Sunday, April 13, 2008

Anecdotal observations of stress recently

On 12 April 2008, a group of volunteers from Team Seagrass and Chek Jawa guides were out at Chek Jawa. There were some blog postings reported about some signs of unhealthy animals especially for sea stars and a few carpet anemones. Below are a compilation of their observations from various blog posts. All photos and commentary credit to the author of that particular post.

1. Ria Tan's Wildfilm blog: Chek Jawa with TeamSeagrass

"Also rather disturbing, I encountered TWO Biscuit sea stars (Goniodiscaster scabra) that looked like they were unwell. Here's the underside of the first one. The tip of the arm looks more like it's disintegrating rather than having been chomped on by a predator."

"Here's the upperside of the same sea star."

"Nearby, I found another sea star with similar injuries. Oh dear. The last time sea stars disintegrated when there was massive flooding in Johor in early 2007, resulting in a drop in salinity at Chek Jawa. This badly affected some of the marinelife there, especially the sea stars and carpet anemones. And it has been raining quite a bit recently..."

2. Sam Yeo's Ramblings of a Peculiar Nature blog: Back to Chek Jawa: Sat, 12 March 2008

"Found this dead biscuit star under the boardwalk. It looked like it imploded and something that happened to many of the sea creatures during the mass death of Chek Jawa in 2007. Could it be due to the rain of recent days?"

3. Ron Yeo's The Tide Chaser blog: Chek Jawa Walk on 12 Apr 2008

"Some sandstars don't look that healthy though. I found at least 2 more sandstars, which look like they were disintegrating, and part of their body were turning white in colour."

"We also saw a few overturned carpet anemones, and placed them in little tidal pools."

"This poor sea cucumber also looks like it's slowly rotting.The last time we witness all the above phenomenon was during last year's flood, which brought a lot of fresh water into Chek Jawa and many animals die! That certainly got me a little worried, since we have been experiencing heavy rainfall for the past few days."

According to my study, three areas were hypothesized to cause hyposalinity at Chek Jawa.

1. Increase in discharge of freshwater output from Johor River
2. Direct rainfall
3. Incidence of low tides when point 1 and/or 2 is occuring

Due to the Johor river water level website that is inaccessible at the moment, I can't comment on point 1. Neither do I purchase the rainfall data every month for point 2. But it is true that recently there was quite a number of heavy rain events over the week which coincidented with the low spring tides that started on Monday (7th April 2008) till Sunday (13th April 2008). Though the low tide series is well recorded in the Singapore Tide Tables Year 2008, quantitative data is needed for the rainfall, preferably from Pulau Tekong station.

Echinoderms are stenohaline (unable to withstand wide variation in salinity of surrounding water) in nature and therefore it is not a surprise to see them disintegrating when salinity is lowered beyond a certain limit, which the latter needs to be verified. Anemones like carpet anemones also respond to extreme lowering of salinity. Below is a flow chart of the effects of hyposalinity.

It is yet heartening on another side that the health of Chek Jawa is being looked after and checked by shore volunteers.

Engebretson, H and Martin, KLM (1994). “Effects of decreased salinity on expulsion of zooxanthellae in the symbiotic sea anemone Anthopleura elegantissima.” Pacific Science, Vol. 48, no. 4, pp. 446-457


ria said...

Thanks for the excellent summary and more scientific analysis of our separate observations!

I was quite disturbed to read of other sightings too.

Yes, we should keep up with regular monitoring of Chek Jawa, especially when the weather is extreme.

koksheng said...

Yes I agree with you. Thanks for mentioning about the stress in your blog post. Will keep a lookout during extreme weather events.