Richter, Claudio

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Richter, Claudio

Official Name

Richter, Claudio

ORCID

0000-0002-8182-6896

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1261501780

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Primary production in coral reefs, Key players and adaptive strategies to natural environmental variations
(2010-03-10)
Jantzen, Carin
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Bischof, Kai
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Richter, Claudio
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Richter, Claudio
Coral reef ecosystems sustain their high productivity in an oligotrophic environment by the efficient recycling of nutrients and tight benthic-pelagic coupling. The basis for productivity within coral reefs is the primary production, which is accomplished by diverse benthic photosynthetic organisms and, to a minor contribution, by phytoplankton in the waters aloft. Photosynthesis is determined by the availability of light, influenced by water depth and turbidity, and the availability of inorganic nutrients, essential for the organic synthesis of vital substances like amino acids. Benthic photosynthesis in coral reefs is characterised by the high abundance of manifold zooxanthellae bearing hosts, in particular scleractinian corals. Findings of the following chapters are presented from the organism to the ecosystem level (chapter 1-5), concerning organic matter recycling (nutrient availability) and energy conversion (light availability and photosynthesis) within a coral reef ecosystem. Nutrient and light availability vary likewise between ecosystems and are comparatively investigated at the Similan Islands in the Andaman Sea of the Indian Ocean (chapter 6-8), concerning environmental conditions, benthic community composition, primary production and heterotrophy.
Dissertation
388 339
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Chemical ecology of Western Indian Ocean reef sponges
(2016-09-29)
Helber, Stephanie
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Schupp, Peter
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Richter, Claudio
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Richter, Claudio
Sponges are among the dominant benthic organisms on coral reefs, representing important spatial competitors for reef-building corals. Coral reefs have experienced drastic declines in coral cover and corresponding increases in the abundance of other spatial competitors, such as macroalgae, corallimorpharians and sponges, due to a combination of global and local stressors. The ability of sponges to chemically defend themselves against predators, microbes and other competitors may partially explain their high abundance on reefs worldwide. Nonetheless, studies investigating sponge abundance and chemical ecology are rare, particularly in the Western Indian Ocean, which is considered a hotspot of coral and sponge biodiversity. Thus, this thesis is the first study that provides insights into the chemical ecology of sponges from the Western Indian Ocean. The thesis consists of a general introduction, three chapters investigating in detail different aspects of chemical defence mechanisms in sponges from Zanzibar and a general discussion. In Chapter 1 I assessed the benthic community composition of the reef at Bawe, an island on Zanzibara s West Coast. This reef was dominated by reef-building corals, but sponges also represented a diverse and abundant component of the reef fauna. Moreover, laboratory experiments were conducted to investigate if predation was a key factor in structuring the sponge community. Findings revealed that the reef was dominated by palatable rather than chemically defended sponge species, demonstrating a lack of predatory control on the sponge community likely due to overfishing. In the absence of predation, palatable sponges could potentially undergo uncontrolled growth in the future and thus subject reef-building corals to greater competitive pressure. Chapter 2 focused on the antimicrobial and cytotoxic activities of secondary metabolites extracted from the most abundant sponges at the reef around Bawe. The experiments revealed that the most abundant sponges were remarkably well defended against co-occurring marine bacteria and in particular against potential pathogens. Moreover, the majority of the sponge extracts also displayed cytotoxic activities. Metabolites with either antimicrobial or cytotoxic properties can provide sponges with a competitive advantage over corals. Antimicrobial compounds could alter the coral microbiota while cytotoxic compounds are able to impair the cell division of corals. Consequently, the potential allelopathic properties of sponge crude extracts from the three most abundant and bioactive sponges were further examined in field experiments under natural conditions in Chapter 3. These experiments showed that the extracts of all three sponges possessed allelopathic compounds that adversely affected the photosynthetic efficiency of the corals symbiotic zooxanthellae. Despite this, experiments with live sponge fragments were unable to detect significant impairments on the physiology of corals. However, the presence of allelopathic compounds, and their significantly negative effect on coral photo-efficiency, suggests that allelopathy by sponges does play a role in spatial competition with corals. As a result, sponges might be able to exert negative effects on the corala s fecundity, their reproduction or even their associated microbiome making corals more vulnerable towards further natural or anthropogenic disturbances and pathogenesis. Collectively, the present study demonstrated that sponges on reefs in Zanzibar are serious spatial competitors against reef-building corals. The increased sewage input in combination with other local stressors, such as destructive fishing practices or damage to the reef through tourism activities, will most likely result in more frequently occurring sponge-coral interactions. Thus, management strategies for Zanzibarian reefs should focus on minimizing anthropogenic stressors, like the establishment of a sewage water treatment facility to minimize stress on the benthic community, in order to reduce the risks to coral reef health. Fisheries regulations should also be enforced as an important component of coral reef management plans in order to restore healthy herbivorous as well as spongivorous fish populations on the reefs, which limit the proliferation of competing macroalgae and sponges.
Dissertation
364 157
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Patterns and controls of calcification in tropical reefs: from skeletal microstructure to reef framework
(2012-10-15)
Wall, Marlene
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Wild, Christian
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Richter, Claudio
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Richter, Claudio
The global distribution of coral reefs is mainly limited by temperature and light; further factors controlling reef development include nutrients, salinity, oxygen concentration and aragonite saturation state. The most vigorous reef growth can be found within the tropics, where corals build a massive 3-dimensional carbonate framework. However, in some tropical areas reefs are confronted with strongly fluctuating or marginal environmental conditions. Both can hamper reef formation and prevent framework development. In such areas coral growth and reef functioning can be studied under sub-optimal conditions. Investigating the potential of reefs to adapt to such unfavorable environmental conditions provides further insight on the fate of coral reefs in a changing climate. Here it was investigated how strong environmental variability due to internal waves (changing inter alia temperature, pH, nutrients) affect reef development in the Andaman Sea. Moreover it was investigated how these environmental fluctuating conditions reflect at the skeletal level by studying growth properties (linear extension, density, calcification) and skeletal proxies for temperature.
Dissertation
275 212
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Zooplankton spatial and temporal dynamics, community composition and bentho-pelagic coupling in Comau Fjord, northern Chilean Patagonia
(2023-03-22)
Garcia Herrera, Nur
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Havermans, Charlotte
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Richter, Claudio
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Richter, Claudio
Zooplankton are key players in the functioning of the marine pelagic food web of high latitude ecosystems as they constitute an essential link between primary producers and higher consumers. In addition, zooplankton provide food for benthic invertebrates, such as cold-water corals. The steep walls of Comau Fjord, northern Chilean Patagonia, harbor a diverse and rich benthic community, including dense aggregations of cold-water corals that thrive even in adverse conditions such as aragonite-depleted waters. This paradox has been attributed to a rich food supply, zooplankton being the main diet of the corals. However, the information on zooplankton seasonal and vertical distribution, together with its community composition, is still very fragmentary in Patagonian waters. Furthermore, abiotic and biotic drivers influencing the zooplankton dynamics under seasonal environmental variations (e.g. changes in solar radiation and rainfall) and their potential linkage to the corals in Comau Fjord are so far unknown. The aim of this thesis is to identify the drivers governing the zooplankton dynamics in Comau Fjord, and to understand the role of zooplankton in the bentho-pelagic coupling. To achieve this objective, the zooplankton distribution and composition were investigated both spatially and temporally. Stratified vertical hauls from surface waters to near the seabed were carried out both seasonally and during day and night by a closing Nansen net at different locations in the fjord. Subsequently, zooplankton samples were scanned with state-of-art digital imaging system (ZooScan), and zooplankton abundance, biovolume and biomass were determined for 41 zooplankton and 11 meroplankton taxa out of a total of 163,840 vignettes identified in EcoTaxa. The zooplankton availability was used to estimate spatial and temporal differences in food availability for benthic coral communities and were further compared to measured trophic markers in corals from different coral populations along the fjord. The zooplankton distribution in Comau Fjord showed a pronounce seasonality (chapter 2). Its abundance peaked in austral spring, suggesting a close link between zooplankton reproduction and phytoplankton spring bloom. However, zooplankton biomass was the highest in summer and lowest in winter, indicating that during the warmer season, bigger individuals or larger taxa developed and during the cold season the low primary production was not enough to support a high zooplankton growth. Higher zooplankton biovolume were observed in the outer part of Comau Fjord compared to the central-inner fjord and could clearly be associated with a higher chlorophyll a concentration at the fjord mouth (chapter 3). Throughout the year and along the horizontal transect, zooplankton abundance was concentrated in surface waters, while highest biovolumes were found in intermediate waters during daytime, and in surface layers during nighttime, indicating the diel vertical migration of large zooplankton (chapter 2 and 3). The community composition of zooplankton in Comau Fjord was mainly dominated by copepods, both in abundance and biovolume, followed by chaetognaths, mysids, cnidarians, and amphipods (in terms of biovolume) and meroplankton, appendicularians and ostracods (in terms of abundance) (chapter 2 and 3). Meroplankton, defined as planktonic life stages of benthic organisms, have an important role in the bentho-pelagic coupling of marine ecosystems. Meroplankton abundance concentrated in the upper 50 m of the water column (chapter 4), and was highest in spring, coinciding with higher chlorophyll a and oxygen concentrations, suggesting a close coupling between macrobenthos reproduction and meroplankton feeding with the phytoplankton spring bloom. The dominance of the different meroplankton taxa shifted seasonally, being echinoderms the most abundant in spring, gastropods in summer and autumn, and bryozoans in winter. The fatty acid composition of corals from both shallow and deep water sites revealed strong differences in their main food source (chapter 5). In shallow, fatty acid markers indicated a phytoplankton-based (dominated by diatom) diet with contribution of small copepods, while corals from the deep sites showed a dominance of calanoid copepod-related markers that may explain the higher energy stores in deep corals. However, this is not reflected by the low zooplankton assessment (chapter 2 and 3). This discrepancy may derive from ecological differences at the two different depths as well as methodological issues, both discussed in this thesis. Overall, this thesis provides novel insights into (a) the zooplankton community composition in Chilean Patagonian waters, mainly dominated by copepods, with an unprecedented level of spatial and temporal detail; (b) the main drivers governing the zooplankton dynamics, such as water column stratification, estuarine circulation or diel vertical migration; and (c) how the strong seasonal environmental variations of Comau Fjord affect not only the pelagic system (holo- and meroplankton), especially in the highly variable surface waters, but also the coral communities that populate the fjord. Furthermore, this thesis highlights the importance of zooplankton as an essential food supply to opportunistic benthic invertebrates that seasonally need to adapt to the high variations in zooplankton distribution and affect their trophic ecology. Additionally, the data clearly underscores the information gain through regular monitoring of pelagic communities in coastal ecosystems that allow to assess the natural extent of bentho-pelagic coupling as well as how anthropogenic perturbations may impact the functioning of the marine food web.
Dissertation
352 353
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Impact of climate change on the distribution of sponges and cold water corals in the Antarctic and Subantarctic
(2013-09-02)
Fillinger, Laura
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Freiwald, Andre
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Richter, Claudio
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Richter, Claudio
Climate change and ocean acidification, fuelled by the release of anthropogenic carbon dioxide in the atmosphere, impact the physico-chemical dynamics of the ocean. Current changes are undeniable and their rate is believed to be much faster than anywhere else in the geological records. Modifications of the seawater temperature and pH, amongst other parameters, impact marine organisms across all levels of biological organisation and extinctions or shifts in the distributional range of several species are expected. Unable to escape the alteration of their environment, sedentary benthic organisms are particularly exposed. The fate of corals and sponges, the main habitat-forming species in the benthos, is considered critical because of their aragonite skeleton (corals) and slow growth (sponges). In this thesis, I intended to estimate the impact of climate change and ocean acidification on the distribution of sponges and cold water corals in the Antarctic and the Subantarctic. For this purpose I focused on two main case studies: Case study I: Climate-induced changes in megabenthic communities along the Antarctic Peninsula and their consequences on the distribution of glass sponges. Case study II: Sensitivity of the cold water coral Desmophyllum dianthus to ocean acidification inferred from its distribution along a pH gradient in a Chilean fjord. In both cases, I chose to work mainly with non-destructive sampling devices, namely Remotely Operated Vehicles (ROVs) acquiring underwater videos for quantification of the benthos and simultaneously recording several physico-chemical parameters. For monitoring purposes a standardized method was needed to obtain comparable abundance data from videos recorded by different vehicles.
Dissertation
501 255
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Macroscopic and microscopic perspectives on habitat-forming Antarctic hexactinellid sponges
(2024-06-11)
Luisa Federwisch
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Richter, Claudio
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Barnes, David K. A.
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Richter, Claudio
Sponges of the class Hexactinellida, commonly known as glass sponges, are conspicuous members of the Antarctic benthos. They grow to considerable sizes and can form dense aggregations on the continental shelf of the Southern Ocean. These sponge grounds are associated with a high biodiversity as the large barrel-shaped hexactinellid sponges provide a complex three-dimensional structure and various micro-habitats for other animals. Their role as habitat-forming species has been well established, but other aspects of their biology remain largely unexplored. This thesis investigates Antarctic hexactinellid sponges from different perspectives that have previously been understudied or neglected. It presents new insights on their in-situ identification, their microbiomes, and their relevance for pelagic top predators. Ecological studies on Antarctic benthos regularly use seafloor imaging for in-situ observations of habitats and communities. However, in-situ species identification of Antarctic hexactinellid sponges has often been problematic due to unprecise species descriptions focusing on microscopic skeletal spicules while disregarding external macroscopic features, as well as several taxonomic changes. Therefore, the first objective of this thesis was to develop a practical and reliable macroscopic approach to image-based species identification of the common hexactinellid sponges of the Antarctic shelf, comprising Anoxycalyx (Scolymastra) joubini and eight currently accepted species of the genus Rossella. In order to identify diagnostic macroscopic characteristics of each species, I combined the examination of trawl-collected sponges, previous species descriptions, and a large collection of in-situ photographs and videos. Manuscript I describes all aspects of the external morphology of each species, accounting for their morphological variability and identifying species-specific characteristics. Special emphasis is put on the differentiation of species that have been mixed up in the past. The manuscript shows that each species in fact has unique macroscopic features that can be used to distinguish them in situ and without expert taxonomic knowledge. This provides a basis for species-specific observations on Antarctic hexactinellids in image-based studies. The second objective of this thesis was to elucidate the role of Antarctic hexactinellid sponges as habitat on different scales beyond the direct macroscopic associations. Therefore, I investigated them from a microscopical perspective and from a top predator’s perspective. It is well known that sponges can host a variety of symbiotic microorganisms in their tissue. The sponge-associated microbial communities are species-specific and tightly coupled with their host regarding metabolic processes, chemical defense, and health. However, the microbial associations of Antarctic hexactinellids have barely been investigated before. Even less explored is the relevance of hexactinellid sponges for pelagic megafauna like seals or other top predators, despite descriptions of various fish species using them as habitat and nursery ground. In order to describe the microbiomes of Antarctic hexactinellids and to compare them to those of Antarctic demosponges and deep-sea sponges from other regions, I have sampled deep-water hexactinellid and demosponge specimens for inclusion in two studies. Their microbial communities were analyzed by 16S rRNA gene sequencing and generation of amplicon sequence variants (ASVs). In addition, histological and ultrastructural analyses were conducted for several sponges. Manuscript II provides a detailed description of the microbiomes of Antarctic hexactinellids and demosponges in relation to sponge histology. All sponges were characterized as low microbial abundance sponges, but the denser the sponge tissue, the higher was the number of hosted microbes. Furthermore, the microbial community composition in hexactinellids and demosponges was significantly different. Although the hexactinellids showed a lower microbial richness than the demosponges, their microbiome comprised a higher percentage of class-specific ASVs. Manuscript III integrates these findings into a global analysis of deep-water sponge microbiomes. It shows that hexactinellid sponges in general have a characteristic microbiome distinct from that of demosponges. Compared to sponges from other regions, the Antarctic hexactinellids were among the species with the lowest microbial richness. Taken together, both studies show that Antarctic hexactinellid sponges host unique microbial communities. Scaling up to a wider ecosystem context, Manuscript IV describes a previously unknown interaction of Weddell seals with Antarctic hexactinellid sponges. In a study on the foraging behavior of female Weddell seals during lactation period using animal-borne video recorders, several seals were found to investigate the cavities of large hexactinellid sponges, presumably searching for prey. This behavior was observed for the first time and it is currently unknown how widespread it is. All sponges in the videos were identified as Rossella cf. racovitzae, but other hexactinellid species may likewise serve as foraging ground for seals. Overall, this thesis shows that the role of Antarctic hexactinellid sponges as habitat extends beyond the well-described associations of benthic fauna and that their relations with other organisms are more complex and diverse than previously recognized. They also host specific microbial communities and are relevant as foraging habitat for Antarctic top predators. Both aspects require further dedicated research to elucidate their ecological implications. As demonstrated in this thesis, changing perspectives may help to further broaden our understanding of the various roles of hexactinellid sponges in Antarctic marine ecosystems.
Dissertation
41 28
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Corals&Waves: Calcification and bioerosion in Large Amplitude Internal Wave affected coral reefs
(2010-04-07)
Schmidt, Gertraud Maria
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Bischof, Kai
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Richter, Claudio
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Richter, Claudio
The results of this work are a contribution to the understanding of the influence of dramatic natural variations of the physico-chemical environment in coral reef areas caused by Large Amplitude Internal Waves (LAIW).LAIW are a worldwide oceanographic phenomenon generated in areas with a rich underwater topography, strong density stratification and tidal currents. They deliver sub-thermocline water upslope into shallow shelf regions but their possible biological impact especially on benthic communities and ecosystems such as coral reefs is so far largely unknown. In this work the impact of LAIW on coral reefs was investigated at the Similan Island chain in the Andaman Sea. The unusual coral reef distribution with reefs flourishing only on the sheltered eastern island sides and no true reef framework in the west was shown to be consistent among the islands and related to LAIW. Temperature records revealed that LAIW have their strongest impact on deeper west slopes where they cause frequent and abrupt drops in temperature with peak activity during the north-east monsoon (January through April). LAIW advect deep cold, nutrient rich, suboxic and low-pH waters coming with strong currents into shallow near shore areas. In contrast to low numbers of frame-building species in east, the west slopes harbour loose yet more divers communities of scattered corals. This might be due to the alternating impact of south-west monsoon (May to October) and LAIW from above and below maintaining the coral community in a non-equilibrium state of intermediate disturbances which enhances species diversity.Coral growth of and bioerosion on Porites lutea revealed both, lowest rates at the site of highest LAIW-impact in west deep areas and highest rates within the dense coral reef of the sheltered east shallow. A calculated carbonate budget confirmed that carbonate accretion by reduced coral growth and carbonate erosion by alike reduced grazing and boring organisms are balanced but only barely positive under highly variable LAIW conditions in west deep. Coral recruitment on natural reef substrate revealed significantly higher abundances in shallow west than in east. However with increasing exposure period of experimental settlement tiles, the proportion of juvenile corals increased in east but decreased in west, indicating a failure of recruits to establish permanently on the LAIW-exposed sides in spite of the higher initial spat fall. Early stages of settlement and growth seemed to occur independently of LAIW exposure while the subsequent establishment of juvenile corals appeared to be related to LAIW intensity, reflecting the lack of true reefs on the LAIW-exposed west sides of the islands.
Dissertation
326 139
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Reproduction strategies of stony corals (Scleractinia) in an equatorial, Indonesian coral reef. Contributions for the reef-restoration
(2009-01-30)
Romatzki, Sascha
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Kunzmann, Andreas
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Richter, Claudio
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Richter, Claudio
In the present dissertation the sexual and asexual reproduction-strategies of stony corals in an equatorial Indonesian coral reef will be examined. Special attention is applied to the seasonality of sexual reproduction through coral larvae in North Sulawesi, Indonesia.The first chapter of this work deals with the explanation of terms that are often used in context with the present topic.The second chapter deals with the settlement of coral larvae on artificial settlement tiles in a quantitative study.Chapter 3 is focusing on the reproduction strategy and cycles of four selected branching coral species (Seriatopora hystrix, Pocillopora verrucosa, Acropora yongei and Acropora pulchra) by histological examination of their tissues. The fourth and last chapter deals with the hypothesis of enhanced growth of coral fragments transplanted in and exposed to an electrical field.
Dissertation
429 362
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Benthic communities of the Weddell Sea : Past, present and future
(2019-06-03)
Pineda Metz, Santiago E. A.
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Sands, Chester
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Link, Heike
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Richter, Claudio
The present thesis tackles different aspects of the past, present and future of high Antarctic benthic communities of the Weddell Sea. It first compares methodological approaches to sample benthos, showing the complementarity of two quantitative techniques. Then reviews knowledge on bentho-pelagic coupling on Antarctic shelves, showing that bentho-pelagic coupling differs considerably based on local characteristics. This methodological and conceptual knowledge is uses to study the benthic communities in the hard to access Filchner Region (southern Weddell Sea), describing two "novel" communities, and shows the influence of environmental drivers over benthic distribution. The final topic is the temporal dynamics of benthos. For this, a long-term study which considers a unique 26-year time series of benthic data from the southeastern Weddell Sea is used. Here, benthic communities appear severely affected by a decrease of productivity, and increase of scouring potential, especially after the year 2000.
Dissertation
394 155
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Population Demographics and Life History Characteristics of Heliofungia actiniformis: a Fungiid Coral Species Exploited for the Live Coral Aquarium Trade in the Spermonde Archipelago, Indonesia
(2008-05-29)
Knittweis, Leyla
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Kochzius, Marc
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Wolff, Matthias
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Richter, Claudio
A popular coral in the Indonesian live coral trade is the fungiid Heliofungia actiniformis. At non-harvested sites attached polyps aged 0-4 years were found to be most abundant, and growth rates decreased linearly with size. At harvested sites, total mortality rates were significantly higher for polyps sized 0-11 cm, and semi-structured interviews with local fishermen confirmed a size selective fishery towards small polyps. A utility per recruit calculation revealed maximum potential economic yield to occur at an age of 5 years, five years before reaching reproductive maturity. Subsequent Thompson and Bell calculations highlighted the need for a combination of size limits, quota reductions as well as the protection of spawning stocks. Genetic population connectivity patterns of H. actiniformis revealed significant genetic structuring, both among populations in South Sulawesi and throughout the Indo-Malay Archipelago. At both scales the degree of geographic separation and oceanographic features influenced the degree of larval exchange, with historical influences additionally shaping patterns on the large scale.
Dissertation
381 197

Richter, Claudio

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