02 July 2010

How does crude oil harm seagrasses?

In the latest issues of Seagrass Watch Magazine (issue 41, Jun 10), Len McKenzie comments on the recent oil spill in Singapore and shares valuable insights and information on what happens when crude oil hits seagrasses.
Len explains that seagrasses are not so much affected by the "more spectacular oil slick" but are primarily harmed by "the absorption of seawater-soluble fraction (SWSF) of oil."

What is this SWSF thing?

It is a kind of cocktail of dissolved or suspended tiny bits of icky hydrocarbons in the water resulting from turbulence and wave action in oil polluted seawater. Toxic bits are "thought to be able to pass from the SWSF" into seagrass blades where they tend to accumulate in the chloroplasts, the stuff that allows seagrasses to undergo photosynthesis.

What about dispersants?
Len says "dispersants can be toxic in their own right" and "the solvent can also encourage the breakdown of the waxy leaf cuticle allowing greater penetration of oil into seagrass leaves". He also shares that "a mixture of oil and dispersant in some instances can be more toxic than oil alone."

What are the signs to look out for in seagrasses affected by oil spill?
Here's what I gathered from Len's comments:

Crude present on the shore
Seagrasses are hurt by direct contact with crude. Crude can smother and kill intertidal seagrasses.
Scum of crude on the water surface, grey muck on the
sand surface,
and big globs of crude on the mid-shore
near this clump of seagrasses on Tanah Merah, 1 Jul 10.

Bleaching in seagrass blades
Crude also causes seagrass blades to bleach or turn white, after which the seagrasses may die.
Bleaching seagrasses seen on Chek Jawa
about three weeks after the oil spill, 19 Jun 10.

Algae bloom
Another possible consequence of an oil spill is a bloom of algae (seaweed) which can smother seagrasses.

Sad seagrasses
Even if seagrasses are not killed outright, 'sublethal' quantities of petrochemicals incorporated into seagrass tissues can reduce their ability to tolerate other stresses. Thus, for example, they might start to dry up with crispy or dried leaves. And other signs of poor health.

How long before things get back to normal?
It may take a year before things return to normal on a seagrass meadow, and there may be lingering "sublethal" effects for five years or more, says Len.

Len ends the article by saying that our understanding of oil spill impact on seagrasses is limited because "there is a general lack of substantial long-term field data" before and after an oil spill.

It is thus fortunate that TeamSeagrass has been monitoring Chek Jawa's seagrasses well before the oil spill. The data collected will hopefully allow a better understanding of the impact of oil spills in Singapore and elsewhere too.

More about TeamSeagrass and how to join this team of ordinary people, volunteering to monitor Singapore's seagrasses.

Download the Seagrass Watch Magazine (issue 41, Jun 10) for the full articles on a variety of interesting topics. The lead article includes a review of why and how to price seagrass meadows. For a preview of this issue of the magazine, see the TeamSeagrass blog.

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