. The biology of the thalassinidean shrimp Upogebia pusilla was studied on a tidal flat in the Lagoon of Grado (Northern Adriatic). Burrows were investigated using in situ resin casting and with additional in situ and laboratory observations. Burrows show a basic pattern consisting of a U or a double U with turning chambers and a vertical shaft. Mean burrow diameter depends on animal size, it is smaller than the rigid carapace of the animal. Dimensions, distance between openings, depth of U, total depth, volume and surface are size dependent. The burrow wall is smooth and oxidized. Burrows are always inhabited by a single shrimp. Although they overlap, they are never interconnected. They are mainly constructed by compression of the sediment and are relatively permanent structures. A comparison of the burrows of Thalassinidea with regard to shape, number and appearance of openings, dimensions, properties of the burrow wall and dynamics is given.

Among the 516 taxa of thalassinideans so far described, there is a strong latitudinal increase in species numbers from high latitudes towards the equator in both hemispheres. Numbers of species in the northern hemisphere are similar to those in the southern one. Thirty-two percent of the species are found in the Indo-West Pacific and 22% in the Southwest Atlantic. All species are benthic and live either in marine or brackish water. Ninety-five percent of all thalassinideans inhabit shallow water (0-200 m); only three species have been found below 2,000 m. Especially the families Callianassidae, Upogebiidae, Thalassinidae, and Strahlaxiidae occur in the intertidal to very shallow waters (0-20 m), while most members of the Axiidae and Calocarididae are bathyal (200-2,000 m).

No abstract

BackgroundGenetic breaks separating regional lineages of marine organisms with potentially high broadcasting abilities are generally attributed either to dispersal barriers such as currents or upwelling, or to behavioural strategies promoting self-recruitment. We investigated whether such patterns could potentially also be explained by adaptations to different environmental conditions by studying two morphologically distinguishable genetic lineages of the estuarine mudprawn Upogebia africana across a biogeographic disjunction in south-eastern Africa. The study area encompasses a transition between temperate and subtropical biotas, where the warm, southward-flowing Agulhas Current is deflected away from the coast, and its inshore edge is characterised by intermittent upwelling. To determine how this phylogeographic break is maintained, we estimated gene flow among populations in the region, tested for isolation by distance as an indication of larval retention, and reared larvae of the temperate and subtropical lineages at a range of different temperatures.ResultsOf four populations sampled, the two northernmost exclusively included the subtropical lineage, a central population had a mixture of both lineages, and the southernmost estuary had only haplotypes of the temperate lineage. No evidence was found for isolation by distance, and gene flow was bidirectional and of similar magnitude among adjacent populations. In both lineages, the optimum temperature for larval development was at about 23°C, but a clear difference was found at lower temperatures. While larvae of the temperate lineage could complete development at temperatures as low as 12°C, those of the subtropical lineage did not complete development below 17°C.ConclusionThe results indicate that both southward dispersal of the subtropical lineage inshore of the Agulhas Current, and its establishment in the temperate province, may be limited primarily by low water temperatures. There is no evidence that the larvae of the temperate lineage would survive less well in the subtropical province than in their native habitat, and their exclusion from this region may be due to a combination of upwelling, short larval duration with limited dispersal potential near the coast, plus transport away from the coast of larvae that become entrained in the Agulhas Current. This study shows how methods from different fields of research (genetics, physiology, oceanography and morphology) can be combined to study phylogeographic patterns.

Burrows of decapod crustaceans were investigated by in situ resin casting in various mangrove and back-reef environments. Alpheid shrimps (A. floridanus and A. heterochaelis) were the most numerous burrowing shrimps in soft muddy sediments of mangrove channels. Their burrows consist either of a single U or a series of U's inhabited by a pair of shrimp or are Y-shaped and inhabited by a single shrimp and a gobiid associate. Large mounds and deep funnels are produced by the thalassinidean Glypturus acanthochirus, both in bare sediments of mangrove channels and in back-reef subtidal sediments. Their burrows consist of a spiral with several radiating branches leading to the surface and deeper blind chambers often filled with shell particles reaching to a depth of over 160 cm. The thalassinidean Neocallichirus grandimana inhabits the intertidal of protected back-reef sands; it occupies shallow, mainly horizontal burrows. Corallianassa longiventris, characteristic of coarse sediments of the intertidal and shallow subtidal back-reef, inhabits simple J-to U-shaped burrows with blindly ending chambers in 60 to 80 cm sediment depth. Axiopsis serratifrons lives in pairs in sediments with a higher content of coral rubble; its burrows are simple, inclined, and spiral-shaped and reach a sediment depth of 30 cm.All burrows described in this paper are similar to those previously recorded for the respective species. Only the burrows of alpheids are less deep than those described from the intertidal. The burrowing activity of G. acanthochirus greatly influences grain size distribution and accumulation of large shell particles in deeper sediment layers. Burrow types reflect the systematic group to which the animals belong rather than feeding modes.