|dc.description.abstract||Many species of sea stars are considered to be keystone species, meaning they have a considerable effect on the habitat in which they are found. Their feeding within the habitat will often control the distribution of associated species. Investigating feeding activity at an individual level will enable researchers to better understand how they structure marine communities. Also, understanding how food limitations may affect their growth or reproductive potential will give us a better understanding of how populations of sea stars react to changes in their environment, particularly in relation to changes in food availability. Until now there has been little research completed on the individual movement of sea stars, particularly over extended periods.
The first aim of this research was to develop a method of tagging the mobile, subtidal invertebrate Coscinasterias muricata that could be employed easily in-situ and later be used in an effort to monitor the movements of the sea star in relation to the freshwater layer which is found nearly permanently in Doubtful Sound. The second aim of the following thesis was to test the use of electronic archival tags in the field as a method of examining the ecology of a subtidal marine invertebrate, as opposed to more conventional methods, such as direct diver observations. The final aim of this thesis was to determine what, if any, affects food limitations have on the survival, growth and potential reproductive output has on Coscinasterias muricata.
The New Zealand sea star, Coscinasterias muricata, was tagged with small archival electronic tags that recorded water temperature and depth every 5minutes for up to 2 weeks. Tagging was undertaken to test the viability of using electronic tags in research on the ecology of sea stars in a New Zealand fjord, where their vertical distribution is influenced by the presence of low-salinity layers. The effects of tagging were tested prior to in situ use, and tagging showed no significant influence on survival, feeding, righting ability or movements. Tagging of the sea stars in their natural environment at Espinosa Point, Doubtful Sound, New Zealand provided information on their vertical movements over periods of up to 2 weeks. The movement was compared to physical environmental data including the depth of the low salinity layer.
The tagged sea stars showed variation between individuals and between tagging trials in their movements. However in all but a couple of short periods the sea stars remained in water that was close to full salinity. When the low-salinity layer was relatively shallow (February 2008) the sea stars moved into shallower waters, where they were likely feeding on the dense mussel band found in the shallows. It was concluded that the sea stars were able to move at rates that would allow them to track the bottom of the low-salinity layer as the tide moved in and out and when the tide was high and the bottom of the mussel band was exposed to full salinity sea water the sea stars would be able to feed on the mussels and still escape the low-salinity layer as the tide moved out.
Laboratory studies into the effects of food limitations on the survival, growth and reproductive potential of the sea stars were conducted over a period of 185 days. Limited food availability had no effect on the sea star in terms of their survival, somatic growth, pyloric caeca index or gonadal index. Limited food availability had an effect on the timing of gametogenesis as seen through examination of the oocytes and spermatogenic columns of the sea stars. Rather than the development of the oocytes and spermatogenic columns being affected, it was the timing of the stages of this development that appear to be influenced by a reduce quantity of food. From the research conducted it appears that both male and female sea stars fed ad libitum reached maturity earlier than sea stars with restricted quantities of food.
This study is one of the first to utilise electronic tagging to study the ecology of a mobile invertebrate such as a sea star. The success of this initial study suggests that valuable quantitative could be gained by future tagging of these animals.||en_NZ