Palmaria palmata and Chondrus crispus were cultured in the lab at three levels of temperature and two of nitrate, representative of commercial Atlantic halibut farming conditions. Productivity and nitrogen removal by P. palmata were greatest at temperatures <10°C. Productivity of C. crispus was greatest at >10°C, while nitrogen removal was unaffected by temperature, 6-17°C. When cultured in various nitrate and ammonium combinations, nitrogen uptake was highest when available as ammonium. Both species took up 89-100% of ammonium in 24 hours, but only 23-37% and 55-87% of nitrate was taken up by P. palmata and C. crispus, respectively. When P. palmata was integrated with halibut recirculating aquaculture, productivity and nutrient removal were compromised during summer. During winter, <11°C, nitrogen removal by P. palmata was relatively stable at 2.3 gN m-2 d-1. For 50% nitrogen removal from halibut aquaculture during winter, a finfish: seaweed biomass of 1: 1 would be required.

No description available.

No description available.

Low species diversity in the Arctic promotes strong food-web linkages, as changes in abundance of one species may influence many others. Using harvest records, I determined Arctic fox populations are declining in their southern distributional range due to shallower snow potentially limiting density of lemmings, their primary prey, which live and breed beneath snow. Additionally, warm fall and spring temperatures are shortening access to alternative prey, seals on sea ice. Arctic foxes also influence other species through non-trophic interactions, as lemming winter nests were found on 70% of fox dens examined. I determined warmer subnivean temperatures promoted by accumulation of thick snow leeward of tall vegetation on dens attracted lemmings to these dens. Furthermore, lemming reproduction was higher dens compared to traditional lemming habitat. This research highlights the impact of climatic variables on Arctic predator-prey interactions and the importance of understanding impacts of trophic and non-trophic interactions on species demographics. / February 2017

Salt marsh food webs are complex systems, with high levels of in situ primary production supporting a wealth of resident and migratory species. In this study, we use stable isotopes as a tool to trace organic matter utilization within the Nueces Marsh food web. Specifically, we were interested in (1) the use of treated wastewater as a ¹⁵N tracer, and (2) seasonal and interannual variation in food web structure. We hypothesized that treated wastewater would selectively label detrital resourse use within the food web, allowing us to trace grazing vs. detrital pathways within the marsh system. We also hypothesized that marsh consumers would exhibit distinct differences in isotopic composition between summer and winter, and between different years. We found that the Nueces Marsh food web consists of 3.5 consumer trophic levels. The [delta]¹³C values of consumer organisms were similar across the spatial extent of the low marsh, regardless of proximity to wastewater inflow. However, a majority of the organisms collected from the wastewater channel were significantly (p<0.05) enriched in ¹⁵N compared to their reference counterparts. We propose that ¹⁵N-enriched nitrogen is entering the Nueces Marsh food web through detrital rather than grazing-based pathways, making wastewater effluent an effective tracer of detrital integration into a marsh food web system. Hydrologic data indicate that isotopic shifts between seasons and between years reflected larger scale shifts between drought and wet years. During drought years, decreased production by phytoplankton and emergent plants led consumers to rely more heavily on ¹³C-enriched cyanobacterial carbon. In contrast, wet years encourage phytoplankton and emergent plant production, making cyanobacterial carbon relatively less exploited. While the Nueces Marsh food web is supported by a stable detrital carbon pool, it may still be susceptible to larger scale hydrologic events. / text

While the impact of top-down and bottom-up drivers of ecosystem functions has been given considerable argument, here the mid-trophic level is given focus. In marine systems the influence of mid-trophic level species operates in a ‘wasp-waisted’ structure, where they exert regulatory control by acting as a valve to energy flow between large seasonal pulses of primary production and upper level species. In this study I examine the impact of foraging eastern Pacific gray whales (Eschrichtius robustus) on mysid species at the ‘wasp-waist’ (Order Mysidacea), and vice versa, at feeding sites in Clayoquot Sound off the west coast of Vancouver Island. I appraise previously unknown aspects of the ‘prey-scape’, and further explore life-history traits that allow prey populations to persist in a given species array. The set of problems that I examine are all based on the whales’ top-down forcing in a localized area, and the prey response. I use several scales of observation as dictated by the nature of each question. I examine top down forcing and subsequent prey switching over a 25-year period, the variation in foraging intensity over a 15 year period, the differential prey species’ response to persistent predatory pulses that creates dominance and diversity among the mysid species flock, and whales’ within-season response to possible satiation. Each of these studies is linked by the common goal of illuminating the intimate relationship between predator and prey. Gray whale foraging has decimated amphipod prey resources in the study area past the point of recovery over the last 25 years, and the prey resource is no longer a viable energy source. This has led to the abandonment of benthic-feeding by gray whales in the area, and a switch to mysids as a primary prey source. It is in investigating these mysid species’ ability to rebound following severe foraging pressure that I uncovered two principal life history strategies, one held by the single dominant mysid species, and another used by 9 or 10 others consistently sampled. The capacity for renewal of mysid swarms is imperative if Clayoquot Sound is to persist as a productive foraging area for gray whales. The pattern of this relationship that I present, based on a 15 year span, was previously unknown. Intense foraging of mysids by gray whales during a summer affects the reserves for the following season, leading to a biennial fluctuation in the number of whales the area can sustain, although some of the heaviest foraging seasons require several years to show mysid recovery. I state 9 or 10 other species, as through the intense examination of mysids here, there may be a new species designated. The data gathered by myself and colleagues over the past 25 years that whales have been studied in Clayoquot Sound, clearly shows that predation by baleen whales can affect the future quality of their foraging areas, as well as influencing the population, life-stage and diversity of prey species. My work furthers knowledge in life history characteristics of the mysid species present in the study area, particularly growth and reproduction, and ability to capitalize on a release of predation pressure over winter to recover. That, in turn creates a series of following questions about how different life history strategies make use of a variety of possible energy pathways to stabilize ecosystems at least at discrete spatial scales. / Graduate

One advantage of Integrated Multi-Trophic Aquaculture (IMTA) is the potential for bioremediation by organic-extractive organisms. In British Columbia, a number of marine invertebrate species are being considered for use in open-water IMTA with sablefish (Anoplopoma fimbria). These include both filter-feeding bivalves (e.g. cockles, mussels, oysters, scallops) which would consume the finer suspended particulates from the finfish culture component and deposit/detrital feeders (e.g. sea cucumbers, sea urchins, prawns) which would feed on the heavier-settleable solids. The following candidate species were tested for their ability to consume sablefish faeces and uneaten sablefish feed in laboratory feeding trials: green sea urchin (Strongylocentrotus droebachiensis), basket cockle (Clinocardium nuttallii), blue mussel (Mytilus edulis), spot prawn (Pandalus platyceros), and California sea cucumber (Parastichopus californicus). Whether they can remove organic material from aquaculture wastes was tested by measuring ingestion rate or clearance rate and absorption efficiency when they were fed a diet of sablefish waste, relative to those fed a natural control diet. Egestion rates in the candidate species were quantified to estimate the potential amount of waste that may be lost from the organic-extractive component. Biophysical properties including shape, size, and settling velocity were measured in faecal pellets egested by the candidate species to provide input data for models to assess dispersal of faeces from IMTA sites. Results from the laboratory feeding trials demonstrate that all candidate species are capable of consuming wastes from sablefish aquaculture and absorbing the organic material. The relative merits and drawbacks of each candidate species are discussed with respect to the results and within the broader context of IMTA. The general conclusion is that, in order to achieve efficient removal of organic material and successful bioremediation, deposit feeders should be included in the organic-extractive component, whether alone or in conjunction with suspension feeders. / Graduate

Tropical habitats have high taxonomic and ecological diversity, but they are currently subject to high rates of extinction. Amphibian populations are declining globally and while we have some understanding of the causes of these declines, it is unclear how these losses will influence ecosystem structure and function. Secondary production and trophic basis of production analyses link consumers to energy flow and reflect the relative importance of various energy sources and energy flow pathways in food webs. These techniques can yield valuable information on the roles of individual consumers in ecosystem function, and thus the ecological consequences of extinction and extirpation events. I estimated the trophic basis of production in a Panamanian headwater stream to identify major sources of energy, measure energy flow through consumers, and characterize interactions among trophic levels and functional feeding groups. I examined gut contents of 19 dominant macroinvertebrate and two dominant tadpole taxa collected during dry and wet seasons before an amphibian decline. I used previously published estimates of secondary production, assimilation efficiencies, and net production efficiencies, along with gut content data, to quantify food web structure and energy flow pathways. Overall consumption of allochthonous materials was greater than autochthonous (p < 0.001), and the dominant food sources were non-algal biofilm and vascular plant detritus. Autochthonous materials were consumed at higher rates during the dry season (p = 0.012). Total consumption rates varied within and among shredders (0.85 - 12.10 g/m2/yr), scrapers (0.46 - 0.91 g/m2/yr), filterers (1.20 - 4.67 g/m2/yr), gatherers (0.43 - 2.44 g/m2/yr) and predators (0.05 - 0.95 g/m2/yr). Overall consumption rates in pool habitats were higher compared to riffles. The degree of omnivory in the food web was much higher than has been observed in similar temperate streams. Omnivory was prevalent across all functional feeding groups, but more pronounced in predators, especially Anacroneuria (55% animal and 45% plant materials in guts). There was also an ontogenetic shift among most dominant macroinvertebrates from smaller, energy rich food sources (e.g., non-algal biofilm) to larger, less nutritious materials (e.g., vascular plant material) with increase in size. My research is the first to provide quantitative estimates of energy flow through a neotropical headwater stream food web. Information from this study is central to understanding and conserving tropical headwater streams. Further, my results, along with post-amphibian decline analyses from the same stream, will allow for a comprehensive assessment of the ecological consequences of amphibian declines.

Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol) / The basic biology and ecology of Etrumeus wongratanai was investigated from samples of fish collected by jigging off Scottburgh, Kwazulu-Natal throughout 2014 and 2015. A total of 516 otoliths, 401 gonads, 140 stomachs and 163 samples of white muscle tissue was examined, and length and weight data of 3 637 fish caught between 2013 and 2016 was also analysed. Counts of annuli deposited on sagittal otoliths indicate that sampled E. wongratanai ranged from 0 to 3 y. (year/s) of age. Length-at-age for males (females) was estimated at 15.5 cm (16.2 cm) for 1 y. olds, 17.7 cm (17.4 cm) for 2 y. olds and 19.6 cm (18.8 cm) for 3 y. olds. The length at 50% maturity was estimated to be 15.6 cm for males, and 16.1 cm for females. Etrumeus wongratanai showed high gonadosomatic index values from June to December indicating that the breeding season lasts for 6 and 8 months for males and females, respectively, and that spawning takes place from the onset of winter to early summer. Condition factor was lowest in May through to August and increased from September. The low condition factor values from May through to August could be due to the physiological strain before and during the spawning season. Fish larvae were the most important food item in samples collected in summer, whereas eucalanids were the most important prey item in autumn and winter. Overall, large copepods were the dominant prey items in terms of frequency and importance. Stable isotope data suggests that there are gradual changes in the trophic level and diet of E. wongratanai as it increases with size, and whilst δ¹⁵N values differed between seasons δ¹³C did not. The results obtained here are compared with other species of Etrumeus, regionally and globally. / National Research Foundation (NRF) and ACEP Phulisa

Although climate change is a global phenomenon, the Arctic is warming faster than any other region on earth. These climatic changes have driven rapid regional changes over the past half-century in both the physical landscape and the ecosystems therein. One such ecological interaction is between migratory shorebird survival and local insect emergence. Annually, tens of millions of migratory shorebirds travel to the Arctic to rear their young in the relative absence of predators, but in a relative abundance of food (insects). Over evolutionary time, these trophic levels have coupled: shorebird chicks tend to hatch during the period of highest terrestrial insect availability. However, climate change is currently uncoupling this food-web synchrony, creating potential for trophic mismatch. In the High Arctic near Utqiaġvik (formerly Barrow), Alaska, trophic mismatch between nesting shorebirds and their insect food base is already detectable. In this ecosystem, flies in the Family Chironomidae (non-biting midges) dominate the prey trophic level in the avian food web. We have found that the pre-emergence development of one particular midge, Trichotanypus alaskensis, defies conventional wisdom of the Family, as this species molts to an additional fifth larval instar prior to pupation and emergence (all other chironomids are known to have four larval instars). We discovered an Utqiaġvik midge that reproduces asexually, a species that was not documented in the 1970s. Utilizing controlled temperature rearings of Utqiaġvik midge larvae, we discovered that as temperatures rise, emerging chironomid adults are generally smaller in size. We have found that chironomid pre-emergence developmental rates follow a positive exponential relationship as temperatures increase, can vary by taxon, yet are consistent across field and lab settings for a given taxon. At Utqiaġvik in the 2010s, chironomid emergence occurs 8-12 days earlier than it did in the 1970s. These findings shape our understanding of trophic mismatch in this arctic food web. / Arctic Landscape Conservation Cooperative; NDSU Graduate School Dissertation Fellowship; U.S. National Fish and Wildlife Foundation; Environmental and Conservation Sciences Program; Department of Biological Sciences