Correlation between Gracilaria parvispora (Rhodophyta) biomass production and water quality factors on a tropical reef in Hawaii

The factors controlling the growth of the edible, red seaweed, Gracilaria p arvispora Abbott (long ego), on the south reef of Molokai, HI, were investi gated to determine where productive new plantings could be located. Experim ents were conducted in October, 1997, and March and June, 1998, in which G. parvispora biomass production was correlated with water quality factors me asured at six sites over each 21-day experiment. Water motion, temperature, salinity, nitrate and phosphate varied among sites and experiments, but we re not significantly (P > 0.05) correlated with growth. A strong correlatio n, however, was found between biomass production and ammonia concentration (r = 0.91, P < 0.001). Ammonia levels ranged from 0.2-4.0 mmol(-3) over sit es and experiments but were skewed towards low values, as was biomass produ ction. The transient nature of ammonia distribution on this reef explains t he patchy distribution of locations at which G. parvispora is productive, n oticed in previous experiments. Large-scale Gracilaria culture on such a re ef would require adding an external source of fertilizer, which may disrupt the reef ecology. An alternative is to develop a dispersed form of cultiva tion at sites that receive ammonia enrichment from the land, in which case the crop can help absorb excess nutrients entering the reef. (C) 1999 Elsev ier Science B.V. All rights reserved.