Date of Award

5-2001

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Robert L. Vadas

Second Committee Member

William A. Halteman

Third Committee Member

Ian R. Davison

Abstract

Harvesting of natural resources usually entails substantial removal of the target species. Where such species are dominant members of natural communities, their removal can have important consequences for their own regeneration as well as for the species assemblages associated with them. Rockweed is an ecologically and commercially important intertidal alga in the North Atlantic, and is increasingly being harvested in Maine. The effects of harvesting on regrowth are well known but little is known about its effects on the species that use this alga as habitat. This research focused on the ecological implications of A. nodosum harvesting on the associated community. Three different harvesting regimes (uncut/control; cut at 18 cm; and cut at 36 cm) were imposed on four separate sites in mid-coast Maine, USA. Post-harvest changes in community structure were followed for two years (July 1997 to June 1999). Removal of the seaweed canopy resulted in a loss of habitat and a decrease in several associated species. Significant effects were detected in individual species analyses and in community-level analyses. The intensity of the disturbance was an important factor in the rate of recovery. Although numerous species within the community experienced short-term effects (1-2 years), few effects persisted through time. This suggests that a single harvest event can cause Short-term changes to the community structure but that the community is resilient to this type of disturbance. Considerable differences were found in the overall community structure. Species composition and relative abundances varied within and among the four sites. The apparent homogeneity of the Ascophylhm beds does not necessarily mean that the associated communities are similar. The spatial heterogeneity associated with the Ascophyllum community structure made it difficult to detect overall harvesting effects. Ascophyllum population and morphological characteristics were affected by the harvest. The number of medium-sized shoots increased by 108% in the harvested plots. The number of branches at 18 cm and the number of apical dichotomies also increased in harvested areas. At the end of the experiment, control plants were found to be significantly longer (-32%) than the plants in the cut plots indicating a lack of complete recovery.

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