ARCHITECTURE OF BURROWS OF EXTANT LAND CRAYFISHES FROM SOUTH-CENTRAL CHILE

BEDATOU, E.; RUDOLPH, E.; GENISE, J.F.; GONZÁLEZ, M.; MELCHOR, R.N.

Lepe, España

Workshop; WORKSHOP ON CRUSTACEAN BlOTURBATlON - FOSSIL AND RECENT - LEPE 2010; 2010

Fossil burrows of crayfishes from Patagonia have been recently described (Bedatou et al., 2008), and when trying to compare them with extant burrows of Patagonian crayfishes it resulted that little research has been accomplished about them. The only previous studies are those on Parastacus nicoleti burrows of Killian (1959) and Rudolph (1997). Their description of burrows is based only on excavations and morphologies seem to be simplified. For this study land crayfish burrows were casted with: a) low density polyurethane foam, obtained by mixing polyol VO 715 and isocyanate in a proportion of 100:85; and b) polyester resin. For burrow portions located above the water table, polyurethane foam proved to give better results, whereas for waterlogged burrows polyester resin was more appropriate. After curing the casts they were carefully excavated by removing the surrounding soil using shovels, spatules and by hand (Fig. 1a). In the studied locality (Rucapihuel, Chile; 40 34’ 58” S; 73 34’ 43”W) crayfishes inhabit areas locally known as “hualves” (Fig. 1b). They are wetlands, with a swampy forest of a Temo-Pitra association (Blepharocalyx cruckshanksii - Myrceugenietum exsuccae). During the rainy season water table is near or at the surface and during the dry season it descends up to 100-150 cm below surface. This study was conducted during April, 2010 at the end of the dry season. The soil profile includes two soil horizons composed of clayey very fine sand, the upper one displays abundant iron oxides mottles. At 80 cm depth there is a sandy gravel layer. Crayfish burrows are easily identified by their chimneys on surface made by soil ellipsoidal pellets (Fig. 1c). Three crayfish species inhabit this locality: Parastacus nicoleti, Virilastacus retamali and Virilastacus rucapihuelensis (Figs. 1d-f). Previous studies showed that V. retamali lives in areas with water table close to the surface all year round. One of these galleries was casted with polyester resin. The other two species co-exist in more drained areas. Selection of one burrow of each species was possible because P. nicoleti chimneys have larger pellets (major axis about 15 -20 mm) and larger diameter of burrows than those of V. rucapihuelensis (major pellet axis between 8-10 mm). One burrow of the former and two of the latter were casted with polyurethane foam. Burrow reoccupation by different crayfish species and generations is common; therefore assignation of burrows to the latter two species is tentative. Obtained casts show four different morphologies. The V. retamali cast (Fig. 2d) is 65 cm long, 45 cm high, and 40 cm wide. It is formed by six main entrances from 3-3.5 cm in diameter. Three of them joined 15 cm below the surface into a short sub-horizontal tunnel with a small short blind burrow branching upward at one ending and connected to a main subhorizontal tunnel at the other ending. The other three entrances converge 30 cm below the surface into the main tunnel, located mostly under a buried piece of log, where it follows a sinuous path and is connected to the other entrances. The main subhorizontal tunnel shows also two short sections that project upwards and finish under buried rocks. At one ending the main tunnel continues in a short, downward and oblique tunnel. The V. rucapihuelensis type 1 cast (Fig. 2a) is 110 cm long, 76 cm high, and 40 cm wide. It is composed of several entrance tunnels, 2.5 to 3.5 cm in diameter, converging at a depth of approximately 35 cm in a sub-horizontal irregular tunnel formed by short and nearly straight segments assembled at obtuse angles, 3 to 5 cm in diameter. The union of entrance tunnels forms common upwards “Y” branching, and in one case two entrances have a short horizontal connection. In one extreme the sub-horizontal tunnel continues downward with a 30 cm long burrow that connects the system to two short and gently enlarged subhorizontal burrows located at two different depths. The V. rucapihuelensis type 2 (Fig. 2b) cast is 66 cm high, 30 cm long, and 15 cm wide. It is composed of a single, subvertical, burrow 3 to 4.5 cm in diameter, formed by straight segments connected at obtuse angles. It has some short and blind burrows that branch upward. The lowermost portion of the system is a subhorizontal, 4.5 cm wide and 2.2 cm high terminal enlargement The P. nicoleti cast (Fig. 2c) is 100 cm high, 60 cm long and 55 cm wide. It is composed of a central, subvertical chamber 30 cm long, and 13 cm in diameter. Six upward subvertical burrows originate from the chamber, one of them reaches the surface and the others were incompletely casted. These burrows could either be connected to other ones or reached the surface. Some of these burrows branch upward in short blind burrows. Diameter of burrows ranges from 3.4 to 4.5 cm. The bottom of the large chamber is connected with a 30 cm long horizontal tunnel and with a 35 cm long downward and oblique burrow. During the excavation it was noticeable the large number of tunnels into the soil that probably belong to more than one system inhabited by more than one generation of different species. Common features observed in V. rucapihuelensis and P. nicoleti type burrows are: upward blind burrows reaching almost the surface probably for root feeding purposes; chambers located in the upper part of the gravel level; and short penetration of burrows into the gravel. Location of chambers is controlled in crayfish burrows by the water table level, and/or the presence of a gravel layer as in this case. The simple architecture of the V. rucapihuelensis type 2 cast resemble the trace fossil Loloichnus baqueroensis (Bedatou et al., 2008). The other casts show more complex morphologies that would represent more evolved burrow designs; but re-occupation of burrows by different species or long occupation by the same must not be discarded.