ISOPOD MINERS IN THE LEAVES OF 2 WESTERN-AUSTRALIAN POSIDONIA SPECIES

Isopods of the genus Lynseia have been found burrowing (leaf mining) i n 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 leaflamina. At Rottnest Island in January 1991, 75% of Posidonia a ustralis Hook. f. and 66% of Posidonia sinuosa Cambridge and Kuo leave s were burrowed by isopods. Isopods were found in leaves of all sizes, but number of burrows, number of isopods and the length of burrows in creased in older leaves. In P. australis, there were 3.15 +/- 0.1 burr ows and 2.6 +/- 0.1 isopods per burrowed leaf, in P. sinuosa there wer e 2.9 +/- 0.1 burrows and 2.48 +/- 0.2 isopods per burrowed leaf. Isop ods were mobile, vacating older burrows and forming new ones. Male and female isopods were found in pairs within burrows and young isopods w ere then brooded within the burrows, forming new branches from the par ent burrow. Within monospecific stands of P. australis and P. sinuosa there were 2950 and 2280 isopods m(-2) respectively. Mean length of in dividual burrows was 22 mm in P. australis and 28 mm in P. sinuosa. To tal burrow length per leaf (mean +/- SE) was 69.6 +/- 3.6 mm in P. aus tralis and 81.7 +/- 4.7 mm in P. sinuosa. The consumption of leaf tiss ues and the resulting lines of weakness along burrow lines may have ne gative effects on the seagrass. Burrows facilitate entry of water, bac teria and fungi to the blade, leading to localised tissue death. Epiph ytes may proliferate along burrow lines, owing to surface roughness or solute loss associated with the burrow. Burrows also split and increa se fragmentation of leaves in storm events. Loss of photosynthetic are a due to epiphytic growth and fragmentation of the leaves may reduce t he growth of Posidonia. These potential effects of lynseid seagrass le af miners may be important if the seagrass meadow was already under st ress.