Master's programme Landscape Ecology, 181 pages (first reviewer)

Due to the adverse effects on the ecosystem caused by the laying of the EUROPIPE I and II natural gas pipelines through the Wadden Sea in Lower Saxony in the 1990s, the summer dyke on the East Frisian island of Langeoog was dismantled in 2003/2004 as a compensatory measure. The Langeoog salt marshes had been poldered for almost 70 years and, in conjunction with the construction of an artificial drainage system, had been made suitable for agricultural use. The main aim of the renaturalisation was to increase the ecological conservation value of the salt marshes by restoring them to a near-natural salt marsh ecosystem. This paper describes the effects of the summer dyke removal on Langeoog's salt marsh vegetation and assesses the success of the renaturalisation of the summer polder to date.

Based on the phytosociological survey of 76 permanent plots, 13 plant communities of the halo series have been identified. Taking into account the permanent plots recorded in 2000, 2002, 2007 and 2013 and deriving the indicator values for nutrient, salt and moisture content, it can be seen that the restored flooding dynamics are initially accompanied by a large-scale regressive development of the salt marsh vegetation into early successional stages. The proportion of upper salt marsh communities and glycophytic plant species decreases, while halophilic communities of the pioneer zone and lower salt marsh, such as Salicornietum strictae or Halimionetum portuiacoidis, spread, and the temporary increase in nutrient availability increases the cover of nitrophytic species such as Suaeda maritima and Atriplex prostrata after the dyke is rebuilt.

These developments are reflected in the general increase in salt and moisture content as well as the temporary increase in nutrient content. The further course of succession is determined by interspecific competition along a developing salt and height gradient. The restored tidal influence in conjunction with the largely intact artificial drainage system and the cessation of grazing favours the rapid spread of Aster tripolium and the formation of monodominant stands of Halimionetum portulacoidis in the Lower Salt Marsh to the detriment of Puccinellietum maritimae. In the upper salt marsh, the Atriplici-Agropyretum pungentis and the Festuca rubro community spread equivalently on the sites of the grazing-dependent Juncetum gerardii of the middle salt marsh. The species diversity and the species inventory of valuable plant species typical of the natural habitat are categorised as high and present with the potential to increase.

It should be emphasised that the Langeoog salt marshes provide a habitat for endangered and specially protected plant species such as Sagina nodosa and Limoniumvulgäre . Overall, there is a near-natural, mosaic-like interlocking of characteristic salt marsh vegetation in the former Langeoog polder areas, which is orientated towards a superordinate altitudinal zonation and the given abiotic site factors.

Incipient geomorphological changes towards a near-natural, meandering tidal flat system can be observed in the area of the pioneer zone and the lower salt marsh in the Westheller. However, the regression of the anthropogenic drainage system at higher elevations and in the Ostheller is questionable. At present, a progressive deepening of the system can be observed.

The Langeoog salt marshes have the potential to approximate a natural salt marsh ecosystem following their dyking. The positive effects of the restored flooding dynamics can be seen more clearly in the West Heller than in the Ostheller due to its deeper location. The Lower Saxony Wadden Sea National Park Authority is still considering further targeted management measures to increase the naturalness of the former summer polder. The ecological conservation value of the Langeoog salt marshes has been increased in accordance with the objectives of the compensatory measure, even without further intervention in the ecosystem.

Bachelor's degree programme in Environmental Sciences, 56 pages (first and second reviewer)

No new neophytes have been found on Mellum since the mapping by Hahn (2006). For the colonisation of Mellum by the neophytes present, a direct link to an anthropogenic introduction can be assumed in most cases. However, it is likely that Conyza canadensis, the Oe-nothera species, Rosa rugosa and Senecio inaequidens were able to spread to Mellum without humans due to their natural long-distance dispersal mechanisms. Overall, there is an opportunity to further reduce the anthropogenic sources of introduction of neophytes and cultivated plants on Mellum and to minimise the current occurrence.

The extent of neophyte occurrences and the number of neophyte species on Mellum compared to the East Frisian Islands cannot be attributed solely to a lower anthropogenic influence. The age of Mellum and the associated lower habitat diversity and number of species are also differences to the East Frisian islands that influence the general occurrence of neophytes on Mellum. Overall, the development of Mellum is still so young and dynamic that Mellum is not generally suitable as a basis for comparison when researching the human influence on the immigration of neophytes to the East Frisian Islands. As soon as all natural habitats of the East Frisian Islands have formed on Mellum, it can actually be investigated whether Mellum can be used as a basis for comparison in this context. As a result, it is to be expected that further neophytes will colonise Mellum in the future.

Mellum can be used to investigate the long-distance dispersal vectors of individual neophytes due to its currently lower human influence compared to the East Frisian Islands. This makes it possible to investigate which neophytes will migrate there in the future even without humans as a dispersal vector. Nevertheless, the existing human influence remains a source of error (cf. Kowarik 2003).

Bachelor's degree programme in Environmental Sciences, 25 pages (first reviewer)

The problem of marine litter pollution is a global one and these days current research topic. In 2006 it was observed that in the nests of European Spoonbills and on the Island of Mellum in the German bight plastic waste can be found. In this study a systematic recording was established to get informations about the quantity and quality of plastic waste in nests of European Spoonbills and Great Cormorants on Mellum. Therefore, a number of nests from both species were recorded after the breeding season of 2018. The nests were disassembled and the total amount of plastic waste per nest was counted. In 92 % of the examined nests from the European Spoonbills and 85 % of Great Cormorants plastic waste was recorded. There is also a difference between the species noticed. European Spoonbill shows a significantly higher amount of plastic waste in nests then Great Cormorant.

Bachelor's degree programme in Biology, 58 pages (first and second author)

Since the renaturalisation measure in 2003/2004, the vegetation in the eastern part of the former summer polder on Langeoog has changed significantly in some places due to the altered flooding conditions and the reduction in grazing. For this reason, the vegetation was mapped again 15 years after the re-diking and compared with the mapping from 2002 and 2006.

The pioneer zone showed a strong increase in area directly after the re-diking, but has since been replaced in many areas within the former summer polder by higher zones, such as the lower salt marsh, due to soil elevation through sedimentation. As predicted, the area of the lower salt marsh has therefore increased significantly compared to the expansion before and shortly after the dyke was rebuilt. This is primarily due to Halimionetum portulacoidis, which colonised a significantly larger area in 2019.

In contrast to this and to the previously predicted development, the middle salt marsh colonised a smaller area compared to 2002 and a larger area compared to 2006. The reduction in area since the dyke was removed is mainly due to the reduction in the area occupied by Juncetum gerardii, which is dependent on the cessation of grazing. On the other hand, the Atriplicetum littoralis shows a clear increase in area in the middle salt marsh due to the colonisation of the remains of the salt marsh. The upper salt marsh dominated the vegetation of the study area in all years, although as expected it lost area by 2019, even if this decrease was not as severe as predicted due to the influence of salt water.

The Festuca rubra community and the Artemisietum maritimae were displaced in many areas by the more competitive Atriplici-Agropyretum pungentis, which colonises higher areas. Increased sedimentation as a result of the renaturalisation measure increased the height of the soil, so that areas where Atriplici-Agropyretum pungentis did not occur in 2006 were (re)colonised by 2019. The expected dominance of Atriplici-Agropyretum pungentis has been confirmed and will presumably continue in the coming years as long as grazing is discontinued on most areas and there is no natural drainage system.

Due to the dynamic nature of this habitat, the developments in the study area should be followed up with further mapping, as the climax stage was probably not yet reached in 2019 and the fauna, such as the avifauna, is also dependent on the development of this habitat. The development of the vegetation in the eastern part of Langeoog's summer polder is indicative of the objectives of the reclamation management, which was not intended to maximise species diversity, but instead aimed for natural development. Over time, the natural conditions of a salt marsh will presumably develop and this renaturalisation measure will therefore serve as a forerunner for other similar measures in the Wadden Sea.

Master's programme in Landscape Ecology, 40 pages (first and second reviewer)

Senecio inaequidens , a neophyte native to South Africa, has been known as part of the dune vegetation on the East Frisian island of Spiekeroog since 2000. Between 2001 and 2003, its distribution there was recorded in detail for the first time. How the population has developed since then, what requirements S. inaequidens places on its habitats and what possible potential for expansion results from this were investigated as part of this study.

To this end, the species' habitats were first mapped over large parts of the island. Subsequently, 36 sites were selected according to the criterion of diversity and analysed for a number of soil properties as well as the structure and composition of their vegetation cover. The same surveys were also carried out on 33 sample areas without current S. inaequidens occurrence to assess their suitability for potential colonisation.

The results of the mapping show that S. inaequidens has spread very strongly on Spiekeroog since 2003. As was the case 15 years ago, its distribution is currently concentrated in young grey dunes. In addition, however, it now colonises all developmental stages of dune succession from the foredunes to the brown dunes, as well as different biotope types of salt marshes and transitional biotopes between dunes and salt marshes.

Its ability to thrive in such diverse biotopes demonstrates the wide amplitude that S. inaequidens has in relation to biotic and abiotic site factors. It invades very patchy pioneer vegetation, but can also thrive in the midst of a closed plant cover of herbaceous species, shrubs, lichens or mosses. It can be found on moderately acidic to slightly alkaline, salt-free to slightly saline, dry to moderately moist, extremely nutrient-poor to nutrient-rich and purely sandy to silt- and clay-rich soils. A significantly increased vitality of S. inaequidens was not observed in any part of the colonised amplitude. There was also no detectable correlation between the vitality and the species richness of the sample areas.

The site characteristics suspected to be outside the species' tolerance range after comparing areas with and without the presence of S. inaequidens include a strongly acidic pH value, severe dryness in the seedling stage, high soil moisture and a moderate or high salt content. However, their influence on the spread of the species cannot be clarified with certainty here, as exclusion by the existing vegetation or a lack of seed input cannot be ruled out as causes for the absence of S. inaequidens at sites with the aforementioned characteristics. Reliable predictions about the further spread of the species are therefore hardly possible on the basis of this study alone.

Bachelor's degree programme in Environmental Sciences, 24 pages (first reviewer)

The problem of plastic waste is particularly evident in the extent of plastic bag usage behaviour in the fruit and vegetable department. The figures for the consumption of these thin plastic bags are only slowly decreasing and have hardly changed in comparison to previous years. This raises the question of whether there are alternatives that could reduce consumption or whether other methods such as mandatory payment are necessary. With the help of a survey, the benefits were analysed and avoidance concepts developed.

The results show that the respondents are not prepared to pay money for the thin plastic bags. In addition, over 70% would use an alternative such as a reusable net, even if free plastic bags were available. Communication to customers and the presentation of alternatives must be improved, as many stores already offer these and yet consumption is comparatively high. This awareness would probably be achieved by making it compulsory to pay. Consequently, the plastic problem in relation to thin plastic bags for fruit and vegetables can be reduced by simple means such as offering a reusable net, but mandatory payment would be effective and target-oriented.

Bachelor's degree programme in Environmental Sciences, 50 pages (first reviewer)

Many of the consequences of litter in the oceans for nature, society and the economy are already known. The sources of this waste have also been largely researched. Nevertheless, plastic waste in the world's oceans appears to be growing into an ever greater problem and there seems to be no solution in sight. There are many stakeholder groups involved in this problem. One important group is local authorities, especially along the coastline. They are the level of government that has the closest contact with citizens and knows their wishes and interests and are economically affected by plastic waste in the oceans. In this study, municipalities are analysed in terms of their opportunities and challenges in the fight against macroplastics in the North Sea. Among other challenges, it was found that municipalities lack the financial resources to combat plastic waste. However, co-operation can be one way of overcoming this challenge.

Bachelor's degree programme in Environmental Sciences, 34 pages (first and second reviewer)

In this thesis, a winter mapping of a salt marsh in Cäciliengroden was carried out. Due to the seasonal absence of some species, there are deviations in the community composition compared to a summer mapping. The lower degree of cover of some species in winter had no influence on the community composition. This means that a comprehensive plant sociological study of the site is only possible to a limited extent.

From the point of view of hydrodynamics, winter mapping makes sense in any case. Only during this period can it be mapped which species are present that can have an effect on the waves. For the larger vegetation associations of hydrodynamically relevant species, the changes to the 2006 surveys were analysed. The mapping could be compared, although there are some differences in the approach, such as the naming of the vegetation units.

The distribution of all species considered to be hydrodynamically relevant has changed considerably. It should be reconsidered to what extent the non-native species Tripolium pannonicum and Atriplex spec. should actually be taken into account in the hydrodynamic analyses. To this end, the annual fluctuations in the distribution of these species in relation to the entire salt marsh must be determined. As all salt marshes exhibit regional differences, further and, above all, larger-scale mapping is necessary in order to obtain a better overall picture of the distribution of all hydrodynamically relevant species.

Bachelor's programme in Environmental Sciences, 50 pages (first and second reviewer)

Marine litter is a global problem and as such it effects the North Sea as well. To understand the role of the tidally influenced rivers Elbe, Weser and Ems as sinks or sources for pollution, over the span of 2 years a total of 27,400 wooden drifters were released at three points long the rivers Elbe and Weser respectively, and at two points along the Ems. Overall, 30.20 % have been reported. The drifters of the Elbe have had the largest response with 38.10 %, the Ems the second largest with 28.37 % and the Weser with 26.80 % as the lowest. For every river, reports of drifters along the riverbanks have been more common than sightings outside the rivers. Drifters in every river which have been reported more than once along the river course, show the influence of tidal waves on floating objects, as they keep them floating up- and downstream. In every river, hotspots have been detected. Drifters which have floated outside the rivers, mainly followed the major currents inside the German Bight, with sightings along the west coast of northern Germany, especially in the North Frisian Islands and Denmark. Strong gusts of wind from the east in spring 2018 turned these currents and lead to findings of drifters from the Elbe and Weser at the British coast and the east Frisian Islands.

For all three rivers, most drifters were generally reported in autumn, as winds and floods lead to a higher probability of beaching. The drifters of the Weser reached on average with 35.10 km the furthest distances to their release points. Drifters of the Elbe reached a similar average distance with 33.90 km and the drifters of the Ems reached on average 26.03 km. There is no definite conclusion if the rivers are sinks or sources responsible for Marine Pollution in the North Sea. Nevertheless, it is conceivable, the further upstream the litter enters these rivers, it is more likely to stay inside the river courses.

Master's programme Marine Environmental Sciences, 59 pages (first and second reviewer)

As part of this master's thesis, a population mapping of the neophytic moss Campylopus introflexus (Hedw.) Brid. was carried out on the East Frisian island of Spiekeroog in order to determine its current distribution and to enable a comparison with the populations documented by Hahn in 2001/2002 (Hahn 2006a). A 67.2 % decline in C. introflexus populationswas observed, thus falsifying the hypothesis of a population increase.

In the second part of the study, various soil parameters were investigated with regard to their possible significance as a colonisation factor. For this purpose, 30 presence and absence points were compared with each other with regard to the site factors pH, conductivity, soil moisture, loss on ignition, C and N content, C/N ratio, mean grain size and silt content. With the exception of the C/N ratio, lower values were expected for the presence areas than for the absence areas. Significant differences were found with regard to conductivity, soil moisture, loss on ignition, C content and silt content.

In order to explain the lack of colonisation of the eastern plateau, 5 dune sites were also compared with the presence and subsidence areas of the western part in terms of the significant parameters, with the values used coming from the investigations carried out by Laura Schmidt in 2018 (Schmidt 2019). None of the factors investigated proved to be a clear colonisation-inhibiting or -preventing factor. For this reason, it can be assumed that the eastern plateau has suitable sites for colonisation, but that the moss has not yet been able to reach these sites through spores or fragments.

Master thesis Landscape Ecology, 62 pages (first reviewer)

This thesis analyses the vegetation and settlement history of the peat cores GTU 12 + 600-4 and GTU 16 + 350 - 3H . These represent further components for the reconstruction of the vegetation and settlement history of the so-called "Ur-Jadebusen". Both core sites are located in the southern Jade Bay. The GTU cores are intended to supplement the results of four cores already analysed, which are located on a west-east transect in the more northerly Jade Bay. The aim is to generate a standardised picture of the landscape development from a moorland landscape to a marine landscape. For this purpose, comparative data will be determined by macro-residue and pollen analyses of both peat cores. The GTU 12 + 600 -4 was also dated using the ¹⁴C method.

The analyses showed that the GTU 12 + 600 - 4 is a pure fen peat. Its origin is dated to approx. 4500 years BP. The peat layer is interrupted by a presumably brackish-fluviatile inclusion and finally erosively cut. It is therefore impossible to determine whether and for how long the peat continued to grow. What is particularly interesting is that it is particularly deep compared to the other cores and presumably lies in a channel. The ¹⁴C dating confirmed that it must have formed in the same period as the other peat layers, despite its deep location. A comparison of all the cores mentioned also revealed pollen floristic parallels.

The peat layers of GTU 16 + 350 - 3H are only just below sea level and show almost undisturbed growth. The development from a fen peat to a raised bog peat can be observed here. The local vegetation in both GTU cores initially shows a swamp forest, which gradually thins out. Both cores can be categorised in the Subboreal period. From a regional perspective, a mixed oak forest occurred.

The synthesis shows that the influence of the sea increased from west to east, contrary to the growth of the bog. It can also be assumed that the marine influence decreased towards the south and the growth of the bog increased.

Master thesis Landscape Ecology, 44 pages (first reviewer)

The Grayling butterfly (Hipparchia semele) and the Silver-Spotted Skipper butterfly (Hesperia comma) are typical butterflies of nutrient-poor open areas with high amount of bare soil. Both species are endangered in Germany and their populations are declining throughout Europe. To improve the protection of these species, this study is investigating their ecological preferences within yellow and grey dunes of the East Frisian Island Norderney. Further, management suggestion for these butteflies are given for the islands, as well as the mainland. The focus of this study is on Hipparchia semele.

The habitat selection of Hipparchia semele is best explained by the aspect. North- and northwest facing slopes are less occupied than southward facing slopes. Being discussed as a possible explanation for the preference of southward facing slopes are: the microclimatic higher temperature and the shelter from wind (the main wind direction in july: northwest). Vegetation parameters such as Vegetation density or abundance of hostplants and nectar-plants don't show an influence on the number or the occurence of Hipparchia semele in this study.

The latest record of Hesperia comma was from 2010. 13 butterflies of this species were found in 2018. The distribution area was bigger than expected in 2010. The dunes of the East Frisian Islands offer an adequate habitat for both species. On the mainland, the promotion and conservation of nutrient-poor grassland and dry heathland biotopes is fundamental to protecting Hipparchia semele, Hesperia comma and other species dependent upon these habitats.

Bachelor's degree programme in Environmental Sciences, 68 pages (first and second reviewer)

A total of 36 neophyte species were documented on Wangerooge as part of this thesis. Thirteen of these species were classified as invasive and 21 as non-invasive. Although the species Pinus nigra and Spartina anglica were detected, they were neither mapped nor assessed in terms of potential invasiveness.

A comparison of the results with those of Hahn from 2006 showed that the species Fallopia japonica and Prunus serotina , which Hahn classified as invasive, were able to spread significantly on Wangerooge. A comparison of the 2017 biotope type mapping with Hahn's results (2006) showed that Rosa rugosa was also able to spread. The species Senecio inaequidens and Impatiens glandulifera were not classified as invasive by Hahn (2006), but are categorised as invasive in this study and have also been able to spread on Wangerooge since 2006. The populations of the invasive neophytes Campylopus introflexus, Solidago gigantea and Helianthus tuberosus have decreased since 2006.

Thus, the hypothesis that all neophytes classified as invasive by Hahn (2006) that were found on Wangerooge in 2006 are still detectable in 2018 can be accepted. Although the neophyte Heracleum mantegazzianum is considered invasive and was not documented in 2018, it was considered a non-invasive species in 2006 (Hahn 2006).

The hypothesis that these neophytes have spread since 2006 can only be partially confirmed, as the populations of Rosa rugosa, Fallopia japonica and Prunus serotina have increased, but the area distribution of Campylopus introflexus has decreased significantly. The invasive neophytes Aronia prunifolia, Crassula helmsii, Quercus rubra and Lonicera involucrata only migrated into the natural vegetation on Wangerooge after 2006 and have been able to spread since then.

On the basis of the above comparisons and the results presented, an individual assessment was made for each invasive species, taking into account the relevant specialist literature, as to whether control is necessary and feasible.

The invasive neophytes Fallopia japonica and Impatiens glandulifera have also been able to spread, but almost exclusively in areas characterised by anthropogenic influences and of less importance in terms of nature conservation, such as roadsides. Fallopia japonica is already being controlled and should be continued in any case. The species Impatiens glandulifera should not be controlled due to its limited spread. The neophyte Senecio inaequidens was able to spread expansively on Wangerooge and colonised various areas in 2018, both in the natural vegetation and in the direct sphere of human influence. However, as Senecio inaequidens poses no demonstrable threat to biodiversity, the species does not yet need to be combated.

However, if research projects prove otherwise, control will have to be discussed again. As the area covered by the cactus moss, Campylopus introflexus, has decreased significantly, the species does not need to be controlled either. Instead, an investigation should be carried out on the areas in question to record the subsequent vegetation and possible colonisation by lichens. The spread of Lonicera involucrata has so far been limited to the edges of a road and also does not yet require any measures, but it should be regularly monitored to see whether the species manages to establish itself in the natural vegetation away from this occurrence. The occurrences of Quercus rubra are also currently still supposedly small and most probably do not yet cause any damage in the colonised areas. However, in order to prevent the species from spreading, the individuals should be removed. It has been shown that the spread of the species Prunus serotina, Aronia prunifolia, Crassula helmsii and Rosa rugosa in particular is highly problematic from a nature conservation perspective. Combating these species should therefore be a top priority, especially in endangered areas of the island that are valuable from a nature conservation perspective.

In addition to combating existing occurrences of neophytes, efforts should also be made to prevent new occurrences in future. In the past, the improper disposal of garden waste on roadsides on Wangerooge in particular has led to the spread or establishment of some, sometimes invasive, neophytes. In order to prevent this from continuing to be a factor in the spread of neophytes in the future, the issue of neophyte problems should also be increasingly discussed with the locals of Wangerooge. In addition to dealing with garden waste, there could also be a fundamental discussion about which species should be cultivated in gardens. It has been observed that invasive neophytes are being cultivated in numerous gardens on Wangerooges. In order to prevent invasive species from spreading from gardens into the natural and valuable vegetation of Wangerooges, garden owners could be recommended alternative garden plants that are likely to pose a lower risk of invasion. Such a recommendation on alternative garden plants has already been formulated by the Zentralverband Gartenbau e.V. for each potentially invasive garden plant (Zentralverband Gartenbau e.V. 2008).

This work was able to close gaps in knowledge regarding the species spectrum and the spread of neophytes on Wangerooge since 2006. The cartographic representations of the occurrences and the discussion of measures to combat them can serve as an aid to future nature conservation efforts in the national park. The results can also be used as a basis for comparison for future surveys. In order to create such a data basis for the other East Frisian islands, finalisation work such as this could also be carried out there in the future.

Bachelor's degree programme in Environmental Sciences, 35 pages (first and second reviewer)

Two hypotheses are put forward and analysed in this thesis. Firstly, that easterly wind phases cause higher quantities of litter at western North Sea locations. Secondly, that a high volume of litter at western North Sea beaches results in a lower volume of litter at eastern locations. These hypotheses are based on increased reports of wood drifters from the Macroplastics in the Southern North Sea project. Drifters were documented on the east coast of England and Scotland following a prolonged easterly wind period in spring 2018.

Data from selected mapping routes of the OSPAR Commission on the western and eastern North Sea coast are considered and the abundance and composition of the recorded litter are analysed. The data from the western North Sea sites are then analysed for correlations with wind data from nearby weather stations. Similarly, the OSPAR data from the western and eastern locations are tested for negative correlation.

Significant positive or negative correlations confirm both hypotheses for some locations. Factors such as ocean currents, wave motion and landfall processes were not taken into account in this study. Due to the interplay of wind direction and the other factors mentioned, different results for the locations analysed are conclusive. The results of this study confirm the hypotheses for some OSPAR stretches.

Bachelor's degree programme in Environmental Sciences, 63 pages (first and second reviewer)

Crassula helmsii is an invasive neophyte which was documented on the East Frisian Island Wangerooge for the first time in 2017. Other studies - also from Norderney - have shown a huge potential for dispersal and an enormous growth rate concerning this species. In this thesis, the population on Wangerooge was determined. There was only one pond where the plant grew, which showed that Crassula helmsii has not spread into neighbouring ponds so far.

At 11 presence points (in 1 water body) and 40 absence points (in 25 water bodies) different environmental parameters (soil, water, illuminance and surroundings) were measured and identified. The results showed no clear preferences of Crassula helmsii. The wide range of values which were measured suggested that the species has a great adaptability and can live in many different habitats. Crassula helmsii has already colonized one fifth of the pond and further observations verified that the population is still rapidly increasing.

Therefore, practical and appropriate controlling methods are urgently needed. The discussion of many different mechanical, physical, chemical and biological approaches led to the recommendation of burying the population. This procedure was successful in other experiments and negative side effects can be reduced by creating a new pond as compensation. In general, monitoring the population and the effects of controlling methods is very important.

Bachelor's degree programme in Environmental Sciences, 21 pages (first and second reviewer)

There are currently 27 alien aquatic plant species in Germany, and their numbers are steadily increasing. Of these 27 species, 11 are categorised as invasive (Hussner et al., 2013). Crassula helmsii (C. helmsii) is one of these invasive neophytes. It is a semi-aquatic plant with a natural distribution in Australia and New Zealand and the potential to grow and spread rapidly. The plant arrived in Europe at the beginning of the 20th century as an aquarium and garden pond plant. In the early 1980s, C. helmsii was discovered for the first time in the wild in Germany (Nault, M. E. & Mikulyuk A., 2011). In the Lower Saxon Wadden Sea National Park, the occurrence of the plant on Norderney was documented in the early 2000s, since when it has spread there in the south beach polder and on the Meierei meadows (Peterson, J. & Pott, R., 2005).

Various measures are needed to control the populations of C. helmsii . Physical and mechanical removal of the plant are the most common, but these methods have not been shown to be effective enough. In addition, chemical control agents have been used against the plant, but these have not been successful either.

In order to consider an alternative approach to controlling and containing the spread of C. helmsii , the reaction of this neophyte to salt stress was investigated. Furthermore, it was examined whether shading has an additional influence on the vitality of the plant.

For this purpose, an experiment was carried out at the Institute of Chemistry and Biology of the Marine Environment in Wilhelmshaven. The underground and above-ground biomass of C. helmsii was recorded over a trial period of 44 days, allowing the relative growth of the plant to be determined in order to investigate the possible influence of salinity and shading.

It was found that there is an influence of salinity on the growth of Crassula helmsii . However, this influence decreases with increasing shading. It seems that from a certain degree, shading itself acts as a stressor on the growth of the plant.

The results of this work are not yet sufficient to be able to make detailed statements about the use of high salinities as an alternative control method for C. helmsii . Smaller gradations of salinities between 6 ppt and 10 ppt would have to be investigated over a longer period of time. Furthermore, it would be useful to carry out a field trial to document the influence of salinity on C. helmsii in the wild. Further research is therefore needed to combat and contain the spread of this invasive neophyte and the use of high salinity levels.