University of Tasmania
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Coastal zooplankton communities of south eastern Tasmania

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posted on 2023-05-26, 03:01 authored by Cazassus, F
The spatial variations of zooplankton communities (i.e. dispersion and retention) between an inshore embayment and an adjacent offshore coastal site were investigated. Water enters the bay by its northern shore and circulates through it in a clockwise direction during an outgoing tide and an anticlockwise direction during an incoming tide. Distribution of some species, such as Calanus australis, Temora turbinata, Noctiluca scintillans, Podon sp, Penilia sp., showed a retention time in the bay of around 4 to 6 weeks. Although there is clear evidence that mixing occurred between the bay and the channel via a complex combination of winds and tides, and no barrier or gradient could be identified, some species were found only in the bay: examples are Oikopleura sp., crustacean larvae, Clausocalanus ingens, and Oithona sp., which were retained in the bay probably through a combination of behavioural strategies e.g. vertical migration or selective predation. Some oceanic species even maintained their position outside the bay (Labidocera cervi), and were not found inshore. Temporal and spatial variations of the surface zooplanktonic and neustonic communities of the south east coastal waters of Tasmania were studied. Data on the neuston in Australia are scarce and distribution atld life history of most of these species are poorly known. Pontella novaezelandiae (Pontellidae, Copepoda) (Farran 1929) was recorded for the first time in Tasmanian waters. Fifteen specimens were encountered during summer 2000-01, whereas the previous records in the region were mostly in autumn-winter off the North Island, New Zealand. In vitro observations of another neustonic species, Labidocera cervi (Pontellidae, Copepoda) (Kramer, 1895), revealed some diel migration patterns. Adults live within the surface 10 em layer during daylight 11 and spread throughout the water column just after dusk, and juveniles spend most of their time at the surface, day or night. Some observations on the life history and ecology of these two neustonic species are described. The data obtained during 2000-01 sampling season were compared with earlier data from 1971-73 sampled in nearby coastal waters. At the same site, using the same methodology, two distinct communities were obtained in 1971-73 and 2000-01. The importance of Antarctic and subantarctic species is greatly reduced compared to 1971-73 and the abundance of subtropical species has increased. These observations are supported by changes in sea surface temperature and salinity off this coast during the last 45 years. Changes in the zooplankton community cannot be explained by the ENSO cycle. These changes are consistent with a regime shift that has been described in the North Pacific.


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