Flexible diel vertical migration behaviour of zooplankton in the Irish Sea

The diel vertical migration (DVM) of the whole plankton community was investigated in the central and coastal Irish Sea. Generally, more than 60% of the plankton did not perform significant DVM. A correlation analysis of the weighted mean depths of different organisms and their potential predators suggested relationships between two groups, Oithona spp., copepod nauplii and fish larvae, and between Pseudocalanus elongatus, Calanus spp. and chaetognaths. The organisms showing significant DVM were chaetognaths (Sagitta spp.), Calanus spp. and P. elongatus. Calanus spp. showed clear ontogenic variations in DVM, and along with P. elongatus demonstrated great flexibility both in the amplitude and direction of migration. P. elongatus did not migrate in the coastal area and Calanus spp. showed a clear reverse migration. The direction of migration appeared to be related to the vertical position of the chaetognaths in the water column during the day.

Comments On The Pseudo-Microfossil Linotolypen

Hollow, black reticulate ‘microfossils’ of unknown affinity found in Ordovician to late Cretaceous sediments from North America, Europe and Australia were given the name Linotolypa by Eisenack in 1962. In 1978, he recognised that they were pseudo-microfossils consisting of asphalt, and noted that their structure resembled that of soap bubbles formed in agitated suspensions. These objects are well known as a component of the particles caught from the air by pollen and spore traps at the present day. They are correctly termed ‘cenospheres’ and are formed from coal and possibly pitch and fuel oil by incomplete combustion. If their presence were to be confirmed in Palaeozoic sediments, this would provide important new evidence for the occurrence of fire in the geological record and of the history of levels of O2 in the atmosphere.

Distribution Of Sublittoral Macrofauna Communities In Bristol Channel In Relation To Substrate

Grab and dredge samples have been collected on a grid of 155 sublittoral stations in the Bristol Channel. The faunal data have been analysed using a hierarchical sorting technique to cluster stations with similar species compositions. At a similarity level of 18%, groups of stations with a species composition similar to the classical Petersen communities were defined. Three of Petersen's communities were recognized in the outer part of the Channel, the Venus, Abra and Modiolus communities. The fauna of the inner part of the Channel is reduced and does not correspond with any previously recognized community type. Possible causes for this faunal reduction are discussed. The substrate distribution and the macrofaunal community distribution are mapped. Side-scan sonograms are shown to be a useful adjunct to the interpretation of faunal distributions.