Limited seasonal variation in food quality and foodweb structure in an Adirondack stream : insights from fatty acids

Abstract

Together terrestrial and aquatic resources fuel stream food webs. Past work suggests that both terrestrial and aquatic resources can vary in multiple metrics of food quality, such as elemental, macronutrient, and fatty acid (FA) composition, and that resource quality may vary seasonally in temperate systems. However, studies on FA composition in stream food webs, especially those quantifying seasonal patterns, remain scarce. We documented foodweb structure and examined FA composition as a metric of food quality in an Adirondack stream throughout the temperate growing season to understand from where stream consumers derived energy, how food quality varied among resources, and whether these patterns shifted seasonally. In spite of major seasonal shifts in environmental factors, such as light availability and temperature, we found limited seasonal variation in the FA composition of basal resources and macroinvertebrates. Instead, we found consistent differences in FA composition between aquatic and terrestrial basal resources and between macroinvertebrate functional feeding groups. Foodweb structure also was consistent throughout the growing season, and macroinvertebrates and fish relied on a mix of terrestrial and aquatic resources. Our results suggest that stream consumers in heavily forested reaches rely upon low-quality terrestrial resources supplemented with higher-quality aquatic resources throughout the year.