55 research outputs found
THE ECOLOGY OF POOR FEN & WILLOW CARR ON GOSS MOOR NNR, CORNWALL
Goss Moor NNR is a unique, rare and nationally-important wetland habitat in Mid-
Cornwall. The majority of the habitats were created as a result of a long history of tin-stream
mining, which ceased in the early 1900s. Phytosociological surveys of poor-fen and willow carr communities
provide the first formal descriptions of the vegetation at this site. The poor-fen survey
revealed twelve poor-fen vegetation types, which were distributed along a primary environmental
gradient of organic matter depth, surface water height and bare substrate. Separation of the poor-fen
communities by a moisture gradient was considered as spatial evidence for hydroseral
succession, which begins with the colonisation of open-water pools created by tin excavations. The
Salix cinerea ssp. oleifolia willow carr was divided by eight understorey communities, according to
age, defined by reference to five sets of aerial photographs of Goss Moor taken over the last six
decades. The average number of poor-fen species per unit area in the understorey generally
decreased with age. This relationship was related to the increase in canopy cover and, therefore,
shade. Willow was found to invade areas with the greatest amounts of accumulated organic
material and a low water table. In the oldest and driest willow, oak saplings were found, indicating
the beginning of secondary woodland. An architectural analysis of willow showed that useful age
descriptors were the height of the first fork, the number of live secondary shoots, tree height and
dbh, all of which generally increased with age.
Spatial successional patterns were characterised using the lattice-wombling technique in
three large rectangles or 'tranomes'. Plant communities were associated with either abrupt or
diffuse boundary types. Abrupt boundaries or ecotones were found between heath communities and
densely vegetated tall-herb fen and species-poor willow carr wetland vegetation. Diffuse or
ecocline transitions occurred between communities with subtle differences in their composition.
Spatial relationships between swamp and poor-fen communities were taken as evidence for space-for-
time successions, these patterns varied according to location and microtopography.
Investigations into the water regime showed water depth was governed by substrate
heterogeneity. Homogeneous microtopography was associated with deep inundations and greatest
amplitude in water depth, and most closely resembled rainfall fluctuations. The most complex
microtopography resulted from the most intense tin-streaming activity. Therefore the
anthropogenic history of Goss Moor plays an important role in governing the contemporary water
regime and vegetation distribution. Of the wetland communities, rush pasture was the driest and
poor-fen the wettest. The communities of open habitats were wetter than the willow communities.
The youngest willow community was drier in the summer than the other five vegetation types
studied, which was indicative of the conditions necessary for willow scrub colonisation to take
place.
The N:P ratio revealed that nitrogen was the limiting nutrient in all of the wetland
vegetation types suggesting an early stage of successional development. High water levels were
thought to be responsible for the prevalence of N-limitation on Goss Moor, creating deoxygenated
substrates and leading to the demise of nitrifying bacteria and thus a reduction in the rate of soil N
mineralisation. Plant strategies were used to classify the species from a number of wetland
communities ranging from open-water pools to willow carr, in order to apply them to Grime's
triangular model. The ten communities were ordered into a logical successional sequence.
However, the model needs to be modified to account for succession in the aquatic environment.
Based on the findings of this thesis, a number of suggestions were made for the effective
management of the wetland habitats on Goss Moor. These include: evaluation of willow scrub
before removal so those areas of vegetation subsequently opened-up can be monitored; and the
creation of new ponds to encourage the growth of certain poor-fen communities, which are species-rich,
but only account for a small area of the whole resource
Basking sharks and oceanographic fronts: quantifying associations in the north-east Atlantic
Understanding the mechanisms linking oceanographic processes and marine vertebrate habitat use is critical to effective management of populations of conservation concern. The basking shark Cetorhinus maximus has been shown to associate with oceanographic fronts – physical interfaces at the transitions between water masses – to exploit foraging opportunities resulting from aggregation of zooplankton. However, the scale, significance and variability of these observed associations have not yet been established. Here, we quantify the influence of mesoscale (10s – 100s km) frontal activity on habitat use over timescales of weeks to months. We use animal-mounted archival tracking with composite front mapping via Earth Observation (EO) remote sensing to provide an oceanographic context to individual shark movements. We investigate levels of association with fronts occurring over two spatio-temporal scales, (i) broad-scale seasonally persistent frontal zones and (ii) contemporaneous mesoscale thermal and chl-a fronts. Using random walk simulations and logistic regression within an iterative generalised linear mixed modelling (GLMM) framework, we find that seasonal front frequency is a significant predictor of shark presence. Temporally-matched oceanographic metrics also indicate that sharks demonstrate a preference for productive regions, and associate with contemporaneous thermal and chl-a fronts more frequently than could be expected at random. Moreover, we highlight the importance of cross-frontal temperature change and persistence, which appear to interact to affect the degree of prey aggregation along thermal fronts. These insights have clear implications for understanding the preferred habitats of basking sharks in the context of anthropogenic threat management and marine spatial planning in the northeast Atlantic
Global Spatial Risk Assessment of Sharks Under the Footprint of Fisheries
Effective ocean management and conservation of highly migratory species depends on resolving overlap between animal movements and distributions and fishing effort. Yet, this information is lacking at a global scale. Here we show, using a big-data approach combining satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space use hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines (up to 76% and 64%, respectively) and were also associated with significant increases in fishing effort. We conclude that pelagic sharks have limited spatial refuge from current levels of high-seas fishing effort. Results demonstrate an urgent need for conservation and management measures at high-seas shark hotspots and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool for near-real time, dynamic management
Diving into the vertical dimension of elasmobranch movement ecology
Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements
Diving into the vertical dimension of elasmobranch movement ecology
Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements
Diving into the vertical dimension of elasmobranch movement ecology
Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements
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