COMPARISONS OF SPECIES RICHNESS, SIZE-STRUCTURE AND PRODUCTION OF BENTHOS IN VEGETATED AND UNVEGETATED HABITATS IN WESTERN-PORT, VICTORIA

Invertebrate faunas associated with vegetated and unvegetated habitats were sampled over a 15-month period in Western Port, Victoria, in ord er to identify consistent faunal differences between the two habitat t ypes. Intertidal seagrass habitats in Western Port supported much high er numbers of macroinvertebrate species per 150 mm core (xBAR = 33) th an intertidal unvegetated habitats (xBAR = 15 species), with a mean of 17 species per core found in the deeper unvegetated channel habitats. Species within channel habitats were more patchily distributed than e lsewhere; consequently, the total number of species collected from cha nnel habitats over all sampling occasions was high (265 species) and c lose to that collected from seagrass habitats (300 species), with a lo wer number (185 species) collected from intertidal unvegetated habitat s. Estimated annual epifaunal production was much higher in intertidal seagrass habitats (17.2 g.m-2.yr-1) than in unvegetated habitats (3.3 g.m-2.yr-1). A substantial decline in seagrass cover in Western Port over the past twenty years is inferred from these data to have reduced epifaunal production by an estimated almost-equal-to 2500 tonnes ash- free dry weight (AFDW) per year within the bay. Annual infaunal produc tion differed little between intertidal seagrass (62 g.m-2.yr-1) and u nvegetated habitats (54 g.m-2.yr-1), so total infaunal production has probably changed little over that time. However, infaunal production w as significantly correlated with the amount of organic material in the sediment, so long-term declines in infaunal production may have occur red as a consequence of declining production levels of seagrass detrit us. Two corers with different diameter were used to obtain data on fau nal size-distribution patterns within the 125 mum to 16 mm animal size range. Small diameter (50 mm) corers were significantly more effectiv e at sampling benthos < 2 mm sieve size than large diameter (150 mm) c orers. Faunal size-distribution patterns differed greatly between samp ling locations, and meiofauna and small macrofauna were disproportiona tely abundant in the presence of seagrass. While faunal size-distribut ion plots were polymodal at most sites, production was rarely low at t he macrofaunal/meiofaunal boundary, and size-related maxima and minima did not correspond with modes in sediment particle sizes, as was expe cted following Northern Hemisphere studies.