Burrow structure, burrowing and feeding behaviour of Corallianassa longiventris and Pestarella tyrrhena (Crustacea, Thalassinidea, Callianassidae)

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 debris-related 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.