2003 20C4 20D5 2006 2007 2008 Harvftsî ssasm
Figure 6. Incidence (percentage of biomass) of Fucus vesiculosus on rockweed (A. nodosum) landings from ASL lease of southwestern NS from 2003 to 2008 and from field samples taken in the same locations from 2005 to 2007 (vertical bars are ±2 SE).
Sharp, 2001, Ugarte et al., 2006). The deliberate targeting of F. vesiculosus by the harvesters also is unlikely, as it is lighter than A. nodosum and, therefore, it is not of economic benefit for them to harvest a Fucus-Ascophyllum mixture. Also, F. vesiculosus is a fast growing seaweed; large plants can be observed in as little as 2 years after colonization of a disturbed or available "free space" in this region (McCook and Chapman, 1991; R. Ugarte, 2005, personal observation). Therefore, the increased incidence of F. vesiculosus appears to be related to a recent event or physical factors. The ice damage occurring in the 2003 and 2004 season could be a possible explanation for the increased amount of F. vesiculosus in the landings. Though there was an increase in F. vesiculosus in certain denuded sectors, it was not the case in all sectors; the highest incidence was observed in protected areas with no occurrence of ice damage.
A heavy recruitment of the blue mussel Mytilus edulis on the lower part of the rockweed beds was observed during the spring of 2005 in several harvesting sectors of area 6 in southern NB (see Figs. 3 and 7). The mussels attached to the free rocky substratum and to the rockweed clumps. As the mussels gain in weight, they
prevent the normal flotation of the colonized clumps and consequently interfere with the A. nodosum harvest. The excessive weight of the mussels also resulted in the detachment of the affected plants from the substratum during the fall storms of 2006. Losses of up to 30% of the rockweed biomass were observed in some of the worst affected sectors as recorded in the 2007 survey.
Cold surface seawater temperatures in winter and spring in the Maritime region appear to keep the spawning and recruitment of certain invertebrates under some form of control (Lemaire et al., 2006). Although temperature is only one abiotic factor controlling the recruitment of M. edulis (Dobretsov and Miron, 2001), the mild temperatures experienced in the springs of 2005 and 2006 apparently favored, directly or indirectly, the rapid recruitment and survival of mussels in the Passamaquoddy Bay area of NB. An inspection in June 2008 in Grand Manan Island, an important rockweed harvesting area in southern NB, detected another massive recruitment of blue mussels in the lower part of the intertidal zone. The winter of 2008 was one of the mildest on record for NB.
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