Anne Brearley

Isopod miners in the leaves of two Western Australian Posidonia species

Isopods of the genus Lynseia have been found burrowing (leaf mining) in meadow forming seagrasses (Posidonia) from Western Australia. These small (1.5–1.8 mm) isopods burrow beneath the epidermis consuming the mesophyll, forming a linear mine of similar width to the isopod along the leaf lamina. At Rottnest Island in January 1991, 75% of Posidonia australis Hook. f. and 66% of Posidonia sinuosa Cambridge and Kuo leaves were burrowed by isopods. Isopods were found in leaves of all sizes, but number of burrows, number of isopods and the length of burrows increased in older leaves. In P. australis, there were 3.15 ± 0.1 burrows and 2.6 ± 0.1 isopods per burrowed leaf, in P. sinuosa there were 2.9 ± 0.1 burrows and 2.48 ± 0.2 isopods per burrowed leaf. Isopods were mobile, vacating older burrows and forming new ones. Male and female isopods were found in pairs within burrows and young isopods were then brooded within the burrows, forming new branches from the parent burrow. Within monospecific stands of P. australis and P. sinuosa there were 2950 and 2280 isopods m−2 respectively. Mean length of individual burrows was 22 mm in P. australis and 28 mm in P. sinuosa. Total burrow length per leaf (mean ± SE) was 69.6 ± 3.6 mm in P. australis and 81.7 ± 4.7 mm in P. sinuosa. The consumption of leaf tissues and the resulting lines of weakness along burrow lines may have negative effects on the seagrass. Burrows facilitate entry of water, bacteria and fungi to the blade, leading to localised tissue death. Epiphytes may proliferate along burrow lines, owing to surface roughness or solute loss associated with the burrow. Burrows also split and increase fragmentation of leaves in storm events. Loss of photosynthetic area due to epiphytic growth and fragmentation of the leaves may reduce the growth of Posidonia. These potential effects of lynseid seagrass leaf miners may be important if the seagrass meadow was already under stress.

Influence of Sargassum spp. Attached to Rhodoliths on Sampling Effort and Demographic Analyses of Sargassum spp. (Sargassaceae, Phaeophyta) Attached to a Reef

Sargassum species at Rottnest Island, Western Australia form extensive subtidal beds on a limestone reef. Thalli are also attached to rhodoliths which collect in hollows in the limestone reef. Size frequency histograms demonstrate that the sample population consisted of two discrete components, thalli attached to rhodoliths and thalli attached to the reef. Sargassum thalli on rhodoliths were a small (2-4%) but persistent component of the total adult Sargassum population. Recruitment on to rhodoliths was also lower (30%) than on to the reef and mortality was higher. Despite their low abundance and contagious distribution, Sargassum attached to rhodoliths contributed to biasing estimates of population density, reproductive output and recruitment potential for Sargassum attached to the limestone reef. Sargassum plants attached to rhodoliths also appear to move thus they may have implications for dispersal and gene flow of Sargassum populations and for other organisms found on limestone reefs.

A new species of Tellina (Tellinides) (Bivalvia: Tellinidae) from Western Australia

Abstract A new bivalve species, Tellina (Tellinides) cockburnensis, is described from inshore localities in Western Australia between Warnbro Sound and Bernier Island. Fossil records are from Quaternary deposits between Kalbarri and Albany.