Preliminary evidence for post‐settlement movement of juvenile and adult pipi, Paphies australis (Gmelin, 1790) (bivalvia: Mesodesmatidae)

Adults and juveniles of the infaunal bivalve, Paphies australis (pipi), were observed drifting in raid‐water, in a small harbour in northeastern New Zealand. The animals were buoyed up by the secretion of long mucus threads which extended out through their siphons. Quantitative information from netting experiments over a period of five months from May 1993 to September 1993, collected a total of 509 drifting pipi. These were mainly juveniles (<15 mm shell length) but a small number of adults (up to 58 mm shell length) were also collected. The numbers of pipi caught was highly variable, however, there was a trend for more drifting pipi to be caught on the flood tide (n=386) than the ebb tide (n=123). Overall there was little difference in the number of pipi caught between spring (n=263) and neap tides (n=246), however, this was heavily influenced by one neap tide in May 1993 (n=207). Three other bivalve species (Soletellina sp, Gari stangeri, Macomona lilliand) were also caught drifting. Pipi were also observed to attach themselves to debris, such as dead branches of trees, which then moved them with the tidal currents. Large epiphytic algal growths on the shell also acted to buoy individuals which moved them around in tidal currents. It is hypothesised that mucus drifting in pipi is an active process, adopted for movement to other areas triggered by very high densities (over 4000 m²) in the harbour entrance.

Key words:

• Pipi
• Paphies australis
• mesodesmatidae
• post‐settlement
• movement
• mucus drifting