Ecological energetics of the sea-weed zone in a marine bay on the Atlantic coast of Canada. II. Productivity of the seaweeds

Abstract

The growth of the seaweeds Laminaria longicruris, L. digitata and Agarum cribrosum were followed by SCUBA divers for two years, by punching holes 10 cm from the junction of stipe and blade, and recording at intervals the distance the holes had moved. As the holes approached the tip of the blade, new holes were punched at the base. It was found that the blades behaved like moving belts of tissue, eroding at the tips while growing at the bases, so that a total year's growth amounted to 1 to 5 times the initial length. Larger, older plants had wider and thicker blades, and the biomassincrease was roughly proportional to the square of the lengthincrease. Growth was most rapid in January to April, slow in July to October. As a conservative estimate, the summer biomass of the various species of seaweeds had a turnover of 4 to 10 times in the course of 1 year. Applying these figures to an earlier survey of biomass, it is estimated that annual production of seaweeds in St. Margaret's Bay, Nova Scotia, Canada, amounts to 603 gC/m2 averaged over the whole bay, 1750 gC/m2 averaged over the sea-weed zone, or 648.000 gC/m of shore line. Approximate calorific equivalents are 6030 kcal/m2 over the whole bay, or 6480×103 kcal/m of shore line.