Bacterial recolonization of deposit-feeder egesta: In situ regrowth or immigration?

The related processes of disturbance, recolonization, and succession can pl ay major roles in structuring communities and in generating spatial heterog eneity. Nonequilibrium processes have been little studied with respect to m icrobial community dynamics. Here we report experimental efforts to identif y the mechanisms of recolonization of egesta employing two intertidal depos it feeders. Balanoglossus aurantiacus and Nereis succinea. Using direct mic roscopic counts and Biolog plates, we compared the quantitative and qualita tive patterns of recovery in egesta isolated from underlying sediments on " latrines" to recolonization in naturally incubated fecal casts. Significant recovery over the 2-h observation periods was never seen on latrines. Rapi d recovery in metabolic potential was observed in the naturally incubated F ecal casts of both animal species. Likewise, a rapid numerical recovery was seen in the egesta of N. succinea casts on sediments. In contrast, no nume rical recovery was evident in any fecal casts of B. aurantiacus over 2 h, r egardless of treatment. For these two species, recolonization appears to be dominated by migration of bacteria from underlying sediments as opposed to repopulation by survivors of ingestion. These findings indicate that renew al of available (digestible) microbial resources to deposit feeders is more rapid than would be predicted if regrowth was the dominant process of reco lonization. Furthermore, because recovery time is short relative to the int erval between disturbances, deposit feeding is unlikely to play a major rol e in structuring benthic microbial communities.