[Coral-List] Tsunamis and blast fishing

[Hoeksema, B.W.]

Re: fish bombing and tsunami effects (Helen E. Fox)
RE: Tsunami effects on coral reefs - previous examples
      (Tegan C. Hoffmann)
Re. Stabilizing Acropora fragments over rubble (mmain)

In addition to previous messages on this topic (see above), I would like to comment that comparisons to blast fishing come indeed to our mind when we discuss the possible effects of tsunamis on reef damage and its recovery. Reef communities affected by oceanic swell and monsoon-related storms are predominantly composed of species that have settled after storm damage took place. Such communities mostly consist of species that can survive wave action. Like blast fishing, the force of tsunamis may have different effects on reefs, but apparently we do not know much about this. Blast fishing is operated on a very small scale but it occurs frequently. The reef organisms hit by explosives are not adapted to this kind of destruction. I examined the effects of blast fishing on reefs at South Sulawesi and found that the first visible damage consisted of coral fragmentation inside the blast crater and that occasionally some corals around the blast crater have become covered by sand. Weekly re-examination revealed that much of the soft coral tissue of the fragments was dead and that the rubble fields have become an unconsolidated substratum only fit for free-living mushroom corals and living coral fragments that immigrated from around the crater. 

Corals fragmented as a result of tsunamis may have better chances for survival than corals hit by explosives if no secondary damage occurs. The fragments resulting from tsunamis may regenerate in case they have not become covered under sediment washed from the shore. However, in addition to burial, corals may also suffer long-lasting effects of fine dust that has become suspended after a tsunami. About two months after a tsunami hit Biak in 1996 (Indonesia), the water above the reef flats looked like milk due to a white dust in the water column. Since Biak consists of limestone, this white resuspended dust may most likely have originated from Biak's eroded soil. This entire reef flat was dead. Recent satellite images on the internet, comparing before-and-after tsunami situations, also show an increase of sediment in the water along some of the affected shorelines. For more information on the occurrence of tsunamis in reef areas I refer to http://www.usc.edu/dept/tsunamis/worldmappage.htm. The maps of this site show many epicentres but the Indian Ocean appears to be nearly absent. Since the last tsunami hit coastlines around much of the Indian Ocean, I wonder how the present tsunami will be illustrated, just by its epicentre or by the extend of the affected area.

Bert Hoeksema
National Museum of Natural History Naturalis
Leiden, The Netherlands
Tel. +31.71.5687631 / Fax +31.71.5687666
E-mail: Hoeksema at naturalis.nnm.nl