Trophic dynamics in the San Juan Channel during fall 2012

Abstract

The seasonal dynamics of trophic interactions in diatoms, calanoid copepods, and Pacific sand lance in the San Juan Channel were examined over the fall season. There was a very large diatom bloom on October 10th (118,707.53 diatoms L-1) after which density remained low. Calanoid copepod density also peaked on the 10th (5,159.31 individuals m-3) then decreased with slight fluctuations. Nauplii decreased in abundance during the season, especially relative to adult calanoids, probably due to their life history pattern which favors development to copepodite stage V before over-wintering diapause. Lipid reserves in calanoid copepods increased immediately following the diatom bloom, then remained low the rest of the season. The greatest percent of sand lance with calanoids in their stomachs (23.1%) was found before the plankton blooms. It is suggested that this may be because they begin hibernation without regard to a fall bloom, since fall bloom timing is very inconsistent. Overall, a temporal linkage in trophic dynamics was evident between primary and secondary productivity, but not between the plankton and sand lance. Sampling the sand lance feeding in the water column would strengthen further evaluation of sand lance trophic interactions with diatoms and copepods.