Now showing items 98-117 of 198

• #### Kelp bed variability and fish population dynamics in Kachemak Bay, Alaska

Understanding interactions between kelp beds and fishes is essential because anthropogenic changes and natural variability in these beds (composition, density, and distribution) may affect available habitat for fishes. In Alaska, little is known about the annual and seasonal variability of macroalgal cover in kelp beds and corresponding changes in associated fish populations. This study investigated natural variability using monthly SCUBA surveys in Kachemak Bay, Alaska from May 2002 to September 2003. Ten shallow (approximately 7m water depth) nearshore kelp beds with varying degrees of macroalgal cover were surveyed visually for fishes and kelp, and measurements of environmental variables were collected. These kelp beds had a persistent, perennial-dominated understory with sporadic, sparse populations of annual canopy kelp. Understory and canopy kelps had affinities with greater bottom structure, and annual kelp density was greatest during periods with higher temperatures. Hexagrammids, especially kelp greenlings, existed year-round in the more structurally complex beds and were typically more abundant during periods with higher temperatures, and at sites with denser annual kelp populations. Most other fishes were transient and generally present only during summer months. Monthly changes in kelp and fish communities reflected a strong seasonal component.
• #### Kelp forests and barren grounds: phlorotannin production and holdfast community structure in the Aleutian dragon kelp, Eualaria fistulosa

The canopy forming kelp Eualaria fistulosa inhabits two organizational states throughout the Aleutian archipelago, kelp forests and barren grounds. Urchin abundance and behavior determines which state dominates in any given area. Sporophyll phlorotannin content and holdfast epibiont fauna were investigated at multiple islands along the Aleutian archipelago to determine how the organizational state affects the production of secondary metabolites and the taxon richness, abundance and biomass of holdfast communities. Barren ground sporophylls had higher phlorotannin content than kelp forest sporophylls, although grazing rates on sporophylls from each state did not differ during in situ grazing experiments. The taxon richness, abundance and biomass of holdfast communities were similar between kelp forests and barren grounds at all islands, although these communities varied among islands and were mostly driven by holdfast volume. These results suggest that physical differences such as light and nutrient availability in the kelp forest structure between organizational states may be responsible for differences in phlorotannin content, but that these differences are not reflected in the holdfast community structure. It appears that barren ground holdfast communities are remnants of a once forested area.
• #### The life history of the intertidal barnacle, Balanus balanoides (L.) in Port Valdez, Alaska

The life history of the boreo-arctic barnacle Batanus balanoides was examined at three study sites in Port Valdez. Ovarian tissue development began in early summer. Fertilized eggs, evident by September, were brooded throughout the winter. Larval release was synchronous with the spring phytoplankton bloom. Settlement was observed in April and continued until June. Maximal shell growth occurred immediately subsequent to assimilation of organic material from the spring bloom. Seasonal fluctuations in body weight were noted and reflect feeding, spermatogenesis, and energy transfer to other biological processes (i.e., shell growth and reproduction). Mortality, greater for juveniles than adults, resulted from seasonal stresses (lowered salinity and heightened sedimentation), spatial competition, predation, and pollutants (hydrocarbons). Once life-history events were confirmed for barnacles in Port Valdez, comparisons of trends observed at the three sites were possible. Differences between populations were evident and were attributed to the unique micro-habitats of the study sites.
• #### Light adaptations of plants: a model based on seagrass Zostera Marina L.

Adaptations to light by a temperate seagrass, Zostaro: marina L. (eelgrass), were investigated along a depth transect representing a gradient of plant development. Various light adaptive strategies are proposed in a conceptual model and tested along the natural gradient and under in situ light manipulation experiments. The major light capturing strategy which Zostera employs is that of changing leaf area. Chlorophyll a to b ratios and amounts, measures of adaptation to light quality and quantity, demonstrated little or no adaptive trends when integrative samples were used. The altered light experiments did not affect chlorophyll content but did affect leaf production rates. Although the relative vertical distribution of leaf area is constant along the transect, the absolute leaf area varies, as measured by leaf area index (LAI = area of leaves/area of bottom). A measured maximum LAI of 17 is higher than other aquatic and most terrestrial ecosystems.
• #### Metabolic hormone levels and immunocompetence of neonatal harbor seals (Phoca vitulina) in rehabilitation settings compared to wild harbor seal pups

Health of harbor seal pups in rehabilitation and in the wild were compared using two metabolic hormones (cortisol and total thyroxine, TT4), two cellular immunity components (lymphocytes and eosinophils) and morphometric measurements. Neonatal harbor seals in two rehabilitation facilities were compared to wild harbor seal pups. Permanently captive harbor seals housed at the Alaska SeaLife Center were also studied. High levels of cortisol at weaning suggest changes in the stress response may be due to diet adjustments in pups during rehabilitation. The lower cortisol concentrations post-weaning suggest that pups in rehabilitation had overcome the challenge of pre-weaning diet, handling or environment and avoided chronic stress. TT4 concentrations were higher in wild pups, likely attributed to a more energetically demanding life in a dynamic environment. The rehabilitated pups showed lower lymphocyte counts and higher eosinophil counts compared to wild pups. Wild harbor seal pups were heavier and longer than post-weaned pups in rehabilitation. Animals in rehabilitation are possibly compromised at stranding, but it is also possible that current rehabilitation practices do not mimic what a healthy pup would receive from maternal investment, thus pups undergoing rehabilitation likely remain smaller and possibly immunologically compromised despite repeated and constant care in rehabilitation.
• #### Milk fatty acid composition of perinatal and foraging Steller sea lions: examination from pup stomachs

To investigate the relationship of milk fatty acid composition between perinatal and foraging Steller sea lions and within each maternal state (i.e., perinatal or foraging), milk samples were collected in 2010 and 2011 via gastric intubation from Steller sea lion pups on a small rookery in the central Gulf of Alaska. Subsamples of initial milk samples were taken over four hours post-collection to examine changes of fatty acids within milk over time. Maternal states of lactating females of sampled pups were determined via remotely operated video cameras on the rookery. Fatty acid composition within milk, collected from Steller sea lion pup stomachs, did not change over the four hour post-collection period, and thus milk fatty acids were not modified within milk over time. Milk fatty acid composition between Steller sea lion maternal states was different, and thus can be utilized to distinguish between perinatal and foraging Steller sea lions of the same geographic region. In the absence of direct observations, this study demonstrated the use of a viable method to determine maternal state. Milk fatty acid composition remained relatively constant within perinatal Steller sea lions, suggesting steady mobilization of fatty acids from blubber to milk, and within foraging Steller sea lions, implying females forage in the vicinity of the rookery and on similar prey species. Differences in milk fatty acid composition between maternal states, including differences in the relative percentages of polyunsaturated fatty acids, may have implications for growth and development of offspring. For lactating Steller sea lions, foraging after the perinatal period is important for continued delivery of fatty acids needed by young pups.
• #### Molecules to marinescapes: the characterization of microbial life in the Arctic Ocean

Microbes are the base of all marine food webs and comprise >90% of all living biomass in the world’s oceans. Microbial life and functioning in high-latitude seas is characterized by the predominance of unknown species that encode uncharacterized genes, replenish nutrients, and modulate ecosystem health by interfacing with disease processes. This research elucidates eukaryotic microbial diversity and functionality in Arctic and sub-Arctic marine environments by describing the culturable and genetic diversity of eukaryotic microbes and the life histories of marine fungi belonging to the Chytridiomycota. This work includes the description of two new mesomycetozoean species, the assembled and annotated genome of Sphaeroforma sirkka, the first description of a cryptic carbon cycle (the mycoloop) mediated by fungi from any marine environment, and the description of large-scale eukaryotic microbial diversity patterns driven by temperature and latitude in the eastern Bering Sea. These results help establish a valuable baseline of microbial diversity in high latitude seas.
• #### Monitoring stress hormones in rehabilitated and captive otariids

Cortisol and corticosterone are the primary mammalian stress hormones released in response to a perceived stressor. Cortisol is rapidly metabolized in the blood, while corticosterone is the dominant product in fecal material. Radioimmunoassay procedures to measure fecal corticosterone and serum cortisol in California sea lions were validated, and adrenal response to surgical and non-surgical procedures was assessed. Other objectives included seasonal and behavioral variability in fecal corticosterone concentrations in captive Steller sea lions, as well as adrenal response to various stressors of a rehabilitated Steller sea lion. There was a significant (P ... 0.05) adrenal response for rehabilitated California sea lions that underwent minor invasive surgical procedures. The small sample size in this study allowed the identification of a correlation of season and behavior in three captive Steller sea lions. This study found that peak fecal corticosterone values reflected responses to acute stressors during rehabilitation for a Steller sea lion pup. Overall, fecal corticosterone was an adequate tool for monitoring stress non-invasive1y in California and Steller sea lions. In turn, the results indicate that California sea lions may be a suitable surrogate species to study the adrenal response to more invasive procedures that may be used in Steller sea lions.
• #### A multi-proxy approach to determine paleoecological change of mangroves, during the holocene, in Belize, Central America

This thesis presents multiple analyses of mangrove peat cores from Spanish Lookout Cay (BT - 79) and from along the banks of the Sibun River (SR-63), Belize to examine ecosystem responses to environmental change during the Holocene. Radiocarbon measurements showed these sites were colonized by mangroves ~8,000 cal. yrs BP and have decreased sedimentation rates from ~6,000 to ~1,000 cal. yrs BP, which is attributed to a decrease in sea-level inundation. Core SR-63 has a change in lithology from primarily mangrove peat to fluvial material at 2,500 cal. yrs BP, which is attributed to erosion inputs of the drainage basin. Changes in the pollen assemblage, such greater input from non-mangrove pollen, are coeval with changes in sedimentation rates at both sites. Subfossil mangrove leaves, from core BT-79, are used for stable isotope ([delta]¹⁵N, [delta]¹³C, and [delta]¹⁸O) analyses to illustrate past physiology and seawater inundation. The composition of organic material in core SR-63 changes from autochthonous to allochthonous sources, which is coeval with the change in lithology. A decrease in the rate of sea-level rise is assumed to be the cause of the significant changes seen in these mangroves, which counters existing sea-level curves.
• #### Multiple stable isotopic analyses ([delta]¹³C, [delta]¹⁵N, [delta]¹⁸O, and [delta]D) of the Boulder Patch, a high arctic kelp community: trophic and temporal perspectives

The Boulder Patch, a high Arctic kelp community, is a rarity in the Alaskan Beaufort Sea. Considered a biodiversity oasis, this area provides habitat for many organisms. Trophic relationships, spatial patterns, and isotopic changes over time were examined within the Boulder Patch using stable carbon and nitrogen isotopes. 394 samples, representing over 55 species were analyzed. Isotope values showed considerable variability in the food web base, particularly for the kelp Laminaria solidungula. Isotopic values for most animals fit their known feeding strategies. Little spatial variation was observed in isotope values, however temporal differences were found in L. solidungula isotope values between 2002 and 2004, and between archived samples collected during the 1980's. To better understand patterns in stable oxygen and hydrogen isotopes, values were assessed and applied in an ecological context. Sixty-four samples were analyzed, encompassing 29 species. Results indicated distinct differences between primary producers and animals, offering insights into a possible application of [delta]¹⁸O and [delta]D in ecological studies. By defining trophic structure and elucidating feeding strategies of organisms, this study enhanced the biological knowledge in the Boulder Patch, providing ecological information on a high arctic kelp community.
• #### Natural abundance of nitrogen(15) in a subarctic lake and biogeochemical implications to nitrogen cycling

Stable isotope ratios of nitrogen ($\delta\sp{15}$N) were employed to track the origin and fate of nitrogen in a subarctic lake, Alaska. The annual planktonic nitrogen cycle was dominated by N$\sb2$ fixation in spring and NH$\sb4\sp+$ assimilation in summer. In winter, microbial nitrification was the major sink for NH$\sb4\sp+$ and denitrification was accounted for most of the loss of NO$\sb3\sp-.$ The small isotope fractionation in nitrification is proposed as a result of substrate (NH$\sb4\sp+)$ limitation. The temporal and spatial homogeneity of the $\delta\sp{15}$N of dissolved organic nitrogen may be related to its large pool size and refractory nature. A stable isotope mass balance suggests that the winter phytoplankton was only composed of 10 to 20% of the suspended organic matter in water column due to low primary productivity during the ice cover period. A close correlation between $\delta\sp{15}$N of phytoplankton and $\delta\sp{15}$N of dissolved pools indicates that NH$\sb4\sp+$ was the predominant nitrogen source for non-N$\sb2$-fixing algae. The similarity of $\delta\sp{15}$N between a spring blue-green bloom and N$\sb2$ suggests an atmospheric origin for nitrogen. A mixing model estimated that the blue-green algal bloom derived approximately 70% of its nitrogen from molecular nitrogen. This fixed nitrogen was further transferred to higher trophic levels via the food chain and to other primary producers following mineralization. The $\delta\sp{15}$N of aquatic macrophytes indicates that non-rooted species obtained their nitrogen from the water column while rooted species obtained their nitrogen largely from the sediment. Evidence from dual isotope tracers ($\delta\sp{15}$N and $\delta\sp{13}$C) suggests that the zooplankton were supported by phytoplankton throughout the growing season despite an apparent abundance of detritus in the water column. Benthic fauna relied on either phytoplankton detritus or other organic matter in the sediment. The $\delta\sp{15}$N data exhibit only two to three trophic levels in both planktonic and the benthic communities in Smith Lake.
• #### Nitrogen utilization during spring phytoplankton bloom development in the southeast Bering Sea

Interactions between a high latitude, continental shelf, spring phytoplankton bloom and water column physics and chemistry were studied using measured rates of nitrogen uptake. Peak bloom conditions commenced when the mixed layer shallowed and minimized respirational losses. Integrative light-mixing growth models were accurate during early bloom stages. An advection-diffusion model associated peak bloom nitrate uptake with pycnocline mixing rates of 2.1 m d * in an 18 m mixed layer. The accumulation of surface buoyancy was a reliable index of peak bloom temporal and spatial "patchiness" since mixing rates influenced both respirational losses and nutrient supply. Maximum nitrogen specific uptake rates (h r .- 1 ), unlike those of carbon, coincided with peak bloom conditions. Although species com positions among peak bloom periods were similar, particulate C/N ratios were not. Apparently, both intercellular factors and prevailing mixing conditions influence specific uptake rates and cell composition. A large proportion of new (nitrate) to total productivity was associated with the dominance of the early bloom forming diatoms in the mixed layer. In the absence of these net plankton the residual nanoplankton dominated community exhibited a greater dependence on regenerated nitrogen. Nitrate uptake averaged 700 mg-at m during the spring bloom and 1 g-at m-2 year-1 The yearly f factor was 0.40. Nitrogen uptake based carbon productivity was 188 g C m -2 year -1 A mass balance of the inorganic carbon system indicates that nitrate uptake alone cannot account for all the carbon leaving the surface layer. The correspondence between 1SN0~ uptake measurements and nitrate decreases suggests the diffusion of slope water into the middle shelf is slow. Large scale meteorological patterns may be responsible for the inter annual variability observed in production. Frequent May storm activity prolonged peak bloom periods, while calm conditions promoted extensive Chijl layers. The passage of atmospheric low pressure system s was also associated with the cross shelf "pumping" of water masses.
• #### Non-linear dynamics of marine ecosystem models

Despite a rapid trend towards more realistic Nutrient-Phytoplankton-Zooplankton (NPZ) models, in which zooplankton are presented with multiple nutritional resources, investigations into the fundamental dynamics of these newer models have been limited. The objective of this dissertation was to explore the dynamical behavior of such NPZ models parameterized for the coastal Gulf of Alaska. With alternative stationary forcing regimes and zooplankton grazing functions, the dynamics of one-dimensional NPZ models were investigated for a range of specific predation rates (h) and predation exponents (q), which together define the form of the predation (model closure) function. Oscillations in state variables are shown to be an intrinsic property of the NPZ models, not dependent on variable seasonal forcing for their existence. Increasing mixed layer diffusivity or reducing mixed layer depth increased model excitability; it is hypothesized that this is due to the resultant increase in flux of utilizable nutrient. Model behavior was also strongly influenced by the form of both the grazing and predation functions. For all of the grazing functions implemented, Hopf bifurcations, where the form of the solution transitioned between steady equilibrium and periodic limit cycles, persisted across the q-h parameter space. Regardless of the values of h and q, with some forms of the grazing function steady equilibrium solutions that simultaneously comprised non-zero concentrations for all model components could not be found. The inclusion of sinking detritus in the model had important implications for the composition and excitability of model solutions, generally increasing the region of q-h space for which oscillatory solutions were found. Therefore, in order to correctly simulate the depth-explicit concentrations of model components, or to have an accurate understanding of the potential excitability of the system, inclusion of this component is valuable. This dissertation highlights the importance of understanding the potential impact that choice of functional response may have on the intrinsic oscillatory nature of a model prior to interpreting results from coupled bio-physical simulations. As we come to rely more on ecosystem models as a tool to interpret marine ecosystem functionality it will be important to improve our understanding of the non-linear behavior inherent in these models.
• #### Numerical Method For Tsunami Calculation Using Full Navier -Stokes Equations And The Volume Of Fluid Method

A two-dimensional numerical model was developed to study tsunami wave generation, propagation and runup. The model is based on solving the Navier-Stokes (NS) equations. The free-surface motion is tracked using the Volume of Fluid technique. The finite difference two-step projection method is used to solve NS equations and the forward time difference method to discretize the time derivative. A structured mesh is used to discretize the spatial domain. The model has been conceived as a versatile, efficient and practical numerical tool for tsunami computation, which could address a comprehensive understanding of tsunami physics with the ultimate aim of mitigating tsunami hazards. The prediction capability of tsunami generation, propagation and runup is improved by including more accurately the effects of vertical velocity/acceleration, dispersion and wave breaking. The model has the capability to represent complex curved boundaries within a Cartesian grid system and to deal with arbitrary transient-deformed moving boundaries. The numerical model was validated using laboratory experiments and analytical solutions. The model was used as a tool to determine the adequacy of the shallow water (SW) approximation in the application of tsunami simulations. Numerical results were compared with experimental data, analytical solutions and SW results in terms of the time-history free surface elevations and velocity. Reasonable agreements were observed based on the spatial and temporal distributions of the free surface and velocity.
• #### Nutrient Dynamics In The Northern Gulf Of Alaska And Prince William Sound: 1998--2001

The northern Gulf of Alaska (GOA) shelf is a productive coastal region that supports several commercially important fisheries. The mechanisms supporting such high levels of productivity over this shelf are not understood, however, since it is a downwelling-dominated shelf. In an effort to understand the mechanisms underlying such high biological productivity, nutrient distributions were determined 25 times throughout 1998, 1999, 2000, and 2001 from over the northern GOA shelf and in Prince William Sound (PWS). Deep water (>75 m) nitrate, silicate and phosphate concentrations were positively correlated with salinity indicating an offshore nutrient source. The average annual cycle was established, in which nitrate, silicate and phosphate responded seasonally to physical and biological processes. Ammonium concentrations were generally low and uniform (<1.2 muM) with occasional patches of higher concentrations. During each summer, an onshore flux of dense nutrient-rich bottom water onto the shelf was evident when the downwelling relaxed. This seasonal flux created nutrient reservoirs over the deeper shelf regions that were eventually mixed throughout the water column during the winter months. This annual evolution may be vital to the productivity of this shelf. A large degree of interannual variability was found during the study, which included El Nino (1998) and La Nina (1999) years. Spring phytoplankton biomass over the shelf was highest in 2000 when the upper waters were nutrient enriched and strongly stratified. The highest phytoplankton biomass was measured in May 1999 during the passage of a slope eddy, which demonstrated the potential of these phenomena to greatly enhance primary productivity. A large degree of spatial variability was also found, both cross-shelf and along-shelf. Hinchinbrook Canyon was found to consistently have high salinity, nutrient-enriched bottom waters suggesting it plays an important role in the transport of slope waters onto the shelf and probably into PWS. Along-shelf trends were found in the upper coastal waters in the winter and spring, with higher salinities, temperatures, and nutrient concentrations upstream of PWS. The nutrient dynamics were similar in PWS and over the shelf/slope in 2001; however, nutrient drawdown, followed by depletion, and the spring bloom appeared earlier and stronger in PWS.
• #### Nutritional and behavioral aspects of reproduction in walruses

Walruses (Odobenus rosmarus) at Marineland, California consumed food in increasing amounts as they grew larger out ate less per unit of body weight. Adult males consumed the most food in November - December, then fasted throughout the breeding season. Females apparently fasted during ovulation and birth. Females consumed 50% more energy while pregnant or lactating than when not pregnant or lactating. Male walruses spent more time displaying, and their displays were more stereotyped, during the breeding season. Females initiated and terminated interactions with the males during the breeding season, and those interactions were preceeded by displays. Females vocalized to the calf to initiate suckling bouts, reassure the calf, and to call the calf. Calves vocalized to initiate suckling bouts and indicate danger. When the calf was threatened, the female responded quickly by tusk strikes, kinesic tusk threats, vocal threats, or calling the calf. The calf tended to follow the female.
• #### Odors And Ornaments In Crested Auklets (Aethia Cristatella): Signals Of Mate Quality?

Crested auklets (Aethia cristatella) are small colonial seabirds that display an ornamental feather crest and emit a citrus-like odorant during the breeding season. In this study odors and ornaments were investigated as possible signals of mate quality. Crest size was negatively correlated with the stress hormone corticosterone in males, but this was not the case in females. Body condition was negatively correlated with corticosterone in females, but this was not the case in males. Corticosterone levels were interpreted as an index of physiological condition, and it was concluded that males with longer crests were more competent at meeting the social and energetic costs of reproduction. I hypothesized that the crested auklet odorant: (1) functions as a chemical defense against ectoparasites, (2) is assessed as a basis for mate selection, (3) is facilitated by steroid sex hormones. Laboratory and field experiments showed that synthetic replicas of the crested auklet odorant repelled, impaired, and killed ectoparasites in a dose-dependent fashion. Chemical concentrations in plumage were at least sufficient to repel and impair ectoparasites. Chemical emissions from breeding adult crested auklets peaked at the time of egg hatching when young are most vulnerable to tick parasitism. In males, chemical emissions were correlated with crest size, a basis for mate selection. Presentation of synthetic aldehydes elicited behaviors similar to those that occur during courtship. Captive crested auklets responded preferentially to synthetic replicas of their odor, and the highest frequency of response occurred during early courtship. These results show that the chemical odor could be a basis for mutual mate selection. Production of the chemical odorant may be facilitated by steroid sex hormones since octanal emission rates were correlated with progesterone in males. Finally it was determined that the chemical composition of odorants in crested auklets and whiskered auklets (A. pygmaea) differed in three key respects. This suggests that an evolutionary divergence occurred in the odorants of the two species similar to what has been suggested for ornamental traits. In conclusion, crested auklets appear to communicate with odors and ornaments, and these signals may convey multiple messages regarding condition, quality, and resistance to parasites.