Biology of the seagrasses, halophila ovalis (R.Br.) Hook.f. and halophila beccarii ascherson under laboratory conditions

Two tropical seagrasses, Halophila ovalis (R.Br.) Hook.f. and H. beccarii Ascherson, in Malaysia were selected for this study. Seagrasses play an important role in Malaysian marine ecosystems. Little were known of their morphology variations in the natural habitats and these variations could be attributed to environmental factors. To understand these effects, both plants species responses were assessed under laboratory cultures conditions. These were archived via experiments conducted to investigate effects of different substrates, salinity, light availability and nutrient enrichment to the plants' morphology i.e., leaf length, leaf width, petiole length and no. of paired cross veins (H. ovalis) or no. of leaf per shoot (H. beccarii). Both plants species were collected and observed at their natural habitats, from two study sites, Punang-Sari-Lawas, Sarawak and Merambong Shoal, Johor. At the natural habitats, H. ovalis grew on substrates from sandy to loamy sand. Halophila beccarii which was only observed at Punang-Sari -Lawas, grew on muddy substrate. Both plants species variability in leaf morphology at their natural habitats were compared with the plants cultured under laboratory condition. Both plants species were tested under different substrates for eight weeks of growing, i.e., substrate from a river, medium sand and substrates from beaches, fine sand, loamy medium sand, coarse sand and mixed sand (mixture between loamy medium sand and coarse sand). Halophila ovalis showed better growth performance in medium sand and H. beccarii in both loamy medium sand and mixed sand in term of leaf morphology changes. With respect to salinity ranges, both plants species were tested under decreasing and increasing salinity. Halophila ovalis tolerated low salinity of 5 psu to as high as 55 psu, while H. beccarii tolerated salinity range of 0 psu (freshwater) to as high as 80 psu. Both plants species showed better growth performance in the salinity range of 20-25 psu. In the light availability experiment which corresponded with four different water depths (10 cm, 20 cm, 30 cm, and 40 cm) for indoor and outdoor were tested. Halophila ovalis and H. beccarii showed significant morphology changes under indoor and outdoor light conditions, on leaf length, leaf width, petiole length and shoot density with all different light availability. Both plants species responded to reduced light intensity by producing bigger leaf and longer petiole but with less leaves density and vice versa when light intensity increased. Selected nutrient e.g., Ammonium chloride, Sodium nitrite, N:P:K (15:15:15) and slow release fertilizer tablet enrichments were used to evaluate both plants species responses to fluctuation of nutrient in water on their morphology. Relatively in solid fertilizers, Halophila ovalis and H. beccarii showed better growth responses with slow release fertilizer tablet. In soluble fertilizers, both plant species showed better growth responses with Ammonium chloride.

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