Banks of microscopic forms and survival to darkness of propagules and microscopic stages of macroalgae

Abstract

Previous studies have found that the number of species conforming a bank of microscopic forms in tide pools in central Chile accounted only for half the number of species present in the macroscopic vegetation around the pools. An elemental condition for survival in these banks is the ability of microscopic forms to tolerate darkness or very low irradiances for extended periods. To test this ability, spores of 17 green, brown and red algal species, present and absent from the bank, were incubated at different combinations of irradiances and day lengths. Propagules of 47% of the species tested (eight species) germinated in total darkness while the propagules of the other nine species germinated under conditions of very low irradiance (2-10 μmol m-2s-1). In most species, microforms showed a higher tolerance to darkness than the propagules. Some survived for over a year and one species (Gelidium lingulatum) could live under complete darkness for 500 days. The ability to survive in total darkness did not relate to presence or absence of a species in the banks of microscopic forms previously studied, to phylogenetic relatedness, life history style, propagule size, morphology of microscopic forms or to successional status (fugitive versus late successional). Thus, tolerance to darkness appears to be common to propagules and microscopic stages of most benthic algae. The growth patterns exhibited by the microforms of Lessonia nigrescens, Chaetomorpha firma and Glossophora kunthii suggest high irradiances on these recruits might determine the shallower limits of distribution of these species.