Variability in the supply of essential fatty acids and food-web linkages through red drum egg boons

Abstract Availability of essential fatty acids (EFAs) in marine ecosystems can have important consequences for organisms, populations, and communities. EFAs are highly concentrated in eggs of marine animals, and coordinated spawning creates superabundances of these nutritional resources in spatially and temporally discrete patches, known as egg boons. The objective of this study was to document the magnitude of temporal and geographic variability in the three dominant EFAs in egg boons (docosahexaenoic acid, DHA; eicosapentaenoic acid, EPA; and arachidonic acid, ARA) and to assess the changes in trophic linkages that are responsible for that variability using 14 diet-related fatty acids and 5 trophic biomarkers in egg boons of red drum (Sciaenops ocellatus). Egg boons were sampled from sites in the eastern and western Gulf of Mexico (Florida and Texas). In Florida samples, EPA was the most variable EFA; its highest annual mean was 1.5 times its lowest annual mean. The corresponding values for DHA and ARA were 1.3 and 1.2. There was even more variability in Texas samples. EPA levels varied 1.9 times between the highest and lowest annual means, while the range of variation in ARA and DHA was equal or slightly lower (1.9- and 1.7-fold). The observed differences in egg boon composition represent a change in the availability of EFAs to egg consumers by as much as 19%–89% between years. Patterns of variation in diet-related fatty acids and trophic biomarkers were the same at both sites and were congruent with differences in fatty acid compositions among various species of crustaceans and fishes. Thus, availability of EFAs to egg boon consumers was driven by shifts in the proportions of crabs and fishes in the diet of adult red drum during the summer before their autumn spawning. In this way, factors that have large-scale impacts on populations of crabs and fishes can alter the flow of EFAs to lower trophic levels (planktivores) in marine communities. This study also demonstrates that shifts in fatty acid composition of egg boons can be used as an ecosystem indicator of changes in prey availability and food-web linkages.