REMOVAL OF FUNGAL AND TOTAL ORGANIC-MATTER FROM DECAYING CORDGRASS LEAVES BY SHREDDER SNAILS

Several lines of evidence from the literature have pointed to the salt marsh periwinkle (Littoraria irrorata [Say]) as a potentially importan t shredder of standing, decaying cordgrass (Spartina alterniflora Lois el.) shoots. Periwinkles prefer to ingest dead-shoot material and poss ess enzymes capable of lysis of cordgrass plant-structural and fungal- wall polymers. We offered natural, standing-dead leaf blades to periwi nkles in an attempt to determine the rates at which the snails would r asp away and ingest material of the decaying-shoot system, and whether the snails would selectively remove living-fungal mass (measured as e rgosterol) from the system. The larger snails tested (14 mm shell heig ht) took 42% of the total organic mass of the blades during 6 days of exposure, and exhibited selectivity for fungal-occupied portions of bl ades by removing 69% of the living-fungal organic mass. Based on obser ved removal rates, about 2-3%. day-1 of the organic mass of standing-d ead leaf blades could be lost to snail grazing in marsh areas where th e snails are most densely concentrated (> 400 individuals . m-2 of she ll length > 5 mm). In a preliminary comparison of adjacent marsh areas of equivalent canopy height, the one without periwinkles had a 4 x gr eater standing crop of dead leaves. Periwinkles are likely to be impor tant controlling agents of fungal standing crops and important shapers of fungal community dynamics in cordgrass marshes, in that the standi ng, decaying substratum for fungal growth and the potential for fungal species successions are radically changed by the snails' activities.