Subject: Timor Sea coral mortality
Date: Fri, 21 May 1999 08:40:11 +1000
From: Tim Skewes <tim.skewes@marine.csiro.au>

The CSIRO (Commonwealth Scientific and Industrial Research Organization; so
you see why we mainly use the acronym) is Australia's largest research
organization (http://www.csiro.au/).  It is divided into divisions that are
largely autonomous; mine is the Marine Division
(http://www.marine.csiro.au/).  We carry out research in the fields of
fisheries, marine habitats, oceanography and aquaculture to name a few.

In September/October 1998, we carried a survey of the shallow reefs and
shoals (<50m deep) in an area of the Timor Sea called the MOU74 Box
(centre, 122.82 deg E, 13.37 deg S).  It includes several large reefs
including the Scott Reefs, Seringapatam Reef and Ashmore Reef.  We also
surveyed Hibernia Reef just north of the MOU74 Box.  In all we surveyed
over 550 sq km of shallow reef and 1200 sq km of shoal area and the study
area extended over about 300 km from north to south.  The reefs were
surveyed by divers and the shoals by video and acoustics.

The study had two main objectives. 1) To assess the status of marine
resources on the reefs and shoals that are subject to fishing by Indonesian
fishers, and 2) To map the structural and biological components, and
describe the important marine habitats, of the reefs and shoals.

As for the coral mortality, we were very surprised to see the extent of it
when we first visited Scott Reef, even though we had been warned by AIMS
researchers, who have an ongoing long term monitoring program at Scott
Reef.  From our survey in September 1998,  we estimated that there was 2290
Ha (+/- 14%, 95% CI) of live hard coral , and 2570 Ha (+/- 13.5%, 95% CI)
of recently dead coral on the shallow reefs in the study area (down to 15 m
depth); a mortality rate of almost 53%.  However, the by-reef total
mortality rates ranged from 76% at Scott Reef North (121.88 deg E, 13.95
deg S) to only 6 % at Ashmore Reef (123.07 deg E, 12.24 deg S).  The cause
of this variability is not obvious, but may have something to do with the
local oceanographic conditions surrounding the reefs.

Also the corals were not all affected similarly.  We found that over 83% of
branching coral in the study area had died, compared to only 22% of
massives.  The highest mortality rates occurred on the lagoon or protected
reef edges; areas where branching Acropora corals flourish.

Interestingly, we found large areas of what appears to be live foliose
corals, probably dominated by Montipora, in the large deep (~ 50 m) lagoon
of Scott Reef South (121.82 deg E, 14.10 deg S).  We mapped the extent of
this habitat using video and acoustics, and although we have yet to fully
analyze this data, our initial estimates are that there is over 5000 Ha of
live coral in the deep lagoon with little evidence of mortality.  This is
over twice the amount of live coral we found on the shallow reefs in the
entire study area!

We are about to submit the last of our reports from the study to the
Australian Government. When a review has taken place the info will be made
available to the wider scientific community. 

Timothy Skewes, Marine ecologist   E-mail:  tim.skewes@marine.csiro.au
CSIRO Division of Marine Research  Phone :  +61 7 3826 7249
PO Box 120, Cleveland, Q 4163      Fax   :  +61 7 3826 7222
Australia
                                        

On Fri, 21 May 1999, andrew heyward <a.heyward@aims.gov.au wrote:

I received a copy of Tim Skewes's question about the Timor Sea SST
data and thought you might find the following information of interest.

AIMS have been monitoring Scott and Seringapatam Reefs in this region,
using standardized, quantitative survey methods, since late 1994. This
dataset  has captured the bleaching event. The NOAA-derived SST data and
animations I have seen correlate well with this impact. AIMS
oceanographers also have had various temperature loggers  in
situ over this period, although the time series is incomplete.

105 permanently marked 50m benthic transects there  have been resurveyed
every year. We  also have been running parallel studies on coral
reproduction and recruitment on the same locations every 3 months. The
reefs were affected by the 1998 bleaching event in the period
March-May.

Overall average live coral abundance dropped from around 40% to 10% but
some areas were much more dramatically affected, eg. 66% down to 7%.
Direct diver observation confirmed  bleaching down to at least 30m.

I have attached a location map and an example of data for your interest.
We have completed analyses of the bleaching impacts for both sessile
benthos and fish communities and  should be able to make this available
to you  in a short while if it is of use.

Dr Andrew Heyward
Scientist in charge, WA
Australian Institute of Marine Science
Dampier WA 6713
Australia