GROWTH OF THE SEAWEEDS KAPPAPHYCUS-ALVAREZII, KAPPAPHYCUS-STRIATUM AND EUCHEUMA-DENTICULATUM AS AFFECTED BY ENVIRONMENT IN HAWAII

Three commercial gel-producing seaweed species native to the Philippines were grown experimentally in pens on an algal reef-flat in Kaneohe Bay, Oahu, Hawaii. Growth rates and environmental conditions were measured for 55 consecutive weeks. The normal northeast trade winds created a flow of water through the 272-m2 farm, one side of which faced northeast. Upstream thalli of Kappaphycus alvarezii grew at an average relative growth rate of 5.06%/day, whereas K. striatum and Eucheuma denticulatum grew at 3.50%/day. These growth rates and the overall productivity of 20.8 tonnes dry wt/ha per year were similar to those obtained on Philippine reef-flat farms. Growth rates tended to be independent of season, and correlations between growth rates and environmental variables were low. The study suggested a range of conditions under which these eucheumatoids can be productive in a farm setting: temperature maxima of 24-30°C and minima of 21-22°C; nitrogen levels of 2-4 μ-atm/l; phosphate levels of 0.5-1.0 μ-atm/l; and high solar energy levels. The pH and salinity were near 8.0 and 32 ppt, respectively, throughout the study period. The degree of water motion per se was not correlated with growth rate but the direction of wind across the farm was important. Downstream thalli generally appeared unhealhy and grew at half the rate of upstream thalli. When the normal trade winds reversed, the (formerly) upstream thalli grew poorly. None of the measured environmental factors was correlated with the downstream growth reduction, and its cause remains unknown. © 1990.