The Roebuck Bay Intertidal Benthic Mapping Programme
A cooperative study of CALM, NIOZ, Curtin University
& BBO in June 1997
Roebuck Bay, near Broome in Western Australia, is now fully recognized as
an internationally important site for shorebirds in the Asia-Pacific flyway.
It is home to 150,000 waders in the nonbreeding season. The undertaking
of a series of wader-catching and ringing expeditions over the last 10 years,
and the establishment by the RAOU of a research- and visitor-centre on the
shores of Roebuck Bay (Broome Bird Observatory, BBO), have lead to detailed
assessments of the great ornithological importance of this area. However,
the resource base for all these waders has hitherto received scant attention.
An unpublished study by G. Pearson and D. Rogers on densities of benthic
organisms and the work of I. Tulp and P.de Goeij in 1991 (published in Emu
in 1994) on benthic food stocks and wader foraging in Roebuck Bay are the
only ones to date. As an important complement to the monthly co-operative
Benthic Invertebrate Monitoring Project, run most successfully since March
1996 by the Broome Bird Observatory and CALM, with samples processed at
the Netherlands Institute for Sea Research (NIOZ), Texel, The Netherlands,
we have just completed the field phase of the Roebuck Bay Intertidal Benthic
Mapping Program (ROEBIM-97). This program was centred at the BBO from 14
June to 1 July 1997, with advance work by Marc Lavaleije, Ed Oldmeadow and
Markus Pepping, and post-expedition efforts at BBO by Markus Pepping, Petra
de Goeij, Danny Rogers and Theunis Piersma. This note summarizes the initial
objectives and our achievements so far.
ROEBIM-97 was envisaged as a pilot study which would provide the groundwork
for future foodweb studies, mapping studies of foraging waders, environmental
impact assessments, and sedimentological and geological investigations
in the Roebuck Bay area. This would be achieved by producing:
- Detailed comparative maps of sediment characteristics and the distribution
of all macrobenthic invertebrate species (i.e. those retained on a 1-mm
mesh sieve) living in the upper 40 cm of the sediments of Roebuck Bay
exposed at low tide.
- Preliminary data on the sedimentology of Roebuck Bay based on a small
number of longer cores at selected sites.
- Maps showing the other sediment features, vegetation cover and densities
of crab- and mudskipper holes over the same area.
- Preliminary data on nutrient loads, organic matter and carbonate content
of the sediments.
- An interpretation of any association between sediment characteristics
and the diversity of the intertidal benthic community, and also comparison
with intertidal wetlands elsewhere in the world.
- A detailed interpretation of the population variation of different
benthic taxa on a tropical intertidal flat, something that has never
before been achieved at the envisaged scale.
- Benthic and sedimentological sampling of as much of the intertidal
area of Roebuck Bay as possible based on a predetermined grid with intersections
every 200 m north of Crab Creek and every 500 m south of Crab Creek.
The latter area to be sampled mainly by hovercraft.
- At every sampling station three cores were taken with a diameter of
10.2 cm covering three times 1/120 mē (1/40 mē) to a maximum depth of
40 cm (or less if a shell layer was encountered). This sediment was
sieved over a 1-mm mesh, with sieved samples carried ashore to BBO's
new wet laboratory (the Pearson Laboratory) for sorting and processing.
In addition, a sediment sample was cored to a depth of 10 cm with diameter
5 cm for grain-size analyses. Crab- and mudskipper-holes were counted
and notes of the remaining visible epifauna were made, as were notes
on sediment grain size, surface colour, etc.
- Sampling points were located according to their geographical coordinates
by hand-held GPS.
- Longer geological cores to be taken at selected sites after exploratory
ground surveys of the geology and sedimentology of the area.
CALM: Grant Pearson, Tanya Butler, Jim Lane; Curtin University: Ron Watkins,
Lee Coshell (Coshell & Associates), Ed Oldmeadow, Bob Hickey, Markus Pepping
(on exchange from the University of Kiel, Germany), Ross Carew; NIOZ:
Marc Lavaleije, Theunis Piersma, Pieter Honkoop, Petra de Goeij; BBO:
Mavis Russell, Danny Rogers (ANCA/University of Melbourne), Ali Pentelow,
Helen MacArthur, Ian Snadden, Olivier Vachez, Sheila Foster-Nixon, Kathy
Fletcher, Chris Hassell, Janet Sparrow; miscellaneous volunteers: Ted
Costello, Betty Gilbert, Colma Keating, Grecian Sandwell, Carmen Benck,
Rob from Broome, Matt from somewhere. It should be pointed out that the
great majority of participants in ROEBIM-97 were self-funded, with limited
logistical and financial support from the participating institutions.
- For 14 successive days at almost every low tide, day and night, between
two to four, three-person 'walking' teams were sent out to sample parts
of the intertidal flats. In addition there was a two-person hovercraft
team working the least accessible areas and a further team working from
a boat sampling sites distant from the shore close to the Low Water
Mark. When not involved in the sampling, participants spent time sorting
and processing the samples, as well as maintaining/ repairing equipment.
- 800 stations were visited covering the entire northern shore of Roebuck
Bay (i.e. the intertidal flats) north of Crab Creek. In addition, we
covered approximately half of the eastern shoreline, the strip of soft
mud that stretches towards Bush Point along the mangroves of Thangoo
Station. A few exploratory cores were taken on the extensive sandy intertidal
flat at Bush Point.
- Sediment and benthos cores were taken at 550 suitable stations representing
about 45 kmē of intertidal area: the remaining 250 sites visited were
occupied by rocks and high beach and thus not habitable by benthic invertebrates.
All 550 samples were quantitatively analysed for macrobenthic animals.
The sediment samples were processed with regard to colour and texture
and made ready for laboratory analyses at Curtin University.
- Each station has yielded a list of invertebrate species, along with
their number and sizes. Most molluscs and many crustaceans were sorted
to species level (even though many of these species may be presently
unknown or even undescribed), but all worms (including the polychaetes,
but also groups such as phoronids, nemertines and sipunculids) were
sorted and counted to family level at best (polychaetes) or phylum level
at worst (phoronids and nemertines, for example).
- We processed a total of about 17,000 individual animals, about 10,000
of which were tubeworms. Some of the tubeworms and all other specimens
were conserved and stored for future study.
- This yielded a total of more than 200 different taxa (either species,
families, or larger taxonomic groupings), suggesting a total diversity
of at least 300, and possibly no fewer than 500, intertidal invertebratespecies
in Roebuck Bay.
- As we extended the surveyed area, the number of taxa grew steadily.
Most taxa appear quite limited in their distribution, each segment of
the Roebuck Bay intertidal flats thus offering a unique assemblage and
range of species!
- Five 'long' geological cores to a depth of up to 3 m, and 15 geological
cores to a depth of 50 cm were taken along traverses out from the shoreline
at five localities in the northern part of the bay in order to enable
preliminary description of the sedimentological characteristics of the
Roebuck Bay intertidal region.
- 16 sets of duplicate sediment cores (32 samples) to a depth of 20
cm were taken at equivalent stations to those of the geological cores,
to enable a preliminary analysis of total organic carbon, carbonate,
and nutrient elements in the surface layer of sediment from the bay's
- Laboratory work at the home institutions will include finalization
of the identification of selected invertebrate specimens that were too
difficult to bring to name with the present means, analysis of sediment
samples and geological cores, analysis of nutrient levels in the intertidal
surface sediments, and production of maps summarizing the distribution
of the different sediments and life forms.
- All data of diverse types will be entered into a multilayer GIS developed
at Curtin University (School of Surveying and Land Information). These
data will then be analysed and output (maps) using the GIS software.
The big advantage of the GIS being the ability to analyse and view the
relationships among the disparate datasets. ArcView 3.0 has been chosen
as the GIS software because of its relative ease of use and combined
- All invertebrates need close taxonomic scrutiny to ascertain certainty
about species identification, and to get to grips with species identity
or composition for all remaining taxa (over 80% of the total!). It is
predicted that, given appropriate attention and support, many new and
unique species will be described based on the material collected during
- It is planned that a report bringing together the basic biological
and geological data from the study will be assembled over the next year
and published early in the second half of 1998.
- The completed fieldwork and material collected will provide the basis
for (1) a MSc thesis by E. Oldmeadow, School of Applied Geology, Curtin
University; (2) a Diploma thesis by M. Pepping at the University of
Kiel; and (3) will provide the macrozoobenthic baseline data for a PhD
project on wader foraging by D. Rogers at Melbourne University; and
(4) give material for several other types of investigation in which
other expedition members will be involved.
- Information regarding the project will be placed on a web page for
viewing by any interested party (http://www.cage.curtin.edu.au/~rhickey/roebuck/).
- Even at the present state of assessment it is clear that the intertidal
flats of Roebuck Bay are the richest known, i.e. the most biodiverse,
in the world.
- This high biodiversity may be due to the intriguing sedimentology
of the area that has generated a large number of different microhabitats,
to its tropical location (tropical habitats generally harbouring greater
biodiversity than temperate ones) and/or to its relatively pristine
- We believe that ROEBIM-97:
- will generate baseline data that will be useful in a managerial
context for many years to come;
- has provided an excellent model for future large scale intertidal
- has yielded a wealth of intriguing data that await analysis over
the forthcoming months and years.
Broome, 4 July 1997, Theunis Piersma, Ron Watkins, Bob Hickey