Now showing items 1-20 of 209

    • Gradients of deposition and in situ production drive Global glacier organic matter composition

      Holt, Amy D.; McKenna, Amy M.; Kellerman, Anne M.; Battin, Tom I.; Fellman, Jason; Hood, Eran; Peter, Hannes; Schön, Martina; De Staercke, Vincent; Styllas, Michail; et al. (American Geophysical Union, 2024-09-19)
      Runoff from rapidly melting mountain glaciers is a dominant source of riverine organic carbon in many high-latitude and high-elevation regions. Glacier dissolved organic carbon is highly bioavailable, and its composition likely reflects internal (e.g., autotrophic production) and external (i.e., atmospheric deposition) sources. However, the balance of these sources across Earth's glaciers is poorly understood, despite implications for the mineralization and assimilation of glacier organic carbon within recipient ecosystems. We assessed the molecular-level composition of dissolved organic matter from 136 mountain glacier outflows from 11 regions covering six continents using ultrahigh resolution 21 T mass spectrometry. We found substantial diversity in organic matter composition with coherent and predictable (80% accuracy) regional patterns. Employing stable and radiocarbon isotopic analyses, we demonstrate that these patterns are inherently linked to atmospheric deposition and in situ production. In remote regions like Greenland and New Zealand, the glacier organic matter pool appears to be dominated by in situ production. However, downwind of industrial centers (e.g., Alaska and Nepal), fossil fuel combustion byproducts likely underpin organic matter composition, resulting in older and more aromatic material being exported downstream. These findings highlight that the glacier carbon cycle is spatially distinct, with ramifications for predicting the dynamics and fate of glacier organic carbon concurrent with continued retreat and anthropogenic perturbation.
    • Forecasted changes to the timing of Pacific herring Clupea pallasii spawn in a warming ocean

      Harley, John R.; Grinnell, Matthew H.; Herbert, Kyle; Cleary, Jaclyn; Thompson, Matthew; Rooper, Christopher N. (Inter-Research, 2024-07-25)
      Pacific herring Clupea pallasii are a critical commercial and subsistence fish species and play a keystone role in the ecology and culture of the North Pacific. The annual herring spawn, in which mature herring migrate nearshore to deposit eggs along the coastline, is an important event linked to the migration of seabirds and marine mammals as well as a subsistence harvest for Alaska Natives and First Nations in British Columbia. Previous work has suggested that environmental variables and broad teleconnection indices play a role in the magnitude and phenology of spawning; however, the effects of these drivers have not been examined in the context of future climate scenarios. Here, we modeled variability in the timing of herring spawn across British Columbia and Southeast Alaska using survey data from 1951-2022. We created a model using Pacific teleconnection indices, sea surface temperature (SST), tidal height, and lagged data to predict spawn date anomalies (SDAs) across 9 spawning regions. SDAs were significantly affected by the Oceanic Niño Index, Pacific Decadal Oscillation, SST, and lagged SDAs. We then used this model to predict SDAs using projected SST from climate models and bootstrapped teleconnection data from 2025-2100. Future herring spawn timing trends earlier on average with warming SSTs, although the magnitude is relatively small, occurring 9 d earlier on average by 2100. This changing phenology, though small, varied by region and may have ecosystem-level ramifications and create timing mismatch for migratory species. However, our findings also reinforce the importance of other physical factors not measured in this study, such as photoperiod, which drive herring spawn timing.
    • Clam Size Explains Some Variability in Paralytic Shellfish Toxin Concentrations in Butter Clams (Saxidomus gigantea) in Southeast Alaska

      Harley, John R.; Blair, Kellie; Cellan, Shannon M.; Lanphier, Kari; Pierce, Lindsey; Scott, Cer; Whitehead, Chris; Gribble, Matthew O. (MDPI, 2024-10-29)
      Harmful algal blooms (HABs) are a reoccurring threat to subsistence and recreational shellfish harvest in Southeast Alaska. Recent Tribally led monitoring programs have enhanced understanding of the environmental drivers and toxicokinetics of shellfish toxins in the region; however, there is considerable variability in shellfish toxins in some species, which cannot be easily explained by seasonal bloom dynamics. Persistent concentrations of paralytic shellfish toxins (PSTs) in homogenized butter clam samples (n > 6, Saxidomus gigantea) have been observed in several communities, and relatively large spikes in concentrations are sometimes seen without Alexandrium observations or increased toxin concentrations in other species. In order to investigate potential sources of variability in PST concentrations from this subsistence species, we assessed individual concentrations of PSTs across a size gradient of butter clams during a period of relatively stable PST concentrations. We found that increasing concentrations of PSTs were significantly associated with larger clams using a log-linear model. We then simulated six clams randomly sampled from three size distributions, and we determined large clams had an outsized probability of contributing a significant proportion of the total toxicity in a six-clam homogenized sample. While our results were obtained during a period of low HAB activity and cannot be extrapolated to periods of intoxication or rapid detoxification, they have significant ramifications for both monitoring programs as well as subsistence and recreational harvesters.
    • Advancing an integrated understanding of land–ocean connections in shaping the marine ecosystems of coastal temperate rainforest ecoregions

      Hunt, Brian P. V.; Alin, Simone; Bidlack, Allison; Diefenderfer, Heida L.; Jackson, Jennifer M.; Kellogg, Colleen T. E.; Kiffney, Peter; St. Pierre, Kyra A.; Carmack, Eddy; Floyd, William C.; et al. (Wiley Association for the Sciences of Limnology and Oceanography, 2024-11-18)
      Land and ocean ecosystems are strongly connected and mutually interactive. As climate changes and other anthropogenic stressors intensify, the complex pathways that link these systems will strengthen or weaken in ways that are currently beyond reliable prediction. In this review we offer a framework of land–ocean couplings and their role in shaping marine ecosystems in coastal temperate rainforest (CTR) ecoregions, where high freshwater and materials flux result in particularly strong land–ocean connections. Using the largest contiguous expanse of CTR on Earth—the Northeast Pacific CTR (NPCTR)—as a case study, we integrate current understanding of the spatial and temporal scales of interacting processes across the land–ocean continuum, and examine how these processes structure and are defining features of marine ecosystems from nearshore to offshore domains. We look ahead to the potential effects of climate and other anthropogenic changes on the coupled land–ocean meta-ecosystem. Finally, we review key data gaps and provide research recommendations for an integrated, transdisciplinary approach with the intent to guide future evaluations of and management recommendations for ongoing impacts to marine ecosystems of the NPCTR and other CTRs globally. In the light of extreme events including heatwaves, fire, and flooding, which are occurring almost annually, this integrative agenda is not only necessary but urgent.
    • An analytical approach for simulating effects of avalanches on mountain goat population dynamics: Implications for management and conservation

      White, Kevin; Levi, Taal; Hood, Eran; Wolken, Gabriel J.; Peitzsch, Erich H.; Bühler, Yves; Jones, Katreen Wikstrom; Darimont, Chris T. (ResearchGate, 2024-09)
      Mountain environments with snow avalanche hazard cover about 6% of Earth’s land area and occur on all continents. Whereas human risks associated with avalanche hazard have been widely studied, little is known about how avalanche activity affects population dynamics in mountain wildlife. Globally, 32 species of mountain ungulates across 70 countries occupy avalanche-prone terrain. Avalanches comprise the leading cause of mortality in coastal Alaskan mountain goats (mean = 36%, range = 23 - 65%, depending on area), and disproportionately remove prime-aged individuals from populations. The implications of such rates and patterns of mortality on population growth rate are likely to be significant given the species’ low reproductive productivity, but further clarity is needed. To fill this knowledge gap, we developed a sex- and age-specific population modeling approach that integrates both reproduction and mortality to simulate the effects of avalanche-caused mortality on population growth rate across a range of empirically-observed states of avalanche-caused mortality (minimum, mean, maximum). Simulations were conducted to illustrate model functionality, and also provide insight about potential avalanche impacts on population demographic processes. For example, when severe avalanche years occur populations can experience significant additive mortality and declines (up to 15%). Due to low reproductive rates and slow life-history strategy of the species, such impacts can lead to long demographic recovery times (up to 11 years). From a species conservation perspective, such impacts are striking, and highlight the utility of employing a quantitative modeling approach to predict possible effects of avalanches on mountain ungulate population dynamics and viability. Our work explicitly builds upon recent findings about the importance of avalanches on mountain-adapted animal populations, and associated implications for the cultural and ecological communities that depend on them.
    • Seasonal patterns in riverine carbon form and export from a temperate forested watershed in Southeast Alaska

      Delbecq, Claire; Fellman, Jason; Bellmore, Ryan; Whitney, Emily J.; Hood, Eran; Fitzgerald, Kevin; Falke, Jeffery A. (Springer Nature, 2024-08-23)
      Riverine export of carbon (C) is an important part of the global C cycle; however, most riverine C budgets focus on individual forms of C and fail to comprehensively measure both organic and inorganic C species in concert. To address this knowledge gap, we conducted high frequency sampling of multiple C forms, including dissolved organic C (DOC), inorganic carbon (as alkalinity), particulate organic C (POC), coarse particulate organic C (CPOC), and invertebrate biomass C across the main run-off season in a predominantly rain-fed watershed in Southeast Alaska. Streamwater concentrations were used to model daily watershed C export from May through October. Concentration and modeled yield data indicated that DOC was the primary form of riverine C export (8708 kg C/km2), except during low flow periods when alkalinity (3125 kg C/km2) was the dominant form of C export. Relative to DOC and alkalinity, export of particulate organic C (POC: 992 kg C/km2; CPOC: 313 kg C/km2) and invertebrates (40 kg C/km2) was small, but these forms of organic matter could disproportionately impact downstream food webs because of their higher quality, assessed via C to nitrogen ratios. These seasonal and flow driven changes to C form and export likely provide subsidies to downstream and nearshore ecosystems such that predicted shifts in regional hydroclimate could substantially impact C transfer and incorporation into aquatic food webs.
    • The relationship between submarine melt and subglacial discharge from observations at a tidewater glacier

      Jackson, Rebecca H.; Motyka, Roman J.; Amundson, Jason M.; Abib, Nicole; Sutherland, David A.; Nash, Jonathan D.; Kienholz, Christian (John Wiley & Sons, Inc., 2022-10)
      At tidewater glacier termini, ocean-glacier interactions hinge on two sources of freshwater—submarine melt and subglacial discharge—yet these freshwater fluxes are often unconstrained in their magnitude, seasonality, and relationship. With measurements of ocean velocity, temperature and salinity, fjord budgets can be evaluated to partition the freshwater flux into submarine melt and subglacial discharge. We apply these methods to calculate the freshwater fluxes at LeConte Glacier, Alaska, across a wide range of oceanic and atmospheric conditions during six surveys in 2016–2018. We compare these ocean-derived fluxes with an estimate of subglacial discharge from a surface mass balance model and with estimates of submarine melt from multibeam sonar and autonomous kayaks, finding relatively good agreement between these independent estimates. Across spring, summer, and fall, the relationship between subglacial discharge and submarine melt follows a scaling law predicted by standard theory (melt ∼ discharge1/3), although the total magnitude of melt is an order of magnitude larger than theoretical estimates. Subglacial discharge is the dominant driver of variability in melt, while the dependence of melt on fjord properties is not discernible. A comparison of oceanic budgets with glacier records indicates that submarine melt removes 33%–49% of the ice flux into the terminus across spring, summer, and fall periods. Thus, melt is a significant component of the glacier's mass balance, and we find that melt correlates with seasonal retreat; however, melt does not appear to directly amplify calving.
    • Clustering for the neophyte: An R Shiny app for self-organizing maps

      Akman, Olcay; Betzab-Marroquin, Zury; Hay-Jahans, Christopher; Wlash, Joshua; Wesley, Trenton (Intercollegiate Biomathematics Alliance, 2022)
      This article provides an outline of clustering, key stages in creating self-organizing maps for purposes of clustering, instructions on how to use a free online R Shiny app that constructs self-organizing maps for data provided by users, and interpretations of the graphics produced.
    • Agent-based modeling for the neophyte: An application of NetLogo

      Akman, Olcay; Bhumpelli, Siddharth; Hay-Jahans, Christopher (Intercollegiate Biomathematics Alliance, 2024)
      Agent-based modeling has found applications in a wide range of fields including economics, sociology, ecology, epidemiology, transportation planning, and more. Its versatility allows researchers to investigate various “what-if” scenarios, test the effects of different policies or interventions, and gain insights into the underlying mechanisms driving complex systems. This article is intended for the curious student or researcher who is unfamiliar with agentbased modeling and is looking for a quick but reasonably informative exposure to the field.
    • Linking dissolved organic matter composition to landscape properties in wetlands across the United States of America

      Kurek, Martin R.; Wickland, Kimberly P.; Nichols, Natalie A.; McKenna, Amy M.; Anderson, Steven M.; Dornblaser, Mark M.; Koupaei-Abyazani, Nikaan; Poulin, Brett A.; Bansal, Sheel; Fellman, Jason; et al. (American Geophysical Union, 2024-05-03)
      Wetlands are integral to the global carbon cycle, serving as both a source and a sink for organic carbon. Their potential for carbon storage will likely change in the coming decades in response to higher temperatures and variable precipitation patterns. We characterized the dissolved organic carbon (DOC) and dissolved organic matter (DOM) composition from 12 different wetland sites across the USA spanning gradients in climate, landcover, sampling depth, and hydroperiod for comparison to DOM in other inland waters. Using absorption spectroscopy, parallel factor analysis modeling, and ultra-high resolution mass spectroscopy, we identified differences in DOM sourcing and processing by geographic site. Wetland DOM composition was driven primarily by differences in landcover where forested sites contained greater aromatic and oxygenated DOM content compared to grassland/herbaceous sites which were more aliphatic and enriched in N and S molecular formulae. Furthermore, surface and porewater DOM was also influenced by properties such as soil type, organic matter content, and precipitation. Surface water DOM was relatively enriched in oxygenated higher molecular weight formulae representing HUPHigh O/C compounds than porewaters, whose DOM composition suggests abiotic sulfurization from dissolved inorganic sulfide. Finally, we identified a group of persistent molecular formulae (3,489) present across all sites and sampling depths (i.e., the signature of wetland DOM) that are likely important for riverine-to-coastal DOM transport. As anthropogenic disturbances continue to impact temperate wetlands, this study highlights drivers of DOM composition fundamental for understanding how wetland organic carbon will change, and thus its role in biogeochemical cycling.
    • Rapid submarine melting driven by subglacial discharge, LeConte Glacier, Alaska

      Motyka, Roman J.; Dryer, William P.; Amundson, Jason M.; Truffer, Martin; Fahnestock, Mark (American Geophysical Union, 2013-09-27)
      We show that subglacial freshwater discharge is the principal process driving high rates of submarine melting at tidewater glaciers. This buoyant discharge draws in warm seawater, entraining it in a turbulent upwelling flow along the submarine face that melts glacier ice. To capture the effects of subglacial discharge on submarine melting, we conducted 4 days of hydrographic transects during late summer 2012 at LeConte Glacier, Alaska. A major rainstorm allowed us to document the influence of large changes in subglacial discharge. We found strong submarine melt fluxes that increased from 9.1 ± 1.0 to 16.8 ± 1.3 m d1 (ice face equivalent frontal ablation) as a result of the rainstorm. With projected continued global warming and increased glacial runoff, our results highlight the direct impact that increases in subglacial discharge will have on tidewater outlet systems. These effects must be considered when modeling glacier response to future warming and increased runoff.
    • Movement and diving behavior of satellite-tagged male sperm whales in the Gulf of Alaska

      Wild, Lauren A.; Mueter, Franz J.; Straley, Janice; Andrews, Russ D. (Frontiers Media S.A., 2024-09-02)
      Male sperm whales (Physeter macrocephalus) are known to interact with and depredate from commercial longline fishing vessels targeting sablefish (Anoplopoma fimbria) in the Gulf of Alaska (GOA). This study aims to better understand their movement patterns and diving behavior in this region, and in relation to depredation behavior. Between 2007 and 2016 a total of 33 satellite tags were deployed on sperm whales interacting with fishing vessels in the eastern GOA. A subset of these tags also collected dive characteristics. We used state space models to interpolate hourly positions from tags and estimate behavioral state from 29 usable tag records, 14 of which had associated dive information. Whales exhibited slower horizontal movement (1.4 km/hr) within GOA waters compared to south of the GOA (5.5 km/hr), indicating tagged whales sped up when they left the region. Behavioral states indicated primarily foraging behavior (82% of locations) in the GOA and primarily transiting behavior (74% of locations) when whales left the GOA. Dive data showed average ( ± Standard Deviation) maximum dive depths of 396 m ( ± 166), and dive durations of 32 min (± 9). Generalized additive models indicated that dives were significantly deeper and longer during the daytime than dawn, dusk, or nighttime, and dives were significantly deeper and shorter during quarter moons, when tidal currents are weakest. Maximum dive depth decreased in areas of higher sablefish CPUE, suggesting a potential link between the sablefish fishery and depredation behavior. As seafloor depth increased, up to 800 m, dives became deeper, indicating that whales were likely targeting both bathypelagic and mesopelagic prey. This highlights the importance of the GOA continental slope as a foraging ground for male sperm whales. This enhanced understanding of sperm whale foraging ecology informs management and conservation efforts in high latitude foraging grounds.
    • Compartmental modeling for the neophyte: An application of Berkeley-Madonna

      Akman, Olcay; Bhumpelli, Siddharth; Cline, Cody; Hay-Jahans, Christopher (2024)
      Compartmental modeling serves as a necessary framework in many fields, especially biomathematics and ecology. This article introduces readers to a user-friendly approach to constructing compartmental models and solving the resulting systems of differential equations to simulate real-world applications. The platform used is Berkeley Madonna, a software package that has an intuitive graphical interface which empowers users—even those with limited mathematical and programming backgrounds—to focus on modeling concepts rather than mathematical or programming intricacies. This makes Berkeley Madonna an ideal platform for students, educators, and researchers.
    • Eroding permafrost coastlines release biodegradable dissolved organic carbon to the Arctic Ocean

      Bristol, Emily M.; Behnke, Megan; Spencer, Robert G. M.; McKenna, Amy; Jones, Benjamin M.; Bull, Diana L.; McClelland, James W. (John Wiley & Sons, Inc, 2024-07-27)
      Coastal erosion mobilizes large quantities of organic matter (OM) to the Arctic Ocean where it may fuel greenhouse gas emissions and marine production. While the biodegradability of permafrost‐derived dissolved organic carbon (DOC) has been extensively studied in inland soils and freshwaters, few studies have examined dissolved OM (DOM) leached from eroding coastal permafrost in seawater. To address this knowledge gap, we sampled three horizons from bluff exposures near Drew Point, Alaska: seasonally thawed active layer soils, permafrost containing Holocene terrestrial and/or lacustrine OM, and permafrost containing late‐Pleistocene marine‐derived OM. Samples were leached in seawater to compare DOC yields, DOM composition (chromophoric DOM, Fourier transform ion cyclotron resonance mass spectrometry), and biodegradable DOC (BDOC). Holocene terrestrial permafrost leached the most DOC compared to active layer soils and Pleistocene marine permafrost. However, DOC from Pleistocene marine permafrost was the most biodegradable (33 ± 6% over 90 days), followed by DOC from active layer soils (23 ± 5%) and Holocene terrestrial permafrost (14 ± 3%). Permafrost leachates contained relatively more aliphatic and peptide‐like formulae, whereas active layer leachates contained relatively more aromatic formulae. BDOC was positively correlated with nitrogen‐containing and aliphatic formulae, and negatively correlated with polyphenolic and condensed aromatic formulae. Using estimates of eroding OM, we scale our results to estimate DOC and BDOC inputs to the Alaska Beaufort Sea. While DOC inputs from coastal erosion are relatively small compared to rivers, our results suggest that erosion may be an important source of BDOC to the Beaufort Sea when river inputs are low.
    • ONeSAMP 3.0: Estimation of effective population size via SNP data from one population

      Hong, Aaron; Cheek, Rebecca; De Silva, Suhashi Nihara; Mukherjee, Kingshuk; Yooseph, Isha; Heim, Mark; Tallmon, David; Boucher, Christina (Genetics Society of America, 2024-07-12)
      The genetic effective size (Ne) is arguably one of the most important characteristics of a population as it impacts the rate of loss of genetic diversity. Methods that estimate Ne are important in population and conservation genetic studies as they quantify the risk of a population being inbred or lacking genetic diversity. Yet there are very few methods that can estimate the Ne from data from a single population and without extensive information about the genetics of the population, such as a linkage map, or a reference genome of the species of interest. We present ONeSAMP 3.0, an algorithm for estimating Ne from single nucleotide polymorphism (SNP) data collected from a single population sample using Approximate Bayesian Computation and local linear regression. We demonstrate the utility of this approach using simulated Wright-Fisher populations, and empirical data from five endangered Channel Island fox (Urocyon littoralis) populations to evaluate the performance of ONeSAMP 3.0 compared to a commonly used Ne estimator. Our results show that ONeSAMP 3.0 is is broadly applicable to natural populations and is flexible enough that future versions could easily include summary statistics appropriate for a suite of biological and sampling conditions. ONeSAMP 3.0 is publicly available under the GNU license at https://github.com/AaronHong1024/ONeSAMP_3.
    • If you choose not to decide... Alaska’s budgeting process in 2023

      Wright, Glenn (eScholarship, University of California, 2024)
      Alaska in 2023 is experiencing the first results of the new election system—the top-four all-party primary and Ranked Choice Voting. So far, that system seems to be generating results consistent with what advocates expected; a more moderate and collegial policy-making environment, and possibly even more sensible budgetary policy. This, coupled with relatively strong (though declining) oil prices, and abundant sovereign wealth led to a relatively low-drama, low-conflict budgeting process in spring 2023, as well as relatively moderate budgeting outcomes.
    • Increasing multi-hazard climate risk and financial and health impacts on northern homeowners

      Schwoerer, Tobias; Schmidt, Jennifer I.; Berman, Matthew; Bieniek, Peter; Farquharson, Louise M.; Nicolsky, Dmitry; Powell, James E.; Roberts, Rachel; Thoman, Rick; Ziel, Robert (Springer Nature, 2024-03)
      Currently, more than half of the world’s human population lives in urban areas, which are increasingly affected by climate hazards. Little is known about how multi-hazard environments affect people, especially those living in urban areas in northern latitudes. This study surveyed homeowners in Anchorage and Fairbanks, USA, Alaska’s largest urban centers, to measure individual risk perceptions, mitigation response, and damages related to wildfire, surface ice hazards, and permafrost thaw. Up to one third of residents reported being affected by all three hazards, with surface ice hazards being the most widely distributed, related to an estimated $25 million in annual damages. Behavioral risk response, policy recommendations for rapidly changing urban environments, and the challenges to local governments in mitigation efforts are discussed.
    • Responses of chlorophyll a content for conchocelis phase of alaskan porphyra (bangiales, rhodophyta) species to environmental factors

      Lin, Rulong; Stekoll, Michael (Science Publishing Group, 2013-06-30)
      Investigations were performed on variations of photosynthetic pigment in conchocelis of Alaskan Porphyra species, P. abbottae (Pa), P. pseudolanceolata (Pe), P. pseudolinearis (Pi) and P. torta (Pt), in response to environmental variables. Conchocelis were cultured under varying conditions of irradiance (0, 10, 40 and 160 µmol photons m-2s-1), nutrient concentration (0, f/4, f/2 and f) for up to 60 days (with temperature 11°C and salinity 30ppt). Chlorophyll a (Chl a ) content was measured by spectrophotometry. Results indicated that Chl content varied with different culture conditions and species. Photosynthetic pigment was significantly affected by irradiance, nutrient concentration and culture duration, including some interactions of major factors for different species. Light had the most obvious influence on pigment content. For all four species and culture conditions tested, the higher Chl a content (3.6-8.6 mg/g.dw) generally occurred at 0-10 µmol photons m 2 s 1than at higher irradiances (≥40 µmol photons m-2s-1 ) culture. For all culture conditions, Chl a content in conchocelis culture with no nutrients added was the lowest. Although there was some difference in Chl a content for cultures with f/2-f nutrient concentration, it was not statistically significant. ANOVA results showed that culture duration had influence on Chl a content of Pa, Pe and Pi species. However, pooled data analysis indicated there was no obvious difference in Chl content for four species of 10-60day culture. There were significant differences in photosynthetic pigment content for different species. Pa and Pi produced much higher pigment content than the other two species responding to different environmental conditions. Maximal Chl. a content (8.6 mg/g.dw) for Pa occurred at 0 µmol photons m-2s-1, f/2 nutrient concentration and 10 day culture duration. Pt contained the lowest pigment content for all culture conditions. Photosynthetic pigment remained relatively higher content under the complete darkness or the low irradiance continuously as long as 60 days for all tested species, which demonstrated the unique survival feature of Porphyra conchocelis. Variation patterns of pigment content, ecological significance and adaptation strategy to low or dark light conditions for microscopic conchocelis stage of Porphyra were discussed.
    • Coexistence despite recruitment inhibition of kelps by subtidal algal crusts

      Okamoto, Daniel K.; Stekoll, Michael; Eckert, Ginny L. (Inter-Research, 2013-11-20)
      In temperate subtidal reefs, kelp species often dominate light, while encrusting algae often dominate the substrate and are well adapted to low light conditions. Yet whether changes in algal crust cover impact recruitment dynamics of kelp species remains largely unexplored. To address this gap, we combined field surveys with laboratory and field experiments to investigate (1) the impact of algal crusts on kelp settlement and recruitment and (2) the potential effect such inhibition may have on density of subtidal kelps in a southeast Alaskan fjord. Experimental removal of algal crusts in the field resulted in dense kelp recruitment, whereas in plots where algal crusts dominated space, kelp recruitment was sparse. Kelp zoospores settled in the laboratory with no apparent selectivity for bare rock over crust surfaces, yet kelp sporophyte densities were reduced by 97 to 99% on non-coralline algal crust patches compared to bare rock, suggesting post-settlement recruitment inhibition. Despite such strong inhibition, we show that very low kelp recruit density, such as that observed in the algal crust dominated patches of our experiment, can yield high adult densities. Such observations are supported by positive correlations between kelp density and crust percent cover in field surveys of 1 m2 plots across 6 reefs, suggesting broad-scale coexistence. Thus, the strong ability of kelps to colonize bare substrata in this region appears to facilitate persistence of kelps despite strong dominance of space by certain algal crusts.
    • Effects of density and substrate type on recruitment and growth of Pyropia torta (Rhodophyta) gametophytes

      Conitz, Jan M.; Fagen, Robert; Stekoll, Michael (Walter de Gruyter GmbH, 2013-10-29)
      Does density affect recruitment and growth in the annual, blade phase of Pyropia sp., does self-thinning occur, and does substrate affect recruitment? These questions were investigated in laboratory-cultured Pyropia torta, a naturally occurring species in Alaska with mariculture potential. Three density levels were produced from conchospores. Measurements were made, initially at settlement and germination and, subsequently, at approximately 3-week intervals, in 12 randomly selected cultures from each density level. Settled spores, germlings, or growing blades were counted microscopically and standardized to unit area. Blade surface area was measured microscopically using image analysis software. Three density levels were still distinct at germination, but the high and medium levels were not significantly different. The germination rate of conchospores was highest at the medium density level, suggesting facilitation at moderate densities but inhibition at higher densities. Significant self-thinning occurred at each density level but differed among levels, while overall blade growth was about 10-fold greater at low density than at the other two levels. In a separate experiment, counts of attached spores per unit area on artificial substrate materials were greatest on materials with interstitial spaces large enough to trap spores until they become firmly attached.