Plankton trophic structure and particulate organic carbon production during a coastal downwelling-upwelling cycle
نویسندگان
چکیده
We evaluated plankton trophic structure in a short-term temporal survey performed throughout a downwelling–upwelling cycle at the SE Brazilian coast. Size-fractioned phytoplankton biomass (PB), microzooplankton (MiZA) and mesozooplankton (MeZA) abundances along with primary (PP) and bacterial production (BP) were estimated for 5 consecutive days at a fixed station in the Cabo Frio upwelling core area. During the downwelling period, the dominance of picoand nanoplankton in PB, and higher BP (0.1 μgC l–1 h–1) and MiZA (170 ind. l–1), characterized a microbial food web structure. After the South Atlantic Central Water (SACW) upwelling, the decrease in BP (0.02 μg C l–1 h–1), MiZA (50 ind. l–1) and picoplankton contribution to PB, along with the appearance of microplankton in PB and the increase in opportunistic herbivorous copepods densities (Paracalanus parvus: 2.0 ind. l–1) indicated the establishment of a herbivorous food web structure. Particulate organic carbon (POC) production was mainly due to phytoplankton (98%) and did not differ between periods. However, the observed variability in plankton trophic interactions should affect the magnitude of POC export from this dynamic system.
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