A study of algal biofouling on pearl nets in Charles Arm, Notre Dame Bay, Newfoundland

Mouland, Derek J. (2003) A study of algal biofouling on pearl nets in Charles Arm, Notre Dame Bay, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

This study examined the development of biofouling on pearl nets used for culture of the sea-scallop (Placopecten magellanicus) in Charles Arm, Notre Dame Bay, Newfoundland over a two year period, May 1998 until July 2000. The site showed salinities of approximately 30 ISU and surface seasonal temperature fluctuation between -1.5C and 20C. The greatest part of the fouling biomass consisted of macroalgae : Chlorophyta (10 species), Phaeophyta (24 species), Rhodophyta (19 species), together with Cyanobacteria (33 species) and two species of tube dwelling diatoms. All the species recorded were common members of the local benthic flora. Fouling biomass was measured on nets placed at two, and four metre depths. Rapid colonization occurred with growth initially faster at the shallow depth, but after the first year biomass stabilized at approximately I kg per net wet weight, with no significant differences between depths. The fouling community was analyzed using two multivariate techniques, Detrended Correspondence Analysis (DECORANA) and Two-Way Indicator Species Analysis (TWINSPAN). The first year's growth showed considerable floristic changes as the algal fouling developed, with samples from the latter part of the year showing considerable differences from the late spring and early summer. After one years growth few floristic changes were noted. There was no obvious difference in the algal communities between the two depths. -- Two algal grazers, the periwinkle, Littorina littorea and the green sea urchin Strongylocentrotus droebachiensis were investigated as potential biofouling control organisms. Two experiments were conducted, one in the summer months and one over winter. The pearl nets with the urchin treatment showed no significant decrease in fouling, while the periwinkle treatments significantly reduced fouling in the summer. DECORANA and TWINSPAN analysis showed no differences in algal community structure between the experiments and controls, showing that grazing was not species preferential. -- During the course of this study there was a large, and as yet still unexplained, die-off of the cultured scallops at the site, which confounded attempts to determine if the inclusion of algal grazers in the nets affected growth and survival of the scallops. These preliminary studies, however, showed no differences in the growth rate of the scallops with depth, or treatment with snails or urchins. Survival of the scallops was, however, significantly enhanced by the snail treatment in both experiments including enhanced survival in the summer experiment, when scallop loss was greatest.

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