We therefore employed a time-based sampling method,
as discussed by Ashton (1999). Three independent timebased samples were conducted in each 100-m2
vegetation
plot. One sample (= one replicate) represents one person
collecting crabs for 15 min. This generates an index of
crab abundance that can be compared between the plots,but is not a true density value. The true crabs (Brachyura)
and hermit crabs (Anomura) encountered during these
periods were collected by hand using a trowel and a plastic beaker. To offset bias in favour of the most common
or slow-moving species, more time and effort was allocated to catching the larger, faster-moving crabs. This risks
an opposite collecting bias, but previous experience has
shown that this gives a more representative overall assessment of species composition, enabling comparison
between sites (Ashton 1999). The area covered in each
15-min timed period was approximately one third of the
100-m2
plot and was covered by one person. The collections were done at low neap tide and then repeated at low
spring tide. The specimens obtained were stored carefully
to ensure that no appendages were lost due to stress. They
were placed briefly in a freezer to sedate them, before
being washed, measured (carapace width and wet biomass
recorded) and preserved in 4% formalin for subsequent
identification. All specimens were deposited at the Sarawak Biodiversity Centre (SBC), Kuching in accordance
with SBC and Sarawak State regulations (Salleh &
Ashton 2001).