Resource availability determines seasonal variation of phytoplankton size structure in the Kuroshio east of Taiwan
Date Issued
2015
Date
2015
Author(s)
Lin, Fan-Sian
Abstract
We examined the relationship between phytoplankton normalized biovolume size spectral (NBSS) slopes versus hydrographic variables in the Kuroshio region east of Taiwan and tested two classic hypotheses. First, phytoplankton size structure follows temperature-size relationship that the NBSS slopes become steeper with increasing temperature. Second, resource-size relationship prevails for phytoplankton, of which NBSS slopes become shallower with nutrient enrichment. Here, we used total biomass of phytoplankton community as a proxy for resource supply instead of more commonly used inorganic nutrients because inorganic nutrients are deplete and cannot be a reliable proxy for resource supply in oligotrophic oceans. Our results do not support the temperature-size relationship, as NBSS slopes became shallower with increasing temperature. In contrast, we found a positive relationship between NBSS slopes versus total biomass, generally supporting the resource-size relationship. The only exception occurred in spring, during which the NBSS slopes deviated downward from the regression. In spring, we observed that small cells were dominant as nutrient pulses in the Kuroshio region, which is contrast to expectation from the resource-size relationship. This discrepancy can be explained by the none-steady state theory, where in the initial stage of nutrient enrichments in oligotrophic regions in spring, that small cells with a high surface-area-to-volume ratio uptake nutrients faster than the larger ones. Later in summer and early autumn, NBSS slopes became shallower because large phytoplankton won the competition after nutrient enrichments and/or predators ate small phytoplankton. In autumn and winter, NBSS slopes became steeper again when nutrients were barren. In general, phytoplankton size structures in the Kuroshio east of Taiwan can be explained by the resource-size relationship; nevertheless, the none-equilibrium condition needs to be taken into consideration.
Subjects
phytoplankton
size structure
normalized biovolume size spectrum
temperature-size relationship
resource-size relationship
nutrient limitation
oligotrophic oceans
Type
thesis
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