Implications of the meteoric rise in atmospheric CO2 concentrations on natural and human systems are far reaching. It is imperative that CO2 emissions are reduced, but even the most optimistic scenarios for future emissions indicate mitigation will be required (e.g. carbon capture) and that the natural ecosystems and food supply systems critical to human wellbeing will be impacted. Global macroalgal and macrophyte health and resilience is central to a healthy planet. Macroalgae and macrophytes are at the nexus of the climate crisis as they are both vulnerable to climate change and have roles to play in delivering a sustainable future. Not only are they foundational species in the aquatic environment, oxygenating surface waters, providing habitat structure and fueling higher trophic level organisms, but they also provide humans with ecosystem services including carbon sequestration/removal, sources of human nutrition, animal feed, and biofuels. However, macroalgae and macrophytes are particularly vulnerable to climate change and environmental degradation. For example, crustose coralline and fleshy macroalgal species alike are distributed across the globe from the tropics through the high Arctic, including some of the fastest changing ecosystems on earth. As aquatic environments change, the fate of these communities, the ecosystems they support, and the carbon they sequester is poorly understood. Plants and algae can also tell us about past climate and their own history, to offer clues about our shared future. For example, past environmental variability (e.g., in temperature and sea-ice extent) can be reconstructed using macroalgae by investigating the growth and chemical makeup of long-lived marine coralline algae. The variations in these species’ distributions and physiologies through time as climate changed also offer insight into how they may respond to ongoing climate change. This session welcomes research across all macroalgae (including fleshy and coralline species) and macrophyte species, from all geographies (tropical to Arctic and marine to fresh water), and all perspectives concerning macroalgae and macrophytes in a changing world. Examples of topics welcomed include (i) the effects of environmental variability on macroalgal and macrophyte growth and biogeography, (ii) implications of change on coralline algal growth for reconstruction of the environment, (iii) macroalgal and macrophyte cultivation and associated applications – aquaculture, human consumption, biofuels, animal feed, and carbon dioxide reduction/sequestration (CDR) (iv) remote sensing, monitoring, and mapping of productivity. We hope this session will improve collaboration across disciplines within and between the macroalgal and macrophyte research community and accelerate our ability to understand, protect, and harness aquatic macro-photosynthesizers as we seek to build the good, sustainable Anthropocene.
Lead Organizer: Jessica Gould, Northeastern University (jlagould@gmail.com)
Co-organizers:
Natasha Leclerc, University of Toronto (natasha.leclerc@mail.utoronto.ca)
Tom Bell, WHOI (tbell@whoi.edu)
Aron Stubbins, Northeastern University (a.stubbins@northeastern.edu)
Presentations
04:00 PM
ASSESSING MACROALGAL ORGANIC CARBON RELEASE AND SUBSEQUENT BIO- AND PHOTO-DEGRADABILITY (7940)
Primary Presenter: Jessica Gould, Northeastern University (jlagould@gmail.com)
As macroalgae grow, they release C, primarily as dissolved organic carbon (DOC). In natural systems, most macroalgal C (MA-C) sequestration is hypothesized to occur when DOC is exported into deeper waters. Thus, MA-C sequestration is a function of MA-DOC release and the resistance of MA-DOC to bio- and photo-degradation. Current estimates of MA-C sequestration efficiency rely on scarce data on 1) rates of DOC release as macroalgae grow, and 2) how rapidly MA-DOC is remineralized back to CO2, with most of the latter studies focusing only on biodegradation. Thus, it is unclear whether bio- and photo-degradation processes acting on MA-DOC in the ocean are slow enough to allow DOC to persist long enough to be exported and sequestered below the mixed layer. Here we present an accounting of MA-DOC release during ca. month-long laboratory growth experiments and during subsequent bio- and photo-degradation experiments using 7 common macroalgal species: Ascophyllum nodosum, Fucus distichus, Ulva lactuca, Gracilaria hayi, Gracilaria parvispora, Spermothamnion species, and Laminaria saccharina. We present DOC release and degradation kinetics in the context of natural macroalgal OC cycling and report on the potential recalcitrant fraction of DOC from each species that might have the capacity to contribute to C sequestration.
04:15 PM
The Release and Bioavailability of Macroalgal Derived Dissolved Organic Carbon (8189)
Primary Presenter: Cassandra Vongrej, Northeastern University (vongrej.c@northeastern.edu)
Macroalgal growth (net primary production; NPP) occurs at a high areal rate compared to terrestrial ecosystems and other vegetated coastal habitats. This study aims to quantify the amount and rates of dissolved organic carbon (DOC) produced by macroalgae during growth and the subsequent biolability of this DOC in the surface ocean environment. During growth, macroalgae sequester C as biomass but also releasing some as DOC. The fraction of this DOC that persists in the environment long enough to be sequestered in deeper ocean waters is poorly defined. Here, sugar kelp (Laminaria saccharina), rockweed (Fucus distichus and Ascophyllum nodosum), Ulva lactuca, Gracilaria hayi, Gracilaria parvispora, and a Spermothamnion species were grown and analyzed for DOC release and subsequent resistance of the DOC to biodegradation. Results provide knowledge on algal C cycling, helping to elucidate the potential role of macroalgae in C sequestration and broader biogeochemical cycles.
04:30 PM
Evaluation of recalcitrant dissolved organic matter production during degradation of commercially important Northwestern Atlantic kelp species (8351)
Primary Presenter: Sarah Douglas, Bigelow Laboratory for Ocean Sciences (sarahvdouglas@gmail.com)
Macroalgal aquaculture is a globally important commercial industry, with increasing focus on farmed kelp as a marine carbon dioxide reduction (mCDR) strategy. Sinking kelp offshore could potentially sequester carbon in the deep sea, however this approach has several drawbacks, including unintended ecological consequences for the deep sea benthos. Alternatively, while nearshore sinking of kelp exposes it to higher remineralization rates, this approach mimics the higher organic matter regime of coastal ecosystems and is more feasible on a local scale. In Maine, up to 20% of farmed kelp is made up of less valuable biproduct (holdfasts/biofouled blades). To evaluate this mCDR potential, we incubated blades and holdfasts from Saccharina angustissima and Saccharina latissima under dark aerobic conditions at 19 ºC for 90 days to isolate microbial processing. Degrading kelp releases both dissolved and particulate organic matter (DOM and POM), which can contribute to recalcitrant carbon pools. Initial analysis of DOM optical properties showed a logarithmic increase of cDOM, with production and microbial degradation rates stabilizing after 30 days. Further analysis of fluorescent DOM and macromolecular composition is underway. The spectral slope ratio SR (S275-395:S350-400), an inverse proxy for relative molecular weight (MW), rapidly increased to a maximum by day 17. This indicates that high MW compounds released during initial senescence were transformed into lower MW, the persistence of which suggests production of recalcitrant DOM under coastal conditions.
04:45 PM
Applying coralline algal sclerochronology to Arctic fishery implications: Geochemical evidence of primary productivity variability over 200 years (8022)
Primary Presenter: Natasha Leclerc, Memorial University of Newfoundland (natasha.leclerc@mail.utoronto.ca)
The Arctic is one of the regions most affected by climate change, globally. Recent hydro-ecological studies have pointed to increasing primary productivity due to greater riverine or terrestrial nutrient runoff and solar irradiance as a result of warming temperatures and sea ice loss. This has significant implications for Arctic marine food webs and fisheries management, as any shift in primary producers can cause ecological cascades within the Arctic ecosystem. However, there is a lack of highly resolved long-term instrumental data from many Arctic regions, limiting our ability to disentangle hydro-ecological dynamics and track its inter-annual variability prior to the satellite record (1979-present). Here, we present annually-resolved geochemical data – barium/calcium and stable carbon isotope ratios (Ba/Ca and δ13C) – from the calcifying coralline red algae, Clathromorphum compactum, collected in Lancaster Sound, Nunavut, Canada, suggesting larger and longer-lasting phytoplankton blooms over the last 30 years. Through this proxy data, we also demonstrate the variability of primary productivity over the last 200 years and its links to atmospheric, cryospheric and oceanographic trends. We compare these data to those derived from C. compactum specimens collected in other regions including glacially impacted sites in the Canadian Arctic Archipelago and Svalbard, as well as subarctic sites in the Labrador Sea. The contrasting results from these different Arctic regions reveal geographic variability in in barium and carbon dynamics in coastal ocean waters due to nearness to freshwater and glacier runoff. We conclude by discussing the implications of these findings for fisheries management and Indigenous livelihoods.
05:00 PM
SS33B - Macroalgae and Macrophytes in a Changing World
Description
Time: 4:00 PM
Date: 6/6/2024
Room: Meeting Room KL