Environmental impacts on fouling assemblages

Mariana Mayer Pinto (Supervisors: Professor Tony Underwood, Associate Professor Ross Coleman and Dr Trevor Tolhurst)


Background
A fouling panel

Pollution can have impacts at all levels of biological organization from cellular to ecosystems. The most severe form of pollution results in the elimination of life. Exposure to moderate concentrations of pollutants can, however, produce a variety of recognizable effects without actually killing an organism, such as changes in its shape and colour, physiology, growth-rates or behaviour. Pollution has the potential to reduce densities of organisms in an assemblage, thus reducing biomass and number of species, and altering its composition and structure. The effects (direct and/or indirect) of pollutants depend on the assemblage and/or organisms being studied and differ in relation to season, habitat, stage of life, i.e. if the assemblage is in the beginning of its development or if it is a mature assemblage, the current species composition, etc. Understanding and predicting the effects of contaminants on assemblages is therefore essential for management and conservation of systems.

Aims

The main objective of this project was to evaluate effects of contaminants on benthic assemblages in different habitats and at different stages of development.

Importance

Only doing well-designed manipulative experiments in the field, we will be able to have reliable and relevant information on how the effects of contaminants affect organisms and/or systems. Understanding how and why these effects occur is extremely important for conservation and management of organisms and/or habitats.

Results
Contaminating limpets

The effects of zinc were studied on assemblages in intertidal and subtidal habitats, using settlement panels and assemblages already established on pilings and rocky shores. Although a smaller amount of biofilm (bacteria, diatoms and micro-algae that colonize surfaces that were submerged in sea-water) was found on settlement panels exposed to zinc than on control panels, no differences in the assemblages between treatments were observed. There were some effects of zinc on mature assemblages. These were, however, inconsistent, varying from time to time and place to place. To determine whether there is a general pattern of the effects of contaminants on assemblages, algicide and pesticide, two common contaminants in aquatic environments were studied. Their effects were also evaluated in intertidal and subtidal habitats for assemblages in initial stages of development (using settlement panels) or mature assemblages. There were no effects of pesticide on assemblages in any of the experiments. Algicide also did not affect the whole assemblage. Nevertheless, this contaminant decreased the abundance of bryozoans and limpets in subtidal and intertidal habitats, respectively. Further experiments were done to investigate the ecological processes being affected by algicide and whether these effects were direct or indirect. In intertidal habitats, there was a direct effect of the algicide on the limpet Patelloida lastistrigata. The contaminant reduced the densities of the animal. Although algicide did not have a clear indirect effect on limpets, the contaminant reduced the amount of biofilm (limpet’s food) in places where biofilm was not experimentally removed. This reduction was not large but could also indirectly affect the density of limpets. So, an extra reduction of biofilm caused by algicide could increase this effect. Where abundance of food is just enough for consumption of limpets, algicide can greatly influence their density, not only directly, but also indirectly, via interactions involving micro- and macro-algae. In subtidal habitats, algicide decreased the abundance of bryozoans, by reducing growth and recruitment, depending on the place studied. In the case of recruitment, effects may be indirect, via influences on the biofilm.
This project demonstrates that the effects of contaminants on assemblages are not as straightforward as most of the existent literature tends to describe, demonstrating the importance of properly designed manipulative experiments, under natural conditions.