Estimating biomass from the cover of Gelidiella acerosa along the coasts of Eastern Philippines

• Main Authors: Rollon, Rene N., Samson, Maricar S., Roleda, Michael Y., Arano, Karen G., Vergara, Mark Windell B., Licuanan, Wilfredo Roehl Y.
• Format: text
• Published: Animo Repository 2003
• Subjects: Red algae > Philippines; Marine algae > Philippines; Biology
• Online Access: https://animorepository.dlsu.edu.ph/faculty_research/1482
• Institution: De La Salle University

In three Gelidiella acerosa beds on the poorly-studied eastern coasts of the Philippines, cover and biomass of this commercially important agar-producing red alga were measured. The three selected G. acerosa beds represented low (mean cover < 5%), medium (approximately 10%) and high cover (> 20%) vegetation. In each of the sites, we estimated the cover of G. acerosa fronds within 10 x 10 cm grids (n ranged from 33-36) in various strata. All G. acerosa fronds within each grid were harvested, cleaned of attached epiphytes and sediments, and subsequently, oven-dried at 60°C to constant weight. We applied regression analysis to establish empirical relationships between cover and biomass. All linear regression lines were highly significant (p < 0.001, R2 > 0.6) indicating that biomass could be confidently estimated from cover estimates: low cover (y = 0.017 + 0.310; R 2 = 0.67, p < 0.0001), medium cover (y = 0.0363x + 0.118, R 2 = 0.83, p < 0.0001) and high cover (y = 0.0304x + 0.481, R 2 = 0.80, p < 0.0001). Evidently though, sites with higher overall mean cover (also longer thalli) had significantly steeper regression slopes, which was most pronounced when comparing sites with the lowest (< 5%) and highest (> 20%) mean cover. Nevertheless, we subsequently projected a minimum annual yield from the known 51 ha along the eastern coasts amounting to, at a minimum, 23 t dw y-1. Such yield may translate to approximately 68.8 million pesos (US$ 1.38 million) in gross sales of agar.