Neo Mei Lin’s Giant Clam talk reaches the Twitterverse!


(1) Ivan Kwan (VaranusSalvator) on Twitter
Mei Lin’s seminar reaches the twitterverse

Neo Mei Lin gave her pre-thesis seminar today and amongst the audience were members of the naturalists community who have become features of our marine life and who have supported her work. They were enjoying the talk and indeed Ria Tan would later remark

Some of us spent many special moments with Mei Lin on her Giant Clam hunts last year and were thrilled by her awesome presentation on these fascinating animals.”

Neo Meo Lin
Mei Lin with a giant clam on a reef on Pulau Jong, Singapore, 17 May 2010.

Amongst the naturalists was Ivan Kwan who came ready to twitter highlights. So, unbeknownst to Mei Lin, she was speaking to an audience beyond the confines of the seminar room, as an attentive audience following his tweets.

Down with the flu, I was unable to attend Mei Lin’s seminar and wishing I was there. When my twitter feed came alive with Ivan’s updates, I knew I had a virtual ring-side seat. He is a famed naturalist-blogger/twitterer with tenacity and multi-tasking abilities to boot, so I knew he’d keep it up. And indeed he did, chronicling Mei Lin’s seminar with 56 updates over the hour, prompting Grace Chua to holler this out as a #followfriday special.

Loh Kok Sheng later remarked on facebook, “I felt I was listening to Mei Lin!”

The tweets are reproduced below and you can see why congratulations began peppering her facebook page soon after, even from those of us who weren’t there. Mei Lin who started the day with a “Good day at Changi! :)” has surely ended it with a “Good day at Kent Ridge :)”

Thanks to Ria Tan for the photos.

Department of Biological Sciences, NUS
Pre thesis seminar

“Giant Clams (F. Tridacnidae) in Singapore: Past, Present and Future”

By Neo Mei Lin (Graduate Student, Dept.of Biological Sciences, NUS)
Friday, 20 May 2011: 2pm
DBS Conference Room (S3, Level 5, #05-01)
Supervisor: Asst Prof Peter Alan Todd

Abstract – “Giant clams (family Tridacnidae) are the largest of all bivalve mollusks. They are found in shallow coral reef habitats throughout the Indo-Pacific where they play important ecological roles. Reports from the 1950s indicate that Singapore’s reefs once supported four clam species—Hippopus hippopus, Tridacna crocea, T. maxima and T. squamosa. Local tridacnid populations have, however, declined significantly since the 1980s due to human exploitation and habitat degradation.

To quantify their current status, I surveyed 29 reef sites covering an area of 85,715 m2. Only two species, Tridacna crocea and T. squamosa, were found, and only in very low densities. The genetic structures of the T. crocea and T. squamosa populations were examined and shown to exhibit high genetic diversity but low nucleotide diversity. With ten unique COI haplotypes scattered across the islands, fine-scale structuring is apparent for T. crocea while gene flow is not so restricted for T. squamosa, as one out of the six COI haplotypes shows dominance.

Giant clam larval transport was explored using the Delft3D-WAQ coupled to a 3D hydrodynamic model (Delft3D-FLOW). Results indicate that regional connectivity is driven by residual flows and time of spawning. Exchange of larvae among Singapore’s southern islands varied substantially in relation to spawning times. The model also indicated low chances of successful fertilization due to low clam densities.

How these results may affect efforts to restock giant clams in Singapore will also be discussed.”


Proud supervisor, Peter Todd

VaranusSalvator aka Ivan Kwan tweets:
3 hours ago – Here at NUS Department of Biological Sciences for Mei Lin’s presentation on her study of giant clams (Tridacna) in Singapore.

Ivan smiling in anticipation
  • There are 10 known species of tridacnid clams, in 2 genera – Tridacna & Hippopus
  • Giant clam populations add topography to the seabed and serve as nurseries. Lithophagy prevents accumulation of rubble & elevation of reefs.
  • Tridacnids are highly prized as a resource – adductor muscle, mantle flesh and shells. There is also trade of live juveniles for aquaria.
  • Declining populations of giant clams evident along eastern coast of Australia, Indonesia, Malaysia & the Philippines.
  • Historically, Singapore had 4 species of giant clam – Hippopus hippopus (last sighted 1963), Tridacna maxima, T. squamosa, T. crocea.
  • Mei Lin referred to archaeological excavation sites along Singapore River, with records of giant clam shells.
  • 4 archaeological sites from 14th-19th century: Pulau Saigon, Parliament House Complex, Empress Place & St. Andrew’s Cathedral.
(1) Ivan Kwan (VaranusSalvator) on Twitter
  • St. Andrew’s Cathedral site has records of all 4 species of giant clam; some could date back to as early as 14th century.
  • Shell valves were found opportunistically on reef flats and collected, mostly on surface or semi-buried.
  • Ageing of shells was attempted, but it was difficult to determine how old they were. Still, it indicates their presence on our reefs.
  • Giant clam records were concentrated around Southern Islands, with 2 mainland records – Labrador & Tanjong Teritip (Jurong East)
  • Last live Hippopus hippopus seen in 1963; Tridacna maxima last seen in 2003. T. squamosa & T. crocea are still present at very low densities
  • Overfishing alone does not account for extremely low density & recruitment of giant clams in Singapore; loss of coral reefs also to blame.
  • Last survey covered only 7 reefs in 2003 with no genetic work undertaken; Mei Lin did much larger & comprehensive survey including new sites
  • Genetic relatedness between giant clam individuals was also investigated.
  • 29 reef sites were surveyed between September 2009 and August 2010, covering intertidal & subtidal areas. 75 trips were made.
  • A total of 87,515 square metres of reef in Singapore was surveyed for giant clams.
(1) Ivan Kwan (VaranusSalvator) on Twitter
  • 59 adult giant clams were found; 31 T. crocea (0.035 per 100 square metres) and 28 T. squamosa. (0.032 per 100 square metres)
  • Tridacna crocea burrows into rock and is relatively cryptic, hence some individuals in survey area could have been missed.
  • Highest clam density was at Raffles Lighthouse (0.34 per 100 square metres), much lower than reefs elsewhere in the region.
  • Previous survey covered 7 accessible reef sites, where human impact on giant clams may be greater.
  • This survey covered 29 reef sites, including rarely visited patch reefs, and reefs in live firing areas.
  • Mantle samples were taken from the giant clams; T. crocea had overall higher polymorphism and genetic diversity compared to T. squamosa
  • Despite similar sample size and distribution for both species populations, disparity observed in genetic diversity between the 2 species.
  • Present day current patterns may explain reef connectivity of T. squamosa among Southern Islands; not observed in T. crocea population.
  • Also, T. crocea is more vulnerable to post-settlement mortality than T. squamosa. High turnover of individuals may increase outbreeding.
(1) Ivan Kwan (VaranusSalvator) on Twitter
  • 4 existing problems for sustainability of giant clam populations
  • Genetic bottleneck; poor reef conditions in Singapore; variable hydrographic conditions; low clam densities
  • Mei Lin also did larval transport modelling to study how giant clam larvae might be dispersed within the region.
  • Using hydrodynamic and transport models to simulate currents and water quality, Mei Lin modelled the possible dispersal of giant clam larvae
  • Because spawning behaviour of giant clams in the wild in Singapore is unknown, conditions were modelled for different times of year.
  • These were based on the monsoon seasons, and 1 of the time periods chosen corresponds to the known coral mass spawning season.
  • Buoyancy changes and diel vertical migration do not affect transport success of giant clam larvae greatly.
  • However, mortality affects overall transport success.
  • According to the model, high mortality of giant clam larvae would result in almost no settling of giant clams.
  • Poor regional connectivity between western and eastern regions of the Malay Peninsula & Riau Archipelago
  • April spawning sees larvae spawned in Singapore being washed up west coast of Malay Peninsula.
  • June/July spawning (southeast monsoon) sees retention of most of the larvae in the waters around Singapore
  • Reefs in Southern Islands were divided into 4 clusters; poor settlement in clusters around live-firing areas, Semakau, Hantu & Jong
  • Settlement was much higher around Cyrene and the Kusu-Sisters Islands clusters
(1) Ivan Kwan (VaranusSalvator) on Twitter
  • Connectivity between giant clams in Singapore is very low, even on Semakau, where 5 clams are present.
  • Mei Lin is confident that someone will continue her project after she submits her thesis! =D
  • Strong evidence of Allee effects in remaining populations of giant clams in Singapore.
  • Consequences include impaired mating systems, reduced fertilisation success, functional extinction.
  • Mariculture programmes began in 1990s by Tropical Marine Science Institute
  • However, mortality rate of these clams was extremely high; it is believed that most if not all died
  • 52 individuals remained from Mei Lin’s 2007 culture efforts and were transplanted onto Raffles Lighthouse and Pulau Hantu in February 2011/
  • Mei Lin has submitted 1 paper and is preparing several more papers based on her research on giant clams.
  • Lots of people acknowledged for their assistance, including the shore trip folks like @budak @koksheng @Sonnenblume @spoonrabbit. =)
  • And Mei Lin finishes her presentation; apologies for spamming the Twitter feed. And thanks to @gracechua & @spoonrabbit for the mentions!
  • Q & A: Mei Lin notes that “black sand” substrate around giant clam shells found in archaeological sites indicates charcoal deposits.
  • This “black sand” supposedly suggests that these giant clam shells may date back to the 14th century.
  • Potential for further archaeological study of shell middens from traditional coastal communities in the rest of South-east Asia.
  • 1 hour ago – Some of the cultured clams transplanted onto Raffles Lighthouse were apparently killed after a boat struck the reef. =(
  • Only accurate way to determine age of clams found on the reefs is through sectioning of shell; lethal research is out of the question.
(1) Ivan Kwan (VaranusSalvator) on Twitter

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