http://hdl.handle.net/1956/912 Search the Channel search http://bora.uib.no/simple-search http://hdl.handle.net/1956/2353 Title: Gelatinous zooplankton in western Norwegian fjords : ecology, systematics and comparisons with adjacent waters <br/> <br/>Authors: Hosia, Aino <br/> <br/>Abstract: Gelatinous zooplankters, also known as jellies, are ubiquitous in the marine pelagic. Medusae, siphonophores and ctenophores are voracious predators that can, when abundant, have significant structuring effects on the pelagic community. Many jellies exhibit opportunistic life history characteristics such as short generation times, asexual reproduction or hermaphrodism, high fecundity, rapid growth, and ability to exploit high food concentrations effectively. While siphonophores and ctenophores are generally holoplanktonic, most scypho- and hydromedusae are meroplanktonic with a benthic polypoid stage. These characteristics contribute to the naturally pulsed occurrence of jellies in the plankton. In order to assess the role of jellies in the fjord ecosystems, information on the identity, seasonal abundance, distribution and behaviour of the species constituting the gelatinous community is necessary. This thesis attempts to fill in several gaps in knowledge regarding the systematics and ecology of gelatinous zooplankton in western Norwegian fjords. In order to do so, both net based sampling and remotely operated vehicles (ROVs) have been utilized. Seasonal changes in the gelatinous community as a whole as well as the abundances of the individual species in Korsfjord and Fanafjord, western Norway, were examined. The gelatinous communities showed a clear seasonal succession, with maximum diversity and abundance occurring in April-June. Aglantha digitale was numerically dominant in both fjords. Meroplanktonic hydromedusa species appeared sequentially and were most common during the summer months. During the winter, the siphonophores Nanomia cara, Lensia conoidea and Dimophyes arctica formed the bulk of the community especially in Korsfjord. While the two fjords had rather similar faunas, they differed in terms of the relative importance of the observed groups. Siphonophores were prominent in the more oceanic Korsfjord, while Fanafjord was characterized by meroplanktonic hydromedusae. A community of deep-water hydromedusae was found at the deeper stations at Korsfjord. Two new species presumed to be members of this deep-water community, Foersteria quadrata and Parateclaia norvegica, are described in this thesis. The vertical distribution of animals in a fjord has relevance in terms of degree of overlap with prey and predator distributions as well as the likelihood of being advected from the fjord. Exchange of fjord water is most pronounced in the layers occurring above sill depth, while the sill promotes the retention of basin water. The holoplanktonic Aglantha digitale and Nanomia cara both seem to facilitate their retention in the fjords by residing below sill depth when mature. Younger stages of both species are known to have a shallower distribution, and may thus be more susceptible to advective transport. Comparison with results from the northern portions of the Mid-Atlantic Ridge (MAR) show that the same species of planktonic cnidarians (A. digitale, N. cara, L. conoidea and D. arctica) dominated the epipelagic both in Korsfjord and the corresponding latitudes at the MAR. However, the mesopelagic siphonophores and medusae common at the MAR (e.g. Chuniphyes multidentata, Gilia reticulata, Pantachogon haeckeli and Aeginura grimaldii) seem to have been unable to colonize the fjords. The notable exception to the above rule is Periphylla periphylla, a coronate midwater scyphomedusa with abundant populations in certain west Norwegian fjords. Large P. periphylla in Lurefjord were shown to feed primarily on Calanus spp., but also on krill and ostracods. They behaved as ramming predators, approaching their prey tentacles first in order to minimize fluid disturbance, and were found to have clearance rates comparable with other gelatinous predators of similar size. The horizontal and vertical distributions of siphonophores were found to be negatively correlated with P. periphylla distribution. http://hdl.handle.net/1956/2303 Title: Biology and distribution patterns of some deepwater demersal fishes in the North Atlantic, with special reference to Antimora rostrata : a study related to the project “Patterns and Processes of the ecosystems of the northern Mid-Atlantic”, MAR-ECO, 2001-2008 <br/> <br/>Authors: Fossen, Inge <br/> <br/>Abstract: The study seeks to increase our knowledge on deepwater demersal fish assemblages and the biological adaptations of Antimora rostrata. This widespread deep-living demersal teleost is essentially used as an example species. Managing deepwater resources and communities is especially difficult since our knowledge of the community structure, ecology and biology of individual species is limited, and fishery independent information is scarce. In this account focus is directed towards the use of longlines in describing deepwater assemblages. New information on the biology of A. rostrata is presented, and experimental and alternative ageing methods are explored. The study was an element of MAR-ECO, a field project of the Census of Marine Life (www.coml.org), studying the diversity and biology of biota along the mid-Atlantic Ridge (MAR). As part of the 2004 MAR-ECO expedition to the mid-Atlantic Ridge, the chartered Norwegian fishing vessel M/S Loran deployed longline sets across the ridge axis, sampling a depth range of about 4000 m. Overall, chondrichthyans dominated the catches on the MAR and contributed nearly 60% in terms of weight and numbers. Multivariate analysis (MDS) using species-by-station data indicated an assemblage distribution that related primarily to factors varying by depth and latitude. Grouping patterns of stations were not very pronounced, suggesting a gradual rather than abrupt change in species composition by depth or latitude. Catch rates peaked at the shallower stations in the Charlie-Gibbs Fracture Zone (CGFZ), and generally decreased with depth. Relatively large individuals dominated, and the overall mean weight was 2.4 kg. Average fish weight was higher in the sub-area sampled just north of the Azores archipelago than in the CGFZ sub-area. No depth-related pattern of individual fish size was found. The findings suggest that the use of longline is a valuable and possibly necessary tool for describing the larger scavenging fish assemblages on rough bottom at greater depths. Among the many different species caught frequently on longlines A. rostrata was analysed in more detail. Additional data from MAR, off Greenland and the British Isles were included, and used to exemplify adaptations of a deepwater species with respect to distribution and life history traits. Data on A. rostrata are presented from 42°N on the MAR to 65°N on the slope off West and East Greenland, along a northsouth range of approximately 1400 nm (~2600 km). The species occurred in the depth interval 670-3060 m in trawl and longline experiments sampling the depth range 400-4300 m. Length frequencies indicated both latitudinal and depth-related variation. Along the ridge abundance peaked between 1200 and 2700 m with generally low or no catches outside this range. Examination of growth patterns in transverse sections of otoliths suggested a strong cyclic zonation pattern in A. rostrata. Similarly, frequency distributions of fish length and otolith weight showed a number of modes, suggesting groups of specimens of similar size and age. Distances between modes were consistent and corresponded to what was expected based on the interpretation of the zonation pattern in otoliths. Assuming that the otolith growth zones counted represent annuli and that unbiased age readings was achieved, the growth of A. rostrata seemed linear with age for both otolith weight and fish length within the length range investigated. This corresponded to approximately 25 mg/y and 4 cm/y respectively. The oldest fish recorded was about 25 years old and sexual growth dimorphism, where females grow larger, older, and possibly faster, was suggested. The results indicate that more attention should be directed towards using frequency distributions, especially of otolith weight, for deriving information on age structure and population growth data for certain fish stocks. For A. rostrata, and many other deepwater species, greater efforts should be made to validate age determination methods. http://hdl.handle.net/1956/2293 Title: From notochord to vertebral column: studies on Atlantic salmon (Salmo salar L.) <br/> <br/>Authors: Nordvik, Kari <br/> <br/>Abstract: The notochord initially form a single-cell file stage of chordoblasts covered by a three layered sheath comprising a basal lamina, a main collagenous layer and an external elastic membrane. During early ontogeny, the collagenous layer of the sheath goes through changes in configuration from a circular orientation, with fibres oriented perpendicular to the long axis, and to a lamellar organization where alternating layers of parallel collagen fibres form helices, with a tangent angle of 75-80° to the long axis. The shift in collagen arrangement is taking place shortly after hatching and may reflect an adaptation of the notochord to functional demands related to stage of development. The serrated surfaces of the elastica externa encasing the notochord seem to provide an interconnection between the notochord and the myosepta, with a function related to transmission of force from the musculature. The subsequent segmentation process leading to formation of vertebral and intervertebral regions seems to be initiated within the notochord through formation of cellular chordoblast segments. Formation of the cellular segments is closely followed by a segmental pattern of ALP activity within the chordoblast layer and formation of mineralized chordacentra within the collagenous layer of the notochord sheath. Development of the vertebral column thus seem to involve a dual segmentation where notochord derived chordacentra define the vertebral segments and the sclerotome external to the notochord provide further growth to the vertebrae. The salmon vertebral column comprises notochord and sclerotome derived structures that tightly interconnect the vertebrae and the intervertebral regions. There are four distinct layers of bone and mineralized tissues that form the vertebral body. The two inner layers comprise the chordacentrum (mineralization of the notochord sheath) and the inner layer of the amphicoel (mineralization of the intervertebral ligament). The third layer is deposited by osteoblasts, forming the main portion of the amphicoelous centrum, and on its external surface, trabecular bone is deposited. The three inner layers have a lamellar organization, with collagen matrixes oriented perpendicular from layer to layer, while the fourth layer has a woven structure. The 6 layers also differ in osteocyte content. The notochord remains within the full length of the vertebral column and form the inner part of the intervertebral ligament. The sclerotomal external portion of the ligament is incorporated in the vertebrae as it is covered by bone during vertebral growth, while remaining unmineralized intervertebrally. The present studies on salmon shows that the notochord constitutes the main axial support during embryonic and larval stages and that the enforcing rearrangement of the collagen layer of the notochord sheath seems to be important for the properties of the notochord as a fibre-wound hydrostatic skeleton. The notochord further reinforces through formation of chordacentra, generating the segmental pattern of the vertebral column, while sclerotomal tissue external to the notochord provides further growth to the vertebrae and intervertebral structures. http://hdl.handle.net/1956/2292 Title: Collective behaviour of herring during spawning <br/> <br/>Authors: Skaret, Georg <br/> <br/>Abstract: The thesis focuses on the collective behaviour of Norwegian spring spawning herring (NSS-herring; Clupea harengus L.) in the specific ecological context of reproduction. The major part of the work is based on field research using quantitative echo sounders and sonar in combination with biological sampling. In addition, an individual based schooling model is applied to investigate underlying mechanisms of the collective formations and dynamics. All studies are founded in a classical mechanistic ecological approach interpreting behaviours as optimal evolutionary strategies given an individual’s physiological and cognitive constraints, internal state and the specific ecological context. Two of the works are case-studies from historical spawning grounds of NSSherring well-known to fishermen and scientists; the shallow (30-40 m) banks off Karmøy (Paper 1) receive a small proportion of the spawning stock, whereas deep (80-250 m) areas off Møre (Paper 2) comprise the main spawning grounds. In both works the areas are covered through repeated acoustic surveys in combination with sampling of herring and predators throughout the 24-h-cycle over several days. Fisheries scientists apply similar acoustic surveying when making abundance estimates of herring that serve as basis for advices of catch quotas. A major challenge during such surveying is the fact that herring tend to avoid the approaching research vessel, rendering them unavailable to detection. How this potential source of error operates during spawning is given the focus in one of the works (Paper 3). In this study we use a simple experimental design where a standard research vessel passes a presumably neutral stationary vessel that records the herring reaction. In the fourth work we apply a rule-based simulation model with high temporal resolution able to recreate life-like collective behaviours (Paper 4). The model is used to explore how collective dynamics and formations are affected when varying the amount of herring present and their degree of motivational synchronisation. In the final work (Paper 5) we investigate 11 years of acoustic data from herring spawning surveys along the Norwegian coast. We frequently find evidence of vertical hourglass formations, and based on knowledge gained from previous studies and the simulation model we formulate and test out a concrete hypothesis; are these formations founded in conflicting individual motivation for spawning? An overall evaluation of our field results strongly supports that herring behaviour during spawning reflects a compromise between survival and reproduction. We find that herring spawn in highly synchronous waves where individuals aggregate (Paper 2) and move together (Paper 1) in their quest for a successful spawning. This strategy is likely to be advantageous for survival since a synchronous emergence in high numbers will decrease an individual’s risk of being targeted by a predator (dilution effect). A similar advantage is gained through spawning in the dark hours when predators are less active. Shoals at night-time were observed to have a stable loose packing density, whereas a variable, but generally high packing density at daytime corresponds well with a presumed higher frequency of predator attacks, since it is known that shoals become more densely packed under attack. At the deep spawning grounds, large proportions of the herring became scattered in pelagic layers at night-time. Interestingly, these layers were positioned according to the thermocline in a way that indicates active use of the vertical temperature profile to fine-tune maturation rate in the days prior to spawning. The shallow spawning grounds had a different dynamic and such layers were not observed. In these areas, the vast majority of herring were in layers at the bottom at night-time. In this situation, herring did not react to the research vessel (Paper 3), probably because the focus on the spawning activity increases their reaction threshold. At both spawning grounds (Papers 1 and 2), there were substantial vertical dynamics that corresponded well with the results from the schooling model. In the model simulations, shoal height is dependent on the difference in individual motivation for spawning. With strong conflicts in motivation, shoals tend to split in the same way as we observed during spawning in the field (Paper 2), whereas with intermediate conflicts shoals maintain cohesion but become vertically extended like we observed during pre-spawning. A special case of the latter is the vertical hourglass formation that emerges in the model assorted according to maturation state. Similar assortment was observed in the hourglass formations in the wild, where spawners dominated in the lower parts relative to pre- and post-spawners, strongly indicating that motivational conflict is the driving force of the observed formation. Whether such formations are purely emergent from decisions made from local stimuli or implying communication between the two shoal parts is an interesting question open to future investigations. http://hdl.handle.net/1956/2240 Title: Competition between marine osmotrophs for phosphorus and nitrogen : implications for the microplanktonic food web <br/> <br/>Authors: Løvdal, Trond <br/> <br/>Abstract: Understanding how competition for nutrients structures the flows of C, N, P, and other elements through the microbial food web may seem central to our understanding of the role and function of this part of aquatic ecosystems, both in biological and biogeochemical contexts. Competition between phytoplankton and heterotrophic bacteria potentially influences the species composition of the respective communities and the flow of carbon (C) and energy to higher trophic levels. The dominating hypotheses on algal – bacterial competition for inorganic substrates are based on studies from freshwater environments, there is relatively little work on the competition for organic substrates, and previous studies on this topic may seem contradictive. This thesis includes studies performed in nutrient manipulated coastal mesocosms where the algal – bacterial competition for organic and inorganic forms of P and N were assessed. Algal – bacterial competition for these substrates was compared by means of biomass-specific affinity estimates. Biomass-specific affinity is regarded as the best index to measure competitive ability. However, we are not aware of any published papers reporting such data on organic P- and N-compounds. Results from two mesocosm studies, one focusing on P-competition and the other focusing on N-competition, demonstrates a potential for different structuring of the microbial food web in P- versus N-limited environments. One paper considers possible theoretical solutions to the coexistence of organisms competing for the same limiting nutrient. Traditionally, the smallest organisms have been viewed as superior competitors, based on a relatively constant relationship between volume and the intracellular content of the limiting element. However, the paper points out strategies in which organisms can benefit from other resources to change their stoichiometry and thus obtain competitive advantages, as well as predator defense. Experimental evidence to support this theory was obtained from a chemostat experiment. The results demonstrated that Vibrio splendidus could use excess organic C (glucose) to increase in size thereby optimizing uptake of the limiting element (P). http://hdl.handle.net/1956/2233 Title: Salamonid alphavirus (SAV) : genetic characterisation of a new subtype, SAV3, and implementation of a novel diagnostic method <br/> <br/>Authors: Hodneland, Kjartan http://hdl.handle.net/1956/2218 Title: Mortality, Recruitment and Change of Desert Tree Populations in a Hyper-Arid Environment <br/> <br/>Authors: Andersen, Gidske L.; Krzywinski, Knut <br/> <br/>Abstract: Background: Long-term vegetation changes in hyper-arid areas have long been neglected. Mortality, recruitment and change in populations of the ecologically and culturally important and drought persistent Acacia tortilis and Balanites aegyptiaca are therefore estimated in the Eastern Desert of Egypt, and are related to the primary agents of change, water conditions and human intervention. Methodology: A change analysis using high-resolution CORONA images (1965) in combination with field data (2003) is the basis for recruitment, mortality and change estimates. For assessing the influence of water conditions on patterns in recruitment and survival, different types of generalized linear models are tested. Conclusions: The overall trend in population size in that part of the Eastern Desert studied here is negative. At some sites this negative trend is alarming, because the reduction in mature trees is substantial (>50%) at the same time as recruitment is nearly absent. At a few sites there is a positive trend and better recruitment. Frequent observations of sprouting in saplings indicate that this is an important mechanism to increase their persistence. It is the establishment itself that seems to be the main challenge in the recruitment process. There are indications that hydrological variables and surface water in particular can explain some of the observed pattern in mortality, but our results indicate that direct human intervention, i.e., charcoal production, is the main cause of tree mortality in the Eastern Desert. http://hdl.handle.net/1956/2217 Title: Long-term dynamics of wadi trees in a hyper-arid cultural landscape <br/> <br/>Authors: Andersen, Gidske L. <br/> <br/>Abstract: This study focuses on the long-term dynamics of wadi (dry river valley) trees, in particular Acacia tortilis (Forssk.) Hayne, in the hyper-arid Eastern Desert of Egypt. The project was motivated by the importance of drought enduring trees for the local indigenous population, by the lack of studies on vegetation changes in hyper-arid areas, and in particular by the fact that understanding the long-term dynamics of trees is essential responding to ongoing changes effectively. Lack of data and methods offering appropriate spatial and temporal resolution has impeded research on long-term dynamics, so the use of high resolution, historical satellite data, 14C content and the anatomy of wood to obtain the necessary data is emphasised. Imagery from the first generation US reconnaissance satellite CORONA, taken already in 1965, offer a spatial (2.7 m) and temporal dimension for ecological information which other data sources cannot furnish at a comparable cost, coverage, resolution or accessibility. The vast majority of mature trees mapped in 2003 is identifiable in the imagery. A change analysis (1965-2003) reveals a negative trend in population size at most of the sites studied. Of mature trees 41 % have died. Recruitment was in general very poor at all sites, but the great capacity of saplings to resprout seems to be a major strategy to increase their persistence. A set of parameters related to water conditions, derived from the SRTM DEM, could not explain observed patterns in recruitment among sites, although it could explain some of the observed variation in mortality. Nevertheless, charcoal production seems to be the major cause of mortality. A method was developed to assure that image-based mortality estimates derived without contemporaneous reference data can be applied with great confidence. This is of particular importance when appropriate management strategies are to be adopted. The pre- and post-bomb 14C content in A. tortilis wood is used to estimate age and growth. Annual growth varies in space and time (0.2 – 2.4 mm), and the ages of the trees studied seem to lie between 200 and 650 years. In combination with the low recruitment observed, this suggests that the landscape will need very long time to recover from the ongoing and rapid deforestation. If this current trend is to be arrested, urgent action is required and must take into account the traditional management practices of the pastoral nomads who for millennia have lived in and developed sustainable strategies in accordance with local climatic conditions and available resources.