R. James A. Atkinson

SEDIMENT BIOTURBATION BY THE ECHIURAN WORM MAXMUELLERIA LANKESTERI (HERDMAN) AND ITS CONSEQUENCES FOR RADIONUCLIDE DISPERSAL IN IRISH SEA SEDIMENTS

Bioturbation by the deep-burrowing echiuran Maxmuelleria lankesteri was studied in Loch Sween, Scotland. Results were used to evaluate the animals likely effects on the movement of radionuclides in sediments of the NE Irish Sea, where the species is also common. Individual burrow openings were monitored by video for up to 23 days. There was no consistent relationship between the frequencies of sediment intake and ejection, an anomaly which suggests that the burrow of M. lankesteri has two surface openings rather than one, as believed previously. Sediment output was measured by changes in ejecta mound volume and by direct collection of vented material. Both methods gave a value of approximately 13 g dry matter · day−1, of which about 0.8 g (6%) was faecal matter. The remainder consisted of non-faecal fluidized sediment, for which concentrations of 234Th suggested a surface origin. There were no significant differences in particle size composition between burrow ejecta and ambient surface sediment. Sediment ingestion rate was not directly measurable, but was estimated at about 1.7 g · day −1 using a model derived from studies of other marine deposit feeders. Bioturbation by M. lankesteri seems to result in a short-term redistribution of material (about 13 g · day−1) on the sediment surface, with about 0.9 g · day−1 incorporated into the burrow lining as faecal pellets. In the NE Irish Sea, burrows will act as sinks for surface-derived radionuclides and there is probably little return of deeply-buried material to the sediment surface.

Sexual dimorphism and intersexuality in Upogebia stellata (Crustacea: Decapoda: Thalassinidea)

Evidence of sexual dimorphism in the mud-shrimp Upogebia stellata was observed in the abdomen length, total length, and also in the chelae. For the same carapace length, males had a shorter abdomen and, therefore, total length, whilst their chelae were larger and more robust than the females. Of the 91 U. stellata individuals examined, a single specimen was found to be of an intersex type, i.e. it exhibited both male and female external characteristics. Sexual dimorphism and intersexuality are discussed.

Association between Athanas amazone (Decapoda: Alpheidae) and Squilla mantis (Stomatopoda: Squillidae)

ABSTRACT Burrows of Squilla mantis, studied by resin casting, revealed for the first time the presence of an alpheid shrimp, Athanas amazone, within the burrow of the stomatopod. Colors in life of A. amazone collected from this source are described.

The annual cycle of sediment turnover by the echiuran worm Maxmuelleria lankesteri (Herdman) in a Scottish sea loch

Abstract Rates of sediment ejection were recorded from 20 burrows of the echiuran worm Maxmuelleria lankesteri at monthly intervals over a 13-month period. Environmental parameters, numbers of ejecta mounds and the spatial persistence of burrows were also monitored. All 20 marked burrows retained signs of occupation over the study year. Sediment turnover was recorded in all months, with no cessation of activity over the winter. Volumes of sediment expelled during each 2-day measurement period were extremely variable, up to a maximum of ∼97 g dry weight burrow −1 day −1 . Over the year, the mean ejection rate from 20 burrows was 7.53±5.24 S.D. g burrow −1 day −1 , with peaks of activity recorded in December and April. The superficial sediment (on which M. lankesteri feeds) was very rich in organic matter, with monthly values of 11.7–16.7% sediment dry weight. Thermally labile organic matter, determined by combustion at 250°C, comprised 16.7–71.4% of the total organic content, with highest and lowest values in April and August, respectively. There was no significant correlation between monthly sediment ejection rate and total sediment organic content, but a highly significant correlation was found between ejection rate and the percentage of labile material in the sediment organic matter. Ejection rate remained constant at labile fractions below ∼50%, but increased sharply above this threshold. Topographic relief and numbers of feeding traces at the site suggested that activity level was lowest in late summer (August–September). Burrows appeared to be static, and the animals sedentary in habit. Individual ejecta mounds could persist for up to 15 months. There was no evidence that the worms alternated the functions of the feeding and ejection openings of their burrows. This burrow stasis contrasts with the pattern seen in some deep-sea echiurans, a behavioural difference probably determined by the nutritional status of the respective habitats.

Comparison of the mouthpart setal fringes of seven species of mud-shrimp (Crustacea: Decapoda: Thalassinidea)

A detailed description of the mouthpart morphology is provided for Axius stirhynchus Leach, Calocaris macandreae Bell, Upogebia deltaura (Leach) and U. pusilla Petagna. The distribution of setae on the mouthparts of three additional species of thalassinidean mud-shrimp, Callianassa subterranea (Montagu), Jaxea nocturna Nardo and U. stellata (Montagu), is also given. Particular attention was paid to the mouthpart setal fringes, where major differences were observed in setal type, inter-setal distances and inter-setule distances. The mouthparts of the three upogebiid species examined were characterized by plumed setae with very small intersetal distances. The mouthparts of the other four species of thalassinidean were dominated by more robust serrate setal types. The setal screens of the upogebiids were often made up of a single setal type, whereas those of Calocaris macandreae and Axius stirhynchus were often comprised of a number of different setal types. The observations made for Callianassa subterranea ...

Burrow development, nutrient fluxes, carnivory and caching behaviour by Calocaris macandreae (Crustacea: Decapoda: Thalassinidea)

Using aquaria containing natural sediment, medium-term burrow development was investigated. After initial construction, and over the first month, relatively little burrow development was observed in terms of the number of openings and tunnels created. After an additional six months, however, there was a significant increase in the number of openings and tunnels constructed. In contrast to what might be expected from the number of openings and tunnels created during this period, a significant proportion of the sediment movement was sub-surface and relatively little sediment expulsion occurred. The concentration of nitrite, ammonia and phosphate in the burrow water was generally greater than that of the surface water, whilst the nitrate and sulphate measurements showed no particular pattern. Only the differences in phosphate concentrations were found to be significantly different. These results were indicative of Calocaris macandreae influencing rates of denitrification. This study also provided further evidence of carnivory and caching behaviour in this species.