Lois A Nickell

Bioturbation, sediment fluxes and benthic community structure around a salmon cage farm in Loch Creran, Scotland

Abstract This study examined bioturbation along an organic carbon gradient away from an Atlantic salmon farm and sought to determine relationships between benthic fluxes, mixing intensity and the infaunal community structure. Macrofaunal community structure, abundance and biomass were examined at stations with varying quantities and qualities of organic matter input. In situ benthic chambers were used to determine oxygen and nutrient fluxes and mixing parameters were derived from down core profiles of chlorophyll a (chl a ). Mean oxygen demand of sediments ranged between 8.8 and 467.8 mmol m −2 day −1 , being highest beneath the fish farm and indicating very high rates of community respiration and organic matter diagenesis. Oxygen and nutrient fluxes followed similar trends to community abundance and biomass, declining with increasing distance from the farm. Mixing intensity increased with distance from the farm until returning, at the farthest station, to values similar to those measured beneath the farm. The differences in the community structure between sediments beneath the farm and furthest from it suggest that similar diffusive mixing coefficients are generated by different mechanisms. These results generally follow the successional model of Pearson and Rosenberg [Oceanogr. Mar. Biol. Ann. Rev. 16 (1978) 229.], with the exception of the farthest station, but suggest that the bioturbation potential of the community over short time scales is greatest at stations with intermediate qualities and quantity of organic matter. However, the methods used here to assess mixing over short time scales (i.e. diffusive mixing coefficient and the mixed layer depth) do not account for the activities of deep burrowing infaunal animals, such as Maxmuelleria lankesteri , known to be present at the farthest station.

Burrow morphology of the echiuran worm Maxmuelleria lankesteri (Echiura: Bonelliidae), and a brief review of burrow structure and related ecology of the Echiura

The burrow morphology of the echiuran worm Maxmuelleria lankesteri (Herdman) was investigated in situ using a resin casting technique. Work was carried out in Lochs Sween and Creran on the west coast of Scotland in predominantly fine mud sediments. Burrow casts typically had only 1 opening, although there is evidence to suggest that a second opening may exist. In 58% of burrows, the opening, which was small and funnel-shaped, was associated with a surface mound reaching up to 20 cm in height. The tunnel below the burrow opening, the ‘neck’, was narrow and circular in transverse section with a smooth wall, possibly due to the action of the mucus-laden proboscis which emerges during feeding. The maximum burrow depth recorded was 80 cm and tunnel orientation became more horizontal with increasing depth. In some larger burrows, the tunnel began to orientate upwards towards its end. Below the neck, the tunnel was much wider but had a sub-circular transverse section. The burrows had distinct striations on the w...

Morphology of thalassinidean (Crustacea: Decapoda) mouthparts and pereiopods in relation to feeding, ecology and grooming

The morphology of the mouthparts and pereiopods of three thalassinidean mudshrimps, Callianassa subterranea (Montagu), Jaxea nocturna Nardo and Upogebia stellata (Montagu) (Decapoda: Thalassinidea) are described. The distribution of setae is also described and related to function, in particular to feeding and grooming. The comparative morphology of the maxillipeds and pereiopods showed greatest differences between species and can be related to differences in feeding behaviour. Callianassa subterranea has mouthpart morphology and setation suitable for handling sediment particles and highly specialized pereiopods consistent with the digging activity of a deposit feeder. Upogebia stellata is the most densely setose of the three species and many of the appendages bear layered fringes of setae which are used to trap fine particles during suspension feeding. Jaxea nocturna appears to possess mouthpart and pereiopod setal combinations suitable for a fine sediment diet but is the least morphologically specialized...

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...

Topography as a determinant of search paths of fishes and mobile macrocrustacea on the sediment surface

Abstract Reworking of the sediment surface by the movement and feeding activity of mobile epifauna is likely to affect rates of solute flux across the sediment–water interface, with consequences for the geochemistry of deeper sediment layers. Mobile epifauna are also important scavengers and predators that control the community of sediment infauna and affect the distribution and abundance of other surface-living species. Activity of subtidal epifauna in a sea loch was monitored by video in order to test the hypothesis that patchiness of visits by epifauna to small areas of sediment surface is generated by direct behavioural responses to surface features, such as mounds and holes built by large infauna, and as an alternative hypothesis that patchiness is generated by the properties of the search paths as measured by rates of turning and step lengths. Trajectories of gobies (Lesueurigobius friesii, Pomatoschistus minutus), shrimps (Crangon allmani), and Nephrops norvegicus were digitized in 12 half-metre square quadrats over 24 h. Analysis of frequency of visits to small areas within each quadrat quantified the patchiness of impacts of each species. Trajectories tended to be area concentrated and in many cases more than would be expected on the basis of search path properties alone. Spatial patterns of frequencies of visits showed that movements of gobies L. friesii, P. minutus and Nephrops were strongly influenced by proximity to burrow openings, while shrimps (Crangon) were not affected. Observed patchiness in P. minutus was positively correlated with simulated patchiness, suggesting that properties of search paths may change in response to food and consequently affect patchiness. Crangon allmani often followed furrows, also increasing patchiness. The effect of the characteristics of search paths on patchiness of visits was small compared to the direct response to topographical features.

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 ...