mopdf.com

Zusammenfassung 3ZusammenfassungAktuell lebt die Hälfte der Weltbevölkerung in urbanisierten Regionen und es wird erwartet, dass diese bis 2050 um weitere 13 % steigen wird. In Australien leben 85% der Bevölkerung in Küstennähe und durch die global steigende Bevölkerungsdichte sind dadurch auchinsbesondere die tidebeeinflussten Feuchtgebiete entlang von Küsten, wie Mangroven undSalzmarsche, stark bedroht. In Südostaustralien nehmen insbesondere Salzmarsche einen empfindlichen Platz entlang des Höhengradienten von Gewässerufern ein. Sie kommen zwischenMangroven, auf der seewärtigen Seite, und Süßwasservegetation sowie urbaner Bebauung, aufder landwärtigen Seite, vor. Zusätzlich zur landwärtigen Migration von Mangroven und demsteigenden Meeresspiegel, werden Salzmarsche durch abgeleitetes Regenwasser, insbesonderebei Extremwetterereignissen, bedroht. Das verschmutzte Regenwasser, in dem sich Straßenabfälle, Öl, Benzin und Chemikalien anlagern, wird in vielen Fällen direkt in die Feuchtgebietegeleitet.Die vorgelegte Dissertation kombiniert verschiedene Forschungsansätze, um auf unterschiedlichen geografischen Skalen den anthropogenen Einfluss auf Salzmarsch-MangrovenGesellschaften entlang der Südostküste Australiens zu untersuchen. Zunächst untersuchten wirauf lokaler Ebene den Einfluss von kontaminiertem Süßwasser auf die Komposition und Verbreitung von Salzmarsch- und Mangrovengesellschaften. Wir konnten zeigen, dass das Einbringen von kontaminiertem Regenwasser, die Etablierung von exotischen Süßwasserpflanzenentlang der Salzmarsche begünstigt. Das abgeleitete Regenwasser und die dadurch erhöhtenNährstoffgehalte unterstützen zudem die Ausbreitung von Mangroven. Da die Invasion vonSüßwasserpflanzen von der Landseite, und die Mangrovenexpansion von der Seeseite her geschieht, werden die Salzmarschen von beiden Seiten bedrängt. Dies konnte besonders in industrialisierten Gebieten gezeigt werden.Das zweite Projekt zielte darauf ab, die vorherige Feldstudie unter kontrollierten Bedingungen im Gewächshaus zu überprüfen. Dazu invadierten wir 28 Mesokosmen, bestehendaus nativen Salzmarscharten, mit vier verschiedenen exotischen Süßwasserpflanzen. Die Nährstoffgehalte und der Salzgehalt im Boden wurden den natürlichen Konzentrationen und denenin industriellen Gebieten angepasst. Unsere Ergebnisse zeigten, dass die Etablierung von exotischen Arten unter natürlichen Bedingungen (hoher Salzgehalt und niedriger Nährstoffgehalt)stark eingeschränkt ist. Geringer Salzgehalt im Boden durch Süßwassereintrag erhöhte die

Zusammenfassung 4Überlebensrate der exotischen Pflanzen signifikant. Erhöhte Nährstoffgehalte führten zwar zustärkerer Biomasseproduktion, verbesserten allerdings nicht die Überlebensrate.In einem weiteren Gewächshausexperiment untersuchten wir die Auswirkungen vonerhöhtem CO2 und variierendem Salzgehalt auf das Wachstum von zwei verschiedenen Mangrovenarten. Diese wuchsen zum einen isoliert und zum anderen in Konkurrenz mit einer Salzmarschgesellschaft, bestehend aus drei typischen Salzmarscharten Südostaustraliens. HoheCO2 Konzentrationen unterstützten sowohl den Mangroven als auch den Salzmarschwuchs.Klimawandelbedingte Erhöhung von CO2 wird somit die Migration von Mangroven in Salzmarschhabitate erleichtern. Besonders wenn weitere Faktoren, wie Herbivorie und der Anstiegdes Meeresspiegels, die Konkurrenzfähigkeit der Salzmarsche reduzieren.In einer letzten Studie testeten wir auf regionaler Ebene die Ergebnisse aus der erstenFeldstudie, mit Hilfe von Fernerkundungstechniken. Anhand von Lauftaufnahmen über einenZeitraum von 42 Jahren untersuchten wir, ob die Veränderungen innerhalb der Feuchtgebietvegetation in stark modifizierten Gewässern beobachtet werden können. Unsere Analyse zeigte,dass weite Bereiche von Salzmarschen seit den 1970er Jahren verloren gegangen sind. Im Gegensatz dazu, hat die Fläche von Casuarina spp. und Melaleuca spp. Pflanzengemeinschaftenstark zugenommen, was uns vermuten lässt, dass diese von der Landseite aus in die Salzmarsche migrierten. Jedoch konnten wir anhand der Anzahl der Bilder, den Verlust von Salzmarsche durch Mangroven Migration nicht belegen.Tidebeeinflusste Feuchtgebiete gelten in der Regel nicht als durch Süßwasserpflanzeninvasionsanfällige Ӧkosysteme. Wir konnten jedoch zeigen, dass die Einengung der Salzmarsche, in unmittelbarer Nähe zu urbanen Gebieten, von Mangroven auf der Seeseite und vonexotischen Pflanzen auf der Landseite durch Abwassereinleitung verschlimmert wird. DieserTrend ist besonders stark entlang industrialisierten Ästuaren durch den erhöhten Süßwasserund Nährstoffeintrag. Auch einheimische Süßwasserpflanzen, die natürlich am Rand der Salzmarschzone vorkommen, scheinen über die letzten 42 Jahre stark vom Frischwassereintragprofitiert zu haben. Dieser Trend ist besonders stark entlang industrialisierten Ästuaren durchden erhöhten Süßwasser- und Nährstoffeintrag. Managementstrategien, wie bepflanzte Pufferzonen und Bildungsprogramme, die zum Beispiel auf eine Verminderung des Nährstoffeintrages hinzielen, werden dringend benötigt. Wenn die Verdrängung der Salzmarsche nicht vermindert wird gehen nicht nur Lebensräume für viele Tierarten verloren, sondern auch wichtigeökosystematische Dienstleistungen, die uns Menschen betreffen.

Chapter 1 5

Chapter 1 6Chapter 1Introduction to anthropogenic impacts on mangrove and saltmarsh communities in Eastern AustraliaIna Geedicke

Chapter 1 7IntroductionThe wetland system of mangroves and saltmarshesWetlands currently comprise 5 – 8 % of the earth’s surface however it is estimated thatmore than half of the global distribution of wetlands has been lost, most of it during the twentyfirst century (Mitsch and Gosselink, 2015). By definition under the Ramsar Convention (2016),wetlands are partially or completely inundated areas with static or flowing fresh, brackish orsaline water, where the depth at low tide must be below 6 m. Saltmarshes and mangroves belong to coastal intertidal wetlands and their occurrence is determined by salt concentrationsand tidal inundations, distinguishing these ecosystems from freshwater wetlands (Adam,2009). Because of their ability to create habitat and support entire ecological communities,saltmarsh and mangrove species are considered as foundation species (Osland et al., 2015).They form important habitats and feeding grounds for bats, invertebrates and birds (Kellewayet al., 2017), as well as nursery grounds for many fish species (Alongi, 2002; Lee et al., 2014).A high abundance of juvenile fish and shrimps are found in mangroves, due to the high abundance of food, while at the same time aerial roots provide a shelter against predators (Beck etal., 2001). The infrequently inundated upper saltmarsh is not a constant habitat for juvenilefish, however here the highest concentrations of invertebrate larvae may be found within estuaries (Kelleway et al., 2017) and it has been shown that grazing of saltmarshes reduces the foodavailability of invertebrates to fishes (Friese et al., 2018). Mazumder et al. (2009) showed thatburrowing crabs synchronize their spawning with the spring tide that reaches the saltmarsh,which in turn leads to an efficient feeding opportunity for fishes.Coastal intertidal wetlands also provide important ecosystem services to humans. It isestimated that they provide services worth US 24.8 trillion annually, making them one of themost valuable ecosystems globally (Costanza et al., 2014). These services include the filtrationand trapping of pollutants and nutrients, for example from oil spill and stormwater run-off,carbon sequestration and storage, elevation maintenance and cultural uses (Kelleway et al.,2017). While serving as an ecotone between the terrestrial and oceanic environments, saltmarshes and mangroves are the frontline for stabilization of coastal and intertidal zones bytrapping sediment and providing protection against rising sea level and storm damage (Doody,2008; Krauss et al., 2014; Mcleod and Salm, 2006; Möller et al., 2014). However, the level ofcoastal protection and vertical sediment accretion is variable, depending on the size of wetland

Chapter 1 8area, the height and density of vegetation, as well as the sedimentation rates of the catchment(Craft et al., 2009; Kelleway et al., 2017; Lee et al., 2014).A recent study reported a total saltmarsh area of 54950 km2 across 43 countries andterritories (Mcowen et al., 2017). Mangroves cover 83,495-137,760 km2 of coastal areas across118 countries and territories (Giri et al., 2011b; Hamilton and Casey, 2016) and are only foundin tropical to subtropical regions (Figure 2). The distribution of mangroves is mainly limitedby temperature. As they are intolerant of frost, they are completely replaced by saltmarshes atlatitudes above 32 N and 40 S (Stuart et al., 2007) when the water surface temperature dropsbelow 20 C in winter (Alongi, 2009). While species richness of mangroves decreases withdistance from the tropics, saltmarsh species richness increases towards the poles (Duke et al.,1998; Saintilan et al., 2009). The coexistence of saltmarshes and mangroves can be found insubtropical to temperate Australia, Florida and along the northern coastline of New Zealand(Chapman, 1977; Morrisey et al., 2007). Normally, the boundaries between saltmarshes andmangroves are sharp, but at temperate sites they can become patchy, with mangroves interspersed amongst saltmarsh communities (Adam, 2009). Environmental and geomorphologicalparameters controlling the distribution of mangroves and saltmarshes have long been discussed(e.g. Adam, 1990; Woodroffe, 1990). Saltmarshes are governed by the sea-level and sedimentsupply regime, as well as low wave energy (Bakker, 2014). It has been proposed that mangroves establish best at temperatures of the coldest month being higher than 20C, rooting ofpropagules in loose soil or sediment and at shores with low energy waves (Rogers and Krauss,2018). In general, these assumptions hold true, but there are exceptions showing mangrovesadapted to short freezing periods (Stevens et al., 2006; Stuart et al., 2007), and at differentgeomorphic settings (Saintilan et al., 2014; Semeniuk, 2013, 1983).The accretion of sediment particles and low wave energy are a premise for mangrovetrees to establish roots (Alongi, 2002). This is mostly the case in intertidal estuaries, where theyusually occupy the area between mean sea level and mean spring tide (Alongi, 2009). Mangroves are shrubs and trees that grow in periodically waterlogged soil and in water of fluctuating salinity, that can vary between salinity of freshwater and three-times of seawater salt concentration (Feller et al., 2010). Fluctuations in salinity occur through evaporation leading tohigh soil salinity and through freshwater flushing leading to a decrease in soil salinity (Felleret al., 2010). These harsh conditions require special adaptations to overcome the lack of oxygenin the waterlogged soil and the restraint of water uptake due to salt induced negative osmoticpressure. To cope with high salt concentrations, mangrove species have developed different

Chapter 1 9strategies of salt exclusion by the roots, salt sequestration by specialized tissue or secretion ofexcess salt through, for example, salt glands on leaves (Hogarth, 2007). To oxygenize theirroot systems, mangroves have developed aerenchyma and various forms of aerial roots (Scholander et al., 1962), such as the stilt roots in Rhizophora that can make up to 24% of the aboveground biomass of a growing tree (Figure 1A) (Hogarth, 2007). Mangroves of the family Avicenniaceae grow vertical structures known as pneumatophores, that emerge from the soil andcan grow up to 30 cm tall. A single Avicennia tree of 2-3 m in height may grow up to 10,000pneumatophores, emerging from the soil every 10-15 cm in a wide range around the tree (Figure 1B) (Hogarth, 2007). Mangroves often form dense forests with either no ground cover orsparse distribution of understorey herbs, frequently consisting of monospecific stands. Takingadvantage of the tidal inundation, most mangroves have evolved a specialized reproductivestrategy in which they grow viviparous propagules on the parental tree that are photosynthetically active and buoyant and are dispersed by tidal or ocean currents (Rabinowitz, 1978; Stieglitz and Ridd, 2001), often over long distances (Nettel and Dodd, 2007). Tolerances to floodingand salinity and the ability to persist in variable habitats have evolved multiple times throughconvergence, not from common descent, resulting in about 70 mangrove species from 20 families (Alongi, 2009).

Chapter 1 10Figure 1 Australian coastal intertidal wetland vegetation. A shows the typical stilt rootsof Rhizophora stylosa in Darwin, WA, and B the pneumatophores of a mature Avicenniamarina tree in Jervis Bay, NSW. C depicts the mostly strict zonation of mangrove andsaltmarsh communities (Careel Bay, NSW) and D illustrates a coastal intertidal wetlandflooded with pollution and debris (Georges River, NSW).Another vegetation type that inhabits areas subject to periodic flooding by the tide arecoastal saltmarshes; they are restricted to the upper intertidal environment, in general betweenthe elevation of the mean high tide and mean spring tide (Adam, 2009). They are found on softsubstrate shores of estuaries and embayments, and on some open low wave energy coasts(Adam, 2009). In contrast to mangroves, saltmarsh communities are comprised of a mixture ofherb, grass and low shrub species which are highly specialised to enable survival under salineand partially waterlogged conditions (Adam, 1990). At low-lying intertidal areas (lower marsh)saltmarsh plants experience soil salinity similar to the flooding water but also longer periods

Chapter 1 11of waterlogging due to tidal inundation at least once a day (Bakker, 2014). Saltmarsh plants athigher elevation (upper marsh) need to be adapted to greater soil salt concentrations, due toevaporation of water and less frequent flooding, occurring only during spring tides (Clarke andHannon, 1967). At higher elevations, the interaction of flooding and climate influences the soilsalinity, which can lead to high salinity and salt crust forming during dry periods or diminishsoil salinity to freshwater conditions under heavy rainfall (Adam, 1990). Generally, with higherelevation the species richness in saltmarshes increases, where often only a single species occupies the lower marsh (Adam, 1990; Suchrow et al., 2015). Globally there are approximately500 described saltmarsh species (Silliman, 2014). The adaptation strategies of saltmarsh species to extreme environmental conditions are similar to those described for mangroves: excretion, sequestration and exclusion of salt (Rogers et al., 2017). Saltmarsh seeds are able to survive submergence in salt water; however, germination rates are often low (Adam, 1990;Wolters and Bakker, 2002). The long-term maintenance of saltmarsh communities suggeststherefore that vegetative propagation is of importance (Adam, 1990).Saltmarshes and mangroves of AustraliaIn Australia, mangrove and saltmarsh communities coexist mainly along the east coastof New South Wales (NSW), Victoria and Queensland (Figure 2). The diversity of mangrovespecies declines with distance from the equator (Rogers et al., 2017). For example, NSW hasup to five co-occurring mangrove species at its northern border, while there are more than 41species found in Australian tropical regions and only one species, Avicennia marina, is foundat the southernmost occurrence of mangroves in Victoria (Rogers et al., 2017; Saintilan andWilliams, 1999). For saltmarsh communities the reverse is true; saltmarsh species richness increases with distance from the equator (Adam, 2009). Northern Australian saltmarshes aredominated by grasses, such as Sporobolus virginicus, but Tasmania, Victoria, South Australiaand NSW contain 90% of the saltmarsh flora of Australia, even though they only cover 2.5%of the available saltmarsh and saltpan area (Saintilan, 2009). Even though only a small numberof species are generally found at one site, the total species pool of saltmarsh species in Australiais reported as 103 species of vascular plants (Saintilan and Rogers, 2013). Saltmarshes can beheterogenous due to variability in environmental factors at local scales with 6 – 8 species growing together within a few square meters, rather than in a continuous band or a single community(Zedler et al., 1995). Where mangroves and saltmarshes co-occur in Australia (Figure 3), saltmarshes are usually found landwards of mangroves occupying the lower and upper marsh, aswell as brackish areas, which consist of pools of permanent water of moderate salinity (up to

Chapter 1 12one third of sea water strength) (Rogers et al., 2017; Sainty, 2012). Because the adaptations tosaline conditions and waterlogging comes often at the expense of growth rate, saltmarshes seldom penetrate the upslope freshwater systems (Adam, 1990). Landwards of saltmarshes, nearthe supratidal zone and often occupying the brackish zone as well, Casuarina glauca (SwampShe-oak) and Melaleuca. species occur (Rogers et al., 2017).Figure 2 Saltmarsh and mangrove distribution along the coastline of Australia. Black lines indicatesaltmarsh areas and grey shadings mangrove communities (Rogers et al., 2017)

Chapter 1 13Figure 3 Zonation of subtropical and temperate Australian wetland vegetation across a tidal gradient(Rogers et al., 2017).Threats to mangrove-saltmarsh systemWorldwide it has been observed that the extent of saltmarsh and mangrove communities is declining to an alarming extent. Saltmarshes have been used by humans for centuries(Adam, 2002) and because the total area of global saltmarsh distribution was only recentlyestimated (Mcowen et al., 2017), numbers on general saltmarsh loss are missing. However,over the last 200 years a 60% loss of total saltmarsh area was found in south-eastern Australia(Grayson et al., 1999). In regards to mangrove loss, 35% of mangrove area was lost in the pasttwo decades through deforestation and habitat conversion (Valiela and Cole, 2002). This proportional loss exceeds the loss in global tropical rainforest and coral reefs (Valiela et al., 2001).However, mangrove expansion into saltmarshes where they co-occur has also been observedglobally (Alongi, 2015, 2002; Saintilan and Rogers, 2013), leaving saltmarsh communities theonly option being landwards retreat. Several studies have evaluated mangrove expansion andassociated saltmarsh loss, for example in North America (Cavanaugh et al., 2014; Giri et al.,2011a; Osland et al., 2016, 2013; Stevens et al., 2006), Mexico (López-Medellín et al., 2011),Taiwan (Hsu and Lee, 2018) and New Zealand (Morrisey et al., 2010). Mangrove expansiondoes not necessarily lead to saltmarsh loss, for example in the gulf coast of Texas mangroveexpansion of 74% and saltmarsh loss of 24% within 30 years was recorded by Armitage et al.(2015) but only 6% of saltmarsh loss could actually be associated with mangrove expansion.In south-east Australia, saltmarsh loss of 30% due to mangrove expansion was confirmed bySaintilain and William (1999) and Wilton (2001) from survey data, but there is also evidence

Chapter 1 14that saltmarsh loss is less towards the southern limit of mangrove range in Victoria (5-15%)(Rogers et al., 2005).Climate ChangeAs a transitional ecosystem between the terrestrial and marine environments, saltmarshes and mangroves are particularly vulnerable to climate change and its consequences(Feller et al., 2017), inclu

Reviewer: Assistant Prof. Dr. Kerrylee Rogers (University of Wollongong) 4 th Reviewer: Assistant Prof. Dr. Kyle Cavanaugh (University of California) Disputation (04.07.2019) 1 st Reviewer: Prof. Dr. Gerhard Schmiedl (Universität Hamburg) 2 nd Reviewer: Prof. Dr. Kai Jensen (Universität Hamburg) 3 rd Reviewer: Dr. Jens Oldeland (Universität .