Buoyancy and growth characteristics of three positively buoyant marine diatoms

Abstract

Thc growth rates and buoyancy properties of 3 oceanic diatoms in the genus Rhlzosolenla were examined at light levels from 8 to 211 pm01 quanta m S ' b4aximum growth rates langed froin 0 37 to 0 78 di\rlsions d ' with saturation occurnng between 29 and 164 pm01 quanta m ' S ' Severe globvth rate depressions were noted In R acurnlnata and R formosa at irradiance levcls dbove 50 to 155 ~i m o l q r ~a n t a m-'s-In all 3 species the percentage of positively buoyant cells was inversely related to light intenslty In R formosa both growth rate and tolerance to high light levcls decreased substantially as cell s17r decreased Batch culture C chlorophyll latios (130 to 261) replicated values found in field Ethmodlscus and Rhizosolenla mats and suggest that the elevated C chlorophyll ratlos found in buovant oceanic phytoplankton are typical of healthy cells Calculations suggest that carbohydrate ballasting can dccount for buo~clncy changes and that these reserves are adequate to support dark NO; uptake Under steady-state conditions In slt11 the observed growth and buoyancy properties would lead to subsurtace population maxrma In all 3 species However, the dynamlc 11ght-related buoyancy changes probably occur on a shorter time scale than these batch culture expenments These results indicate that vertical m~gration is a property basic to these dlatoms life h~story strategy, and, like multispecies Rhlzosolenla mats, soli tar)^ Rhlzosolenla chains transpoit new nitrogen to the euphotic zone in oligotrophic seas KEY WORDS Rhizosolenla .