Annual carbon retention of a marine-plankton community in the eutrophic Masan Bay, based on daily measurements

Abstract

Marine plankton comprise the largest portion of the marine biomass, and play critical roles in the global carbon cycle. The carbon retention of marine-plankton communities is as important as their primary production; however, data on the annual carbon retention of marine-plankton communities based on daily sample analysis are limited. Using our published and unpublished data, we calculated the one-year integrated carbon retention of a marine-plankton community at an innermost fixed station in the highly eutrophic Masan Bay, Korea, collected daily from June 2004 to May 2005. The total one-year integrated carbon retention of all plankton taxa in the study period was 471 g C m(-3) yr(-1). The integrated carbon retentions by phytoplankton, heterotrophic protists, and heterotrophic bacteria were 344, 76, and 40 g C m(-3) yr(-1), respectively, whereas those by photosynthetic ciliates and metazooplankton were 9 and 2 g C m(-3) yr(-1), respectively. Among the plankton subgroups, the integrated carbon retention by the phototrophic dinoflagellates (109 g C m(-3) yr(-1)) was highest, followed by raphidophytes (88), cryptophytes (73), diatoms (43), heterotrophic bacteria (40), and heterotrophic dinoflagellates (39). The total duration of the red tides by diatoms that grow using only photosynthesis (42 days), was considerably shorter than that of phototrophic dinoflagellates, raphidophytes, or cryptophytes, which can grow mixotrophically (56-135 days). The shorter duration of red tides by diatoms was primarily responsible for their lower carbon retention, although the maximum growth rates of the diatoms were considerably higher than those of the flagellates. The percentage of the 1-year integrated carbon retention of the heterotrophic protists relative to that of the phytoplankton was approximately 20%, similar to the mean-gross-growth efficiency of heterotrophic-protist grazers on phytoplankton, indicating a good balance between these two components in the planktonic food web. This study reported one-year integrated carbon retention of marine plankton at the species level, calculated based on daily samples, and thus gave an insight into which, and to what extent, species and groups contribute to the total carbon retention of plankton for one year in a highly eutrophic bay.