28 August 2013

Tiny but mighty: Halophila beccarii on Singapore's northern shores

Often mistaken for scum, this tiny seagrass is mighty! There's lots of them in our northern mangroves from Mandai to Sungei Buloh.
I'm doing a presentation of this awesome seagrass for the upcoming Mandai mangrove and mudflat workshop on 31 Aug (Sat). Come for this session and join the people who care about Mandai mangroves. For easier access, here's the full text article on this awesome seagrass done some time ago.

Tiny but mighty: Halophila beccarii on Singapore's northern shores
by Ria Tan, Siti Maryam Yaakub and Andy Dinesh
First appeared in Seagrass-Watch Issue 44 Nov 2011

Considered globally rare, Halophila beccarii is listed as 'Vulnerable' worldwide. According to the IUCN, this seagrass is estimated to occupy less than 2,000 km² with a patchy and fragmented distribution in the Indo-Pacific. It also has a narrow, restricted depth range. The intertidal area where they grow are subject to much human disturbance. Although it is fast-growing and may recover quickly from disturbance, global population trends indicate this species is declining.

In Singapore, this diminutive seagrass is listed as 'Critically Endangered' in the Singapore Red Data Book (2008) due to its limited distribution on Singapore's shores.

Halophila beccarii is easily overlooked. It is tiny, often occurs in small patches, and resembles scum or algae when out of water. In some specimens found in Singapore, Halophila beccarii have a reddish-brown banding pattern resembling stripes on the leaves which has earned it the moniker "tiger seagrass" amongst some seagrass nerds here in Singapore.
Beccari's seagrass (Halophila beccarii)
Previously, Halophila beccarii was seen at Sungei Buloh Wetland Reserve proper (near the Mangrove Boardwalk) [during a sea anemone survey in 2007] and at Chek Jawa, Pulau Ubin [probably first recorded during Joseph Lai's Chek Jawa survey in 2001], with small patches on the northern shore, near the boardwalk's T-shaped extension, and larger patches on the southern shore besides House No. 1.
Chek Jawa after the oil spill: Beccari's seagrass (Halophila beccarii)
Recently, extensive Halophila beccarii meadows have been seen on Singapore's northern shores that face the Johor Strait. First spotted in Dec 10 [by Andy Dinesh], field trips in Jan-Mar 2011 discovered more about the full extent of vast meadows which lie outside the Sungei Buloh Wetland Reserve proper.
Photo by Andy Dinesh
At Kranji Nature Trail that lies east of Sungei Buloh Wetland Reserve, Halophila beccarii meadows were seen to form an almost continuous 500-metre strip along the Trail. The seagrass was growing under almost every large mangrove tree, particularly among trees with pneumatophores like Avicennia alba which are plentiful here. The meadows range in width from 1m to about 10m, starting from under mangrove trees, extending seaward to about where the pneumatophores end. The seagrass was also found among trees growing on sand bars in front on some parts of the shore. The only areas without the seagrasses were those heavily impacted by trash, and these areas were not large.
Beccari's seagrass (Halophila beccarii)
Lush meadows were also seen on both sides of Sungei Mandai Besar, a small mangrove stream that divides Kranji east from Mandai mangroves. On the Kranji east bank of the stream, the Halophila beccarii meadows covered an area of about 100 metres square. On the Mandai mangroves bank of the stream, the meadows stretched about 250m along the stream and varied in width from 10m to 20m.
Beccari's seagrass (Halophila beccarii) at Kranji (East)
The Halophila beccarii blades here grew densely, close to one another forming a thick carpet. In some small spots, the seagrass grew so lushly that the blades 'stand up' even when out of water.
Beccari's seagrass (Halophila beccarii) at Mandai mangroves
The seagrass meadows are fully exposed at low spring tide. The seagrass was seen growing on soft silty mud as well as sandier areas, both under mangrove trees and in unshaded areas. In the Mandai mangroves, the meadows even extended to the back mangroves growing along small streams that wind their way towards the sea.

Many egrets were seen resting in deeper water near these meadows at low tide.

Few patches of Halophila beccarii were found along the northern shore between Kranji Nature Trail and the Kranji east shore next to Sungei Mandai Besar. Although this stretch of shore also has mangroves, the trees here form a narrow band and this area is heavily affected by debris, much of which seem to have been dumped from land and did not drift in by sea.

It was interesting to observe that mangrove saplings are often seen in these Halophila beccarii meadows. Stands of regularly spaced Sonneratia alba saplings of similar height are particularly commonly seen in the meadows that grow beyond the shade of large mangrove trees.

Why were these Halophila beccarii meadows only recently observed? Have they been overlooked all this time? Or did the year end monsoon and particularly the heavy rains in Jan 2011 lead to better growth of the seagrass?

We shall have to keep a closer eye on these precious meadows to find out more about them!

More about Halophila beccarii

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