Isopod borers in seagrass species from South-Western Australia

Abstract

Consumption of living seagrass leaf tissue by isopod borers is recorded in seagrass species from Western Australia. Two different strategies of tissue consumption are documented. Limnoria agrostisa (Limnoriidae) enters the leaf cluster of Amphibolis griffithii and consumes the leaf meristem in up to 40% of leaf clusters, resulting in malformation of new leaves and, in some cases in leaf cluster death (maximum 8% of leaf clusters). Lynseia spp. (Lynseiidae) enter the leaf lamina of Posidonia and Heterozostera, and consume the middle leaf tissues, avoiding epidermal cells. Members of the Lynseiidae are small (1.5-1.8 mm) and elongate and live within the leaf lamina. Their activity may be considered analogous to that of terrestrial leaf miners. Three species of Lynseia are recognized, each species appears to be associated with a specific species or species complex of seagrass. In January 1991 at Rottnest Island, 75% of Posidonia australis, 66% of P. sinuosa, and 38 % of Heterozostera tasmanica were bored by lynseiid isopods. There were 3.1 and 2.9 burrows and 2.6 and 2.5 isopods per leaf in Posidonia australis and P. sinuosa, respectively. The numbers of individual lynseiid isopods per square metre of substratum occupied by seagrass were 2,876 and 2,257 for Posidonia australis and P. sinuosa, respectively. Leaf mining by lynseiid isopods results in lines of weakness in the leaf along burrow lines. Isopod tissue removal, whether by Lynseia spp. or Limnoria agrostisa may facilitate the premature fragmentation, entry of pathogens, attachment of algal epiphytes, and cause disruption of gas, nutrient, and photosynthate transport in leaves.