Ecology and taxonomy of mysids (Mysidacea : crustacea)

The total number of species of mysids known from Australian waters is 94, spanning 38 genera. Distribution records and keys to their identification are provided. Of these species, three new genera and twelve new species from Tasmania and Bass Strait have been described herein. In addition, numerous new records have been reported. Forty-seven of the mysid species and eight genera are endemic to Australia. The Australian mysid fauna exhibits strong links with that of the Indo-West Pacific region. A 12-month field study was conducted at One Tree Point, Bruny Island Southern Tasmania, to investigate the role of mysids in an inshore coastal community. Fourteen species were recorded from the study site; of these, three i.e. Tenagomysis sp.2 n.sp., Anisomysis mixta australis and Paramesopodopsis rufa n.g. n.sp., formed dense swarms. The major peaks of abundance for each species were temporally separate. T.sp.2, A.mixta australis and P.rufa were found to exhibit a number of ecological differences, i.e. habitat partitioning (in zones parallel to shore), diet and diel activity, which may explain their co-existence. These three species bred continuously during spring, summer and autumn. Breeding continued at a lower level during winter for T.sp.2 and P.rufa, but A.mixta australis appeared to cease breeding over winter. The breeding pattern was quite similar to that reported for most temperate mysids throughout the world. The annual production was calculated from the field data for each species. Production was found to be greater for T.sp.2 than P.rufa and A.mixta australis, but the annual turnover (P:B) was higher for A.mixta australis (7.7) than T.sp.2 (5.5) and P.rufa (5.3). The values obtained were high compared to those reported for mysid species in colder climates. Trophic relationships within the mysid community were examined. Gut contents analysis of the three mysids revealed a basically omnivorous diet, but P.rufa fed to a greater degree on small crustaceans while the diet of T.sp.2 was composed mainly of large fragments of macroalgae. The stomach contents of A.mixta australis was composed of fine particulate detrital matter. Comparison of stable isotope ratios ( 13C: 12C and H:D) of the mysids with those of potential food sources supported these conclusions. In addition, several fish that fed on mysids were identified by analysis of their gut contents and others were implicated by comparison of their stable isotope ratios. The results suggest that apart from their importance in the diet of several fish species, these mysids play a significant role in the turnover of the macroalgal biomass, and may also be important in structuring the zooplankton and/or meiobenthic community. The results presented here have provided a major contribution to the knowledge of both taxonomy and ecology of Australian mysids. However, the need for continued examination of the taxonomy, biology and ecology of Australian mysids is recognized, and consequently, avenues for further research are suggested.