1. Euphausiids are an important component of high latitude pelagic ecosystems, but there is a paucity of information on their distribution, abundance and population processes on within-year time scales. This thesis encompasses new research into the euphausiid-ocean component of two important high latitude ecosystems (South Georgia and the Irminger Sea) on sub-annual time scales. 2. A new method for measuring abundance of Antarctic krill (Euphausia superba) continuously at South Georgia (Southern Ocean) was devised using upward-looking acoustic devices deployed on moorings. These novel platforms provide a new window of observations onto marine systems not open from conventional research vessels. At South Georgia, the moorings provided data at a high temporal resolution giving completely new insight to the function of the coupled biological-physical marine ecosystem. The use of moorings may aid ecosystem-based management at South Georgia and elsewhere. 3. Analysis of mooring data collected between October 2002 and December 2005 indicated a regular annual cycle in krill density: high in summer and low in winter. Mooring estimates of krill density were not statistically different from estimates derived from standard ship-based surveys in adjacent time periods suggesting that the mooring point estimates had relevance in a wider spatial context (c. 100 x 100 km). The results indicated that because of the sharp peaks in the biomass cycle, the exact timing of repeated ship-based acoustic surveys might be critical. Surveys that differ in their timing by only a few weeks might exhibit quite different estimates of biomass because they fall at different points of the cycle. Additionally, within this intra-annual framework, annual ship-based surveys may be able to detect differences between high and low krill years only if they differ by densities of c. 35 g per square m. in summer and c. 20 g per square m. in winter. 4. The mechanisms driving intra-annual variability in Antarctic krill density at South Georgia are likely to be complex. Analysis of mooring data revealed a possible association between high krill density and low water temperatures (at 200 m) at South Georgia. There was evidence that seasonal variation in krill density off-shelf was linked to seasonal variation in current velocity: marked increases in velocity at the end of summer coincided with marked decreases in krill density and abrupt changes in water temperature characteristic of the Sub-Antarctic Current Front (SACCF). Oceanographic data indicated that the SACCF might have impinged in proximity to the moorings during the winter season. However, krill densities were low during these periods and analyses suggest that seasonal variations in krill density were not driven by seasonal oscillations in the position of the SACCF. The data are not consistent with a pattern of seasonal growth, production and mortality of a resident krill population at South Georgia, but are consistent with the notion of large influxes of krill in early summer, and of a predator-driven reduction at between mid- and late-summer. 5. The seasonal distribution, abundance and growth of key euphauiids in the Irminger Sea, North Atlantic was quantified using the first net haul data from the region since the 1930s. Results show a high degree of spatial heterogeneity in the seasonal distribution of euphausiid abundance/biomass during 2001-2002. There was evidence to suggest regional variation in growth and population processes of Meganyctiphanes norvegica and Thysanoessa longicaudata, and this corresponded broadly to distinct physical zones in the Irminger Sea. There were, however, no significant links between growth and temperature and chlorophyll a concentration. This was attributed to high spatial and temporal variability in biological and physical sampling. These data are a prerequisite for understanding ecosystems dynamics in the North Atlantic, and are important for robust ecosystem-based management strategies. 6. Controls on euphausiid spatial heterogeneity at high latitudes are likely to be complex. Important factors include horizontal advection, temperature, resource availability and behavioural mechanisms. Short-term (intra-annual), small-scale (basin-scale) data are fundamental to understanding variability in euphausiid abundance and distribution on broader spatial and temporal scales in these ecosystems.

Physical processes in the Gulf of Mexico (GOM) and mesoscale (10-300 km) processes associated with the Loop Current are fairly well known. However, little is known about the physical/ biological interactions of the frontal boundary system of the Loop Current. Zooplankton abundance and distribution was determined at 28 stations in the vicinity of the Loop Current. Species richness was high at all stations. Copepods comprised 60% of the total zooplankton collected. Oithona plumifera, Nannocalanus minor and Euchaeta marina were the most abundant copepods. Chaetognaths and ostracods were also very abundant and made up 11 and 5 % respectively of the zooplankton total. Total zooplankton abundance was higher at the boundary of the LC than it was inside the LC but not significantly different from abundances outside of the LC. Stations in the western Gulf of Mexico and on the western boundary had the highest abundances of zooplankton overall. The chlorophyll concentrations at the chlorophyll maximum were higher at the boundary of the LC than inside the LC. Physical-biological processes associated with the frontal boundary of the LC appear to influence the abundance and distribution of zooplankton in the GOM.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-02-16T13:22:40Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertaçãofinal_CynthiaLima.pdf: 1671444 bytes, checksum: a618adc7ce746bd89739101831df619e (MD5) / Made available in DSpace on 2017-02-16T13:22:40Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertaçãofinal_CynthiaLima.pdf: 1671444 bytes, checksum: a618adc7ce746bd89739101831df619e (MD5) Previous issue date: 2016-06-29 / CNPq / Este estudo descreve a distribuição vertical de eufausídeos na presença de uma termoclina permanente em águas oligotróficas do Atlântico Tropical (00º 55 'N, 29º 21' W). A amostragem foi realizada de junho de 2010 à outubro de 2011, com arrastos verticalmente estratificados de 100 a zero m durante o dia e à noite. Densidades foram analisadas quanto a sua relação com a profundidade, estações e sazonalidade. A média total da densidade de eufausídeos foi de 2,65 ind. m-³, com valor máximo de 30,4 ind. m-³. A comunidade foi composta principalmente de larvas (80%). As larvas de Euphausia foram mais abundantes, com 56,4% de todos os indivíduos. Eufausídeos foram sempre mais abundantes durante a noite. A distribuição vertical ontogenética de eufausídeos apresentou três padrões: (i) larvas caliptopis foram mais abundantes na camada de transição (ii) larvas furcilia na camada de mistura superior (iii) e para os adultos, os padrões variaram de acordo com a espécie. Padrões de distribuição distintos podem ser descritos para três espécies de Euphausia (E. americana, E. tenera e E. similis) e duas espécies de Stylocheiron (S. carinatum e S. suhmii), sugerindo que espécies congêneres desses dois gêneros realizam partição de recursos na coluna de água. Os nossos dados suportam a ideia de que a camada de transição na base da camada de mistura superior é um hábitat importante para os eufausídeos na área de estudo. Este estudo revelou que espécies e estágios de desenvolvimento possuem padrões específicos de distribuição vertical para este táxon–chave nos oceanos tropicais oligotróficos. / This study describes the vertical distribution of euphausiid in the presence of a permanent thermocline in the oligotrophic waters of the Tropical Atlantic (00º 55 'N, 29º 21' W). Sampling was conducted from June 2010 to October 2011, from 100 to zero m in vertically stratified hauls during day and the night. Densities were analyzed regarding their relation to depth, temporal variability and station. Mean total euphausiids density was 2.65 ind. m-³ with values up to 30.4 ind. m-³. This community was mainly composed of larvae (80%). Larvae of the Euphausia were most abundant, with 56.4% of all individuals. Euphausiids were always most abundant during the night. The ontogenetic vertical distribution of euphausiids presented three patterns: (i) calyptopis larvae were most abundant in the transition layer (ii) furcilia larvae in the upper mixed layer. (iii) and for adults, patterns varied according to species. Distinct distribution patterns could be described three species of Euphausia (E. americana, E. tenera and E. similis) and two species of Stylocheiron (S. carinatum and S. suhmii), suggesting that congeneric species of these two genera perform resource partition in the water column. Our data support the idea that the transition layer at the base of the upper mixed layer is an important habitat for euphausiids in the study area. This study revealed species- and stage- specific patterns of vertical distribution for these key taxa in the oligotrophic tropical oceans.

Beca JAE-Predoctoral CISC; Proyecto LARECO CTM2011-25929

In Saanich Inlet, a fjord located in southern Vancouver Island, British Columbia, dense aggregations of euphausiids exhibit diel vertical migration behavior and their capability of generating turbulence has been suggested. Despite decades of research on diel vertical migration of zooplankton, its variability has not been well studied. In addition, the physical oceanographic environment in Saanich Inlet has not been thoroughly quantified, which raises the possibility of previously observed turbulent bursts of O(10^-5 – 10^-4 W kg^-1) having physical (rather than biological) origin. This work characterizes variability of diel vertical migration behavior using a moored 200-kHz echosounder, complemented by plankton sampling. Physical properties such as barotropic, baroclinic and turbulent signals are described, and the relationship between turbulence and internal waves/scattering layer examined. A two-year high-resolution biacoustic time-series provided by the Victoria Experimental Network Under the Sea (VENUS) cabled observatory allowed quantification of the seasonal variability in migration timing of euphausiids. During spring – fall, early dusk ascent and late dawn descent relative to civil twilight occur. During winter, late dusk ascent and early dawn descent occur. Factors regulating the seasonal changes in migration timing are light availability at the daytime depth of the scattering layers, and size-dependent visual predation risk of euphausiids. Instead of the traditional view of diel vertical migration timing correlated solely with civil twilight, euphausiids also adapt their migration timing to accommodate changes in environmental cues as well as their growth. The pre-spawning period (February – April) is an exception to this seasonal pattern, likely due to the higher energy demands for reproduction. Turbulence and internal waves in Saanich Inlet are characterized based on a one-month mooring deployment. Average dissipation rates are nearly an order of magnitude larger than previously reported values and higher dissipation rates of O(10^-7 – 10^-6 W kg^-1) are occasionally observed. A weak correlation is observed between turbulent dissipation rates and baroclinic velocity/shear. To examine the possibility of biological generation of turbulence, an echosounder at the VENUS cabled observatory is used to simultaneously measure the intensity of the euphausiid scattering layer and its vertical position. Turbulent bursts of the sort previously reported are not observed, and no relation between diel vertical migration and turbulent dissipation rates is found. Physical forcing at the main channel remains as a possible cause of the turbulent bursts. / Graduate / 0416 / 0415

The North Pacific humpback whale (Megaptera novaeangliae) population has been increasing at an average annual rate of ~6% since the early 1990s. In northern Southeast Alaska alone, there are now more whales than estimated for the entire North Pacific several decades ago. An understanding of how this growing population is repopulating traditional foraging grounds will benefit from detailed investigations of their prey preferences and trends in whale abundance and distribution relative to those prey. This dissertation examines these issues from late May until early September 2008 in Frederick Sound and Stephens Passage, a Southeast Alaskan feeding area historically used by humpback whales. The foundation for the study is an analysis of the life histories and abundance patterns of euphausiids, the principal prey of humpbacks in the area, during late spring and summer. Four species, Thysanoessa raschii, T. longipes, T. spinifera, and Euphausia pacifica, were identified in plankton net samples collected at random locations throughout the study site (n = 49) and in locations where a strong scattering layer was observed on a 120 kHz echosounder (n = 48). Both sample types varied in euphausiid species composition. Abundance patterns of immature euphausiids coupled with observations of females carrying spermatophores indicated differences between species in spawning schedules. Thysanoessa spp. began spawning in early April with the spring phytoplankton bloom and continued until late June, whereas E. pacifica began spawning in early June and continued until late August. This protracted recruitment of immature euphausiids was geographically widespread throughout the summer in contrast to adults, which, although present all summer, were found primarily in slope and shallow (< 100 m) areas. To determine if humpback whales preferred one euphausiid species or life-stage over another, net sample and hydroacoustic data collected in the vicinity of whales were compared to similar data collected in random locations throughout the study site. This revealed that whales targeted dense aggregations of adult euphausiids, but did not discriminate between the various species, which was surprising because of presumed differences in the energy density linked to their different spawning schedules. Additionally, whales did not spend time in areas with concentrations of immature euphausiids, which were likely not large enough during the study period to be suitable prey. With this preference for adult euphausiids, the abundance and distribution patterns of humpbacks were examined in relation to prey availability. Whale abundance was lowest at the beginning of the study in late May at ca. 68 whales and peaked in late July at ca. 228 animals – approximately 12% of the region’s estimated abundance for the study year. This study did not detect a concomitant increase in the availability of adult euphausiids, which is unsurprising since immature euphausiids would not recruit into the adult population until after the end of the study, and post-spawning mortality and predation pressure is presumably high during this time. Instead, whales clustered increasingly around comparatively fewer prey as the summer progressed. These observations, combined with a plateau in whale abundance after July, suggest that their abundance in the area was limited by euphausiid availability. Estimates of whales using the study site during the summer have remained similar over several decades despite a dramatic increase in humpback numbers in Southeast Alaska and elsewhere in the North Pacific. The results from this study suggest that, although the study site remains important seasonally to some whales, it is not a significant source of prey responsible for regional population growth in general. More likely, it is part of a network of feeding areas that has influenced the population trend. Further insight into these and the other issues raised in this dissertation could come from several additional analyses. An extended sampling season that captures the recruitment of immature euphausiids into the adult population would reveal whether a given year's prey cohort represents an important resource to whales in that same year, which has potential implications for interpreting mid-late season whale abundance patterns. As well, a photo-identification study would be useful in characterizing whale residency patterns and determining whether the abundance trends reflect a relatively small subset of the regional population using the area for most of the season or a continuous flow of a larger portion of the population. Finally, similar analyses as those outlined here but conducted in other areas within the region would provide additional insight into the network’s capacity to support the recovering whale population. / Graduation date: 2012