Yevhenii Pakhomov

Microplastic pollution now threatens some of the world's most iconic locations for biodiversity, including the Galápagos Islands, Ecuador. This thesis highlights the pervasive and harmful nature of plastic pollution in our oceans, which has significant ecotoxicological implications for marine ecosystems, biodiversity, and human health.Using the Galápagos penguin as an indicator species, this study assessed the concentration of microplastics and other anthropogenic particles in surface seawater near Galápagos penguin colonies, penguin prey, zooplankton, and penguin scat, as well as microplastic bioaccumulation and biomagnification potentials in the Galápagos penguin using trophodynamic Ecopath with Ecosim (EwE) ecosystem modeling with the Ecotracer contaminant tracing routine. The study also investigated Ecuadorian mangrove communities' perceptions of plastic pollution's impact on the environment, economy, and human health, providing localized context for effective strategies to tackle this pervasive problem.Empirical evidence collected in the Galápagos in October 2021 revealed an average of 0.54±0.49 particles/L in surface seawater (
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Gelatinous zooplankton (GZ) biomass is an important, yet often overlooked, vector of particulate organic matter (POM) export in the ocean and a nutritional prey source for the mesopelagic and benthic environments. To better quantify the potential impact of their blooms on surrounding biogeochemistry and food webs, we performed decomposition and sinking experiments under two different temperature regimes, 6 and 12 °C using 260 Salpa aspera, sampled in the Northeast Pacific during May 2021. Salps were suspended in large seawater tanks with continuous water filtration systems and kept in the dark for a maximum of 30 days. Decay was exponential and occurred ~1.5 times faster in the warmer conditions. Comparison of GZ across literature studies supported the strong influence of temperature on their decomposition (Q₁₀ = 3.46) and revealed S. aspera to decay at a lower rate compared to most other GZ taxa. Carcass sinking rates were higher than previously reported for this species but slowed with prolonged decay. Biochemical (proteins, carbohydrates, lipids) and elemental (C: carbon, N: nitrogen) composition was determined for samples at various stages of degradation. Energetic content, estimated from total organics using published conversions, was typical of GZ but notably lower than common crustacean zooplankton. The high water (~97%) and low organic content of 27.8 ± 7.1 percent of dry weight (% DW) was typical of other thaliaceans. S. aspera carcasses were relatively rich in C (15.6 ± 1.66% DW) and somewhat low in N (2.42 ± 0.53% DW). Carbohydrates accounted for the majority of total organics (45.3%), followed by lipids (42.1%) and protein (13.3%). However, possible under-detection of protein could have served to overestimate lipid content and skew macromolecular ratios. The high C:N ratio (6.61 ± 1.14) of S. aspera, in comparison with a typical ratio of
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The cultural and ecological contributions of salmon cannot be understated, as these keystone species have underpinned coastal ecosystems and societies from time immemorial. Despite this millennia-long intimate relationship with Pacific salmon, returns of stocks have become unpredictable and difficult to manage from overfishing and multiple complex stressors. Research has shown that juvenile salmon feeding is a crucial factor for growth and recruitment, and the ocean conditions driving prey availability are tightly coupled with survival of salmon. Pink and chum are abundant co-migratory species of salmon that may exert competitive pressure for food resources during their vulnerable early marine phase. However, competition research on juvenile pink and chum salmon is limited, especially within the complex British Columbia coast. This research aimed to fill gaps in understanding of juvenile pink and chum foraging strategies and interactions in areas of good and poor foraging conditions during their coastal outmigration. In the Discovery Islands and Johnstone Strait regions, there were foraging deserts and oases, where juvenile salmon mean stomach fullness values ranged from 6% body weight. In good foraging conditions, juvenile pink and chum both consumed the same high-quality crustacean prey with limited competition, but under poor foraging scenarios, salmon diets differed. Chum salmon consistently consumed gelatinous prey and pink salmon relied more heavily on copepods and nearshore zooplankton, differing in niche in response to competitive interactions. There was a match between predators and prey in 2015, when salmon fed on larger prey, and were in healthier condition (K = 1.0). There was a potential mismatch in 2016, when small prey taxa may have caused poorer condition for juvenile salmon (K = 0.94). Chum salmon had a stronger relationship to prey size than pink, when larger chum successfully consumed the largest prey. These foraging strategies of opportunistic specialization may indeed provide salmon with resilience to face the challenges of shifting climates. Pink and chum salmon can be monitored as indicators for ecosystem health and zooplankton availability. Salmon reflect the health of socio-ecological systems and require our understanding and care to view them holistically as they migrate through diverse, challenging habitats.

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Pacific salmon hold tremendous ecological, cultural, and economic value to communities and ecosystems throughout British Columbia. The productivity of several populations, however, has declined since the early 1990s. The cause of the decline is still not fully understood, though bottom-up drivers and trophic interactions during the early marine migration are believed to be contributing factors. For juveniles leaving the Fraser River, their migration crosses a range of stratified and well-mixed waters with varying levels of productivity. The purpose of this study is therefore to a) characterize the foraging ecology of juvenile sockeye salmon across the range of environmental conditions they encounter during the early marine migration, and b) test whether foraging success is lower in tidally mixed waters. In 2015 and 2016, environmental conditions, prey dynamics, and sockeye diets were sampled at high spatial and temporal resolution in the Discovery Islands and Johnstone Strait during the outmigration period. Analyses revealed two unique diet types, one dominated by meroplankton, cladocerans, and larvaceans in the warmer, fresher waters of the Discovery Islands and the other dominated by large calanoid copepods in the cooler, saltier waters of Johnstone Strait. In all diets, sockeye exhibited strong selection for prey items larger than 2 mm. Furthermore, foraging success was low throughout the tidally-mixed regions of the Discovery Islands and Johnstone Strait, providing strong support for the hypothesis that this region is a ‘trophic gauntlet’ for outmigrating salmon. Foraging hotspots were also discovered along the interface between mixed and stratified waters. These frontal areas may in fact be important foraging grounds for juveniles to facilitate their migration through otherwise challenging conditions. This research addresses a critical knowledge gap in the foraging ecology of juvenile salmon across different environmental conditions during their early marine migration and can be used to improve our ability to monitor fish condition, growth, survival, and ultimately recruitment.

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Coastal British Columbia is composed of deep channels and shallow sills intricately wovenaround a collection of small islands, creating complex oceanographic conditions. Consequently,seasonal production varies up to several orders of magnitude throughout the region, with someregions undergoing large annual phytoplankton blooms, while others have permanently lowphytoplankton biomass. The region from the northern Strait of Georgia (SoG) to Johnstone Strait(JS) has been vastly understudied from the perspective of zooplankton despite its importance tomany higher trophic levels. The objectives of this study were to: a) describe the annual seasonalcycle of zooplankton in the northern SoG over the course of two years and examine howcommunities differed, and b) examine the spatial patterns in zooplankton communitycomposition and abundance from the northern SoG to JS, a region spanning seasonallyproductive / stratified areas (northern SoG, eastern Discovery Islands (DI)) as well aspermanently high-nutrient, low-chlorophyll (HNLC) regions (JS, western DI). There was astrong signal of intra-annual seasonality in zooplankton community dynamics in the northernSoG, separating into distinct winter, early spring, and summer – fall assemblages. Despite a sixweek difference in spring bloom timing between years, peak zooplankton abundance occurredwithin the same calendar week during both years and community composition was similarbetween years, indicating that there is likely resilience within the zooplankton seasonal cycle toshort scale interannual changes in environmental conditions. Our spatial analysis indicated thatthe northern SoG, DI, and JS each had distinct zooplankton communities with key species anddensities separating regions. We detected minimal overlap in the JS zooplankton communitywith the DI and northern SoG, indicating that while DI zooplankton are likely sourced from theSoG, JS zooplankton likely originate from Queen Charlotte Sound. The DI were comprised ofboth productive and HNLC regions, yet zooplankton abundance was highest in the mixedwestern DI channels. Intense tidal mixing in the DI likely supplies nutrients to stratified surfacewaters in the eastern DI, which in turn supply zooplankton to the western DI with low in-situproduction. These results provide insight into how feeding conditions for higher trophic levelsmay vary throughout the region.

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The sockeye salmon, Oncorhynchus nerka, is economically, ecologically and culturally important for British Columbia and Canada. Currently, ~75% of sockeye populations are declining with a precipitous decline reported in Rivers Inlet (RI). The purpose of this study was to investigate the variability of juvenile sockeye residence and growth in RI during their outmigration to the Pacific Ocean. The point of the marine entry was estimated by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) using otolith elemental composition (Sr:Ca ratio). A significant correlation was found between the day of entry and the duration of the migration. Average transit time through the inlet was ~ 2 weeks in 2011 and 2009, compared to ~ 4 weeks in 2008 and 2010. In terms of BL/s, the fish travel through RI with an average speed of 0.2– 0.5 BL/s. The size of the smolts at the entry to the inlet ranged between 54 and 83 mm. Detailed analysis of the full outmigration period in 2009 identified two possible migration behaviors, dependent on the day of entry and potentially the size of the smolts. Smaller fish that entered the inlet prior to mid-June exhibited a “holding” pattern at the head of the inlet, with an average residence time of 2-3 weeks. Smolts that entered the inlet later in the season swam continuously throughout the inlet. Using GAM models, it was determined that 78% of the weight at catch and 64% increase in weight were explained by the combination of water temperature, freshwater discharge, zooplankton densities and inlet entry size of smolts. The duration of the outmigration was dependent on river discharge and temperature, with 62% of the variation in outmigration duration explained by the model. Results suggest that there is a set of optimal environmental conditions for smolt growth during their outmigration. Outmigration timing was found to be the key determinant of conditions experienced and appeared to act as an equilibration mechanism between small and large smolts, resulting in similar size being attained by both by the inlet mouth.

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Sockeye salmon (Oncorhynchus nerka) populations in BC have undergone varying degrees of decline coinciding with a shift to a warmer phase of the Pacific Decadal Oscillation (PDO) in 1977. The PDO, and other climate cycles, have been shown to significantly affect the physical and biological characteristics of the North East Pacific Ocean. Changes in ocean productivity have implications for pelagic food webs and may cause shifts in the abundance of potential prey for sockeye salmon, impacting their long-term production patterns. We investigated the coupling of ocean conditions and population fluctuations using Rivers Inlet as a case study, a system that suffered probably the most catastrophic sockeye stock collapse in BC history. Stable isotope analysis was used to access information on ocean conditions stored in the carbon and nitrogen isotope ratios of archived sockeye scales for the period 1915-2013. Our results indicated that Rivers Inlet sockeye salmon experienced highly variable open ocean conditions during this period. Both decadal scale shifts in North Pacific climate (e.g., PDO) and interannual scale shifts in climate (e.g., El Niño/La Niña events) were reflected in the physical and biological environment of the offshore Gulf of Alaska. Positive phases of the PDO and El Niño events were associated with a warmer and less productive ocean, while negative phases of the PDO and La Niña events were associated with a colder and more productive ocean. Moreover, the carbon and nitrogen stable isotope time-series indicated that the foraging habits of Rivers Inlet sockeye salmon were affected by these shifts of North Pacific climate. A lengthening (shortening) of the food web was associated to warm (cold) and less productive (more productive) periods. In addition, the isotope data also supports Rivers Inlet sockeye salmon shifting diet depending upon prey availability. We concluded that a combination of the two factors was responsible for the changes in the feeding ecology of Rivers Inlet sockeye salmon during the period 1915-2013. Such variation in the feeding ecology of Rivers Inlet sockeye salmon could potentially have a negative effect in the overall survival rates of sockeye salmon.

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The life cycle of Limacina helicina has been continuously debated within the literature.We believe the current lack of consensus regarding fundamental aspects of its life cycle(e.g. seasonal times of spawning, seasonal development of the population size structure, as well as the life cycle longevity)is primarily due to using datasets of low temporal resolution. Using fort-nightly data, two population cohorts were identified using the mixdist statistical package and tracked for more than 400 days, throughout 2008 to 2010.From this, a life cycle longevity of 1.2--1.5 years was estimated for L. helicina in Rivers Inlet.Throughout the seasons, the population size structure showed a continually high presence of the smaller size-groups suggesting continuous spawning, however, based on total densities of > 600 ind.m^-³, the late spring was put forward as the period of peak spawning.Continuous spawning was confirmed with the use of daily data.Identification of a summer peak spawning established late spring and summer as two periods of enhanced spawning, although continuous spawning occurred throughout the season (in a limited fashion).Short-term periods of significant growth were observed prior to peak spawning in late spring and summer. This was not directly coupled with chlorophyll concentrations, possibly due to the time lag between periods of high chlorophyll biomass and zooplankton response.Attempts were made to estimate the instantaneous mortality of L. helicina, and the seasonal changes experienced from spring to summer.Our estimates were complicated by a combination of 1.) inherent patchiness of L. helicina, 2.) advection, and 3.) merged recruits.Generally, there were no cases of significant mortality throughout the seasons however, short term mortality was observed after peak spawning.It is plausible that the smallest size-groups of L. helicina experiences the highest mortality after peak spawning.Our findings show that in Rivers Inlet, L. helicina has a life cycle spanning 1--1.5 years with spring and summer peak spawning activities. The spring cohort is likely spawned by the summer cohort from the previous year. It utilizes the spring phytoplankton bloom to reach sexual maturity and spawn the summer cohort.

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Pelagic decapods were collected during two cruises in the central North Pacific Subtropical Gyre (NPSG): in 2011 depth stratified samples with a MOCNESS-10 (10 m² Multiple Opening/Closing Net and Environmental Sensing System) were carried out at two stations to the west and north of the Hawaiian island of Oahu (21°20.6'N, 158°16.4'W and 22°45'N, 158°00'W), and in 2004 samples were collected using three different micronekton sampling gears in the shallow backscattering layer (SSL) and deep backscattering layer (DSL) off the southwest coast of Hawaii. A total of 40 decapod taxa were identified. Amongst the 22 species with sufficient representation, three migration classes were identified: full migrators (6 species); partial migrators (13 species); and non-migrators (3 species). Using measured local temperature profiles along with published models of respiration, excretion and mortality, the individual and total active downward carbon flux was calculated. From the 2004 samples, diets of nine pelagic decapod species were established through stomach content analysis. It was found that decapod diet varied not only with size, but also with taxonomy. All decapods fed more in the SSL at night than in the DSL during the day or night. However, decapods did not feed entirely at night in the SSL, a common assumption made in previous estimates of active flux for a wide variety of organisms. Instead, feeding in the DSL was equal to 9.67 – 44.69% of feeding in the SSL by weight. Using these feeding estimates, and assuming a micronekton sampling efficiency of 33.33% for the MOCNESS-10, the active flux due to decapod migrations was calculated to be 382.7 - 625.0 µgC/m²/day. Compared to the local passive flux, this active flux was equal to 4.8 - 7.8% of passive flux at the mean night time residence depth (710.7 m), 2.1 - 3.4% of passive flux at the mean daytime residence depth (261.8 m), and 1.5 - 2.4% of passive flux at the base of the euphotic zone (173 m).

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Stable isotope analysis was used to determine spatial and temporal patterns of suspended kelp-derived detritus (KDD) and its contribution to consumers along a gradient of kelp abundance driven by recovering sea otter (Enhydra lutris) populations along the west coast of Vancouver Island (WCVI). During the summer and winter, ocean surface size-fractionated particulate organic matter (POM), dominant kelp species (order Laminariales), surface plankton and benthic organisms were sampled along offshore transects (0 – 30 km), and analyzed for carbon and nitrogen stable isotopes. Phytoplankton isotope fractionation characteristics were utilized along with principal component analysis to determine seasonally and size fraction specific δ¹³C and δ¹⁵N values. Blooming size fractions of phytoplankton were enriched in ¹³C by 2.5 to 5.4 ‰ and enriched by 0.3 to 3.1 ‰ in ¹⁵N. There were significant within and among region, and between season differences in kelp isotopic values. For example, during the summer, the otter-present Macrocystis pyrifera mean δ¹³C value (-13.17 ± 1.12 ‰) was more enriched than Nereocystis luetkeana (-16.89 ± 1.88 ‰; p 40 %) and similar with size, among regions and between seasons, with the exception of red turban snails (Astraea gibberosa) in the otter-present region where KDD contribution was 41.2 to 96.6 % lower than the otter-absent region.These results indicate that kelp abundance is not the only driver of KDD dispersal spatially and temporally. Factors such as local oceanography, kelp forest community composition, large variation in kelp isotope values, and similarity between kelp and phytoplankton isotope values may affect these patterns and lead to high uncertainty in modeled KDD contributions.

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In the early life history of sockeye salmon smolts, prey availability (quality and quantity) and growth are strongly linked. During this critical period, when ~ 90% of their mortality occurs, they must attain a critical size at which they have sufficient energy stores to survive their long migration with little predation impact, leading to better survival and higher returns. To determine patterns of growth of out-migrating sockeye salmon and to link inter-annual variations in growth to diet and seasonality of the zooplankton community, seine netting and zooplankton tows were conducted in May-June 2008, 2009, and 2010 in Rivers Inlet, British Columbia, a fjord with estuarine circulation. Growth rate, condition factor and mass-length relationships were calculated from length and mass data obtained from fresh fish. Stomachs were analyzed for total prey composition in terms of biomass and abundance. Growth rates were faster in 2009 and 2010 than in 2008; however, the condition factor was highest in 2010, and similar in 2009 and 2008. Mass-length relationships indicated that sockeye smolts were significantly heavier per unit length in 2010 (p
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The establishment of non-indigenous species in natural ecosystems is a growing concern at global, national, and regional scales. Over 100 known marine non-indigenous species (NIS) are found along the Pacific and Atlantic coasts of Canada. It is widely believed that commercial shipping activities associated with international ports (e.g. ballast water discharge, hull fouling) could expose native communities to a variety of NIS. Thus, harbours are recognized as critical entry points for NIS and, pending establishment, can serve as invasion hubs for secondary dispersal vectors (e.g. recreational boats). The aim of this study was to characterize intertidal NIS distributions among ports on the Pacific and Atlantic coasts of Canada and to determine if commercial shipping activities (ballast water discharge, vessel arrivals) can be directly linked to the observed patterns of established NIS. Sixteen major international ports in Canada were surveyed for species composition and abiotic conditions, including both environmental and anthropogenic factors. Species diversity for both NIS and native species were found to be significantly different between the Pacific and the Atlantic intertidal communities. Although both NIS and native species had higher diversity on the Pacific coast, the Invasion index, a novel measurement of the degree of invasion developed in this thesis, demonstrated that the Atlantic coast was actually more invaded by NIS than the Pacific. No direct link was found between commercial shipping activities and the distribution patterns of established intertidal NIS in Canadian ports. Instead, NIS distributions were found to be strongly related to salinity, sediment type, human population, aquaculture and latitude on the Pacific coast and human disturbance at docks, latitude and salinity on the Atlantic coast. In contrast to what was previously suggested, these results demonstrated that ballast water discharge and vessel arrival frequency were not detected as the main variables towards NIS establishment success. However, this study highlighted the importance of environmental conditions and local anthropogenic vectors in the establishment of NIS in new regions. Future research in conservation and management of invaded communities should include environmental conditions and the risk posed by anthropogenic activities, in addition to commercial shipping, when characterizing invasion dynamics.

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Although there are various indications and claims that jellyfish have been increasing at a global scale in recent decades, a rigorous demonstration to this effect has never been presented. As this is mainly due to scarcity of quantitative time series of jellyfish abundance from scientific surveys, an attempt is presented here to complement such data with non-conventional information from other sources. This was accomplished using the analytical framework of fuzzy logic, which allows the combination of information with variable degrees of cardinality, reliability, and temporal and spatial coverage. Data were aggregated and analysed at the scale of Large Marine Ecosystem (LME). Of the 66 LMEs defined thus far, which cover the world’s coastal waters and seas, trends of jellyfish abundance (increasing, decreasing, or stable/variable) were identified (occurring after 1950) for 45, with variable degrees of confidence. Of these 45 LMEs, the overwhelming majority (31 or 69%) showed increasing trends. Recent evidence also suggests that the observed increases in jellyfish populations may be due to the effects of human activities, such as overfishing, global warming, pollution, and coastal development. Changing jellyfish populations were tested for links with anthropogenic impacts at the LME scale, using a variety of indicators and a generalized additive model. Significant correlations were found with several indicators of ecosystem health, as well as marine aquaculture production, suggesting that the observed increases in jellyfish populations are indeed due to human activities and the continued degradation of the marine environment.

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