Standing Stocks of Seaweeds of Commercial Importance on the North Shore of Prince Edward Island, Canada

Abstract

The Standing stock of seaweeds, including the commercially important species, Chondrus crispus (Irish moss) and Furcellaria lumbricalis, was studied seasonally over a five-year period, 1977 through 1981, in northeastern Prince Edward Island, in the southern Gulf of St. Lawrence. Both C. crispus and F. lumbricalis have been harvested äs cast weed ('storm-tossed') in this region. From 1967 through 1981 the annual harvest was quite variable, ranging from around 3000 to 10000 wet tonnes. Estimates of Standing Stocks indicate that there was, however, little annual Variation of either total biomass or individual components, with the Standing stock of all species of seaweeds being around 70000 wet tonnes distributed over an area of 155 km 2 . There is considerable sand within this area, hence the Vegetation was not uniformly distributed, either horizontally or vertically, and the estimated cover of plants was usually 50% or less. Standing Stocks in quantities that could be estimated extended to around 20 m depth, but at depths greater than 15m the Vegetation was sparse. The greatest biomass was in the 2.5 to 5 m depth ränge where C. crispus was the dominant species, whereas F. lumbricalis was the dominant alga in the 7.5 to 10m zone. Together these two species contributed up to 50% of the total Standing stock. The other major individual perennial components included Fucus serratus, F. vesiculosus, Laminaria saccharina, Phyllophora pseudoceranoides and P. truncata. It was not possible to correlate variations of harvest with abiotic or biotic factors.

The settlement, attachment and establishment of marine algal spores

“…It is particularly well known that friable rocks offer poor substrata for algal growth. For example, McLachlan et al (1987) refer to the absence of a stable canopy of laminarians on friable sandstone, Parker & McLachlan (1990) refer to Phymatolithon stabilizing the rock surface and allowing Chondrus populations to recruit whilst refer to magnesium limestone stones as being too friable for Himanthalia establishment. There is also some evidence that different rock types can influence the development and adhesive properties of the attachment cells/ rhizoids.…”

Biology of Furcellaria lumbricalis (Hudson) Lamouroux (Rhodophyta: Gigartinales), a commercial carrageenophyte

“…Calculated average densities in areas where F. lumbricalis constitutes 16-82% of the total macroalgal biomass range from ca 50 to 870 dry g m-2 (Table 1), assuming dry weight to be 20% of wet weight (Ravanko, 1972;McLachlan et al, 1987). Seasonal variations in biomass are to be expected because of periodicity in growth and reproduction.…”

“…On the other hand, areas where harvest is limited to collection of wave-cast plants afford an opportunity to estimate natural year-to-year variation in standing stock. In a fiveyear study of one such location in the Gulf of St. Lawrence, McLachlan et al (1987) concluded that, although significant local fluctuations in standing stock could occur, algal biomass was generally stable in the area as a whole. Year-toyear variations were due largely to unusual episodes of turbulence or ice scour, or absence thereof, and did not persist.…”

“…In contrast, the Canadian harvest has consisted almost entirely of storm-cast benthic weed from the north shore of Prince Edward Island, where collection by raking has been prohibited. McLachlan et al (1987) determined that annual harvests of storm-cast plants, although representing only part of the dislodged biomass, exceeded the standing stock, thereby indicating relatively high productivity and turnover along this coast.…”

“…In Canada, drag-raking of seaweed in the southern Gulf of St. Lawrence was reported as being rapidly detrimental to benthic F. lumbricalis stocks because the rhizoidal holdfast is relatively weak, and raking appeared to remove entire plants (MacFarlane, 1965;Taylor, 1975). Collection by raking was accordingly prohibited in certain areas, particularly those with significant quantities of storm-cast weed (McLachlan et al, 1987). However, dislodgement of plants rarely removes all rhizoidal material, and the regenerative capacity of residual thalli and populations is considerable (Taylor, 1975;McLachlan et al, 1987).…”