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This review paper presents information on the production status of economically important seaweed species in the Philippines, new culture technologies for Halymenia durvillei and also an examination of the present but limited use of Sargassum. The country recorded its highest production volume of seaweeds (mainly eucheumatoids) in 2011 amounting to 1,840,832 metric tons (fresh weight). In the subsequent years, the Philippines recorded a steady decline in production which can be attributed to epiphytism, loss of genetic diversity due to the culture methods used (i.e. vegetative propagation), political unrest in the main farming areas of the Southern Philippines, and the frequent occurrence of typhoons. The more than 200,000 ha of farmable areas along available coastlines remain to be tapped and evaluated in order to determine which areas are suitable for seaweed farming. The haphazard harvesting of Sargassum led to the proclamation of Fisheries Order No. 250 which prohibits harvesting of Sargassum. Exploitation of Gelidiela acerosa remains a concern as there is no currently available culture technology for the species. The lack of comprehensive records on Philippine seaweed production needs to be addressed and its diverse algal resources remain to be explored.

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Numerous attempts to capture the morphological variability of the genus Caulerpa have resulted in an unstable classification of numerous varieties and formae. In the present study we attempted to test taxon boundaries by investigating morphological and genetic variation within and between seven taxa of Caulerpa, supposedly belonging to four species, sampled at different sites in a Philippine reef system. Using both field and culture observations, we described the relation between the variability of a set of morphological characters and ecological parameters, such as wave exposure, light intensity, and substrate type. Statistical analyses showed that the limits between two (out of three) ecads of the C. racemosa (Forsskål) J. Agardh complex were obscured by the presence of morphological plasticity. Other studied taxa of Caulerpa (i.e. C. cupressoides [Vahl] C. Agardh, C. serrulata [Forsskål] J. Agardh, and two formae of C. sertularioides [S. Gmelin] Howe) could be grouped based on morphology despite the presence of morphological plasticity. Our results indicated a strong association between light intensity and several quantitative morphological variables. Genetic diversity of these taxa was assessed by partial sequencing chloroplast rbcL and tufA genes and the ycf10-chlB chloroplast spacer. In all phylogenetic analyses, C. serrulata, C. cupressoides, C. sertularioides, and the three ecads of C. racemosa emerged as distinct genetic units. Despite the presence of morphological plasticity and morphological convergence, a subset of morphological characters traditionally used in taxonomic delimitation still had sufficient discriminative power to recognize the terminal phylogenetic clades.

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