Browsing by Subject "Kelp"
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Item The acoustic ecology of submerged macrophytes(2011-12) Wilson, Christopher James, 1985-; Wilson, Preston S.; Dunton, Kenneth H.; Shank, G. Christopher; McClelland, James W.; Fuiman, Lee A.Underwater acoustics has recently emerged as a viable tool for assessing ecosystem health and exploring the estuarine soundscape. Recent acoustic surveys have mapped distributions of both seagrass meadows and kelp forests, and scientists are currently developing remote sensing capabilities to improve ecological assessments of these communities. Furthermore, researchers are beginning to focus on the propagation and ecological significance of bioacoustic signals within estuarine landscapes. The research presented here includes a thorough examination of the interaction of acoustic energy and macrophyte tissue as it pertains to habitat assessment and ecosystem function. Modeling experiments investigated the interaction of acoustic energy and submerged macrophyte tissue. Both seagrasses and kelp exhibited a similar acoustic response by increasing the acoustic compressibility of a seawater medium. The increase in acoustic compressibility was driven by free-gas volumes contained within the macrophyte tissue. Interestingly, the tissue served to limit the acoustic compressibility of the gas volume below the magnitude predicted by effective medium models. Separate inquiries of high-frequency sound propagation and the seagrass canopy revealed a significant temporal component to acoustic transmission. Specifically, sound transmission throughout a seagrass canopy was altered by the formation of free gas bubbles and the pressurization of aerenchyma channels, which was mediated by photosynthesis. The photosynthetic controls on sound propagation were species-specific, and patterns of acoustic transmission provided a reasonable proxy for gross primary production in Syringodium filiforme plants. Finally, the interaction of sound energy and submerged macrophytes appears to have important ecological implications. This research suggests that seagrass meadows scatter high-frequency sound energy and provide an acoustic refuge to fish from marine mammal predators. This refuge is highly seasonal, specific to different seagrass species and dependent on the abundance of above-ground biomass. Seagrasses also may influence the transmission of low-frequency sounds used by soniferous fish. Propagation characteristics of low-frequency sounds are highly dependent on frequency and result in differential transmission distances among individual fish species. It is clear from this body of work that submerged macrophytes are an important feature of the underwater soundscape. Future research should continue to exploit this feature for remote sensing purposes and examine its ecological significance.Item Factors that influence the distribution of the Arctic endemic kelp, Laminaria solidungula (J. Agardh 1868)(2019-06-21) Bonsell, Christina Elisa; Dunton, Kenneth H.; Erdner, Deana; Black, Bryan; Aumack, CraigFoundation species, including kelps, have a disproportionate effect on ecosystems by exerting strong influence on food webs and community structure. Shifts in kelp species’ distributions are occurring worldwide, and are especially anticipated in the Arctic due to habitat modification by climate change. On Arctic inner shelves, the kelp Laminaria solidungula (J. Agardh 1868) can dominate nearshore rocky areas, and provide physical structure and subsidies of year-round primary production in a highly seasonal region. However, controls over the distribution of this Arctic endemic species are not well understood. A species’ interactions with the abiotic and biotic environment, its dispersal dynamics, and evolutionary history all control its ultimate range and spatial arrangement. This work describes how these factors impact L. solidungula distribution across multiple scales, with focus on the Stefansson Sound Boulder Patch, Beaufort Sea, Alaska. First, although the Stefansson Sound open-water season has lengthened by ~17 days since 1979, annual kelp growth shows no long-term trends because attenuation by suspended sediments causes pervasive low-light conditions during summer (mean light attenuation: 0.5-0.8 m⁻¹), negating any positive impacts of decreased ice-cover. Second, the abiotic environment of the Boulder Patch undergoes significant seasonal changes, mediated by physiography and bathymetry, which impact the spatial arrangement of L. solidungula and other epilithic species. A site within 4 km of river inputs experiences salinity drops of ~30 corresponding to the spring freshet. Crustose coralline algae (0-19% average cover) is completely absent at this site, but cover increases with distance from river inputs. Red algae (47-79%) and kelp (2-19%) cover shows no clear environmental correlations, and are likely regulated by multiple factors. Importantly, no L. solidungula recruited to settlement tiles after three years of deployment. Finally, population genetics suggest Beaufort Sea L. solidungula is one large interbreeding population (population differentiation as global F[subscript ST]: 0.01) assisted by the regional current regime, though smaller scale differentiation occurs within the Boulder Patch. Additionally, Beaufort Sea L. solidungula is genetically distinct from those in other areas of the Western Arctic Ocean Basin. This work represents an important baseline in ecological and genetic characteristics of L. solidungula in the rapidly changing Arctic OceanItem Inorganic nitrogen uptake by two kelp species, Laminaria solidungula and Laminaria saccharina, in the Alaskan High Arctic(1995) Dibble, John Michael; Dunton, Kenneth H.The uptake of inorganic nitrate (NO₃⁻) and ammonium (NH₄⁺) by two co-occurring species of kelp, Laminaria solidungula and Laminaria saccharina, was compared using entire plants incubated under natural conditions in the field and in the laboratory. Field experiments were conducted in situ during ice-covered and open-water periods in the Boulder Patch kelp bed community in the Alaskan Beaufort Sea. The data obtained in these experiments do not provide evidence of Michaelis-Menten saturation kinetics. The uptake of NO₃⁻ and NH₄⁺ by both species appears to be a linear function of substrate concentration with no evidence of a saturating concentration although average substrate concentrations approach 80 μM. There was no significant difference between NO₃⁻ and NH₄⁺ uptake rates in conditions where either NO₃⁻ or NH₄⁺ were supplied at the same concentrations and no significant difference in uptake rates between species. The mean uptake rate at ambient nitrate concentrations in winter (4 - 7 μM) was 0.53 /μmoles gdw⁻¹h⁻¹. Uptake rate values obtained by substrate disappearance at ambient concentrations were corroborated by measurements of ¹⁵N stable isotope incorporation. Dark and light-exposed plants of both species also exhibited equivalent rates of uptake in short-term experiments with either NO₃⁻ or NH₄⁺ present as substrate. L. solidungula also demonstrated equal dark/light uptake with both nitrogen substrates present, revealing no competitive inhibition of either substrate. Time course disappearance for L. solidungula with NO₃⁻ or NH₄⁺ and NO₃⁻/NH₄⁺ followed second order kinetics. Water motion was shown to significantly enhance both NO₃⁻ and NH₄⁺ disappearance for L. solidungula. Linear growth rates in juvenile L. solidungula sporophytes were not affected by NO₃⁻ concentration, but this may be related to the translocation of organic nitrogen to support linear growth at low NO₃⁻ concentrations, based on the bleaching of distal blade tissues in nitrogen-starved plants. The nitrogen uptake rates determined in this study for both species at -1.8 to 5 °C agree closely with published uptake rates for temperate kelp species living at 15 °C, enabling L. solidungula and L. saccharina to maintain high growth rates at the low temperatures characteristic of polar environmentsItem Salinity and pH variations in the nearshore Arctic Ocean : implications for benthic species physiology and biodiversity(2020-08-18) Muth, Arley Frances; Dunton, Kenneth H.; Esbaugh, Andrew; McClelland, James; Hardison, Amber; Kelley, Amanda LBenthic communities are formed by species-specific tolerances to environmental factors and further shaped by biological interactions that inhibit or enhance post-settlement processes. Abiotic conditions affect species differently, and one example of this in the marine world is the influence of ocean water carbonate chemistry on calcifying organisms. Crustose coralline algae (CCA) are dominant space occupiers, ecosystem engineers that often shape community structure are early responders to water chemistry changes, and are prevalent benthic species in the Stefansson Sound Boulder Patch. The Boulder Patch is located off the north coast of Alaska and receives large pulses of freshwater each spring from the Sagavanirktok River, reducing salinities to less than five on the benthos in certain locations. Continuous pH, temperature and salinity data (including under-ice data) revealed seasonal variability and the influence of the Sagavanirktok River runoff, which caused short (3-5 week) pulses of highly buffered pH (>8), low A[subscript T] (<1900 μmEq L⁻¹) and low salinity (<5) waters into the Boulder Patch. Through manipulative laboratory experiments we noted that low salinity waters (10) negatively affected CCA physiology and likely drive their distributions within the Boulder Patch, which range from 77% cover to completely absent on rock substrata at nearshore sites where river runoff is prevalent during break-up in spring. Samples were collected and analyzed for algal and invertebrate species and biomass when CCA were present and absent, with a specific focus on the effects on population densities of the Arctic endemic kelp, Laminaria solidungula, an important foundation species. Areas with CCA had significantly higher densities of L. solidunugla adults (4.72 m⁻¹) than the site without CCA (0.36 m⁻¹). Experiments with early life history stages of L. solidungula raised in culture showed that low salinities (10) prevented recruitment. However, during winter, when early microscopic stages are present in the Boulder Patch, salinity levels are consistently high (32). These results point to other post-recruitment processes affecting the distribution of L. solidungula. In our system, CCA outcompeted turf and fleshy algal and other invertebrate species, creating more habitable space for kelp recruitment. This competitive interaction facilitates L. solidungula recruitment and survival and highlights the importance of abiotic factors in structuring benthic marine communities. The role of CCA in facilitating recruitment of a major foundation species and its susceptibility to low salinity events is critical to our understanding of this complex benthic ecosystem