Abstract
A macrobenthic survey was conducted around the Ishikari Bay New Port in west Hokkaido, Japan, to describe
the community structure of macrobenthos associated with sedimentary conditions. A total of 70 species were
collected at 29 stations using a Smith-Mcintyre grab sampler in September 1998. Dominant species were three
juvenile bivalves (Mactra chinensis, Psendocardium sachalinensis, Megangulus uenulosos), six polychaetes
(Goniada maculata, Spiophanes bombyx, Spio filicornis, Nephtys caeca, Magelona japonica, Glycera capitata),
two echinodems (Scaphechinus griseus, Echinocardium cordatum), and four amphipods (Phoxocephalidae sp.,
Ampelisca brevicornis, Urothoe grimaldii, Corophium sp.). Distribution pattems of the dominant species changed
with feeding type, depth and sediment particle size. Suspension feeders occurred at 2-17m depth in well-sorted
mediate to fine sand. Deposit feeders occurred at 17-23m depth in well-sorted fine to very fine sand. Carnivores
occurred at 7-17m depth in well-sorted mediate to fine sand and at the mouth of Ishikari River in unsorted fine
to very fine sand. Tube-building deposit feeders occurred at the port in unsorted fine to very fine sand. Facultative
deposit feeders occurred throughout the whole survey area, except at the river mouth. At 2-17m depth,
suspension-feeding bivalves, which have a planktonic larval period of 2-4 weeks, occurred densely on the northeast
side of the port, and suspension-feeding amphipods which undergo direct development, were the dominant
species on the southwest side of the port. It was suggested that macrobenthic communities around this port are
strongly affected by hydrodynamic conditions, which influence the food supply to the animals and their recruitment.
