Abstract |
The behaviour of the Caribbean Corallianassa
longiventris and the Mediterranean Pestarella tyrrhena,
two burrowing thalassinideans, was studied in situ and
in laboratory aquaria. Burrows of C. longiventris were
closed most of the time; they consist of a deep U
(down to 1.5 m) with upper and deeper chambers,
some of them filled with macrophyte debris. The
burrows of P. tyrrhena reached down to a maximum
depth of 54 cm and consisted of a shallow U with a
mound and a funnel, and a spiral shaft from which
several, often debris-filled chambers branched off. The
appearance of C. longiventris at the sediment surface
to collect debris is strongly triggered by wave swell or
odours from plant and animal juices; its burrows are
opened within 10 min. The surface activity of P. tyrrhena
was relatively less frequent and less predictable.
Inside the burrows, both species exhibited different
patterns of time allocated to 25 defined behavioural
states. After being offered seagrass debris, P. tyrrhena
spent relatively less time manipulating this debris, but
it handled sediment more often than C. longiventris.
During frequent mining events, both species showed
sediment-sorting behaviour, which brought a parcel of
sediment in close contact with the mouthparts; some
of this sediment may be ingested because the fecal
rods produced by both shrimps contain very fine
sediment particles. Seagrass debris is irregularly tended
by P. tyrrhena after its introduction into the chambers.
Such material ultimately becomes buried. Corallianassa
longiventris frequently returns to its debris chambers
to pick up pieces of seagrass, which are subsequently
cut with the chelae or ripped with the third maxilliped
and then transported to another empty chamber
nearby. Pieces become smaller with time and show
curved cutting edges and bite marks. After 100 to
140 days, 2 to 6 g(dw) seagrass debris are consumed in
this manner by individuals of this species. The debrisrelated
behaviour of P. tyrrhena probably enriches the
sediment around the burrow for stochastic encounters
during later mining events. Such an indirect benefit
may also be effective on a population level because
other individuals may also encounter this buried
nutrient source. |