Aquatic ecosystems face unprecedented challenges due to the rapid pace of global change, resulting in changes in water temperature, increasing eutrophication, and shifting species assemblages. These drivers are altering ecosystems worldwide, impacting their structure, dynamics, and function. Food webs offer a powerful framework to better understand changes within aquatic ecosystems, as trophic interactions and food web structure heavily informs ecosystem structure, function, and long-term dynamics. However, disturbances such as changes to the native biotic community, shifts in climate patterns, and invasive species can reshape food webs, creating novel dynamics and trophic interactions. These changes can be either positive, negative, or benign for ecosystem health and function. For instance, the introduction of an aquatic zooplanktivore may outcompete native zooplanktivores, leading to a proliferation of phytoplankton. Conversely, the reintroduction of a native species could lead to the extirpation of a prolific invasive species. In this session, our aim is to synthesize our current understanding of food web ecology in the context of ongoing global change. We are particularly interested in studies that examine how food webs have been reshaped over time following discrete or continuous disturbances. We encourage studies that advance our understanding of the interplay between food web structure and ecosystem function and dynamics. This includes exploring concepts like trophic cascades, top-down and bottom-up control, species removals and(or) additions, as well as temporal and spatial variations in food web dynamics. Further, we encourage discussion related to adapting to food web shifts. Understanding how food webs change in response to global drivers is critical for enhancing our fundamental knowledge of aquatic ecosystems and developing effective environmental policies and management practices. Indeed, in these trying times of rapid non-linear and dynamic change, there is a need for more ‘food web thinking’.
Lead Organizer: Tyler Butts, University of Wisconsin-Madison (tjbutts@wisc.edu)
Co-organizers:
Holly Embke, United States Geological Survey (hembke@usgs.gov)
Joseph Mrnak, University of Wisconsin-Madison (mrnak@wisc.edu)
Presentations
09:00 AM
Asymmetric Global Change Rewiring (7907)
Primary Presenter: Charlotte Ward, University of Guelph (cward@uoguelph.ca)
Human pressures related to ongoing global change, such as climate change, pollution, species introductions, and land-use changes, are altering the underlying structure of ecosystems, with consequences for their functioning that we do not yet fully understand. We show that human pressures interact with the earth's habitat mosaic differentially, driving asymmetric responses in the underlying food web - a phenomenon referred to as asymmetric global change rewiring. Ecological theory lays a path for conceptualizing how asymmetric global change rewiring alters the structure, function, and resilience of ecosystems. Key examples and a targeted review of consumer habitat coupling in nature show that asymmetric global change rewiring is observed across different human pressures and ecosystem types. By following changes in the underlying structure of food webs, ecosystem managers may identify threats associated with asymmetric global change rewiring and mitigate losses in the ecosystem functions that society relies on.
09:15 AM
HOW HAVE MULTIPLE INVASIONS ALTERED FOOD WEB INTERACTIONS AND STRUCTURE IN A EUTROPHIC LAKE OVER ALMOST 25 YEARS? (7774)
Primary Presenter: Tyler Butts, University of Wisconsin-Madison (tyler.james.butts@gmail.com)
Invasive species have well-documented impacts on food web structure and water quality. However, predicting the interactive effects of multiple invasive species and their long-term impact on food web structure is challenging. Lake Mendota, WI experienced two successive invasions over the past 25 years: spiny water flea (Bythotrephes longimanus) was detected in 2009, followed by zebra mussels (Dreissena polymorpha) in 2015. Short-term investigations following each invasion revealed significant impacts on water quality and ecological interactions in the lower food web. Understanding how aquatic ecosystems respond to multiple interacting drivers through time is critically important yet remains difficult to quantify, especially for lower food web interactions involving bacterioplankton (microbes), phytoplankton, and zooplankton. Leveraging a nearly 25-year record of zooplankton and phytoplankton dynamics, along with a 19-year record of microbial data, we synthesize changes in species phenology and food web structure within and across each invasion regime. We highlight how zebra mussels and spiny water flea altered diatom community phenology in addition to driver-response relationships between nutrient load and several water quality metrics. We also show how successive invasions altered early season phytoplankton community structure and zooplankton-phytoplankton-microbial community trajectories. Understanding these complex interactions is crucial for effective conservation and management strategies in the face of growing invasive species threats.
09:30 AM
TO WHAT EXTENT DOES SELECTIVE DEFORESTATION ALTER MANGROVE TROPHODYNAMICS? A CASE STUDY FROM GHANA, WEST AFRICA. (7717)
Primary Presenter: Andrew Sweetman, Scottish Association for Marine Science (Andrew.Sweetman@sams.ac.uk)
Mangrove forests are highly important ecosystems whose functioning is threatened by numerous anthropogenic activities. In many coastal regions, mangrove wood is used as a source of timer and fuel, but the impact of environmental changes linked to this pervasive long-term selective deforestation on ecosystem functioning is poorly understood. Mangroves act as ecosystem engineers, with their complex root systems trapping allochthonous materials and building up carbon-rich sediments, as well as forming a nursery and foraging habitat for many species. Their degradation through selective deforestation could reduce the diversity of basal resources and energy flow pathways within estuarine food webs, thereby decreasing trophic diversity and resilience. To assess the extent to which mangrove degradation affects trophodynamics, we conducted 13C, 15N, and 34S stable isotope analyses on samples from a range of basal food sources and consumers (fish and crustaceans) at estuarine sites along the coast of Ghana. Our results indicate that the selective deforestation of mangroves may degrade trophic ecosystem functioning, as evidenced by a greater prevalence of generalist feeding strategies, a rise in the extent of dietary niche overlap between groups, and lower trophic diversity at sites with increasingly less mangrove cover. We will discuss these results in light of the interactions between trophic structure and ecosystem functioning and stability.
09:45 AM
Temporal dynamics of ecological networks: Deciphering changes in cladoceran assemblages over the past ~150 years in response to land-use development (7851)
Primary Presenter: Jennifer Pham, McGill University (jennifer.pham@mail.mcgill.ca)
Ecological networks serve as tools to infer community stability. Within these networks, species are depicted as nodes, interconnected by links representing observed or potential ecological interactions. Among the metrics used to evaluate network stability, connectance – the proportion of realized links over possible links – emerged as a key indicator to examine the impacts of global change on aquatic communities. Despite its significance, many gaps remain in network ecology including a lack of studies exploring patterns over extensive spatio-temporal scales. Paleolimnology can bridge this gap – as biological, chemical, and physical proxies preserved in sediments infer past environmental and ecological lake conditions. We focused on cladocerans, which leave subfossils in the sediment record and play a central role in lake food webs, to quantify how aquatic networks have altered between pre-industrial and modern times. Based on the correlation of taxa relative abundances across 101 Canadian lakes, we developed networks quantifying the potential interactions for different time periods and watershed land-use classes. We observed a 10% decline in connectance from pre-industrial to modern times in high human-impacted lakes, while networks generated from low impacted lakes remain unchanged. These patterns were verified by comparing observed networks with random network permutations. With this first Canada-wide study of zooplankton networks, we are developing powerful new insights into how aquatic ecosystem stability has changed over a period of accelerated anthropogenic change.
10:00 AM
ASSESSING MICROBIAL NITROGEN CYCLING CAPACITIES IN MATS OF INVASIVE D. GEMINATA IN NORTH SHORE STREAMS AND NEARSHORE LAKE SUPERIOR (8234)
Primary Presenter: Sarah Clauss, University of Minnesota-Duluth (sarahkclauss@gmail.com)
Didymosphenia geminata (didymo) is an invasive and ecologically destructive nuisance alga whose spread has commonly been associated with the recreational fishing industry. Didymo was first identified in Lake Superior in the 1960s and is likely native to the lake. It has since been found in the Poplar River (in 2018) and eight other rivers along Minnesota’s North Shore. The spread of didymo into streams has two probable causes: aggressive colonization by invasive populations or changing environmental conditions allowing native Lake Superior populations to expand. This study examines shifts in microbial community composition and functioning in the presence of didymo mats, with a particular focus on nutrient cycling. Periphyton samples were collected from twenty-seven didymo-infected stream and nearshore lake sites; microbial communities were characterized using shotgun metagenomic sequencing approaches. Genes associated with nitrogen cycling and urea utilization were identified to describe nitrogen cycling pathways within didymo mats. Despite fully oxic river waters, genes associated with oxidative nitrogen pathways (including nitrogen fixation and nitrification) were either scarce or not present in mats across the samples. However, genes associated with reductive pathways and urea utilization were more abundant and nearly ubiquitous. This suggests that didymo mats create anoxic microenvironments that could serve as sources of nitrous oxide, a potent greenhouse gas. Finally, urea, either from fertilizers or other organisms, may serve as an important source of nitrogen.
10:15 AM
Hydroacoustics describe the role of food web structure as a modifier of Lake Trout (Salvelinus namaycush) activity (7944)
Primary Presenter: Alex Ross, Lakehead University (aross4831@gmail.com)
Activity is a substantial energetic cost in bioenergetic models of fish growth. However, generating accurate estimates of activity in wild, free-swimming fish is still a major challenge because of the logistical and technical constraints of acquiring these data. Using a novel stationary and up-looking hydroacoustic method across lakes ranging in food web complexity, I demonstrate that a coarse consideration of pelagic food web structure successfully predicts lake trout activity metrics (i.e., swimming speed and path), active metabolic costs, and exposure to stressful habitats. The methodological approach presented here provides a way forward for quantifying in situ fine-scale behaviour of free-swimming fish, while the results provide useful context to the life history and management of a cold-water predator facing an uncertain future in warming and more productive environments.
SS28A - Reshaping Aquatic Food Webs in a Changing World: Challenges and Responses to Drivers of Transformative Change
Description
Time: 9:00 AM
Date: 7/6/2024
Room: Hall of Ideas F