/library/oar/handle/123456789/47483 2025-11-04T11:43:46Z /library/oar/handle/123456789/121374 Title: Aspects of the ecology of the potentially invasive alien macrophyte Caulerpa taxifolia var. distichophylla (Sonder) Verlaque, Huisman & Procacini in Maltese waters Abstract: The aim of this study was to obtain information on the ecology of the alien macrophyte Caulerpa taxifolia var. distichophylla in the Maltese Islands, following its introduction in 2013. Three aspects were investigated: the spread of the macrophyte from the initial colonised area, the hypothesis that the alga shows seasonal changes in frond density and frond length and the effect of site characteristics on the frond density, morphology and distribution. The spread of the macrophyte was monitored at 38 different sites around the Maltese islands between June 2016 and September 2016 and between June 2017 and September 2017 either by making observations using SCUBA or through an open call for citizen scientists to report sightings, which were then confirmed. When surveyed by SCUBA diving, frond density was estimated and samples were taken for morphological studies in the lab. Seasonal changes were assessed within a study area measuring 2m X 2m at two different sites which were visited monthly between June 2016 and June 2018 to estimate frond density from 12 replicate quadrat counts. Samples for biomass estimation were collected from a different sites by separating out the different algal species and estimating the biomass of each to determine changes in macrophyte community composition. Patchiness in the distribution of the alga and the morphological variation within a patch were studied at five different sites (Bahar ic-Caghaq, Comino, San Tumas, Sliema and Qawra) from June to September 2016. At each site, density counts, depth and if the alga was located in the centre or periphery, were recorded. Replicate samples of the macrophyte were collected for morphological analysis. The results of these studies indicated that the alga is well established in the Maltese Islands and had spread to at least 22 sites by 2016 and an additional four sites in 2017. Of these sites, 46% were located along the eastern coast of Malta and Gozo where the degree of anthropogenic impact is higher. The least affected coast, with 8% of records was the west coast of the Malta and Gozo probably due to the deep bathymetry and reduced anthropogenic impacts. The results also indicate that the frond density of the macrophyte decreases during the winter months and attains is highest values during autumn months giving a pronounced intra-annual variability. There was also an inter-annual variability in the population as during the second year of the study the macrophyte there was no compete regression of the fronds at both study sites as had been observed during the first year. nMDS results indicated that there were no changes in species abundance relative to the algal occurrence. Of the five sites in which studies of the algal patchy distribution were conducted, the highest frond density was at Bahar ic-Caghaq whilst the longest fronds were recorded from Comino. Linear regression analysis indicated a weak relationship between depth and both frond density and frond length. However, PERMANOVA indicated that the factor ‘site’, affects both frond density and frond length whilst the type of substratum and associated flora affects only frond density. Of the microhabitat types a change in population structure was only shown for the ‘mosaic’ microhabitat, where a statistically different mean frond density value was obtained between the periphery and centre of a ‘mosaic’ patch, whilst for the microhabitats ‘Posidonia oceanica’ and ‘rock with sediment cover’ no statistically significant differences were found. Caulerpa taxifolia var. distichophylla has established itself successfully in Malta, colonising areas with high anthropogenic factors that have facilitated its dispersal. Whilst no changes in community biomass were observed, the alga is taking up space that would be otherwise be made available to native species. The species can be considered as ‘invasive’ given the exponential growth it has attained. Description: M.SC.BIOLOGY 2019-01-01T00:00:00Z /library/oar/handle/123456789/121364 Title: Influence of elevated seawater temperature on amphisteginid Foraminifera in Maltese waters Abstract: Sea warming due to climate change might favour the spread of invasive species by expanding their distribution into new areas. The Mediterranean Sea warming and its particular biogeographic history makes it a hotspot for marine invasions, and a case of a successful thermophilic invader in this sea is the marine benthic foraminifer Amphistegina lobifera, considered to be of Red Sea origin. The range expansion of A. lobifera is likely to trigger changes in ecosystem functions, including the displacement of local foraminiferal species, homogenization of foraminiferal assemblages and drastic alterations in coastal habitats. In the Maltese archipelago, the presence of this alien invasive species could bring about changes to the granulometric characteristics of marine sediments present in bottom habitats, changes which in turn may impact certain benthic species and communities. Elevated temperature has also been identified as causing morphological variations in the shells of benthic Foraminifera, including A. lobifera. The aim of the present study was to use the thermal effluent from the Delimara Power Station, Malta, as a proxy for sea warming in order to assess climate change impacts on the distribution and morphology of the invasive foraminiferan A. lobifera. This was made by comparing populations of A. lobifera at the impacted site (an inlet receiving thermal effluent) with two geographically similar inlets without thermal effluent (reference sites). No significant differences in the thickness/diameter ratio, lateral asymmetry and coiling direction of A. lobifera were noted between the impacted and reference sites. Overall, most of the specimens in the present study were sinistrally coiled, and tests were significantly larger and with a higher incidence of irregular keels at the impacted than at the two reference sites. Both absolute and relative abundances of A. lobifera at the impacted site were significantly different from values of the same attribute recorded from the reference sites, and significant differences were also found in the impact of amphisteginid invasions on the mean sediment grain size. However, no significant differences in sediment sorting values were noted between the impacted and reference sites. These findings match the described westward invasion of A. lobifera in the Mediterranean, and indicate that the colonisation of the alien in the studied sites is temperature-driven and possibly displacing local foraminiferal species. Amphisteginid invasions in Malta will probably intensify as the sea warms up and cause changes in the invaded micro-ecosystem, which is likely to also pose long-term impacts in local meso-ecosystems with significant ecological consequences for presently-occurring marine benthic communities. Description: M.SC.BIOLOGY 2019-01-01T00:00:00Z /library/oar/handle/123456789/121361 Title: Updated assessment of the distribution, status and impacts of marine non-indigenous and other newcomer species in the Maltese waters Abstract: The latest inventory on all newcomer species in Maltese waters dates back from 2015. Several new or additional records of alien and range-expanding species have been reported since, necessitating an update to this work, while no comprehensive assessment of the distribution patterns and impacts of non-indigenous species (NIS) in Maltese waters has been published to date. This project will update and re-evaluate the inventory and compare it to the previous one. The coordinates from the records will be used to look at spatial patterns, and to identify hotspots. Through literature studies the environmental impacts will be assessed. The inventory has increased to 106 species, of which most are still considered casual newcomer species, but the amount of invasive species has increased by two. The amount of unknown pathways has decreased and shipping is the most prominent mode of entry into the Maltese waters. The spatial pattern of the records, show that the harbours are hotspots of NIS, which is also explained by the shipping pathway. Another spatial pattern was the records being in the vicinity of popular diving spots. There is a huge bias in the known literature, since absence of an NIS is not recorded often, and the locations cover the same areas and don’t cover hard to reach coastlines, like the Dingli cliffs. The records of invasive species are not a perfect tool to track the dispersal, since they are often discovered after reaching the establishment phase. The inventory needs to be kept updated, to track the status of the Maltese waters and more information should be collected on ecological impact of the newcomer species. Description: M.SC.BIOLOGY 2019-01-01T00:00:00Z /library/oar/handle/123456789/121359 Title: Global phylogeography and Mediterranean genetic structure of the endangered dusky grouper, Epinephelus marginatus (Teleostei: Serranidae), based on mitochondrial and microsatellite genetic markers Abstract: The aim of this research is to describe the evolutionary relationship, demographic history and connectivity patterns of the endangered marine fish Epinephelus marginatus (Lowe, 1834) on a local, regional and global scale for the purpose of aiding in conservation management strategies. Assessment was based on an integrative approach to molecular population genetics using comparative phylogeography and coalescent based methodologies which has allowed for resolution of evolutionary processes, diversification of lineages, and phylogenetic species delimitation. The basis of molecular analyses were conducted using subsets from 377 E. marginatus samples collected from 17 localities and three continents throughout their global distribution in the Atlantic Ocean, SW Indian Ocean and Mediterranean Sea. Local and regional assessment pertaining to the central Mediterranean Maltese Fisheries Management Zone was based on 14 microsatellite genetic markers and describes a population decreasing in size (θH = 2.2), which has gone through a significant size reduction in the past (M = 0.41) and consequently shows signs of moderate inbreeding (FIS = 0.10, ρ < 0.001) with an estimated effective population size (Ne) of 130. Spatially explicit Bayesian genetic cluster analysis detected two geographically distinct subpopulations within the Fisheries Management Zone and resolved that they are regionally connected to a larger network within the Sicily Channel. Evaluation of global phylogeography was based on a 398 base pair catenated alignment of high density intraspecific variation spanning part of the tRNA proline gene and d-loop from the mitochondrial control region. Spatial Bayesian inference identified five explicit biogeographic populations throughout their global range in the Azores, Brazil, Senegal, South Africa and Mediterranean Sea. Molecular clock convergence analysis founded on within lineage mutation rate divergence surmised that E. marginatus has been present in the Azores since the Calabrian Age during the Pleistocene Epoch, however establishment of the remaining global populations began more recently during the Middle Pleistocene with colonisation of the nouveau Mediterranean lineage occurring around 150,000 years ago. Analysis conducted using a Bayesian model of random coalescence estimated that the global population of E. marginatus’ has grown roughly 25% over the last 100,000 years, mostly owing to expansion in west Africa, with a modern effective population size estimate (Nef) of around 4.4 million. Global AMOVA (ΦST = 0.44647, ρ < 0.001) and an exact test of population differentiation (ρ < 0.001) detected great and significant bifurcation between global populations. These findings are likely a reflection of strong biogeographic barriers to gene flow detected by Monmonier’s algorithm (bootstrap 92-100) leading to vicariance of global lineages. The high haplotype (h = 0.51-0.99) and low nucleotide (π = 0.019-0.037) diversity found is consistent with the hypothesis of itinerant peripatetic pelagic larval dispersal as the main mode of global spatial expansion. A haplotype network constructed with the TCS algorithm also revealed several substitutions between lineages suggesting once established each region has remained historically independent. Long-term estimates of asymmetrical immigration between global populations predicted using the Metropolis-Hastings sampler method of random coalescence were found to be low (ɣ̅ji = 1.73 individuals gen-1), reinforcing the notion of independent lineage trajectory following long-distance founder events. Whilst E. marginatus’ appear to display morphological cohesiveness throughout their global distribution, intraspecific genetic partitioning of lineages can be seen reflected in significant pairwise ΦST (0.31–0.69, ρ < 0.001) and Nei’s DXY (3.5–16.3, ρ < 0.001), where objective use of Nei’s D (DXY > 0.15), ΦST (ΦST > 0.25) and the Poisson Tree Process (bootstrap > 95) collectively identified the Azorean population as a separate phylogenetic unit. Mantel tests revealed genetic isolation by distance was not a fundamental factor influencing global population vicariance or lineage divergence. The process of vicariance leading to allopatric speciation is often gradual, where lineage divergence is representative of cryptic speciation on a continuum. In conclusion, evidence presented suggests that five Evolutionarily Significant Units should be assigned to each of the biogeographically discrete global populations and that assessment of species status and conservation management should be undertaken at a local level due to habitat fragmentation and population substructuring. Description: PH.D. 2017-01-01T00:00:00Z