POSTSETTLEMENT MOVEMENT BY INTERTIDAL BENTHIC MACROINVERTEBRATES - DO COMMON NEW-ZEALAND SPECIES DRIFT IN THE WATER COLUMN

To determine whether post-settlement juveniles of New Zealand soft-sediment macrofauna drift in the water column, samples were collected, day and night, above an intertidal sandflat in Manukau Harbour, New Zealand. Forty benthic taxa were collected in the net samples. Most taxa were Polychaeta (18 taxa), Bivalvia (9 taxa), or Amphipoda (4 taxa). All bivalves and gastropods collected were post-settlement juveniles, 3 mm or less in size. Most of the polychaetes captured were either metamorphosing planktonic larvae or young benthic stages. In contrast, most of the captured arthropods were adults. Generally, benthic species found in the water column were also common in the benthos. Definite patterns in migratory activity were exhibited by some taxa over each 24 h sampling period. Taxa collected in the water column varied with sampling date, time of day, state of the tide, and depth of sampling. Only one of the benthic species collected in the net samples showed some ability to partition itself vertically within the water column. The large number and variety of soft-bottom macrofauna collected emphasises the potential importance of post-settlement dispersal in the survival of post-larval organisms.