In regard to the more and more restrictive legislations on the use of organotins in antifouling coatings the need for the development of 'environmentally friendly' antifouling formulations becomes urgent. This study was initiated by the screening of the antifouling activity of Scottish algae against marine fouling bacteria aI;ld was followed by an examination ofthe chemical ecology ofthe brown alga Halidrys siliquosa. Of eleven algal species tested, eight exhibited good antifouling activity, confirming marine algae as a potential source for the development ofnovel antifouling formulations. H. siliquosa crude extracts tested at concentrations equivalent to whole algal tissue inhibited bacterial growth, with bacteria isolated from the surface orH. siliquosa being less sensitive to the extracts compared to bacteria isolated from stones and open seawater. This suggested for the first time that bacteria associated with the surface of the seaweed had evolved some kind of resistance to the plant antimicrobial activity. Characterisation of the active components using NMR spectroscopy showed the activity to be largely associated with the presence of polyunsaturated fatty acids (PUFAs). Examination of purified fractions using GCIMS allowed identification and quantification of PUFAs 18:2, 18:4, 20:4 and 20:5. A separate study, determining minimum inhibitory concentrations of 18:2 and 20:4 against marine fouling bacteria indicated that both acids were present in sufficient concentrations in the plant to inhibit bacterial growth. The presence of PUPAs on the surface of the seaweed could not be demonstrated using a surface dip technique; however, this technique was originally developed for the extraction of non-polar metabolites only. This study suggests that PUFAs produced by H. siliquosa are potentially able to regulate biofouling by means of disrupting the early stage of biofilm development, i.e. bacterial colonisation. However, to confirm this hypothesis, the presence of PUFAs on the surface of the plant' still needs to be demonstrated.

This study focuses on the seaweed biodiversity around the Antarctic Convergence in the South Atlantic. It integrates field work in the Falkland Islands and surrounding regions with algal culturing, molecular techniques, microscopy and morphological identification. Chapter 2 explores the diversity of seaweeds of the south-western Antarctic Peninsula which is poorly studied, contrasting with the substantial knowledge available for the northern parts of the Peninsula. A baseline seaweed species checklist for the southern Adelaide Island and northern Marguerite Bay region is presented here, combining data obtained during a small number of surveys in 1973-5 and a six week intensive diving-based field campaign in 2010-2011. Subantarctic and Antarctic regions remain little studied in their seaweed diversity. Chapter 3 is based upon field collections in the early 1970s and 2007-2013. It is supported by sequencing COI and reports new records of several macroalgal species and an oomycete. Chapter 4 revisits the enigmatic Subantarctic brown alga Cladochroa chnoosporiformis, which had been collected only on one occasion by Carl Skottsberg in 1907 from Port Philomel, West Falkland, resulting in its formal taxonomic description. Within the framework of this study, Cladochroa was rediscovered after 106 years at its type locality, confirming its existence and morphological features as described by Skottsberg. The recollection enabled molecular studies of its phylogenetic placement by DNA sequencing, suggesting that C. chnoosporiformis is conspecific with Utriculidium durvillei. In Chapter 5, DNA barcoding was applied to both seaweed tissue samples taken while preparing herbarium specimens during 2 expeditions to the Falkland Islands, and to live macroalgal isolates obtained from substratum samples using the Germling Emergence Method. In several cases, this enabled detection of previously unsequenced or undescribed taxa, respectively. The potential and challenges of applying DNA barcoding for cataloguing the biodiversity of remote bioregions such as the Falklands are discussed.

DIC acquisition mechanisms and the use of DIC in photosynthesis were examined in the temperate red macroalga, Palmaria palmata (Linnaeus) O. Kuntze. Photosynthetic O2 evolution was unsaturated at the ambient DIC concentration in seawater. Experiments with inhibitors of the mammalian HCO3 -/Cl- anion exchanger AE1, and the HCO3 - -hydroxylating enzyme carbonic anhydrase (CA), showed that HCO3 - uptake is mediated mainly by a bicarbonate transporter protein. Photosynthesis measured at small increments of DIC addition showed biphasic kinetics, with a hiatus located at 0.625 mM DIC. Inhibitor experiments indicated that extracellular CA is active at low DIC, therefore the biphasic kinetics of photosynthesis may have been caused by the presence of two DIC acquisition mechanisms. Culturing thalli for 6 d in artificial seawater containing 8 mM DIC induced a bicarbonate transporter in the CAuser Chondrus crispus, but no change in activity was detected in P. palmata. Presence of a bicarbonate transporter mechanism was also confirmed by using the polymerase chain reaction. Primers based on the mammalian AE1 gene sequence were used to amplify a 1500bp fragment of bicarbonate transporter gene from genomic DNA extracted from P. palmata and the calcifying microalga, Emiliania huxleyi. Comparison of the algal and mammalian sequences revealed a high amino acid sequence homology, indicating that they encoded structurally and functionally similar proteins. 3 F.F. Blackman’s precept, which implies that carbon limitation does not occur at subsaturating light, was investigated by measuring induced chlorophyll fluorescence at different DIC concentrations and irradiances. Photosynthetic electron transport rate was was stimulated at saturating light, but only slightly at subsaturating light. Thus, Blackman’s theory was upheld. Photosynthesis and bicarbonate transporter activity was monitored in P. palmata growing at St. Margaret’s Bay, Kent, UK. Distinct peaks in photosynthesis occurred in March and October, and coincided with equinoctial tides. Bicarbonate transporter activity was maximal in spring, and decreased during summer. Although it was not possible to show what determined the seasonal patterns of photosynthesis and bicarbonate transporter activity, the possibility that exposure to springwater containing high concentrations of DIC and nitrate is discussed.

Herbivory is a globally important ecosystem function, occurring in all major biome types; including benthic freshwater habitats. Algal biofilms and their herbivore consumers are therefore important components of stream food webs. However there is relatively little empirical data quantifying the strength of these algal-herbivore interactions, or how these vary with herbivore identity, size, and biofilm physiognomy. Interactions across a diverse herbivore guild were investigated in a chalk stream, using mesocosms to determine the distribution of algal-herbivore interaction strengths. A series of experiments were used to assess: herbivore link strength distribution; context-dependency of interaction strength; the relationship of body size with interaction strength; and the effects of competing grazer species on algal resources. The algal-herbivore sub-web was dominated by weak interactions which concurred with empirical and theoretical evidence, and further supporting web stability theory. Interactions were highly context-dependent, with interaction magnitude and species identity both affected by algal biofilm type. Grazer species identity was important for determining body size relationships. Although competitive effects were apparent, they were not statistically detectable. This research builds on previous investigations of algal grazer interactions and food web structure by emphasizing; the importance of grazing as an ecosystem function, and the diversity of interactions occurring in model systems. The use of experimental mesocosms may be limited in terms of 'real' systems, but does provide a valid response of model systems that are both useful and valid tools for assessing community ecology.

No description available.

Microalgae have gained increasing interest over the last ten years for their exploitation for biotechnological applications. A commonly used model organism is Chlamydomonas reinhardtii and many recombinant proteins have been successfully expressed in this green microalga. The chloroplast is of special interest as it allows rather high expression levels and targeted gene integration. Tools for chloroplast transformation and expression systems have advanced remarkably over the last years and the field is developing increasingly faster. In this thesis, existing tools for genetic modification of C. reinhardtii were used to expand further the toolkit, mainly for the synthesis of high-value diterpenes of plant origin, and to examine the potential of using these microalgae in an industrial setting. A strain expressing a large recombinant enzyme, a diterpene synthase, resulting in in vivo synthesis of the diterpene cis-abienol, was generated. The potential for light-driven product synthesis via a chloroplast re-located cytochrome P450 was successfully shown. It was also demonstrated that typically fragile, wall-deficient transgenic strains can be grown on a 100 L pilot scale. This is an important finding as the gap between lab- and large-scale studies needs to be closed to allow a transition to an industrial setting. It was also shown that there is still untapped potential in the algal chloroplast - by utilising a bacterial export signal peptide the chloroplast toolkit was expanded to the thylakoid lumen for recombinant protein production. Three proof of concept studies presented herein and one study looking at pilot scale cultivation of previously generated transgenic strains show that the potential seen in microalgae for biotechnological applications is justified and further developments and improvement of the existing strains could make this a viable competitive platform for diverse applications.

Blooms of toxic, or otherwise harmful phytoplankton species are known to occur in eastern boundary upwelling systems, coincident with the relaxation of upwelling in late summer/autumn. Field studies were carried out in 3 consecutive summers (March/April 06-08) in the Benguela and in the autumn (Sept 06) and summer (June 07) in the Iberian upwelling system (Ría de Vigo), with the aim of identifying common nitrogen nutrition strategies of HAB species that may allow them to succeed in upwelling systems. Two summer field studies were also carried out in the Fal Estuary (UK) to identify possible differences between a UK estuary and these upwelling systems. In the Benguela, three toxic phytoplankton species were dominant under different nutrient conditions. Pseudo-nitzschia spp. were abundant during a period of strong upwelling and high NO3-, peaking during short periods of wind relaxation. During these periods, a switch from high nitrate uptake [(NO3 -)] to regenerated nitrogen uptake [(NH4 +) and (urea)] occurred, with ƒratios dropping from 0.79 to 0.12. Alexandrium catenella bloomed during a period of upwelling, displaying high (NO3-) and ƒ-ratios up to 0.87. Dinophysis acuminata dominated when NO3 - concentrations were <0.5 μmol l-1 and ƒ-ratios <0.1 in 2007, although in 2008 it formed a subsurface maximum, often associated with high NO3- concentrations. Nutrient uptake kinetics showed that Pseudo-nitzschia spp. displayed the highest maximum specific uptake rates (max). D. acuminata displayed the highest affinity for NH4+, as shown by its values (slope of the nutrient uptake vs. concentration curve). Thus, A. catenella was adapted to utilising high NO3- concentrations during upwelling pulses, whereas both Pseudo-nitzschia and D. acuminata were able to acclimate to both high and low NO3- concentrations during the upwelling/relaxation cycles. In the Ría de Vigo, warm water from the stratified shelf entered the ría and downwelled in September, resulting in a well-mixed water column. The phytoplankton assemblage, dominated by Ceratium spp., Dinophysis acuminata and Gymnodinium catenatum, appeared to be advected in to the ría. Nitrate concentrations were consistently low, whereas NH4+ concentrations increased towards the head of the ría and with depth. The phytoplankton community was dependent on regenerated nitrogen, with ƒ-ratios <0.2. In contrast, positive circulation in June resulted in strong vertical gradients in temperature, salinity and nutrients and a community dominated by diatoms. Nitrate and NH4+ were depleted in surface waters although uptake rates were higher than in September, as were the ƒ-ratios (0.1-0.3). In both systems, upwelling winds favoured diatoms, although they were able to utilise regenerated nitrogen when NO3- was depleted, whereas upwelling relaxation created favourable conditions for HAB development. Dinophysis spp. occurred in both systems and were able to grow on recycled nitrogen in the absence of NO3-. The Benguela showed high variability in the selection of particular HAB species, perhaps due to greater variability in upwelling-downwelling cycles. In the Ría de Vigo, the occurrence of downwelling and associated nutrient conditions leading to blooms of Dinophysis spp. and Gymnodinium catenatum seems more predictable. In the Fal Estuary, Alexandrium spp. was favoured by low irradiance and the combination of strong stratification and high nutrient concentrations, and its growth was sustained predominantly by NH4+. A. minutum strains isolated from both upwelling systems and from a UK Lagoon all displayed higher max for NH4+ relative to NO3- but higher growth rates on the latter. This was consistent with field results from all 3 regions, suggesting that the upwelling systems did not display a different order of nitrogen preference, although they did display a higher affinity for NO3-.

The spatio-temporal distribution of microphytobenthos (MPB) on the sediment surfaces during emersions and suspended in water column during immersions was investigated on transects across Fingringhoe Tidal Flat in Colne estuary, on three zones: the mud flat, the transition zone and the salt marsh. The results of this thesis suggest that MPB distribution on intertidal flat was controlled by a set of complex interaction between the MPB with both biotic and abiotic factors. How much MPB are there on the sediment surfaces determines the availability of MPB biomass after immersion period and in the water column during immersion. ‘Sum of sun hours’ and ‘sum of rainfall’ directly affected the MPB biomass on sediment surfaces, and consequently, indirectly affected the MPB that associated with suspended sediment in the water column during immersions. Tidal range did not have significant effect on MPB biomass on sediment surfaces, however was significantly negatively effected the suspended MPB on the mud flat and the transition zone. The Chl a on the salt marsh however was significantly positively correlated with the tidal range. Data of net settlement rate of suspended sediment per hour during immersions displayed positive relationship with MPB biomass availability after immersion. The sediment settlement on the intertidal flat was negatively correlated with mean wind speed and tidal range. Neap-spring-neap tidal cycles were found to nfluence MPB species composition across the tidal flat. Spring tide that was characterized by high water current and high tidal range (4.3 – 5.6 m) showed to increase the occurrence of centric diatom such as species from genus Coscinodiscus, genus Actinoptychus and Odontella on both mud flat and transition zone. Also, the spring tide was responsible to source the salt marsh with species that commonly recorded on the mud flat and transition zone such as Pleurosigma angulatum and species from genus Gyrosigma.

Algal morphology is considered to be influenced by physiological and environmental factors such as stress and disturbance; one key disturbance exerted on algae is grazing pressure from herbivores. The factors upon which herbivores base their food preferences include algal attractiveness and edibility. Steneck and Watling's (1982) functional group model advocates the combination of algal species into seven groups based upon morphology and ecological function; the basic premise being that algal attractiveness and edibility will decrease hierarchically from functional group one to functional group seven, and that species within a group will be similarly attractive and edible. Two grazers commonly found in the intertidal area are the gastropod Littorina littorea and the isopod !dotea granulosa. Attractiveness and edibility experiments were conducted in which both grazers were presented with algae representing functional groups two to seven in single- and two-way choice experiments, in order to determine whether their food preferences could be predicted using a functional group approach. Although L. littorea and I. granulosa exhibited preference for algae between functional groups with regards to attractiveness and edibility, preference for both functional group and algal species differed between grazers. When the effect of algal morphology was investigated by presenting grazers with algal homogenates in agar, both grazers displayed a preference for algal extracts in agar over whole plant material, and exhibited preference for algae both between- and within-functional groups. The fact that not all species within a functional group were consumed in similar amounts contradicts the functional group model. Further investigation of the effect of algal availability on the feeding preferences of L. Iittorea showed their food choices could not be predicted based upon the algal species dominant in their habitat of origin. Results from all experimental manipulations suggest that both the habitat and food requirements of a herbivore, along with algal characteristics such as morphological, structural and chemical defences, algal availability and nutritional composition all influence herbivore food choice. As such, the functional group model proposed by Steneck and Wading (1982) cannot be accurately used to predict the feeding preferences of L. littorea or I. granulosa. It is suggested that unless models are modified to meet the requirements of a specific question, current functional group approaches are not a useful tool for predicting algal-grazer interactions.

Marine phytoplankton are responsible for ~50 % of global primary production and encompass a wide range of microorganisms characterized by being phototrophs. Within this group are the marine picocyanobacteria encompassing the phylogenetically closely related genera Synechococcus and Prochlorococcus. Bacteriophage lysis, as well as grazing by eukaryotic protists, play central roles as the major biotic causes of Synechococcus mortality in pelagic systems. However, Synechococcus populations show no extinction, suggesting high rates of production counteract this mortality, or that specific bacteriophage resistance and prey-selectivity mechanisms exist. This thesis set out to determine the molecular basis of cyanophage resistance in marine Synechococcus, using previously isolated cyanophage resistant Synechococcus sp. WH7803 mutants. Whole genome sequencing (WGS) analysis revealed that these cyanophage-resistant Synechococcus sp. WH7803 mutants, as well as a re-sequenced wild type strain, possessed a distinctive mutation profile, with a high number of mutations present in each mutant and with mutations present at a variable frequency. Such a profile is in stark contrast to what was recently found in Prochlorococcus where specific mutations could be identified at 100 % frequency (Avrani et al., 2011). The mutation profile of Synechococcus sp. WH7803 prevented the precise identification of specific genes involved in cyanophage resistance in this strain. This profile was hypothesised to be related to Synechococcus sp. WH7803 being an oligoploid organism, i.e. possessing more than one chromosome copy. Indeed, a qPCR assay that was optimised showed this strain possesses on average four chromosome copies. Subsequent isolation and WGS characterisation of cyanophage resistant mutants from the monoploid strain Synechococcus sp. WH7805 revealed a completely different mutation profile, most similar to that previously described for Prochlorococcus. This identified mutations in a single gene, encoding a possible glycosyltransferase, that were confirmed by Sanger sequencing, as being potentially responsible for cyanophage resistance in this strain.