BAYONA, IRIS ISABELLE B.; BIYO, JONO ANGELO T.; LAMZON, JESSEL LOISE P. (February 2006)
Philippine Science High School Western Visayas Campus – Department of Science and Technology (DOST-PSHS WVC), Brgy. Bito-on, Jaro, Iloilo City 5000, Philippines
ABSTRACT
The community structure of seagrass meadows in Jawili Bay in Tangalan, Aklan, Bool Bay and Panglao Bay in Bohol, Tubalan Bay in Malita, Davao del Sur, and in Talikud Bay in Samal, Davao del Norte was described in terms of: a) species composition, c) biomass, d) demographic characteristics, e) vegetative strategies, and f) reproductive dynamics of seagrasses in these areas. Results were compared with those obtained for Guimaras Bay (Biyo, 2001) and Bolinao Bay in Pangasinan (Vermaat et al., 1995).
Seven seagrass species were found in Jawili Bay, namely: Thalassia hemprichii, Cymodocea rotundata, Cymodocea serrulata, Syringodium isoetifolium, Halodule uninervis, Halophila ovalis, and Enhalus acoroides. Six species were identified in Panglao Bay, and five seagrass species were identified in Bool Bay, Tubalan Bay and Talikud Bay.
Seagrass density in the five sites ranged from 1910 to 5311 shoots/sq m. Values were comparable with those in Guimaras (Biyo, 2001) and twice as high as in Bolinao. (Vermaat et al., 1995). Seagrass biomass in all sites were comparable, ranging from 289 to 440 g DW/sq m.
The age reconstruction technique based on leaf plastochrone interval (PI) estimates showed that mean, median ages, and maximum ages of T. hemprichii and C. rotundata in the five sites were lower compared with values obtained in Guimaras and Bolinao. Net recruitment rates however indicated relatively stable T. hemprichii and C. rotundata populations in these coastal areas. Vertical internode length showed distinct annual patterns, with growth minima occurring in January and August, and higher growth during the summer months. The same growth pattern was observed in Guimaras (Biyo, 2001) and Bolinao (Vermaat et al. 1995) for these species. Vertical growth rates for T. hemprichii in Bool, Panglao and Samal, and for C. rotundata in Malita were comparable with those in low sedimentation areas in the country and the Caribbean (Vermaat et al. 1995). The high vertical growth rate of T. hemprichii in Jawili however, may indicate high sedimentation in the area.
The age reconstruction technique also revealed that 9.6% of T. hemprichii shoots in Jawili, 1.78 in Bool, 10.9% in Panglao, and 4.7% in Samal are flowering. In Tubalan Bay, 52.3% of C. rotundata shoots produced flowers; a very high reproductive effort compared with most seagrass species in which less than 10% of the shoots flower annually (Gallegos et al., 1992; J. S. Uri et al., unpubl.). that flowering in C. rotundata Results further revealed occurs the whole year round and peaks in March. Flowering for T. hemprichii in Jawili peaks in December; in Panglao, this peaks in September, while in Talikud Bay this peaks in January.
This study demonstrates the use of the age reconstruction technique based on leaf plastochrone (PI) interval estimate as a useful tool in assessing seagrass condition in the coastal areas of the country.