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4. Bryozoa within Sediments

Bryozoa may also be found within archaeological sediment samples. They may be imported to a site attached to seaweed, which has been used widely in the past as fodder, fertiliser and soil stabiliser (Bell 1981). This was the case at Ardnave on Islay where unidentified bryozoans were found among calcareous debris in a sample (Evans 1983, 357) and at Bishopstone in Sussex, where four examples of Turbicellepora avicularis (Hincks 1860) were recovered: two from an Iron Age enclosure ditch, one from the bottom of a pit and one unstratified (Bell 1977, 287). Bell (1981, 121) studied modern seaweed from Saltdean, Sussex, and found colonies of Membranipora membranacea on the stipes of Laminaria sp. Unidentified marine bryozoans were also found during micromorphological analysis of sediments from the Epipalaeolithic to Neolithic site of Ifri Oudadane, Morocco, where they were interpreted as having been introduced by humans (Linstädter and Kehl 2012, 3319).

Where previously intertidal or brackish water deposits are being excavated, in situ colonies may be preserved on the surface of rocks, as at Walpole in Somerset. Ongoing archaeological investigations at the Walpole landfill site have revealed a now-buried lias outcrop that would have been an island until late prehistory (Hollinrake and Hollinrake 2002). Samples from this site are the subject of ongoing study by the author. Recently, a combination of colonies of Conopeum seurati and the molluscs Ecrobia ventrosa (Montagu 1803) and Macoma balthica (Linnaeus 1758) has been found in samples from the south-western edge of this island, suggesting a deposit bearing lithic implements of Mesolithic to Bronze Age date was a lagoon margin. Statoblasts of Plumatella emarginata (Allman 1844) are present in a peat deposit from the same site, suggesting freshwater inputs at the time of peat formation.

Smith and Howard (2004, 118) examined the usefulness of Coleoptera to distinguish low-energy and high-energy fluvial depositional environments. To enhance their method, they suggest studies in parallel with other biological remains, including bryozoa. This does not appear to have been done, although statoblasts are reasonably frequent finds from freshwater sediments. Statoblasts of the freshwater bryozoan Cristatella mucedo (Cuvier 1798) have been reported from North Bridge, Doncaster, where they were interpreted as being derived from flood deposits (Carrott et al. 1997, 68). Statoblasts of Cristatella mucedo and Plumatella spp. were also reported from medieval estuarine sediments associated with the River Fleet at 3 Tudor Street, London (Boyd 1981, table 22.1), and statoblasts of Cristatella mucedo were recorded from sediments dating to the Hoxnian interglacial (marine isotope stage 11) at Nechells, Birmingham (Shotton and Osborne 1965). The majority of the statoblasts were incomplete, and were identified as dorsal or ventral discs based on comparison of measurements to modern data (Shotton and Osborne 1965, 366). Plumatella spp. statoblasts were also recorded in pollen samples from Caldicot, Gwent (Caseldine and Barrow 1997, table 6), and Lophopus crystallanus (Pallas 1768) statoblasts in samples from Enkhuizen, The Netherlands (van Geel et al. 1983). At Flixton School House Farm, near Flixton in Yorkshire, a decline in the number of Cristatella statoblasts before c. 8600 cal BC was attributed to a transition in the depositional environment from permanently to periodically submerged (Taylor 2011, 72). Kenward (2009, 73) lists several examples from north-east England where statoblasts have been recovered in archaeological samples from terrestrial sequences and so are likely to have been introduced by human agency or by flooding.

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