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Impact Assessment of Hand and Mechanical Harvesting of Ascophyllum nodosum on Regeneration and Biodiversity  [2001]

Kelly, L Collier, L Costello, M J Diver, M et al.

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This preliminary study assessed over an 18-month period the effect of mechanical and hand harvesting on seaweed regeneration and biodiversity while also assessing the costs and benefits of mechanical means of harvesting Ascophyllum nodosum in Ireland. Two study sites were used, one in Clew Bay Co. Mayo and the other in south Connemara, Co. Galway, each typical of different types of shore that harvesting takes place from. Sampling was quantitative, stratified by height on the shore and conducted before and after harvesting. According to the results of this preliminary study traditional hand harvesting was clearly more effective and cost efficient than the mechanical harvesting. However, it is recognised that this trial was a first of its kind for mechanical harvesting of seaweed in Ireland and as such could be expected to encounter various operational and design difficulties that with modification could result in greater harvesting efficiency in the future.Rare species of fauna were generally typical of sediment and sublittoral rather than Ascophyllum biotopes. Species richness differed between the Connemara site with 97 taxa and the Clew Bay site with 87 taxa, and varied from the upper to lower shore at both sites. Richness varied over time but an effect of harvesting was not detected. Ascophyllum nodosum cover decreased significantly after harvesting and was nearing recovery after 17 months in Connemara and 11 months in Clew Bay. No significant effects or
changes in red algae or Fucus serratus could be attributed to harvesting. However, increases in ephemeral algae cover in the midshore after harvesting may have been facilitated by removal of the Ascophyllum canopy. Fucus vesiculosus significantly increased in cover after harvesting at both sites. At the Connemara site the abundance of the periwinkle Littorina obtusata increased in the control and decreased in the hand-harvested sections of seashore during the winter. The species was less abundant at the Clew Bay site and no significant seasonal or harvesting trends were apparent. The numbers and cover of other animals, both mobile and sessile, were low which limited analysis. However, the cover of sessile fauna was significantly variable over time in hand-harvested sections at both sites whereas controls were not.