Hydrolysis and mineralization of chitin in the Delaware Estuary

We examined various aspects of chitin degradation in order to estimate degradation rates and the contribution of chitin to supporting bacterial growth in the Delaware estuary. Hydrolysis of the chitin analog, methylumbelliferyl-N,N'-diacetyl-chitobioside (MUF-diNAG), and mineralization of C-14-chitin varied in a complex pattern in the estuary and correlated only weakly at best with various indices of chitin production. Rates of MUF-diNAG hydrolysis and C-14-chitin degradation were within an order of magnitude of each other, with hydrolysis rates usually exceeding chitin mineralization. Consistent with hydrolysis being greater than mineralization, we found substantial release of C-14-labeled dissolved organic matter (DOM) during degradation of the C-14-chitin; DOM release was roughly equal to respiration of C-14-chitin. This DOM release could support growth of bacteria not attached or otherwise associated with the chitin, but rates of DOM release and direct chitin degradation seem low relative to bacterial production. During 2 cruises in July and October, chitin appeared to support 5% or less of bacterial production, whereas during one cruise in September the percentage was about 30%. Estimates of chitin inputs into marine systems indicate that on the order of 10% of bacterial production could be supported by chitin. Although it appears low, few individual biochemicals are likely to support much more bacterial growth than chitin, with the possible exception of protein and amino acids.