3.4 Infestation

Figure 10
Figure 10: Examples of biological infestation of whelks from Carisbrooke midden 7325. (a): burrow of serpulid worm Polydora ciliata; (b): calcareous byssus from attachment of saddle-oyster Anomia ephippium; (c): linear pattern of surface perforations from the sponge Cliona; (d): lower valve of juvenile oyster Ostrea edulis ('spat'). Scale bar: 10mm.

Some of the whelks bore traces of marine organisms that had colonised their shells during life (Figure 10). Of the 48 shells intact or complete enough to measure shell height, one had been bored by the bristle-worm Polydora ciliata (Figure 10a), two had bryozoan mats, one had a sand-worm tube, one had the calcareous byssus from the attachment of a saddle oyster (Anomia ephippium) (Figure 10b), one had infestation by the burrowing sponge Cliona (Figure 10c) and four had shells of juvenile oysters ('spat') (Figure 10d). Like oysters, the large solid shells of whelks are regularly infested by other marine organisms (Hancock 1967, 4) and all these organisms had also infested oysters in the same deposit (Campbell 2013, 22). Oysters in the deposit had the oval form of regularly dredged deeper-water oysters (Campbell 2013, 22), and whelks are attracted to dead or damaged molluscs in areas damaged by bottom-fishing (Ramsay et al. 1998), so these whelks had probably colonised a dredged deeper-water oyster bed. Infestation of whelks by oyster spat was unexpected, since spat tends to settle on stable surfaces, often among other oysters (Bayne 1969), and would tend to avoid settling on one of its predators.