EFFECT OF NUTRIENT PULSE CONCENTRATION AND FREQUENCY ON GROWTH OF GRACILARIA-CHILENSIS PLANTS AND LEVELS OF EPIPHYTIC ALGAE

The effect of nutrient pulse concentration and frequency on Gracilaria chilensis Bird, McLachlan et Oliveira growth and epiphyte abundance w as investigated for plants grown in an indoor culture facility. The fr equency of nutrient pulses (which ranged from 1 pulse to 4 pulses per 14 days) had a strong influence on plant growth, while pulse concentra tion (from 72 to 143 mu M as ammonium) had a lesser influence. Growth became a function of total N flux only when plants received nutrient p ulses at least twice per 14 days. Both pulse frequency and pulse conce ntration affected the abundance of epiphytic algae found attached to G racilaria thalli, but pulse frequency was the more significant of the two factors. Their effects could be combined into the single factor, t otal N flux. Both reasonable G. chilensis growth and low levels of epi phytes were achieved under these conditions (20 degrees C, 25 mu mol p hoton m(-2) s(-1) PAR) if ammonium was pulsed at relatively high conce ntrations (up to 150 mu M) once every 7 days into otherwise nitrogen-d epleted seawater.