Key points are not available for this paper at this time.
Author Posting. © Inter-Research, 2015. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Microbial Ecology 75 (2015): 129-137, doi:10.3354/ame01753.
Apprill et al. (Fri,) studied this question.