouling Role 
 
 Among all the macrofouling organisms, algae are one of the most important 
groups responsible for ship fouling (Fletcher, 1980; Fletcher, 1988; Evans, 1981).  
A lot of algal species from the three main groups are present (Chlorophyta, 
Phaecophyta, Rhodophyta). Algae appear to be physiologically more tolerant than 
animals to the antifouling paints and then they often dominate the fouling 
communities (Evans, 1981; Fletcher, 1976). Another factor which favours the 
domination of algae in the macrofouling community is that the spores’ settlement on 
the ships takes only a few hours, less time than the settlement of animal larvae. 
Additionally, fouling algae can grow in water currents (Houghton et al., 1973) and 
they can live in places where there is not a lot of light, such as the undersides of 
ships’ keels (Fletcher, 1988). The main fouling algae are the genera Enteromorpha, 
Ectocarpus, Ulva, Fucus and Ceramium. The green alga Enteromorpha is the most 
important macroalga found on ships’ hulls as fouling alga (Callow and Callow, 
2000).  
 
        
     Figure 1.6 The macroalga Enteromorpha             Figure 1.7 The macroalga Enteromorpha on a tanker’s hull. 
(Figures 1.6 and 1.7 from NERC, 1995). 
 
Enteromorpha is a long and thalloid green alga (Fig 1.6), which is attached to the 
ships (Fig 1.7) by rhizoids. They have also a high fecundity which allows them to 
rapidly colonize the hulls (Callow and Callow, 2000); the motile reproductive cells 
actually have the ability to photosynthesize, thus increasing their potential viability 
and dispersion (Beach et al. 1995; cited in Braithwaite, 2003). Studies have shown 
that Enteromorpha species are the most common and widespread of all marine