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Production rates reported for canopy‐forming kelps have highlighted the potential contributions of these foundational macroalgal species to carbon cycling and sequestration on a globally relevant scale. Yet, the production dynamics of many kelp species remain poorly resolved. For example, productivity estimates for the widely distributed giant kelp Macrocystis pyrifera are based on a few studies from the center of this species' range. To address this geospatial bias, we surveyed giant kelp beds in their high latitude fringe habitat in southeast Alaska to quantify foliar standing crop, growth and loss rates, and productivity of M. pyrifera and co‐occurring understory kelps Hedophyllum nigripes and Neoagarum fimbriatum. We found that giant kelp beds at the poleward edge of their range produce ~150 g C · m−2 · year−1 from a standing biomass that turns over an estimated 2.1 times per year, substantially lower rates than have been observed at lower latitudes. Although the productivity of high latitude M. pyrifera dwarfs production by associated understory kelps in both winter and summer seasons, phenological differences in growth and relative carbon and nitrogen content among the three kelp species suggests their complementary value as nutritional resources to consumers. This work represents the highest latitude consideration of M. pyrifera forest production to date, providing a valuable quantification of kelp carbon cycling in this highly seasonal environment. [ABSTRACT FROM AUTHOR]

Carbon isotope fingerprinting, or multivariate analysis using δ13C values of individual compounds, is a powerful tool in ecological studies, particularly measurements of essential amino acids (EAA δ13C). Despite the widespread application of this technique, there has been little methodological validation to determine (a) whether multivariate EAA δ13C signatures (fingerprints) of primary producer groups vary across space and time and (b) what biochemical mechanisms drive these patterns.Here, we evaluate the spatiotemporal consistency in EAA δ13C fingerprints among nearshore primary producers: Chlorophyta (Ulva sp.), Ochrophyta (kelps), particulate organic matter (POM) and phytoplankton, and Rhodophyta. We analysed 135 samples from 14 genera collected in Alaska, California and Chile. The collections included historical museum samples (1896–1980 CE) of the giant kelp, Macrocystis pyrifera. We employed canonical analysis of principal coordinates and generalized linear models (GLMs) to, respectively, characterize isotopic fingerprints and evaluate the effect of taxonomy, local upwelling regimes, ecological setting, and time on individual EAA δ13C values and associated fingerprints. We also calculated amino acid discrimination values (∆13C) to identify key biochemical pathways responsible for these patterns.We found remarkable consistency in EAA δ13C fingerprints of marine algae across space and through time. Kelps and rhodophytes exhibited statistically distinct multivariate isotopic patterns regardless of geographical location, species identity or time (kelps). In contrast, isotopic fingerprints of POM/phytoplankton and Ulva overlapped substantially. GLMs indicated that producer family, presumably due to the presence/absence of carbon concentrating mechanisms, and site locality are important determinants of individual amino acid δ13C values. Taxonomy was also a key variable for EAA δ13C fingerprints. The calculated discrimination values suggest variation in (a) metabolism of pyruvate and oxaloacetate‐derived amino acids and (b) production of storage and structural carbohydrates are responsible for taxonomic differences in isotopic fingerprints.We conclude EAA δ13C fingerprinting is a robust method for tracing the contribution of diverse primary producer taxa to coastal food webs. We show that this technique can be applied to modern and historical samples, as well as consumers collected across continental scales. The high fidelity of EAA δ13C multivariate patterns coupled with biochemical mechanisms provides a powerful framework for future studies of carbon flow across broad biogeographical and ecological contexts. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

There has been increasing interest in Alaska regarding the commercial mariculture of kelp. Kelp farming can be an economic engine for coastal communities of Alaska. Other benefits include ecosystem services, including carbon sequestration and mitigation of eutrophication. In support of this interest, several kelp species have been examined for commercial potential. In the 1980s–1990s, experiments were performed on the giant kelp Macrocystis pyrifera. Female gametophytes were exposed to varying levels of chelated iron. Relatively low levels of chelated iron (1–5 μM) stimulated the onset of oogenesis. In contrast, higher iron concentrations inhibited egg production. Outplant experiments with Macrocystis in Sitka, AK showed growth in the winter and spring, slowing down to zero growth by the end of summer. Fertilizing outplants in August allowed plants to survive and grow during the ensuing winter. Mariculture experiments with Saccharina latissima carried out near Juneau, Alaska showed exponential growth for seeded lines set out from September to March. Optimal growth occurred for outplants in October–November, with growth rates of up to 5% per day. The best growth occurred when lines were 2–3 m below the surface. Growth rates declined in May–June corresponding to a decrease in inorganic nitrogen in the water. Slower growth also resulted in severe fouling. [ABSTRACT FROM AUTHOR]

Background and Aims: Coastal Alaska contains vast kelp habitat that supports diverse marine and human communities. Over the past century, the North Pacific Ocean has undergone oceanographic and ecological regime shifts that have the potential to influence the structure and function of kelp ecosystems strongly. However, the remoteness and complexity of the glacially carved region precludes the regular monitoring efforts that would be necessary to detect such changes., Methods: To begin to fill this critical knowledge gap, we drew upon historical and modern surveys to analyse the change in spatial coverage and species composition of canopy kelp between two time points (1913 and the early 2000s to 2010s). We also incorporated decadal surveys on sea otter range expansion following complete extirpation and reintroduction to assess the influence of sea otter recovery on the spatial extent of canopy kelp., Key Results: We found increases in the spatial extent of canopy kelp throughout the Gulf of Alaska where there was coverage from both surveys. Kelp in Southcentral Alaska showed extensive recovery after the catastrophic Novarupta volcano. Kelp in Southeast Alaska showed persistence and spatial increase that closely matched increases in the range of sea otters. Observations of thermally tolerant kelp species increased more than observations of cold-adapted species between the two surveys., Conclusions: Contrary to trends observed at lower latitudes, the kelp forests that ring the Gulf of Alaska have been remarkably stable and even increased in the past century, despite oceanographic and ecosystem changes. To improve monitoring, we propose identification of sentinel kelp beds for regular monitoring to detect changes to these iconic and foundational canopy kelp species more readily., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Annals of Botany Company.)

At small spatial and temporal scales, genetic differentiation is largely controlled by constraints on gene flow, while genetic diversity across a species' distribution is shaped on longer temporal and spatial scales. We assess the hypothesis that oceanographic transport and other seascape features explain different scales of genetic structure of giant kelp, Macrocystis pyrifera. We followed a hierarchical approach to perform a microsatellite-based analysis of genetic differentiation in Macrocystis across its distribution in the northeast Pacific. We used seascape genetic approaches to identify large-scale biogeographic population clusters and investigate whether they could be explained by oceanographic transport and other environmental drivers. We then modelled population genetic differentiation within clusters as a function of oceanographic transport and other environmental factors. Five geographic clusters were identified: Alaska/Canada, central California, continental Santa Barbara, California Channel Islands and mainland southern California/Baja California peninsula. The strongest break occurred between central and southern California, with mainland Santa Barbara sites forming a transition zone between the two. Breaks between clusters corresponded approximately to previously identified biogeographic breaks, but were not solely explained by oceanographic transport. An isolation-by-environment (IBE) pattern was observed where the northern and southern Channel Islands clustered together, but not with closer mainland sites, despite the greater distance between them. The strongest environmental association with this IBE pattern was observed with light extinction coefficient, which extends suitable habitat to deeper areas. Within clusters, we found support for previous results showing that oceanographic connectivity plays an important role in the population genetic structure of Macrocystis in the Northern hemisphere., (© 2015 John Wiley & Sons Ltd.)