Biology subjects

Hessing-Lewis, M.

Publications and source records attributed to Hessing-Lewis, M..

5 recordsLinked to original sources

bioRxiv2024

A blueprint for national assessments of the blue carbon capacity of kelp forests applied to Canadas coastline

Kelp forests offer substantial carbon fixation, with the potential to contribute to natural climate solutions (NCS). However, to be included in national NCS inventories, governments must first quantify the kelp-derived carbon stocks and fluxes leading to carbon sequestration. Here, we present a blueprint for assessing the national carbon sequestration capacity of kelp forests in which data synthesis and Bayesian hierarchical modelling enable estimates of kelp forest carbon production, storage, and export capacity from limited data. Applying this blueprint to Canadas extensive coastline, we find kelp forests store an estimated 1.4 Tg C in short-term biomass and produce 3.1 Tg C yr-1 with modest carbon fluxes to the deep ocean. Arctic kelps had the highest carbon stocks and production capacity, while Pacific kelps had greater carbon fluxes overall due to their higher productivity and export rates. Our transparent, reproducible blueprint represents an important step towards accurate carbon accounting for kelp forests.

ecology↗

bioRxiv2023

Climate benefits of seaweed farming: estimating regional carbon emission and sequestration pathways

Seaweed farming is widely promoted as an approach to mitigating climate change despite limited data on carbon removal pathways and uncertainty around benefits and risks at operational scales. We explored the feasibility of seaweed farms to contribute to atmospheric CO2 reduction in coastal British Columbia, Canada, a region identified as highly suitable for seaweed farming. Using a place-based, quantitative model, we examined five scenarios spanning a range of industry development. Our intermediate growth scenario sequestered or avoided 0.20 Tg CO2e / year, while our most ambitious scenario (with more cultivation and higher production rates) yielded a reduction of 8.2 Tg CO2e /year, equivalent to 0.3% and 13% of annual greenhouse gas emissions in BC, respectively. Across all scenarios, climate benefits depended on seaweed-based products replacing more emissions-intensive products. Marine sequestration was relatively inefficient in comparison, although production rates and avoided emissions are key uncertainties prioritized for future research. Our results show how seaweed farming could contribute to Canadas climate goals, and our model illustrates how farmers, regulators, and researchers could accurately quantify the climate benefits of seaweed farming in local contexts.

ecology↗

bioRxiv2023

Quantifying marine larval dispersal to assess MPA network connectivity and inform future national and transboundary planning efforts

A Marine Protected Area (MPA) network, in which multiple reserves are designated in a region, can promote the protection of biodiversity across space. To be effective as a network, the design must consider whether MPAs are likely to be connected through the movement of individuals of species of interest. Additionally, network design may explicitly incorporate design features that promote biodiversity in unprotected habitats through the dispersal or spillover of multiple species. Patterns of dispersal and the ability of MPAs to function as an interacting network, however, are difficult to estimate at broad and transboundary spatial scales, and therefore connectivity is often not fully integrated in the design and assessment of MPA networks. Here, we model the dispersal of multiple nearshore species to estimate the potential connectivity of the existing MPAs in British Columbia, Canada, including connections to MPAs in the United States by simulating dispersal using a biophysical model with regional oceanographic currents. We found that MPAs in BC potentially meet connectivity design criteria for nearshore invertebrate species: the majority of MPAs (65-90%) are likely to exchange individuals (i.e. functional connectivity) and support persistent metapopulations, and more than half the unprotected coast (55-85%) receives a large proportion of the larvae produced in MPAs. Furthermore, we found that species dispersal abilities and the level of exposure of an MPA to open ocean can predict dispersal distance when we account for the random effects of dispersal location and season. Therefore, future predictions of connectivity are possible based on these core biological and physical attributes, without running new simulations. Together, these analyses provide a robust and novel assessment of multi-species connectivity that can support the design of new MPAs with transboundary connectivity on the northwest coast of North America.

ecology↗

bioRxiv2023

Temperature and food chain length, but not latitude, explain region-specific kelp forest responses to an unprecedented heatwave

Kelp forests are among the most abundant coastal marine habitats but are vulnerable to the impacts of climate change. Between 2014 and 2016, an unprecedented heatwave and associated changes in trophic dynamics threatened kelp forests across the Northeast Pacific, with impacts documented from Mexico to Alaska. However, responses have varied substantially and remain poorly characterized across large stretches of coast, especially British Columbia (B.C.), which represents a significant percentage of the range of floating kelp species in the Northeast Pacific. Here, we explore variation in floating kelp (Macrocystis, Nereocystis) persistence pre- and post-heatwave across a >675 km latitudinal gradient, asking whether B.C. kelp forests are of conservation concern. We assembled and analyzed available quantitative kelp data, comparing snapshots of kelp extent before (1994 - 2007) and after (2018 - 2021) the heatwave in 11 regions spanning a range of temperature and sea otter-occupancy statuses, and contextualizing these with time series analyses, where available (n = 7 regions). We provide strong evidence that kelp forests have declined in many regions but with evidence of refugia at both local and regional scales. Kelp forest persistence was negatively correlated with summer sea temperatures in southern B.C., where temperatures varied by ~6{degrees}C across sites, at times exceeding species thermal tolerances. Kelp dynamics in northern regions appeared instead to be modulated by top-down control by urchins and sea otters. Our results demonstrate that B.C.s kelp forest have been substantially reduced in recent years but that regional and local-scale factors influence the resilience of forests to large-scale perturbations.

ecology↗

bioRxiv2018

Spatial variation in exploited metapopulations obscures risk of collapse

Unanticipated declines among exploited species have commonly occurred despite harvests that appeared sustainable prior to collapse. This is particularly true in the oceans where spatial scales of management are often mismatched with spatially complex metapopulations. We explore causes, consequences and potential solutions for spatial mismatches in harvested metapopulations in three ways. First, we generate novel theory illustrating when and how harvesting metapopulations increases spatial variability and in turn masks local scale volatility. Second, we illustrate why spatial variability in harvested metapopulations leads to negative consequences using an empirical example of a Pacific herring metapopulation. Finally, we construct a numerical management strategy evaluation model to identify and highlight potential solutions for mismatches in spatial scale and spatial variability. Our results highlight that spatial complexity can promote stability at large scales, however ignoring spatial complexity produces cryptic and negative consequences for people and animals that interact with resources at small scales. Harvesting metapopulations magnifies spatial variability, which creates discrepancies between regional and local trends while increasing risk of local population collapses. Such effects asymmetrically impact locally constrained fishers and predators, which are more exposed to risks of localized collapses. Importantly, we show that dynamically optimizing harvest can minimize local risk without sacrificing yield. Thus, multiple nested scales of management may be necessary to avoid cryptic collapses in metapopulations and the ensuing ecological, social and economic consequences.

ecology↗