Burrowing activities of the only European fiddler crab, Uca tangeri, and its resulting influence on biotope in mudflats were investigated during 1989-1990 at Ria Formosa, Portugal. Individuals use the same burrow for ca 1 wk, then occupy another or dig a new one. Overall a burrow is inhabited for ca 3 mo by several individuals before it is abandoned. Vacated burrows decay within 2 to 3 wk. Burrow size and number vary with the season. Burrow density was highest in spring and early summer with ca 17 burrows m-2, and then decreased. Deepest burrows (up to 90 cm long) were found in winter, the shallowest (up to 40 cm long) in summer. Volume of the sediment moved by U. tangen varied monthly between 3000 and 6000 cm3 per m2 of mudflat. Water is only found in the lower third of the burrow. Burrow water contains less oxygen and more nitrate than the surrounding water of the Ria Formosa.

The annual and tidal cycle of behaviour of Uca tangeri (Eydoux, 1835) was studied over a 2 yr period in the Ria Formosa on the Portuguese Algarve coast. U. tangeri settles on the mudflats as well as in the nearby zone of Arthrocnemunl spp.. Individuals smaller than 27 mm carapace width live close to the creek; larger crabs inhabit the salt marsh zone. Newly settled crabs are found in the middle of the mudflat. A surface temperature of at least 18OC is necessary for U.

Specimens of the sponge Halichondria panicea Pallas kept in running sea-water aquaria at 15° C slough off their complete outer tissue layer in regular intervals of three weeks. Sloughing starts at the rim of the oscula and extends over the whole surface within two weeks. Microscopic inspection of the tissue flakes shows them to harbour large numbers of different live organisms, as well as biogenic debris such as pieces of copepod carapaces and diatom frustules. No such community is found on freshly sloughed sponge tissue. After sloughing, the surface skeletal structure of H. panicea is markedly altered, as the characteristic halichondroid reticulum has been replaced by the irregular spicule array typical for the inner sponge tissue. When H. panicea is kept in closed aquaria filled with 0.2 μm filtered sea-water, no sloughing occurs during 3 months of maintenance. As those sponges shedding their outer tissue grow steadily at the same time, the tissue sloughing can be regarded as a reaction to sedimentation of organic material and settlement of small organisms on the sponge surface. The sponge thus counteracts clogging of its ostia and prevents the establishment of a micro fouling community on its surface, inhibiting further fouling processes.

No abstract

The quality of the food, especially origin and size, of the only European fiddler crab. Uca tangeri (Eydoux, 1835), was studied over a 2 yr period. In experiments with fluorescent microparticles, all particles smaller than 250 pm were ingested regardless of thelr chemical composition. Comparisons of sediment, feeding pellets and faeces showed that U. tangeri feeds primarily on microalgae which are completely extracted from the sediment. It also consumes vascular macrophytes (Arthrocnemum spp.), macroalgae, detritus and fish carcasses.