Production of dissolved organic matter and inorganic nutrients by gelatinous zooplankton in the York River estuary, Chesapeake Bay

Large blooms of ctenophores (Mnemiopsis leidyi) and scyphomedusae (Chrysaora quinquecirrha) occur throughout the York River, a sub-estuary of Chesapeake Bay. These gelatinous zooplankton blooms can influence carbon (C) and nutrient cycling through excretion of dissolved organic matter (DOM), and inorganic nitrogen (N) and phosphorus (P). We measured dissolved organic carbon, nitrogen and phosphorus (DOC, DON and DOP), ammonium (NH(4)(+)) and phosphate (PO(4)(3-)) released by M. leidyi and C. quinquecirrha in the laboratory, and estimated their contribution to in situ DOC and inorganic pools. Both species released high amounts of DOC compared with DON and DOP. DOM released by Mnemiopsis was C-rich with higher DOC:DON (29:1) compared with the Redfield ratio (6.6C:1N). Daily turnover of DOC and DON in ctenophores was high (25.2% of body C and 18.3% of body N), likely due to mucus production. In contrast, individual Chrysaora released DOC and DON similar to Redfield stoichiometry, but daily turnover of these compounds was low (< 3% of body C and N). Both species released dissolved N and P in inorganic form but also released sizeable quantities of DON (21 and 35% of total dissolved nitrogen, TDN, for ctenophores and medusae, respectively) and DOP (34 and 46% of TDP). Most of the DOC in the York River came from Mnemiopsis populations during summer (May-July). While their contribution to bulk DOC pools was low (< 1% day(-1)), ctenophore populations released higher amounts of DOC to labile pools (18-29% day(-1)). Contributions to NH(4)(+) and PO(4)(3-) pools were highest at times when the York River was N-limited (5.8N:1P). Despite their potential to release phytoplankton from nutrient limitation, N excretion from gelatinous zooplankton supported < 4% of primary production. Because net NH(4)(+) released by Mnemiopsis populations exceeded standing concentrations, we hypothesize an alternative DIN sink whereby bacterioplankton supplement uptake of DOM released by gelatinous zooplankton with inorganic N and P to satisfy intracellular elemental requirements.