Lipid classes and fatty acids in plankton and settling matter during the spring bloom in a cold ocean coastal environment

Lipid concentration and composition were measured in net-tow and sediment trap samples during the spring diatom bloom in Conception Bay, Newfoundland, to determine the quantity and quality of material settling from the upper mixed layer into the benthic food web. An experiment was also conducted to estimate trap accuracy and precision, in which trap poisoning was found to reduce bacterially mediated dissolution, but to increase variability in particulate lipid data. Total lipid concentrations in plankton reached a maximum of 6.3 ± 2.5% dry weight (mean ± SD) at the height of the bloom in April. Bacterial fatty acid markers were at their lowest during the bloom period (2.0 to 2.8% of total fatty acids), while polyunsaturated fatty acids (PUFA) were at their highest from the beginning of the bloom onwards (44 to 53%). The maximum fluxes of total lipids (75 ± 0.7 mg m–2 d–1) in non-poisoned traps at 80 m depth occurred at the bloom maximum while those at 220 m (35 ± 1.7 mg m–2 d–1) occurred 16 d later. The lipid and PUFA supply to the benthos was over 10 times that accumulated by important amphipod and mysid populations in Conception Bay. In the deep traps, PUFA were maintained at high levels (33 to 35%) throughout the bloom period while bacterial markers were at their lowest (2.3 to 2.9%). A comparison of fluxes showed that over half the PUFA survived transit from 80 to 220 m during the bloom period. These data indicate a rapid transfer of highly nutritious material to the benthos during the spring bloom in Conception Bay.