• Behavioural and metabolic responses of the freshwater mussels Anodonta anatina and Unio pictorum to environmental stimuli with a focus on food and light availability

      Ramsey, Andrew; Huck, Maren; Mehra, Aradhana; Zapitis, Charitos (University of Derby, 2020-07-05)
      Benthic invertebrates play a crucial role in sediment mixing, nutrient cycling, and oxygen fluxes in benthic ecosystems. Despite the broad global distribution and high abundance of unionid mussels in both lentic and lotic ecosystems, the role of their locomotion behaviour and metabolic activity on the aforementioned processes remain understudied. In this thesis, Anodonta anatina and Unio pictorum were exposed to a range of Chlorella vulgaris concentrations between 0.5 and 20.0 mg Ash Free Dry Mass (AFDM) l-1 at 11.0, 15.0 and 19.0 ± 1.0 °C in laboratory experiments. Unionid behaviours were recorded by time-lapse photography. Mussel locomotion probability and duration, opening behaviour, posterior tip movement and the position in relation to the light source were extracted image and video analysis. The diel rhythm was assessed as well as the responses to the light intensity at ~230, 450 and 1200 lux on a horizontal light gradient. The oxygen consumption (OC) during digestion was quantified at 0.05, 6.0 and 12.0 mg of AFDM of Chlorella vulgaris l-1 at 19.0 ± 1.0 °C. The locomotion probability was significantly higher for A. anatina, compared to U. pictorum, increased with increasing temperature (lower for 11.0 ± 1.0 °C), and decreased with increasing algal concentrations. Locomotion duration decreased with the increasing algal concentration in both species, with U. pictorum showing a shorter locomotion duration than A. anatina. Valve opening peaked at algal concentrations of 3.0 mg l-1. A contrasting locomotion pattern was recorded between the two species with A. anatina crawling on the sediment and U. pictorum breaking through the sediment with is umbo covered. Both species showed a significantly higher probability of locomotion in the absence of light and a decreasing locomotion path distance with the increasing light intensity. The specimens which moved towards the light source covered a longer distance than those which moved away. Additionally, A. anatina showed a net movement towards the light source while all activities were recorded in the absence of light. Digestion significantly contributed to unionid metabolism in both species. In addition, the mean OC rate per dry soft-tissue mass (DM) increased with the algal concentration, with A. anatina showing a significantly higher rate. In A. anatina OC DM-1 decreased with the increasing DM. The findings are discussed in the context of eutrophication, unionid bioremediation potential, and the development of species-specific remediation models. A conceptual model developed demonstrates the ecological interactions between unionids and their environment in lentic systems.
    • The cryptic and transboundary nature of ghost gear in the Maldivian Archipelago

      Sweet, Michael; Huck, Maren; Beaumont, Nel; Stelfox, Martin (University of Derby, 2019-06-11)
      Abandoned, lost or discarded fishing gear (ALDFG), more commonly referred to as ghost gear, is a global issue that impacts many marine organisms worldwide. In the Maldivian archipelago a large number of olive ridley sea turtles (Lepidochelys olivacea) are found entangled in these nets (more commonly referred to as ghost nets) each year. However, the origin of these nets or turtles are unknown considering fishing with the use of nets is restricted to the bait fisheries within the exclusive economic zone of the Maldives. Therefore, ghost gear has a transboundary and cryptic nature, making it difficult to assess the environmental impact and origin of the gear. This thesis aimed to develop new tools and techniques which could be utilised to examine these unknowns. I revealed in a literature review (Chapter 1) that research in ghost gear entanglements amongst marine megafauna are predominantly focussed in the Atlantic and Pacific Ocean. However, Indian, Arctic and southern Oceans are far less studied. Additionally, the majority of strategies to tackle ghost gear were centred around curative measures, such as ghost gear retrieval. I advise that future solutions, best practices and research should favour preventative rather than curative methods in ghost gear management and research. Statistical classifies (Chapter 2) were built in R to predict the probability of a net entangling a turtle. It was highlighted that nets with larger mesh sizes and the absence of floats were major gear characteristics that increased the likelihood of turtle entanglement. In addition, the time of year was an important variable with a higher chance of turtle entanglements in nets found during the northeast monsoon (November – April). Unfortunately, grouping of the nets by fisheries was not possible, beyond a broad classification. This was likely a result of the wide variety of nets used in the region. However, gill and trawl nets were recognised as high-risk fisheries. Regardless of the difficulties of assigning an origin of the nets, I was able to estimate the scale of the problem. Between 3,400 and 12,200 turtles could have become entangled in ghost nets over the 51-month study period, meaning this region has the highest turtle entanglement rate in ghost nets worldwide (0.17). Nesting and sightings of free-swimming individuals are rare and therefore the majority of entangled turtles do not originate from the Maldives. To discover the source population of these entangled olive ridleys we utilised a mixed stock analyses of mtDNA from samples of turtles entangled in nets in the Maldives (n = 38) and compared them to nesting stocks from published literature (Sri Lanka, east India and northern Australia). We were able to fill in data gaps in phylogenetics by including samples from previously undescribed nesting populations, such as those in Oman and improved resolution by including longer sequences from east India in our analyses (Chapter 3). Results suggest that the majority of entangled olive ridleys originate from east Indian (73%) and Sri Lankan (23%) genetic stocks when no population estimates were included in model design. This meant we could estimate the impact of ghost nets on these populations. Recorded ghost net entanglements may impact yearly recruitment of east Indian populations by 0.48% however a staggering 41% of the Sri Lankan population are thought to be negatively affected by the drifting nets. I then attempted to age ghost gear found drifting in the Maldives, and provided additional evidence to locate possible sites of origin. Percentage cover of biofouling communities and capitulum length of the goose barnacle (Lepas anatifera) provided the most robust metrics to estimate minimum drift times (Chapter 4). Lagrangian simulations (forced by Ocean Surface Current Analyses Realtime OSCAR) could then be utilised to backtrack drifting ghost gear to a putative origin. This analysis highlighted that the origin of these nets overlapped with purse seine (predominantly from Spain and France) and gill net fisheries operating in the area. Moreover, the models show that some of the nets originate close to the Indian and Sri Lanka shorelines, suggesting that small scale artisanal fisheries may provide additional high risk, contributing to ghost nets drifting into the Maldives and entangling turtles. In summary it is hoped that this thesis advances our knowledge on ghost gear significantly. Moreover, this thesis provides the information and tools necessary for the Olive Ridley Project (a British registered charity, tackling this issue face on), along with other stakeholders (government and non-government) in order to better manage resources and combat the ghost gear issue within the Indian Ocean.