Mossy stones gather more bugs: moss as habitat, nurseries and refugia for tropical stream invertebrates

Bryophytes are known to provide habitat and refugia for stream invertebrates, but there are few reports documenting use of bryophytes in tropical streams. We investigated invertebrate assemblages in moss in pools, runs and riffles from wet to dry seasons in tropical Australian streams. We investigated assemblage dynamics, responses to disturbance, the importance of flow, and use of moss for establishment and habitat. Invertebrates had higher diversity in moss than other habitats (in riffles, 23 vs. 11-19 families in 3 other habitats; in pools, 24 vs. 15-20 families), and greater abundance, especially of small individuals (riffles: similar to 59,000 vs. similar to 9000-23,000 m(-2); pools: similar to 52,000 vs. similar to 10,000-36,000 m(-2)). Densities increased as flow and moss availability declined. Artificial disturbance (heavy abrasion) removed similar to 70% of individuals and 40% of taxa, but responses of different taxa varied between pools and riffles. In a colonisation experiment, natural densities were achieved in 8 weeks. Transplanting of artificial moss between pools and riffles demonstrated high invertebrate fidelity to the moss habitat, except for loss or gain of a few flow-dependent taxa in riffle-pool and pool-riffle transplants, respectively. Thus, moss has a substantial role in providing habitat, refugia and nursery sites for many invertebrate taxa in tropical streams