Doctoral Theses / Doktorsavhandlingar Institutionen för marin ekologi

Permanent URI for this collectionhttps://gupea-staging.ub.gu.se/handle/2077/4718

Browse

Now showing 1 - 9 of 9

Introduced marine macroalgae and habitat modifiers : their ecological role and significant attributes
(2007) Nyberg, Cecilia D.
Invasive, non-indigenous species (NIS) have become an increasing problem worldwide, with impacts on the diversity and ecosystem functioning of native communities. Marine invasive NIS also have a negative economical impact through increased abundance of toxic species, fouling of man-made underwater structures, and reduced recreational values of beaches. Only a small proportion of the NIS becomes invasive (i.e., having a negative ecological and/or economical impact), but once a species has been established much effort and resources are needed to remove it. In the present thesis I discuss possible factors determining the success of macroalgal introductions and their impacts. A species of special concern in this thesis is the non-indigenous marine red alga Gracilaria vermiculophylla (Ohmi) Papenfuss, seen for the first time in the archipelago of Göteborg, Sweden, in the summer of 2003. Firstly, I highlight some positive and negative impacts caused by NIS as habitat modifiers. Secondly, I describe, by quantitative ranking, whether there are any common patterns of species traits increasing the likelihood of macroalgal NIS, introduced into a new area, becoming established and spread. In general, introduced and invasive species were ranked more hazardous than the native and non-invasive species introduced in Europe. Applying the quantitative species traits ranking on G. vermiculophylla rendered it among the most invasive red algae in Europe. Thirdly, I show the ability of G. vermiculophylla to withstand an emerged situation of more than five months, e.g. simulating transportation in a dredger or among fishing nets. The results indicate that G. vermiculophylla can easily survive long transportation in darkness such as in a ballast tank, and without being submerged in water. It also survived salinities down to 2 in a laboratory experiment, indicating that this species can survive in the innermost parts of the Baltic Sea (the Bothnian Bay). With the help of an event tree I illustrate the potential impact an establishment of G. vermiculophylla could have in the Baltic Sea. Fourthly, I show the distribution pattern within 150 km of the Swedish west coast in two years time for G. vermiculophylla. Furthermore, I describe the community associated with this species collected from Sweden, Denmark and the United States. In total, nearly 100 different taxa in twelve phyla were found associated with G. vermiculophylla. Finally, the impact of G. vermiculophylla on the native eelgrass, Zostera marina, was assessed using a modelling approach. The model output showed a negative effect on Z. marina already at low densities of G. vermiculophylla. This thesis contributes to a wider understanding of macroalgal introductions in general and of the ecology and ecophysiology of the invasive red alga G. vermiculophylla in particular. Such knowledge is important for management and stresses the importance of monitoring the Swedish coastline for early detection of NIS.
The evolution of flat periwinkles Littorina fabalis and L. obtusata emhasizing mitochondrial introgression and restricted recombination
(2008-09-12T11:16:50Z) Kemppainen, Petri
The evolution of species takes in general very long time and different mechanisms are likely to operate during the various stages of this process. Accordingly speciation should be studied at different levels of species divergence. In this thesis I have studied ecological and genetical differentiation between two ecotypes of Littorina fabalis as well as between L. fabalis and L. obtusata - two closely related, directly developing, marine, intertidal gastropods. In L. fabalis size is about 25% larger in moderately exposed habitats compared to sheltered habitats and in this thesis I present data showing that this genetically inherited size different is maintained by an interaction of several selective forces, including life history optimisation, size selective crab predation, fucoid algae functioning as refuges from crab predation and wave-induced dislodgement. The two ecotypes of L. fabalis differ also in the protein arginine kinase (Ark) and a Randomly Amplified Polymorphic DNA (RAPD) locus and this linkage disequilibrium persists in locations where both ecotypes are present suggesting that recombination is strongly suppressed between Ark, the RAPD locus and one or several loci influencing size. Chromosomal rearrangement, in particular inversions are very effective in restricting recombination and if locally adapted alleles in at least two loci on the same chromosome occur in heterogeneous environments, an inversion may immediately protect these from being mixed up with alleles (introduced by migration) that are locally adapted for other microhabitats. This model predicts that differential selection on these alleles exist before an inversion appears and I have tested this by sequencing an intron of Ark. The SS-ecotype was nearly fixed for one haplotype while the diversity among LM-ecotypes was much higher supporting a scenario where a recently derived inversion (or other kind of chromosomal rearrangement) restricts recombination between Ark and one or several loci that influence size. In this thesis a novel method used for the sequencing of the Ark intron that does not require the cloning of each sample individually (which is both time consuming and expensive) is also presented. Littorina fabalis and L. obtusata are considered as well defined species with clear differences in ecology, morphology and nuclear DNA (allozymes) and with microsatellites I could show that hybridisation between these species has not been occurring at least during the last 10,000 years (they are easily identified in the field by both size and coloration). Despite this they show no consistent differences in the mitochondrial cyt-b gene, which could either be due to incomplete lineage sorting or introgression. The idea that mitochondrial DNA can be used as a barcode in species identification is attractive but has in recent years gained criticism because the nature of the mitochondrial molecule makes it specifically prone for introgression between species. Locally restricted mitochondrial introgressions are common among closely related species but the flat periwinkle case study in this thesis clearly shows that a lack of mitochondrial divergence can also exist throughout the whole distribution range for a geographically wide spread species (L. fabalis and L. obtusata occur sympatrically from Spain to Iceland and the White Sea, Russia)
Immunotoxicology in Marine Invertebrates - Effects of Manganese on Immune Response
(2009-05-13T09:02:37Z) Carolina, Oweson
Manganese, Mn, is an abundant element in nature, particularly in soft bottom sediments of the oceans and in bedrock. The metal is predominantly bound to the sediment in the colloid state, MnO2. Eutrophication caused by the high nutrient load in coastal waters together with over-fishing cause cascade effects in the ecosystem increasing the algal blooms and enhancement of hypoxic condition over large bottom areas. During hypoxic events MnO2 is reduced and released into the bottom water as bioavailable ions, Mn2+. Mn is essential for several metabolic and enzymatic processes and is necessary for both animals and plants. Elevated levels though, are toxic and severe effects on the nervous system have been known for long. In addition, previous studies have shown an impaired immune system of the bottom living lobster, Nephrops norvegicus, when exposed to concentrations that are realistic to find in nature. In this study I aimed to investigate if immunotoxic effects of manganese are general also for other marine invertebrates. It is widely accepted that invertebrates do not have a documented so called adaptive immune response. They lack the genes, proteins and cells for the highly specific recognition and the long-term memory as found in vertebrates. Invertebrates primarily rely on the innate immune system to effectively combat a wide array of microbial pathogens. The innate immune system comprises of a first line of defence systems such as coagulation and melanization reactions, often followed by cellular reactions such as phagocytosis, encapsulation and production of antimicrobial substances. Many innate immune reactions are highly evolutionary conserved and are found throughout the whole animal kingdom. In aquatic invertebrates the open coelom or semi-open haemal circulatory system continuously expose them to potential pathogens and their immune response has proved to be exceptionally efficient in pathogen elimination as witnesses by the invertebrates’ evolutionary success. In this thesis species from three different phyla within the Bilaterians were investigated; the Norway lobster, Nephrops norvegicus (Crustacea), the blue mussel Mytilus edulis (Mollusca) and the common sea star, Asterias rubens (Echinodermata), differing in preferred habitats, feeding behaviour and somewhat in their strategies of immune defence. Studies were made on molecular, cellular and organism levels. On molecular and cellular levels we investigated the effects of manganese on the renewal of haemocytes (proliferation and differentiation of new cells), manganese effects on viability of haemocytes and the stress responses measured in both haemocytes and haematopoietic tissue. On the whole organism we investigated the effect of manganese on the ability for the animals to clear their cavity form injected bacteria. The results of this thesis show that Mn in concentrations found in bottom waters affects the immune system of marine invertebrates differently. In N. norvegicus the metal severely suppresses the number of circulating haemocytes by inducing apoptosis, programmed cell death. The impaired immunity made them more susceptible to infections, which was also found in M. edulis. In A. rubens the same Mn concentration seemed to have a stimulating effect (hormesis) on the haematopoiesis which increased the number of circulating haemocytes. Although manganese was shown stressful to the haemocytes and affected their ability to phagocyte, the increased number of haemocytes compensates these impairments. There was seemingly a negative correlation between the accumulation of the metal in the tissues of the animals and their ability to eliminate bacteria. Although Mn does not cause chronic effects on immunity, the expanding areas with bioavailable Mn might have an impact on species composition since some invertebrates become more susceptible to infections.
Bloom dynamics and population genetics of marine phytoplankton - Community, species and population aspects
(2009-08-28T09:23:48Z) Härnström, Karolina
Phytoplankton are the most important primary producers in the world’s oceans and coastal waters, accounting for nearly half of the global net primary production. Although they are such important organisms, little is known about the ecology and dynamics of phytoplankton. The importance of phytoplankton resting stages, the coupling between cells in the sediment and watermass and how environmental changes affect the population structure is uncertain. The record of a specific species in a given area is foregone by either advection of the species from adjacent areas, or by growth of a few cells present in the water. Many groups of phytoplankton have the ability to form resting stages to provide short- or long-term survival, and these stages can be resuspended and subsequently germinate and thereby be re-established in the water mass. Diatoms constitute the single largest group of microalgae and they are mainly marine but found in all aquatic environments. Diatom blooms can develop fast, and they can grow at low levels of light, which gives the cells an advantage during spring blooms in temperate areas where light is a limiting factor. To successfully meet selective pressure in a variety of ecological niches, it is hypothesized that diatoms display high phenotypic and genetic diversity. Skeletonema marinoi (Sarno et Zingone) is a marine diatom, often dominating temperate coastal waters during spring bloom. The mechanisms for dispersal and expansion of populations of this species are, as for most diatoms, complex and difficult to predict. Possibly the presence of different populations at different seasons is caused by strong directional selection in a continuously growing population, or by a complete replacement of one population by another. The general aim of this thesis was to study marine phytoplankton dynamics at community, species and population level, and we used S. marinoi as model organism for the population studies. In order to perform some investigations, appropriate methods have been developed. I have focused on the interaction between water mass and sediment, both in temperate waters and in a tropical area, investigated the importance of resting stages and small-scale hydrographical changes for the phytoplankton community structure as well as population genetics and microevolutional processes of population dynamics. The results from a tropical area show that benthic resting stages contribute to blooms by resuspension, germination, and proliferation as planktonic cells in the water column, and thus, the cells can influence the phytoplankton community in the water column. There can be an alternation of the species composition if a plankton community is seeded by resting stages or by planktonic cells, and geographically the strategies of seeding can differ within the same species. The composition of the phytoplankton community is exceedingly affected by small-scale hydrographic changes and several of these factors are potentially tightly coupled. These changes have implications on the sampling, and therefore frequent sampling is important. When clones of S. marinoi were examined, the morphological character defining another species of the same genus–Skeletonema dohrnii (Sarno et Kooistra)–was found in most of the clones. The phylogenetic variation in LSU rDNA in the S. marinoi clade were of the same magnitude or greater than differences between S. dohrnii and S. marinoi. The two species are not suggested to be merged since there may be a separation in the biogeographical distribution of the two species. A series of molecular methods were used to study various aspects of phytoplankton ecology. For estimating the proportion of dinoflagellate versus diatom biovolume or biomass and the absolute diatom biovolume or biomass, real-time PCR technique constitutes a quick and accurate method. Another useful tool is microsatellite markers, and the characterisation and development of primers enabled the study of population genetics of S. marinoi. Resting stages from undisturbed and dated sediment cores from a fjord with anoxic bottom conditions, were germinated and cultures established. The fjord has during a few decades been hypereutrophicated and populations found during this time were significantly different from populations found before and after. The postand pre-eutrophication populations showed no significant genetic difference. Environmental changes may favour only some populations from a pool of several different populations at a specific location, and maybe other changes would favour different populations.
Ecological disturbances: the good, the bad and the ugly
(2010-11-02) Svensson, J. Robin
Abstract. This thesis focuses on the definitions, characterizations and quantifications of ecological disturbances, as well as hypotheses on their impacts on biological communities. The most prominent model on effects of disturbance on diversity is the Intermediate Disturbance Hypothesis (IDH), which is utilized in management of national reserves, has received over 3300 citations and has been corroborated by a multitude of studies from terrestrial and aquatic systems. According to the predictions of the IDH, diversity is high at intermediate levels of disturbance due to coexistence of competitors and colonizers. At low levels of disturbance diversity will be low due to competitive exclusion and few species can persist at high levels of disturbance. In an extension of the IDH, the Dynamic Equilibrium Model (DEM) predicts that the effects of disturbance depend on the productivity of communities, because at high growth rates a stronger disturbance is required to counteract increased rates of competitive exclusion. The IDH and the DEM were tested in a field experiment on effects of physical disturbance (scraping) and productivity (nutrient availability) on hard-substratum assemblages in paper I, where the patterns predicted by the IDH, but not the DEM, were observed. This outcome shows the importance of the nature of productivity alterations, as the productivity treatment had a general positive effect on growth rates but only marginal effects on the dominant species, thereby leaving rates of competitive exclusion unaffected. In paper II I tested another extension of the IDH, which predicts that smaller, more frequent disturbances will have different effects on diversity compared to larger, less frequent disturbances. In this experiment I used two different regimes of disturbance, small and frequent vs. large and infrequent disturbances, while the overall rate (the product of area and frequency) was kept equal for both regimes. At the site where the IDH was supported, the regime with a large proportion of the area disturbed infrequently showed higher richness, due to a stronger decrease of dominants, compared to the regime with a small proportion disturbed frequently. In addition to these significant differences in diversity effects between different disturbance regimes, it may also matter what agent of disturbance that is causing the damage. In paper III I contrasted the effects of a physical disturbance (wave-action) to that of a biological disturbance (grazing), as well as their respective interactions with productivity in a multifactorial design tested on natural epilithic assemblages. The composition of assemblages and the total species richness was significantly affected by physical disturbance and interactively by biological disturbance and productivity. The algal richness was significantly affected by productivity and biological disturbance, whereas the invertebrate richness was affected by physical disturbance. The results show, for the first time, that biological disturbance and physical disturbance interact differently with productivity due to differences in the distribution and selectivity among disturbances. In paper IV I investigate how the choice of diversity measure may impact the outcomes of tests of the IDH, which, surprisingly, has not previously been discussed. This was done by an extensive literature review and meta-analysis on published papers as well as by two different approaches to mathematical modelling. Both models support the IDH when biodiversity is measured as species richness, but not evenness. The meta-analysis showed that two-thirds of the published studies in the survey present different results for different diversity measures. Hence, the choice of diversity measure is vital for the outcome of tests of the IDH and related models.
On the ecophysiology of Baltic cyanobacteria focusing on bottom-up factors
(2010-11-05) Malin, Mohlin
Cyanobacterial blooms in the Baltic Sea are dominated by diazotrophic cyanobacteria, i.e. Aphanizomenon sp. and Nodularia spumigena. The blooms coincide with a stable stratification and the organisms are concentrated to the surface water, exposed to high levels of both photosynthetically active radiation (PAR, 400–700 nm) and ultraviolet radiation (UVR, 280–400 nm), in combination with low ratios of dissolved inorganic nitrogen and inorganic phosphorus (DIN:DIP). The ability of nitrogen fixation, a high tolerance to phosphorus starvation and photo-protective strategies (production of mycosporine-like amino acids, MAAs) may explain their competitive advantage in the Baltic Sea. However, intraspecific variation in the response to environmental factors has been commonly overlooked. The seasonal succession with peaks of Aphanizomenon sp. in early summer followed by peaks of N. spumigena, has been related to their interspecific preferences and response to abiotic conditions. N. spumigena dominates in late summer forming extensive toxic blooms, and its toxin nodularin, a hepatotoxin lethal to wild and domestic animals, may act as a tumour promotor. It has been suggested that the accumulation of nodularin within the N. spumigena cells and its release from the cells are affected by environmental factors. Hence, the seasonal succession may be explained by an allelopathic effect of nodularin on Aphanizomenon sp. The aim of this thesis is to elucidate the factors controlling the cyanobacterial blooms, prevailing seasonal succession, intraspecific differences, toxin production and release. Moreover, to analyze the potential of future toxic blooms in a predicted climate change, e.g. increased UVR and stronger stratification due to increased precipitation and temperature. With a multi-factorial approach in the laboratory and in outdoor experiments, interactive effects of radiation (photosynthetic active radiation PAR and PAR + UV-A + UV-B), nutrients (nutrient replete, nitrogen limited, phosphorus limited) and species composition (monocultures of N. spumigena and Aphanizomenon sp. and mixed cultures with the respective species) were tested on these two species. Although strain-specific differences in UV-B radiation tolerance were observed, N. spumigena is a species that is not generally negatively affected by UV-B radiation corresponding to ambient sea surface intensities/doses. N. spumigena tolerates high ambient UVR also under nutrient-limiting conditions and maintains positive growth rates even under severe phosphorus limitation. Interestingly, the specific growth rate of N. spumigena was stimulated by the presence of Aphanizomenon sp. and in contrast to our hypothesis, Aphanizomenon sp. was not negatively affected by the presence of N. spumigena. Nodularin accumulation and release were dependent on environmental conditions, but the released nodularin did not affect the co-existing species Aphanizomenon sp. The highest intra- and extracellular nodularin concentrations were observed under nitrogen limitation when shielded from UVR. In conclusion, I suggest that the seasonal succession, with peaks of Aphanizomenon sp. followed by peaks of N. spumigena is a result from species-specific preferences of environmental conditions and/or stimulation by Aphanizomenon sp., rather than an allelopathic effect of N. spumigena. Moreover, a possible increased toxin content of the N. spumigena should be considered when planning sewage treatment, since nitrogen removal may cause problems on a recreational level and increased accumulation of nodularin higher up in the food web. The results from this thesis, together with a predicted stronger stratification and increased UVR due to effects of climate change in the Baltic Sea, reflect a scenario with a continuing future dominance of the toxic N. spumigena.
Seals and fisheries: a study of the conflict and some possible solutions
(2011-04-08) Königson, Sara
Interaction between seals and fisheries along the Swedish coast has serious environmental and economic consequences. This thesis describes the conflict as it affects four different small-scale coastal fisheries; the eel fisheries on the west coast, the herring fisheries and salmon fisheries in the northern Baltic and the cod fisheries in the central Baltic. Knowledge gained through studies of the interaction between seals and fisheries has been instrumental for the development of alternative seal-safe fishing gear and mitigation methods. For some fisheries the improved understanding has led to a resolution of certain parts of the conflict. Certain coastal fisheries in the Baltic, such as the herring gillnet fishery, are at the point of collapse because of this conflict. Damage caused by grey seals to this fishery has been shown to be much more extensive than previously recognised. When seals raid nets, a significant part of the catch is lost without trace. Seals remove fish from nets without leaving any remains. This represents a hidden loss. Another hidden loss is caused by the presence of seals around fishing gear, which scares away fish from the area. The result is often a total loss of catch. Hidden losses are also evident in the gillnet fishery for cod in the central Baltic sea. In recent years damage by seals in the cod gillnet fishery has increased significantly. Due to the high value of cod the cod fishery is currently one of the fisheries that suffer the highest economic loss by seal damage. Seal-safe fishing gear is at present the only long lasting solution which would meet the needs of both seals and fishermen. Mitigation of damage to catch and fishing gear as well as the prevention of accidental by-catch are two sides of the same problem; a solution to one is also a solution to the other. However, development of new fishing gear is challenging and time-consuming. It requires better knowledge of both fish and seal behaviour. At present suitable alternative fishing gear is not available for the herring fisheries carried out through the whole season. However, a herring trap has been developed as an alternative fishing gear for catching spawning herring in spring time. In the cod gillnet fishery, promising results have been achieved in trials of an alternative fishing gear - the two-chamber pot. Another coastal fishery in the Baltic subjected to damage by grey seals, is the salmon trap net fishery in the North Baltic. A seal-safe salmon trap has been developed and is used by most of the salmon fishermen. This so called pontoon trap prevents the seal from reaching the catch by keeping the fish in an enclosed seal-safe fish chamber. However, in recent years there have been reports of damage by seals also in the pontoon trap. By filming the seals attacking traps it has been possible to identify 10 individual seals hunting in the traps and to determine that these same animals returned to the traps over a long period of time. It is possible therefore, to limit or decrease damage to the fisheries by limiting access for or by culling the individual seals specialized in raiding fishing gear. On the west coast of Sweden the eel fyke net fishery suffers from damage by harbour seals. In order to find a lasting solution to the conflict, seal behaviour has been studied as well as the fyke nets' fishing efficiency. The issue of whether it is the eels or the by-caught species which motivate harbour seals to attack fyke nets was studied. It was shown that harbour seals raiding fyke nets have a preference for eel. Certain harbour seals that specialise in foraging at fyke nets, have developed different feeding preferences compared to those of most seals. Seal-safe fyke nets, which resisted attacks while still being efficient in terms of yield, have been developed. They are already in use in commercial fishery along the west coast.
Alien Fish Species in the Eastern Mediterranean Sea: Invasion Biology in Coastal Ecosystems
(2011-04-25) Kalogirou, Stefan
The spread of non-indigenous species (NIS) in the eastern Mediterranean Sea is an ongoing and accelerating process. Non-indigenous species are regularly reported from various coastal habitats in the eastern Mediterranean Sea but fundamental knowledge on the assemblage structure of coastal fish communities are lacking. This thesis aims to increase the knowledge on the fish assemblage structure and function of Posidonia oceanica meadows and sandy habitats in a coastal area of the eastern Mediterranean Sea and give insight into invasion biology by investigating the potential impact of introduced fish species to the local ecology and food-web of the marine systems under study. Functional and feeding guilds were developed to investigate the fish assemblage structure and function of coastal fish communities and to assess the potential role of NIS in the food web. In addition, diet nvestigations were considered important first steps in order to evaluate the potential role and impact of recently established NIS in the recipient region. During the sampling campaign two species were for the first time reported in the area. Posidonia oceanica was found to be a multifunctional habitat for fish species. It was found to be a highly important nursery habitat for several species during summer and a habitat that could under certain seasons concurrently be used by both adults and juveniles. Four functional guilds were created to describe the habitat use of P. oceanica meadows for each species encountered; juvenile migrants, seagrass residents, seasonal migrants and occasional visitors. Affinity of each species to P. oceanica was assessed in a comparison with each species distribution on open sand within the same depth range. Among the 88 species encountered, eleven were found to be non- indigenous of Indo-Pacific and Red Sea origin, three of them using segrass mainly as juveniles, and four as residents. In a comparison of fish assemblage structure between seagrass and sandy habitats quantitative sampling in combination with classification of fish species into six major feeding guilds revealed the position and contribution of non-indigenous species (NIS) in the food web of Posidonia oceanica and sandy habitats. In P. oceanica beds and on sandy bottoms 10 and five species, respectively, were non-indigenous of Indo-Pacific and Red Sea origin. The proportional contribution of NIS individuals on P. oceanica beds was lower than that of sandy bottoms (12.7 vs. 20.4 %) a pattern that also followed for biomass (13.6 vs. 23.4 %), indicating that low diverse systems may be more prone to introductions than species-rich communities. The two habitats had similar fish feeding guilds, but the biomass contribution from NIS varied within each guild, indicating different degrees of impact on the available resources. Size was considered highly important due to habitat shift of species with increased size. Two of the aspects considered in this study, the chance of establishing and the chance of being very dominant will depend upon competitive abilities strongly coupled to size and grounds for habitat shift. However, success of establishment will also depend on appropriate food resources in the recipient community as well as competitive abilities and level of competition in the food web within habitats. No support could be found for the theory that taxonomic affiliation could facilitate invasion success. The non-indigenous bluespotted cornetfish Fistularia commersonii was found to be a strictly piscivore predator and the diet consisted of 96 % by number and >99 % by weight of fish. The diet of F. commersonii was related to time of year, and fish size. Size classification and habitat of prey groups (benthic, supra-benthic, and pelagic) showed that with increased body length it extended its diet to larger prey and more generalist feeding. Fistularia commersonii was found to prey on commercial important native species (e.g. Spicara smaris, Boops boops, Mullus surmuletus) and the absence of NIS from its diet was mainly attributed to the absence of NIS with elongated body shape. The feeding ecology of two common indigenous (Sphyraena sphyraena and Sphyraena viridensis) and one abundant non-indigenous barracuda, Sphyraena chrysotaenia, of Indo-Pacific origin, was investigated. Confamilial feeding interactions was studied to investigate overlap in feeding preferences in relation to availability of prey items. Dietary analyses revealed that all three species examined were specialized piscivores with their diet consisting to more than 90 % of fish, both by number and weight. All three predators examined showed a significant selectivity towards Atherina hepsetus. Diet breadth and size of prey increased with increased body size, whereas diet overlap between indigenous and NIS decreased, attributed to increased diet breadth and specific life characteristics of indigenous species developing into larger predators extending their foraging habits. During winter, condition of the NIS was significantly lower than that of the indigenous species, indicating that winter temperature in the studied area may be a limiting factor for further population growth of this Indo-Pacific species. This study filled the gap in knowledge about the feeding preferences of the most abundant piscivorous species found on the coasts of the studied area. Additionally, congeneric affiliation of fish introductions was not found to be an important factor explaining successful establishment of NIS. The non-indigenous toxic pufferfish, Lagocephalus sceleratus, was reported for the first time in the Mediterranean in 2003 and two years later in the coastal habitats of Rhodes. The ecological and societal impact of the pest pufferfish was investigated in coastal habitats of Rhodes. Seasonal quantitative sampling in two common coastal habitats was used to investigate habitat use of different life-stages. Sandy areas were found to be highly important for the early life stages of L. sceleratus. In contrast, Posidonia oceanica habitats were mainly preferred by larger (> 29 cm) reproductive adults with a maximum recorded size of 64 cm. Lagocephalus sceleratus was fond to be an invertebrate and fish feeder while size classification revealed a tendency for an ontogenetic diet shift with increased size to a molluscivore feeding. The ontogenetic diet shift is most probably attributed to a shift in habitat use with increasing size. During early life stages L. sceleratus inhabited sandy bottoms where it fed on various invertebrates, including the genus Nassarius and Dentaliidae. The predominant molluscan species found in the diet of larger (> 20 cm) L. sceleratus individuals was Sepia officinalis while predation of Octopus vulgaris was less successful. Sepia officinalis and O. vulgaris are of economic interest in the area and the impact of L. sceleratus on local stocks of these species is discussed. Societal impacts were also evident in the area due to increased public attention concerning the lethal effects of the toxic L. sceleratus, if consumed. Seasonal variations in the condition of L. sceleratus did not show any significance and the high conditional values together with information on high numbers caught during samplings, signifies its ability to become an important member of the coastal fish community. Combined ecological, economical and social effects clearly classify L. sceleratus a pest in the area.
Spatial distribution and conservation planning of seabed biological diversity
(2011-11-18) Gonzalez Mirelis, Genoveva
Knowledge of spatial patterns of biota has become a commodity for conservation practitioners and spatial ecologists alike. This type of information enables the identification of representative and unique biological features (at some nominal scale) which itself constitutes the application par excellence of knowledge of biodiversity distribution as it relates to the design of reserve networks and the realization of spatial planning. Furthermore, insight into the spatial distribution of the various components of biological diversity provides a way of addressing issues of fundamental ecology relating to the processes influencing the variation of ecosystem structure across space. The present thesis is concerned with methods (and related issues) to document the spatial distribution of diversity at the assemblage (or community) level, which is later proven to be an adequate surrogate for diversity patterns at the species level, and therefore an adequate approach for identifying sites representative of regional biodiversity. This was investigated across the benthic portion of a Marine National Park off the West coast of Sweden. At the center of this thesis is the production of a map of benthic biotopes by use of automated, objective methods, of measurable accuracy, and that can support marine spatial planning. In Papers I and II, I address various aspects related to the data model underpinning this map. Paper I deals with patterns of spatial patchiness of benthic communities, which helped determine the appropriate resolution at which epibenthic biological diversity in this area is best investigated. Here, spatial autocorrelation is measured at a range of scales and used to determine an appropriate grain size for subsequent sampling. This will become a backbone of this study, as it determines the (only) spatial scale for which the findings are relevant. In Paper II I assess the performance of classifications of communities at varying levels of compositional detail as a way of calibrating the classification scheme to be used as the basis for the map. Paper III is a case study of predictive mapping of communities. The process was driven by patterns of occurrence of benthic communities, which were then extrapolated using observed biota-environment relationships, by means of full-coverage variables derived from multibeam data. This approach draws heavily from the field of distribution modelling of species and/or communities. Further, I present a number of analysis techniques that are new to benthic ecology, and virtually new to predictive mapping in general (albeit not to the field of predictive, statistical modelling, and classification algorithms). In Paper IV I evaluate the applicability of the produced map of benthic biotopes as a tool for conservation planning. Particularly, I test the value of the outputs from the model introduced in Paper III (i.e., the biotopes with their associated spatial attributes) as conservation features, or surrogates for biodiversity, in the context of systematic conservation planning, to represent biodiversity at other hierarchical levels and across ecological niches.

Browse

Browsing Doctoral Theses / Doktorsavhandlingar Institutionen för marin ekologi by Issue Date