Ecology and ecophysiology of Katelysia scalarina (Bivalvia: Veneridae), a commercially exploited clam
Creators: name: Bellchambers, LM
Publisher: name: University Of Tasmania
Year: 2023

description: The general aim of this study was to increase knowledge of Katelysia scalarina an intertidal suspension feeding bivalve common in many of the sheltered bays and estuaries of southern Australia. Specifically, attention has been focused on the factors that may determine the distribution and abundance of natural populations. Secondly, information was gathered to help ensure effective management of natural populations to prevent over-exploitation and provide a basis for future aquaculture developments. The effects of density and tidal level on the survival, growth and meat ratio of K. scalarina were examined using a series of caged manipulation trials. Both density (171.5-686.1 clams/m2) and tidal position had significant effects on the survival and growth of K scalarina with a decrease in survival and growth evident with increasing distance from the low tide mark. Shell growth at high tidal positions was approximately half of that lower on the shore, which may be due to the depletion of food resources. In contrast, meat ratio displayed a direct relationship with tidal position, as a result of suppressed shell growth at high tidal positions. In contrast to the above trial, the effects of stocking density were much smaller than that of tidal level. None of the measured parameters displayed a significant response to density manipulations of K scalarina grown at a single tidal position. The failure of K scalarina to respond to density treatments up to thirty times that of the natural population may in part be due to the location of the experimental treatments. Experimental cages situated low in the intertidal zone may provide suspension feeders access to a very abundant food source, negating the effects of artificially enhanced densities. The salinity tolerance of adult and juveniles was investigated using a series of acute (21d) toxicity trials (5-550/oo). Results indicate that adults are intolerant of low salinities (&lt;250/00), while juveniles have a wide salinity tolerance range. Despite differences in the salinity tolerance of adults and juveniles, there were no significant differences in their ability to osmoregulate. K. scalarina is essentially an osmo- and ionic-conformer, with the possible exception of r, that relies on the mechanism of shell valve closure to isolate the body tissues from unfavourable salinities. Results indicate that K scalarina relies on regulation of the free amino acid pool to cope with fluctuations in the external medium. Although K scalarina is capable of surviving a salinity range of 25-500/oo, the zone for optimal growth may be a narrower band within this range. Respiration and algal clearance trials were conducted to determine whether irregular valve closure patterns limit oxygen consumption and algal clearance which may in turn limit growth potential. Oxygen consumption was depressed in salinities outside 350/0o even though these salinities were within the tolerance range. However, evidence from algal clearance trails was not so clear cut. Juveniles display a decrease in algal consumption in salinities &gt; 45Voo and &lt; 300/oo. The potential for K. scalarina to be grown as a by-crop on existing oyster farms in Tasmania promoted the investigation of the natural food sources of the species. Besides using the existing infrastructure of established marine farms these areas offer a number of additional food sources due to organic enrichment from pseudofaeces and biodeposition. The stomach contents of clams situated both below existing oyster racks and away from oyster racks indicated that K scalarina is a suspension feeder that relies primarily on phytoplankton present in the water column for nutrition. This indicates that potential exists for competition for food resources if K scalarina is grown in oyster growing areas in southern Australia. However, K scalarina exhibited poor survival in cages when grown on several commercial oyster leases. Despite commercial exploitation of K scalarina, this study is the first comprehensive investigation of the species and therefore provides a valuable resouce for the management of wild populations and future aquaculture ventures. Finally, this study contributes significantly to the existing knowledge of a dominant component of the southern Australian estuarine fauna.