Rapid attachment of spores of the fouling alga Ulva fasciata on biofilms.

Attachment of spores of Ulva fasciata to natural biofilms was examined to probe the basis for specificity in settlement. Within 30 min from initial exposure in laboratory assays, spores attached to 1-, 3-, 6- or 9-day biofilms formed on acid-cleaned glass slides. The greatest number of spores attached to biofilms aged for 6-day (573.3 +/- 45 spores mm2, p<0.025). The Morisita Index (MI) was used to investigate relationships between the spatial pattern of spores on natural biofilms, and was found to be random for 1-, 3- and 6-day biofilms (MI = 0.93, 0.98 and 0.95, respectively), but non-random on 9-day biofilms (0.82). In addition to the attachment of spores to natural biofilms, experimentally manipulated biofilms that provided potentially specific receptor sites were studied. Epifluorescence microscopy of 1-day biofilms confirmed that experimental sugar was incorporated into natural biofilms. The Jacalin galactose specific probe showed a homogeneous pattem of galactose incorporation on biofilms, whereas Concanavalin Aprobe (mannose) showed a discrete pattem for this sugar. Similarly, the addition offetuin to a biofilm was detected as a heterogeneous pattern. Rapid spore attachment of U. fasciata found on natural biotilms was induced by fetuin (1-day: 1482 +/- 46.6 spores mm2); specific molecules similar to fetuin may play a role in triggering settlement Specific sugars and their analogs are important surface receptors and play an integral role in attachment of Ulva fasciata spores to aged biofilms. Biofilm age and the role of specific sugars on attachment are discussed.