R.J.A. Atkinson

Sulphide metabolism in thalassinidean Crustacea

A phylogeny for the lice (Insecta: Phthiraptera: genus Dennyus) parasitic on swiftlets (Aves: Collocalliinae) was constructed based on mitochondrial cytochrome b DNAsequences. This phylogeny is congruent with previous phenetic analyses of morphometric data for the lice. Comparison with a previously obtained phylogeny for the hosts indicates some degree of cospeciation. These cospeciation events are used to compare relative rates of evolution in the birds and their lice for the same segment of the cytochrome b gene. Cytochrome b is evolving two to three times more rapidly in lice than in birds, and louse cytochrome b is highly divergent compared to that of most other insects. Although generation time has been suggested as an explanation for the disparity in evolutionary rates between lice and their hosts, we suggest that the small effective population sizes of lice coupled with founder events occurring during transmission to new host individuals may be an important factor.

Upogebia deltaura (Crustacea: Thalassinidea) in Clyde Sea maerl beds, Scotland

Burrows inhabited by Upogehia deltaura (Crustacea: Thalassinidea) were studied over a two-year period on two maerl beds at 10 m below Chart Datum (CD) in the Clyde Sea area, Scotland. Labelled burrows proved to be stable features on each ground, with animals able to withstand the impacts of scallop dredging and storm disturbance by re-building the damaged upper sections of their burrows. Resin casts excavated using an air-lift showed that these burrows were inhabited by single individuals. Burrows were deeper, larger and more complicated than was previously thought typical for U. deltaum and other members of the genus. Mapping of burrow systems revealed average densities of 2.9 indm~^ with up to ten openings m~^. These elusive animals were the deepest burrowing megafauna (to 68 cm) and the most abundant large crustaceans within the maerl bed habitat.

Underwater television observations of surface activity of the echiuran worm Maxmuelleria lankesteri (Echiura: Bonelliidae)

Surface activity of the deep-burrowing echiuran Maxmuelleria lankesteri (Herdman) was observed in Loch Sween, Argyll (Scotland, UK) using underwater television. Activity, consisting of proboscis emergence and sediment venting, was observed in all seasons. Proboscis emergence was strictly nocturnal, occurring on average on one night in two. Emergence occurred at irregular intervals during the night, with no consistent rhythmicity. Feeding extensions of the proboscis usually lasted about 10 min, but were often curtailed by accidental contact with ophiuroids or other epifauna. The extending proboscis skims off the top layer of sediment, then rapidly pulls the collected material into the burrow. Animals showed a capacity to select material from particular areas within the feeding radius. The feeding strategy may be to accumulate several loads of sediment in the burrow, then selectively ingest material over the following day. Large volumes of sediment were often vented from burrows, either in a fine suspension...

A Towed Video Survey of Megafaunal Bioturbation in the North-Eastern Irish Sea

In September 1993 the Irish Sea floor near the Sellafield nuclear reprocessing plant was surveyed by towed video to assess the distribution, abundance and behaviour of large burrowing invertebrates believed to be important in the transport and mixing of radionuclide-contaminated sediments. Sixteen stations were surveyed, covering a range of sediment types. Burrow openings and mounds were counted and assigned to species where possible. Particular attention was paid to the similarities and differences between the features observed and those produced by the same species in Scottish sea lochs, the source of most relevant ecological data. Several different burrowing communities were identified from bottom topography. Offshore muddy sands supported dense populations of the thalassinidean crustacean Callianassa subterranea , in burrows similar to those described from the North Sea. Coarse sediments closer inshore had C. subterranea at lower density, with the thalassinidean Upogebia deltaura and the crab Goneplax rhomboides also present. Softer muds were dominated topographically by ejecta mounds of the echiuran Maxmuelleria lankesteri and burrows of the Norway lobster Nephrops norvegicus. The thalassinideans C. subterranea, Jaxea nocturna and Calocaris macandreae were also present at low density. Surface bioturbation features in this habitat were very similar to those described from sea lochs. Population densities estimated from surface bioturbation features were always lower than counts of specimens from box-cores. The visual survey therefore gave minimum estimates of population density. Available data on rates of bioturbation by the species concerned are collated to give rough estimates of biogenic sediment transport in the habitats surveyed.

Measures of hydraulic dredge efficiency and razor clam production, two aspects governing sustainability within the Scottish commercial fishery

A study was made of the efficiency of a commercially available hydraulic dredge design in use on the west coast of Scotland and of the annual biomass production of two different razor clam (Ensis spp.) beds within the Clyde Sea area. These two parameters, viz fishing efficiency and population annual production, are fundamentally important to any proper attempt to assess the long term sustainability of a fishery. The hydraulic dredge used in this study was found to have an absolute efficiency of 90.1% when expressed in terms of the collected wet weight biomass, representing the first time that the efficiency of a hydraulic dredge of this nature has been measured rather than simply inferred from track width. This indicates that this dredge design has the potential to remove the majority of a clam population, including undersized immature individuals, within a 45 cm swath in a single tow. Annual production estimates were also made for two separate razor clam beds. One population of Ensis siliqua was located in Irvine Bay and the other two populations (one E. siliqua and one E. arcuatus) occurred in a mixed bed on Hunterston Sands. Each location was sampled quantitatively on a regular basis using the same hydraulic dredge. Dredged areas were measured by SCUBA divers so that the population densities could be calculated for each sampling event. Size-classes within each population were identified from siphonal shell breadth measurements and production estimates were calculated using a size-cohort analysis procedure designed for stocks exhibiting recruitment but that do not have separable age-classes. Production of all three populations was low during the study (1.82–18.08 g AFDW 10 m-2) as were the production/biomass estimates (0.01–0.11). These data indicate that populations of Ensis spp. on the west coast of Scotland are slow-growing and typical of K-selected species. These data highlight the conflicting pressures facing any razor clam fishery: the design of extremely efficient hydraulic gear and the slow-growth of the target species. It is clear that the future commercial exploitation of these species will need very careful management to ensure sustainability and avoid fishery over-depletion.

A comparative study of the oxygen transporting properties of the haemocyanin of five species of thalassinidean mud-shrimps

Comparative studies of the haemocyanin of five species of thalassinidean mud-shrimps showed that all five species exhibited a high oxygen affinity (P50 range=1.0–9.3 Torr, at in vivo pH, 10°C). Each of the mud-shrimps exhibited a moderately large Bohr coefficient (−1.06 to −1.48) and values for the co-operativity of the haemocyanin did not differ greatly between the species (n50 range=2.3–3.8). The highest oxygen affinities were recorded for the haemocyanin of Callianassa subterranea, Jaxea nocturna and Calocaris macandreae, whereas those for the two species of Upogebia were slightly lower but were still higher than in many other decapods. The higher oxygen affinity of the haemocyanin of the deposit feeding shrimps C. subterranea, J. nocturna and C. macandreae compared with that of the haemocyanin of the filter feeding upogebiids may be correlated with the fact that conditions within the burrows of the deposit feeders may be more severely hypoxic. The oxygen affinity of all five species showed a moderate temperate sensitivity (ΔH −56.8 to −82.1 kJ mol−1 over temperature range 5–10°C). Studies of the haemocyanin of one species (C. macandreae) showed that L-lactate did not affect the oxygen affinity of the haemocyanin as has been reported for a number of other decapod species. The oxygen carrying capacity of the haemocyanin (CHCYO2) was similar in four of the species studied (0.22–0.42 mmol l−1) but that of C. subterranea was significantly greater (0.83 mmol l−1). The higher protein concentration of the haemolymph of this species also resulted in the haemolymph having a greater buffering capacity (−7.67 mmol l−1 pH unit−1). SDS–PAGE studies of the haemocyanin demonstrated the presence of 3 subunits in the upogebiids but additional subunits were observed in the other species (MW range=70 000–90 000 Da). Studies of the association state of the haemocyanin of three of the species showed that the haemocyanin of both C. macandreae and J. nocturna was present mainly in the form of eikositetramers (24-subunit aggregation state) with some hexameric haemocyanin also occurring. The haemocyanin of Upogebia deltaura, however, occurred as a mixture or eikositetramers and dodecamers.

Microbial Flora Associated with the Digestive System of Upogebia Stellata (Crustacea: Decapoda: Thalassinidea)

The digestive system of the thalassinidean mud-shrimp Upogebia stellata was investigated using scanning electron microscopy (SEM). Within the lumen of the midgut both filamentous and rod-shaped bacteria were observed. The hindgut microbial populations were dominated by dense mats of epimural rod-shaped bacteria. The gut contents were often dominated by diatoms but also contained bacteria, dinoflagellates, plant and algal fragments. Direct bacterial counts by epifluorescence microscopy along the length of the gut revealed a slight decrease in numbers within the midgut moving from the anterior to the posterior regions, and then a dramatic rise in numbers within the hindgut. Numbers decreased again in the posterior regions of the hindgut. Common in the transient / resident samples (bacterial population when gut contents were present) were enterobacteria and an unidentified fermenter conforming to an isolate named X-ferm. However, nearly 30% of the bacterial isolates remained unidentified. The resident-only bacterial isolates from the gut (determined when the gut was empty) were dominated by the X-ferm bacteria and to a lesser extent by the genera Vibrio and Aeromonas . With respect to the enzyme capabilities of the gut bacteria, the resident-only collection of bacterial isolates showed much higher levels of amylase, cellulase, chitinase, protease and lipase activity than the transient/resident bacterial isolate collections, suggesting that the indigenous bacteria are likely to play a significant role in the digestion of the gut contents. Thalassinidean shrimps are likely to play an important role in the breakdown of plant and detrital material, and the recycling of nutrients in marine benthic systems.

Distribution, ecology and life-cycle of Maxmuelleria lankesteri (Echiura: Bonelliidae): A review with notes on field identification

This paper summarizes the available information on the distribution and biology of Maxmuelleria lankesteri . This large echiuran was described almost a century ago but its local abundance and potential importance as a bioturbator were recognized only recently. The species is widespread around the British and Irish coasts, most commonly in fine muds. A deep-burrowing, nocturnal deposit feeder, M. lankesteri is unlikely to be seen by divers, but its presence can be deduced from the form of ejecta mounds and proboscis tracks. The worms are very difficult to capture intact. Body size in a sample from Loch Sween, Argyll, was approximately normally distributed. Very small individuals are rarely found. Developing oocytes were found in the coelom over the spring and summer. Mature eggs accumulate in the gonoducts, with maximum loads found from October to December, possibly indicating a single annual spawning during the winter. Despite intensive examination of a large number of adult females, no dwarf males were found, leaving open the question of their existence. The large, yolky eggs indicate lecithotrophy or direct development. Larval stages have not been recognized. The apparent scarcity of developmental stages and of very small adults suggests that recruitment may be sparse and infrequent.

Histriobdella homari on Nephrops norvegicus from the Irish Sea and Clyde Sea area

Histriobdella homari is a polychaete annelid belonging to the Order Eunicida and Family Histriobdellidae. Histriobdella homari is normally found in the gill chambers or among the eggs of the lobster Homarus vulgaris from the English Channel (Roscoff) and in the southwestern part of the North Sea (George & Hartmann-Schroder, 1985). Two independent sightings of H. homari living on the pleopods of Nephrops norvegicus from the Irish Sea and Clyde Sea area are reported.