Life cycles and trophic interactions of Tasmanian coastal zooplankton.

A project undertaken at the Tasmanian Aquaculture & Fisheries Institute, University of Tasmania, and supervised by Kerrie Swadling

Background
Long-term changes in zooplankton are being observed in many of our oceans. These changes have profound implications for the ecology of marine habitats, as zooplankton are important components of all marine ecosystems. Furthermore, they are sensitive indicators of climate and other environmental changes. There are increasing concerns about the effects of climate change on coastal marine fauna, yet, in Tasmania, we have only basic knowledge of the key planktonic species. It has been suggested that zooplankton in coastal Tasmanian waters have undergone a substantial shift in species during the last 30 years, but our understanding of what might have driven this shift is limited. As part of this project we will undertake a strategic sampling effort designed to explore further these possible changes in zooplankton biodiversity.

Zooplankton are abundant in Tasmanian coastal waters, and it is probable that they graze a considerable amount of local primary production. However, little is known about the diets and consumption rates of these organisms and, at present, there are minimal data with which to assess their regional importance. Therefore this study will also examine the dietary preferences and clearance rates of dominant zooplankton in local waters, and will produce the first systematic approach designed to quantify the role of this component of the Tasmanian estuarine and coastal marine ecosystems.

Studies of zooplankton have been seriously neglected in Australia over the last three decades. Although zooplankton samples are quite easy to collect, a large amount of laboratory time is required to sort and identify the animals. There were some important data sets gathered during the 1950s to 1970s, but then the focus shifted away from these groups. However, this same neglect is not evident in Europe or North America, where zooplankton are recognized as important indicators of climate and other change. If similar trends to those observed in the North Atlantic are occurring in Australia it is possible that some zooplankton groups are extending their range southwards by up to 10°. Indeed there is some evidence of a regime shift in the zooplankton of eastern Tasmanian coastal waters, with samples collected in 1973 and 2002 revealing distinct communities. In particular, the 2002 dataset showed that the importance of Antarctic and subantarctic species was greatly reduced compared to the 1973 dataset, while the abundance of subtropical species had increased. Unfortunately there is no other information available with which to assess this trend.

Objectives

The overall objective of our project is to improve understanding of the role of zooplankton in the southeastern Tasmanian estuarine and coastal marine ecosystems, particularly in relation to environmentally and anthropogenically induced changes.

Specifically, this project will:

  1. Compare the current biodiversity of Tasmanian coastal zooplankton to historical data collections and records.
  2. Elucidate the life cycles of key Tasmanian coastal zooplankton.
  3. Describe the potential diet available to zooplankton in Tasmanian estuarine and coastal waters, and determine the dietary preferences of dominant grazers.
  4. Quantify the clearance rates of the dominant grazers, and combine these with biomass estimates to infer the grazing impact of the zooplankton.

The outcomes of this project will lead to a greatly improved understanding of the role of zooplankton in structuring the ecosystems of important southeastern Tasmanian water bodies.

Fig. 1. Female copepod Centropages australiensis (Click on image to enlarge)

Fig. 2. The cladoceran Podon sp. (Click on image to enlarge)

Fig. 3. A larval decapod. (Click on image to enlarge)

Fig. 4. The jellyfish Obelia sp. (Click on image to enlarge)