Population ecology of the commercial seaweed, Gelidium sesquipedale: Biological input for resource management.

摘要

Gelidium sesquipedale harvesting for agar along coastal Portugal is managed with little scientific advise, despite decreasing annual yields since the 1970's. This work provides a resource science bases for management of the resource.;Multivariate analyses of the distribution of dominant macrophytes G. sesquipedale, Saccorhiza polyschides and Laminaria ochroleuca) in relation to local abiotic conditions (depth, sediment loading and substrate topography) in an important commercial bed, suggest that steep slopes and reduced sediment loading favour G. sesquipedale development. By contrast, S. polyschides dominated shallow zones with low slope surfaces and high sediment loading. L. ochroleuca was not significantly correlated to G. sesquipedale distribution, but its interaction with depth suggests that at greater depths (;A tagging experiment along with a 15 month sampling program in a typical, dense, monospecific G. sesquipedale stand, showed that storms and commercial harvesting play a significant role in the regulation of species population dynamics. These disturbances caused high mortality and breakage of larger fronds during summer and fall, thereby keeping intra-specific competition at low levels. During such periods, smaller frond elongation rate was high and mortality low. A pulse in vegetative development of new fronds follows these disturbances, and is probably induced by canopy loss. During spring and early summer, the opposite pattern was found due to faster growth and lower mortality of larger fronds; extensive density-dependent self-thinning was not observed. Annual yields could be enhanced by delaying the season opening.;Demographic simulations using population projection matrix models of machine cutting, recently introduced in Spain, vs. hand-plucking, currently done in Portugal, results in higher population growth rates for cutting than plucking. Assuming the same harvest efficiency, the number of fronds in each size class available the next harvest season will be higher when cut than plucked.