DOI: 10.5061/dryad.djh9w0w3r
title: Data for: Variation in fatty acid content among benthic invertebrates in a seasonally driven system

description: At temperate latitudes where seasonal changing environmental conditions
 strongly affect the magnitude, duration and species composition of pelagic
 primary production, macrobenthic organisms living below the photic zone
 rely on the sedimentation of this organic matter as their primary energy
 source. The succession from nutritious spring blooms to summer
 cyanobacteria is assumed to reduce food quality for benthic primary
 consumers and their fatty acid profiles. In contrast, we find low seasonal
 variability in fatty acid content of five benthic macroinvertebrates
 spanning two trophic levels in the Baltic Sea, a system with high seasonal
 variation in phytoplankton species composition. However, levels of the
 major FA groups vary greatly between benthic species. The results suggest
 that benthic macroinvertebrates have evolved FA metabolism adapted to
 degraded sedimenting material. Moreover, our study shows that species
 composition of benthic macrofauna rather than seasonal changing conditions
 affect availability of essential nutrients to higher trophic levels.
description: Seston, sediment, and benthic
 animals were sampled at a coastal site in the north-western Baltic Proper
 (58° 48’ 39.5” N, 17° 36’ 25.1” E). The site was situated at 40 m depth
 with a bottom water salinity varying from 6 to 7 and temperature from
 0.18°C to 6.84°C during our sampling occasions. Sampling was done in July,
 August, October, November 2018, and March, April 2019, representing
 summer, autumn and spring bloom conditions. Seston was collected as a
 vertical integrated water sample from the surface to 20 m
 depth, pre-filtered
 through a 100 mm mesh and then filtered onto GF/F filters and
 frozen at -80°C. Sediment was sampled with a boxcorer,
 subsampled with plexiglass tubes, after which the upper sediment (ca 9 mm)
 was sliced off, homogenized and frozen at -80°C. Animals were sampled with a benthic
 sled. We selected adult
 stages of common macrofauna species, including the surface and sub-surface
 feeding amphipods, <em>Monoporeia</em>
 <em>affinis</em> and <em>Pontoporeia</em>
 <em>femorata</em>, respectively, the facultative suspension
 and deposit-feeding clam <em>Macoma</em>
 <em>balthica</em>, the deposit-feeding
 polychaete <em>Marenzelleria</em> spp. and the predatory
 priapulid worm <em>Halicryptus</em> <em>spinulosus
 </em>(referred hereafter to their genera). Animals were sieved from the
 sediment, placed in
 aerated filtered seawater for 24 hours in order to facilitate gut
 evacuation, keeping <em>Halicryptus</em> separate. <em>Macoma</em> was separated from their shell and all animals were frozen at -80°C. For FA and SI analysis, samples were freeze-dried at -120°C (one replicate for seston and sediment, three for each species) and pulverized. Further details of sample collection, and FA and SI analysis are provided in the Supplementary Information. FAs were grouped into major groups: Saturated FAs (SAFAs), Monounsaturated FAs (MUFAs), Polyunsaturated FAs (PUFAs, including EFAs and their precursors Alpha-linolenic acid, ALA and Linoleic acid, LIN), and Bacterial FAs (BAFAs); a full list of individual FAs analyzed is provided in Table S1. 
description: Excel R