Department of Biological Sciences, NUS
“The ecological significance of Sargassum on Singapore’s reefs.”
Jeffrey Low Kim Yew
Dept.of Biological Sciences, NUS
Fri 07 Jan 2011: 2.00pm
Seminar Room 1
(S2-04, #04-11; click for map)
Supervisor: Prof Chou Loke Ming
ALL ARE WELCOME
Abstract – Forty-two species of Sargassum have been documented from Singapore. This tally takes into account recent revelations on synonymies and misidentifications in this taxonomically complex group.
Voucher specimens for only 11 species exist in local herbaria, of which only four have been observed in the field. Three others have not been reported before, even thought they were collected in the early 1900s. It is unclear at this point how many of the other species documented from Singapore are still extent.
Of the four species observed in the field, S. siliquosum is the dominant species, occurring at almost all the sites surveyed. S. aquifolium was the next most common species, followed by S. granuliferum and S. polycystum.
Sargassum typically dominates the reef flat (with 26.5 to 54.2% cover) up to the reef crest (6.4 to 31.6% cover), but no further (slope = 0.2-0.8% cover). Why this is so is not known. It is likely that sediment load in the water limits the light penetrating to the reef slope, in addition to causing smothering of juveniles.
Historically, Sargassum is known to “bloom” seasonally, the highest abundance corresponding to the North East Monsoon, and its lowest abundance with the South West Monsoon.
This study has documented the growth of S. siliquosum from August to November, showing very rapid extensions between September and October, extending from 24.3 + 6.6 cm and 23.3 + 6.0 cm to a maximum in November at 227.8 + 43.0 cm to 247.2 + 43.0 cm. During this period, Sargassum forms an almost impenetrable wall (or crown) around the reefs, making surveys particularly difficult.
The physicality of Sargassum as it blooms provides both food and shelter to a diverse range of organisms, including coral reef fish. Only one species (out of 14 species recorded at the survey sites), Siganus javus, has been observed to feed on Sargassum, however. Rapid assessment of the epifauna of Sargassum also shows a depauperate community, comprising of 16 copepods and isopods, 3 marine snails and 6 shrimps (Hippolytes ventricosa).
Future research will focus on quantifying the photo-physiology of Sargassum, to understand the effect of a changing environment on its relative abundance, distribution and growth.