Terrestrial and aquatic food webs are often linked by the movement of energy, materials, and organisms across ecosystem boundaries. Lakes and rivers receive substantial inputs from their surrounding catchments, with cross-ecosystem carbon flows similar to the magnitude of internal fluxes. However, differences in the quantity and quality of subsidies, as well as the location and timing of their input, can significantly impact how terrestrial subsidies drive benthic production. Aquatic ecosystem dynamics in turn drive the production of aquatic macroinvertebrates that can emerge into terrestrial ecosystems as winged adults. Aquatic subsidies to terrestrial systems are generally much smaller than internal fluxes. However, aquatic subsidies can provide potentially limiting resources to terrestrial ecosystems due to their high concentrations of long-chain polyunsaturated fatty acids and trace elements, which can have outsized effects on riparian consumer behavior and fitness. Aquatic subsidies also can have a “dark side,” as they are capable of transporting trace metals and contaminants that can become concentrated in aquatic ecosystems to riparian consumers. The quantity and quality of aquatic subsidies is likely influenced by interactions between aquatic ecosystem dynamics and food web structure. Research on terrestrial and aquatic resource subsidies is often decoupled from one another, which has precluded development of a comprehensive understanding of material fluxes across aquatic-terrestrial boundaries. Furthermore, much of this work has been done in temperate regions, in which seasonal drivers play an important role; however, much less work has been done in tropical river systems, which may function in ways distinct from temperate systems due to differences in seasonality, or in ways that have been lost from many anthropogenically impacted temperate systems. In this session, we will bring together scientists studying aquatic and terrestrial subsidies in both temperate and tropical ecosystems to discuss how quantity and quality of resource subsidies influence ecosystem function and the occurrence of reciprocal subsidies, and how the magnitude and composition of resource subsidies varies across landscapes.
Lead Organizer: Amanda Subalusky, University of Florida (asubalusky@gmail.com)
Co-organizers:
Cornelia Twining, EAWAG - Swiss Federal Institute of Aquatic Science and Technology (cornelia.twining@gmail.com)
Therese Frauendorf, Colgate University (tfrauendorf@colgate.edu)
Tarn Preet Parmar, University of Konstanz (tarn-preet.parmar@uni-konstanz.de)
Carmen Kowarik, EAWAG - Swiss Federal Institute of Aquatic Science and Technology (carmen.kowarik@eawag.ch)
Presentations
05:00 PM
Alteration of resource quality and pulse dynamics influences aquatic ecosystems (5455)
Primary Presenter: Charlie Sarran, Université de Montréal (charlie.sarran@umontreal.ca)
Aquatic ecosystems are deeply connected to riparian environments. It is now known that these two systems are linked by flows of energy and matter – called cross-ecosystem subsidies – possibly occurring through pulsed perturbations events. Terrestrial pulses can generate many changes over lentic systems, such as the benthic-pelagic coupling – and variations in intrinsic parameters of these perturbations can lead to different responses from the recipient ecosystem. However, a knowledge gap remains in the understanding of the consequences of the variations of allochthonous pulses on the structure and the functioning of lentic aquatic ecosystems. This presentation will show the advances of the experimental study in aquatic mesocosms conducted in 2022 at the Laurentian Biological Station – exploring the differential effects of the alteration of 1) allochthonous resource quality (i.e. subsidies) and 2) pulse dynamics (i.e. abruptness) on different parameters of aquatic mesocosms, including physicochemical parameters, zooplankton, and macroinvertebrates communities.
05:15 PM
TROPHIC ECOLOGY OF ANURANS IN A SOUTH AFRICAN RIVER IDENTIFIES POTENTIAL EXPORTERS OF AQUATIC NUTRIENTS (5321)
Primary Presenter: Nicole Richoux, Rhodes University (n.richoux@ru.ac.za)
Anurans can represent important trophic pathways between water and land owing to their amphibious nature and biphasic life cycles, but there remains much to learn about the feeding dynamics of different species. We investigated the feeding ecology of four co-occurring anurans in a small South African river using several approaches (stomach content, stable isotope and fatty acid analyses), with the aims of determining diet compositions and the relative contributions of aquatic- versus terrestrial-derived resources to the anuran diets. We collected anurans in 2012 and 2013 at an upstream and a downstream site in the river. The proportions of aquatic-derived fatty acids were generally higher in tadpoles and a predominantly aquatic species of frog (Xenopus laevis), lower in the semi-aquatic species (Strongylopus grayii and Amietia fuscigula), and lowest in a toad that favours terrestrial habitats (Sclerophyrs capensis) at both sites. Stomach analysis of adult specimens confirmed that X. laevis had recently ingested only aquatic prey, S. grayii and A. fuscigula recently ingested combinations of aquatic and terrestrial prey, and Sc. capensis ingested primarily terrestrial prey. Stable isotope models indicated some differential contributions of aquatic vs terrestrial resources to the species at the different sites. Our results have important implications on the transfer of physiologically-important nutrients from water to land, as tadpoles and adult frogs are consumed by a variety of terrestrial predators.
05:30 PM
EFFECTS OF FORESTED BUFFERS ON STREAM–RIPARIAN METAECOSYSTEMS: IMPORTANCE OF EMERGED AQUATIC INSECTS FOR RIPARIAN SPIDER ASSEMBLAGES (4956)
Primary Presenter: Richard Johnson, Swedish University of Agricultural Sciences (richard.johnson@slu.se)
Stream-riparian meta-ecosystems are connected by resource flows of materials, organisms and energy, with emerged aquatic insects acknowledged as an integral component of riparian food webs. Agricultural land use is a primary cause for lost or impaired connectivity in stream-riparian systems. Here we assessed the role of forested buffers in mitigating the effects of agricultural land use on streams and riparian (spider) food webs using a paired-reach approach, with upstream reaches lacking woody riparian vegetation and downstream reaches having well-developed forested buffers. Richness of emerged insects captured on sticky traps differed between reach types and with season. Dipterans (Chironomidae) and beetles were more abundant at unbuffered reaches with emergence peaks in spring, whilst disturbance sensitive EPT taxa were more abundant at forested reaches and had emergence peaks in summer and autumn. Spider assemblages correlated with both riparian characteristics and the emergence of aquatic insects. Partial redundancy analysis showed that variation in spider composition was explained by aquatic insect composition and emergence. Results of fatty acid analyses and prey DNA from riparian spiders corroborated the significance of emerged aquatic insects for terrestrial (spider) communities, underpinning the importance of forested buffers for biodiversity and cross-ecosystem connectivity in modified landscapes.
05:45 PM
INFLUENCE OF STREAM INTERMITTENCY ON PUFA TRANSFER TO ALPINE RIPARIAN SPIDERS (4757)
Primary Presenter: Carmen Kowarik, eawag (carmen.kowarik@eawag.ch)
An increasing number of streams are becoming intermittent due to global warming and water abstraction. An important ecosystem service likely affected by this increasing intermittency is the export of resources rich in omega-3 polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA), from aquatic to terrestrial systems. Here, we investigated how flow intermittency affected EPA transfer to riparian spiders along 9 headwater streams of an alpine catchment (Val Roseg, Switzerland) with different degrees of intermittency. We used fatty acid analysis to test if there were differences in fatty acid content in spiders sampled along streams varying in degree of intermittency. In addition, we used compound-specific isotope analysis (2H-CSIA) to determine the origin of different fatty acids present in spiders. We found a higher content of the omega-3 fatty acids EPA, stearidonic acid (SDA) and docosahexaenoic acid (DHA), but a lower α-linolenic acid (ALA) content in spiders collected along perennial streams compared to periodically intermittent streams. However, spiders from seasonally drying streams showed similar fatty acid mass fractions as spiders from perennial streams. d2H values indicated that fatty acid sources also differed between streams varying in intermittency. Our results suggest that stream intermittency likely affects subsidy transfers from aquatic to riparian ecosystems, indicating far-reaching consequences for riparian communities especially in resource poor alpine environments, but also lower elevation fluvial networks.
06:00 PM
The Penetration of Essential Aquatic Nutrients into Adjacent Terrestrial Habitats (6051)
Primary Presenter: Tarn Preet Parmar, Brandenburgische Technische Universität Cottbus-Senftenberg (tarnpreet.parmar@gmail.com)
Emergent aquatic insects represent a key vector for aquatic-based nutrients to penetrate adjacent terrestrial food webs. Long-chain polyunsaturated fatty acids (LC-PUFA) have been a recent interest when quantifying the cross-ecosystem transfer of dietary nutrients. Aquatic insects contain higher LC-PUFA, such as eicosapentaenoic acid (EPA), arachidonic acid (ARA), and docosahexaenoic acid (DHA), than terrestrial insects. The importance of LC-PUFA has been demonstrated for several riparian predators (e.g., birds, bats, and spiders), thus the penetration of aquatic insects into terrestrial habitats strongly dictates the availability of these LC-PUFA in terrestrial food webs. We deployed Malaise/window hybrid traps at 8 different distances (ranging from 1 to 1000 m) from the lake shore in two different terrestrial habitats (i.e., forested and meadows) to estimate the terrestrial penetration of aquatic biomass and LC-PUFA (i.e., EPA, ARA, DHA). Terrestrial insect biomass generally did not differ with distance from the lake, but aquatic biomass decreased with distance from lake shore in both habitats at differing rates. Our dataset provides order-level aquatic and terrestrial insect abundance along a distance gradient and demonstrates that physiologically-important aquatic-derived LC-PUFA are only available for terrestrial predators within a few meters of a lakeshore, highlighting the importance of riparian zones for terrestrial food webs.
06:15 PM
COUPLING BETWEEN FATTY ACIDS AND AMINO ACIDS TROPHIC TRANSFER IN SPIDERS ALONG AN AQUATIC-TERRESTRIAL GRADIENT (6113)
Primary Presenter: Maja Ilić, Federal Institute for Forest, Snow and Landscape Research (WSL) (maja.ilic.bio@gmail.com)
Emerging aquatic insects are often rich in essential polyunsaturated fatty acids (PUFAs), which are important for a variety of physiological functions in animals, including growth, reproduction, and immunity efficiency. Furthermore, these insects with aquatic larval stages represent a highly nutritious food source for riparian and terrestrial predators, such as spiders, and play an important role for the linkage and the resource flow between aquatic and terrestrial systems. In this study, we investigate the coupling between the fatty acids (FA) and amino acids (AA) trophic transfer using compound-specific stable isotope analysis (CSIA) and mixing models. We discuss (dis)similarities, as well as (dis)advantages of the different approaches used to quantify the aquatic resource dependency of ground-dwelling (active hunters) and web-building spiders collected along a riparian-terrestrial gradient (0 – 100 m distance from a stream). While mixing models using MixSIAR based on CSIA-AA data of essential AAs (Ile, Leu, Phe and Val) revealed clear results (i.e., stronger aquatic resource dependency of ground-dwelling spiders), the results from mixing models based on fatty acids were less robust, and their interpretation requires more caution. We here propose the use of both CSIA-AA and FA simultaneously to achieve the most robust results and to describe the organic matter fluxes in food webs most accurately, and additionally allow conclusions on dietary preferences of consumers and the dietary quality of their prey.
SS051 Untangling Food Web and Ecosystem Effects of Reciprocal Subsidies
Description
Time: 5:00 PM
Date: 5/6/2023
Room: Sala Santa Catalina