Invariant scaling of phytoplankton abundance and cell size in contrasting marine environments.

Scaling relationships such as the variation of population abundance with body size provide links between individual organisms and ecosystem functioning. Previous work, in marine pelagic ecosystems, has focused on the relationship between total phytoplankton abundance and the assemblage mean cell size. However, the relationship between specific population abundance and cell size in marine phytoplankton has received little attention. Here, we show that cell size accounts for a significant amount of variability in the population abundance of phytoplankton species across a cell volume range spanning seven orders of magnitude. The interspecific scaling of population abundance and cell size takes a power exponent near -3/4. Unexpectedly, despite the constraints imposed on large phytoplankton by limited resource acquisition, the size scaling exponent does not differ between contrasting marine environments such as coastal and subtropical regions. These findings highlight the adaptive abilities of individual species to cope with different environmental conditions and suggest that a general rule such as the 'energetic equivalence' constrains the abundance of phytoplankton populations in marine pelagic ecosystems.

Copepod hatching success in marine ecosystems with high diatom concentrations.

Diatoms dominate spring bloom phytoplankton assemblages in temperate waters and coastal upwelling regions of the global ocean. Copepods usually dominate the zooplankton in these regions and are the prey of many larval fish species. Recent laboratory studies suggest that diatoms may have a deleterious effect on the success of copepod egg hatching. These findings challenge the classical view of marine food-web energy flow from diatoms to fish by means of copepods. Egg mortality is an important factor in copepod population dynamics, thus, if diatoms have a deleterious in situ effect, paradoxically, high diatom abundance could limit secondary production. Therefore, the current understanding of energy transfer from primary production to fisheries in some of the most productive and economically important marine ecosystems may be seriously flawed. Here we present in situ estimates of copepod egg hatching success from twelve globally distributed areas, where diatoms dominate the phytoplankton assemblage. We did not observe a negative relationship between copepod egg hatching success and either diatom biomass or dominance in the microplankton in any of these regions. The classical model for diatom-dominated system remains valid.