Heterotrophic Utilisation of Mucilage Released During Fragmentation of Kelp (Ecklonia maxima and Laminana pallida) II. Differential Utilisation of Dissolved Organic Components from Kelp Mucilage

Abstract

Mannitol, and to a lesser extent sugars plus alginates, released in mucilage during fragmentation of kelp is utilized by bacteria in the water column. Incubation of 6.4 g l-1 dried mucilage from E. maxima and 7.2 g l-1 from L. pallida at 10.degree. C results in a utilization of more than 50% of the mannitol within 48 h; alginates plus sugars reach 50% of their initial concentration in 6-10 days. There are marked seasonal differences in conversion efficiency. In the winter, incubation media were colonized by small cocci and rods and the increase in biomass of bacteria per unit C loss was approximately 12%. Incubation of the same mucilage from L. pallida in seawater collected during the summer resulted in the development of a population of large rods with a biomass about 3 times that of the smaller rods which predominated in the winter incubation experiments. The increase in biomass of bacteria per unit C loss amounted to as much as 29.4% in the summer incubation experiments. The annual dry weight of mucilage production during fragmentation from a small kelp bed of 700 ha is 1458.38 .times. 104 kg and estimated to be capable of supporting a dry biomass of approximately 30 .times. 104 kg bacteria and 3 .times. 104 kg dry biomas of flagellates and ciliates. The high density of filter- and deposit- feeding organisms which characterize the kelp bed suggests that the community as a whole is largely dependent on the flow of energy through these initial stages of the decomposer food chain based on kelp.