Mapping seagrass habitat and characterising Dugong feeding preferences in Sibu-Tinggi Archipelago, Johor / Heng Wei Khang

Heng , Wei Khang (2021) Mapping seagrass habitat and characterising Dugong feeding preferences in Sibu-Tinggi Archipelago, Johor / Heng Wei Khang. Masters thesis, Universiti Malaya.

	PDF (The Candidate's Agreement) Restricted to Repository staff only Download (198Kb)
	PDF (Thesis M.A.) Download (3364Kb)

Abstract

The dugong (Dugong dugon) is a marine mega-herbivore that is a seagrass community specialist. Seagrass meadows are eminently essential to dugongs as their main feeding grounds. The species’ feeding behavioural patterns are often associated with the features of the seagrass habitat. Elucidating such behavioural patterns is vital for understanding how a designated space is used. In Malaysia, the Sibu-Tinggi Archipelago, is regarded as one of the most important habitats for dugongs, hosting a significant local population due to the presence of extensive subtidal seagrass meadows. Field surveys were conducted in 2016 – 2018, across three seasons influenced by the northeast monsoon. An underwater towed video and spatial interpolation method was used to map the meadow extent and seagrass coverage in the Sibu Archipelago, while field sampling of seagrass was conducted around both Sibu and Tinggi Islands to investigate dugong feeding habits and preferences. The mapped meadow was found to be by far the largest known seagrass bed in Malaysia with an areal size of 12.88 km2. The meadows experienced a reduction of areal extent from the inter-monsoon and pre-monsoon to only 76% of the original size during the post-monsoon. Seagrass coverage similarly declined from mode 76-100% cover to mode 0-5% cover. At local scale (<10 km2), dugongs demonstrated a spatially clustered feeding pattern by maintaining a feeding patch size of 1.4 - 4.2 km2 across seasons. Two feeding patterns were detected which are likely influenced by seagrass coverage; 1) dispersed feeding occurred when seagrass meadows were in low (mode 0 – 25% cover) and high (mode 76-100% cover) seagrass covers, while 2) concentrated feeding occurred when the seagrass coverage was moderate (mode 26-75% cover). Feeding hotspots were mainly distributed off the southwest of the Sibu Archipelago, consistently between the southernmost tip of Pulau Sibu Besar and Pulau Sibu Tengah across the seasons, while feeding coldspots were mostly found around the edges of the meadow. Seagrass cover in the feeding hotspots was significantly higher than in the feeding coldspots, indicating that dugongs were strategically feeding in response to seagrass quantity. Generalized linear modelling identified the aboveground biomass and the ratios of aboveground:belowground biomass of Halophila ovalis as the most potential drivers of feeding area selection in the Sibu-Tinggi meadows (with combined explained deviances of 38.0% out of 56.0%), highlighting the role of the quantity of H. ovalis among the other factors. The proportion of silt-clay in the sediment was also selected by the model to explain the presence of dugong feeding (with explained deviances of 11.99% out of 56.0%). Although food quality parameters were absent in the final model, dugong feeding areas were associated with seagrasses with high nitrogen (0.14 - 2.13%), starch (1.53 - 3.11%) and fibre (3.02 - 14.98%) concentrations, but with low carbon (19.08 - 37.08%) and C:N ratios (15.97 - 264.84). Interspecies nutrient comparisons showed that the high starch and low fibre concentrations likely made H. ovalis and Halodule uninervis the most favoured food species, besides their fast regeneration characteristic which provides the benefit of continuous food supply to the dugongs. This in-depth study of dugong spatial and feeding ecology in subtidal seagrass meadows provides important baseline information to monitor changes in the species’ core habitats and identify important areas for conservation and habitat management.

Actions (For repository staff only : Login required)