Bacterial Factors Influencing the Settlement of Ship-Fouling Algae of the Genus Enteromorpha

Abstract

The aim of this study was to assess the effects of selected marine bacteria upon the settlement of algae of the genus Enteromorpha. The ship-fouling alga, Enteromorpha intestinalis, was chosen for the experimental work, and maintained in such a state to ensure the continuous supply of zoospores by means of a specially designed sea-water system and lighting regime. Experiments were carried out to select a suitable growth medium for zoospores produced by this species of Enteromorpha. Bacteria were assessed for their ability to produce thin films on glass attachment substrates. These bacterial films were allowed to interact with suspensions of Enteromorpha intestinalis zoospores, and zoospore attachment and development were followed by optical microscopy. A counting method was developed for the enumeration of growing zoospores, two growth forms were observed, a filamentous form and a clumped, rhizoidal, form. Some bacteria from the genera Pseudomonas and Alteromonas, and the Pseudomonas/Alteromonas group, were shown to encourage the settlement of zoospores. Other bacterial isolates from the genera Pseudomonas and Coryneform, and the Pseudomonas/Alteromonas group discouraged the settlement of zoospores. It was found that a number of bacterial films continued to encourage the settlement of zoospores when the bacterial cells were killed. This also occurred with some of the bacterial isolates which discouraged the settlement of zoospores. Cell-free bacterial extracts were shown to have little effect upon the settlement of zoospores, and there is evidence to indicate that the bacterial factor(s) that effect the settlement of zoospores may be located on the cell walls of the bacteria, or the extracellular polymers produced by these film-forming bacteria. Copper, a common component of antifouling paints, inhibited the growth of the bacteria used in this study, but only at concentrations greater than normally achieved with copper-based antifouling paints.