Arntz, Wolf E.
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Arntz, Wolf E.
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Arntz, Wolf E.
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Arntz, Wolf
Arntz, W. E.
Arntz, W.
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Item-typ:Veröffentlichung, Population dynamics of the Argentinean surf clamsDonax hanleyanus and Mesodesma mactroidesfrom open-Atlantic beaches off Argentina(2008-10-17); ; ; The surf clams Mesodesma mactroides Reeve, 1854 and Donax hanleyanus Philippi, 1847 are the two dominating species in macrobenthic communities of sandy beaches off northern Argentina, with the latter now surpassing M. mactroides populations in abundance and biomass. Before stock decimation caused by exploitation (during the 1940s and 1950s) and mass mortality events (1995, 1999 and 2007) M. mactroides was the prominent primary consumer in the intertidal ecosystem and an important economic resource in Argentina.Since D. hanleyanus was not commercially fished and not affected by mass mortality events, it took over as the dominant species, but did never reach the former abundance of M. mactroides. Currently abundance and biomass of bothsurf clams are a multiple smaller than those of forty years ago, indicating the conservation status of D. hanleyanus and M. mactroides as endangered.Therefore the aim of this study is to analyse the population dynamics (population structure, growth and reproductive biology) of D. hanleyanus and M. mactroides, and to compare the results with historical data in order to detect possible differences within surf clam populations forty years ago and at present.In conclusion, although the commercial fishery of M. mactroides is closed since more than 50 years and extractions are still forbidden and D. hanleyanusis not used as a natural living resource yet, the strong decline of surf clam abundance and biomass within the last four decades implies that populations of the Argentinean D. hanleyanus and M. mactroides are in unstable conditions,due certainly to the increasing anthropogenic impact.Dissertation223 139 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Recruitment dynamics of North Sea macrozoobenthos in intertidal soft bottoms: larval availability, settlement and dispersal(2003-11-04); ; ; This thesis investigates how larval supply, larval settlement and secondary dispersal affected recruitment and recovery of macrozoobenthos living in an intertidal sand flat located in the German Wadden Sea. The temporal availability of meroplanktonic bivalve larvae was related to the timing of sea water temperature increase and/or the timing and magnitude of phytoplankton blooms. Larval settlement of the polychaete Lanice conchilega occurred almost exclusively at exposed sites within the adult habitat and was dependend upon the density of the adults. Model simulations revealed that dense L. conchilega patches develop only in areas of high near-bottom flows. In contrast, bivalve larvae settled mainly in sheltered habitats. Both polychaetes and bivalves undergo phases of postlarval dispersal which rapidly changed the spatial patterns generated by larval settlement. In-situ staining experiments showed that secondary dispersal is strongly size/age dependent. The recovery of two macrobenthic assemblages following the severe winter was rapid (<1 year) and influenced by 1) species life histories, 2) habitat conditions, and 3) biotic interactions, namely facilitation. The temporal course of recolonisation was mainly determined by the availability of settling stages (larvae and postlarvae). This thesis elucidates that both pre- and post-settlement processes contribute to the recruitment and recolonisation of macrozoobenthic communities. In dynamic systems, flexibility of life histories, high mobility of benthic life stages and the existence of functionally distinct life stages provide multiple paths to population maintenance and a high resilience. It is highlighted that at the end tides and currents are the decisive processes because they set the boundary conditions to which organisms respond and mediate the function of many processes such as larval drift, larval settlement and secondary dispersal.Dissertation261 151 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Ecology of larval fishes in the Independencia Bay, Pisco, Peru: Temporal and spatial relationships, taxonomic aspects(2005-02-15); ; ; The plankton of Independencia Bay was sampled during the year 2000. In total, 16,156 fish larvae, representing 34 families, 48 genera and 48 species were collected. 8 families numerically dominated the diverse larval fish fauna and comprised 96.8% of the larvae captured. The monthly mean density of total fish larvae showed two peaks (springtime and summer peaks). The greatest mean density during the spring peak was 7,492 larvae/100 m3, recorded in October. The greatest mean density during summer was recorded in February (2,493 larvae/100 m3). Abundance in October (spring time) at Santa Rosa was higher than at the other 3 stations, but abundance in those other 3 stations was higher in February (summer time). The spring and summer ichthyoplankton abundance peaks in Independencia Bay coincided with high zooplankton standing stocks and also coincided, approximately, with periods of increased upwelling in the area. The occurrence of high larval fish densities and the wide range of larval stages suggest that Independencia Bay is a regionally important spawning and nursery ground for marine fish. A Principal Component Analysis (PCA) showed that temperature and salinity accounted for the largest fraction (74.4%) of the variability in the observed larval fish assemblage patterns. Vertical distribution patterns of ichthyoplankton were examined from two depths (surface and 10 m) at two stations. There were no statistically significant differences between nighttime and daytime densities of fish larvae at either depth. Nevertheless, a small degree of vertical redistribution was apparent for some species that could be interpreted as nocturnal dispersal. Developmental series for individuals of Normanichthys crockeri and Prolatilus jugularis are presented using morphological features and pigmentation patterns. Larvae hatch sizes, information concerning the different stages, main diagnostic features of the larvae and meristic information including fin ray accounts are given.Dissertation292 135 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Environmentally induced responses of Donax obesulus and Mesodesma donacium (Bivalvia) inhabiting the Humboldt Current System(2010-02-25); ; ; The Humboldt Current System (HCS) is one of the most productive ecosystems on earth which is deeply modified by the El Nino Southern Oscillation (ENSO). El Nino (EN, the warm phase of ENSO) and La Nina (LN, the cold phase of ENSO) cause changes in vitally important environmental parameters including water temperature, salinity and oxygen concentration. The changes elicit distinct responses in coastal populations and communities. Thus are documented for the surf clams Donax obesulus Reeve, 1854 and Mesodesma donacium Lamarck, 1818 dominating the benthic communities of sandy beaches of the HCS. Existing knowledge gleaned from field data indicates that EN and LN events affect populations of each species differently, but understanding of the mechanisms underlying the effects are lacking. The life cycle of bivalve species is characterized by a highly mobile meroplanktonic larval stage, lasting from a few weeks to several months. In the wake of EN events, meroplanktonic larval stages may define the medium- and long-term stability of shallow water-species. Unfortunately, the effects of environmental changes and temperature thresholds on both species and the larval stages of D. obesulus have not yet been addressed. The effect of salinity (on M. donacium and larvae of D. obesulus) and temperature on growth and mortality of these clams under controlled experimental conditions were tested. For this, both species were exposed to reduced salinity under normal (NTC), El Nino (ENTC) and La Nina (LNTC) temperature conditions. Growth, mortality and development of D. obesulus larvae were recorded under the different temperature regimes. During a second 48 hour in vitro-experiment at NTC and ENTC, activity and mortality of larvae under reduced salinities (25, 15 and 5 /-1) was documented. Results of the in vitro-experiments with adult and larval D. obesulus indicated that compared with NTC, adults showed lower tolerance to LNTC and higher tolerance to ENTC. Similarly, D. obesulus larvae reared under ENTC grew and developed faster compared to those reared under NTC. Larvae were highly tolerant of salinity changes (15-35). In contrast, M. donacium showed lower tolerance to ENTC, although juveniles are more tolerant than adults when exposed to ENTC and lower salinity. The distinct responses observed to environmental factors may be related to the different evolutionary origins of the two families, which are tropical for the Donacidae and temperate for the Mesodesmatidae, supporting previous hypotheses suggesting that thermal tolerance is a factor in the observed distributional changes of both species during warm and cold episodes of ENSO. The enhanced osmotic tolerance of larvae and juveniles compared to adult specimens may represent an adaptation in early life stages permitting colonization of vacant areas close to outlets of estuaries. Results of this thesis and data concerning the former and current distributions of each species clearly indicate that D. obesulus is better adapted to ENTC than to LNTC. M. donacium on the other hand, appears better adapted to normal temperate conditions of the HCS than to ENTC. Beside the in vitro-experiment of Donacidae and Mesodesmatidae the taxonomy of D. obesulus and D. marincovichi Coan, 1983 was revised. The use of shell morphological characteristics to separate both species frequently revealed incongruences in taxonomically important morphometric parameters. Thus the taxonomy of the two sympatric surf clams was revised by genetics and sperm morphology. Genetic analyses showed no significant mitochondrial differentiation within or among populations, a conclusion supported by observations of sperm ultrastructure, which proved indistinguishable between morphotypes. Thus it is concluded that the two morphotypes should be included together under D. obesulus Reeve, 1854.Dissertation252 140 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Community succession and seasonal onset of colonization in sublittoral hard and soft bottoms off northern Chile(2009-05-11); ; ; Community ecological succession consists of the sequence of changes in species composition through time that occurs after a site has been disturbed or on the appearance of a pristine substratum, and it is one of the key processes modulating patterns of diversity, structure and evolutionary history of benthic landscapes. I have used field experiments to describe the successional development of both sublittoral hard- and soft-bottom communities off northern Chile. The Humboldt Current System off northern Chile is an excellent natural laboratory to study succession because there are several sources of disturbances operating at different scales including the El Nino Southern Oscillation (ENSO), which drastically influences biodiversity patterns. This thesis specifically aimed (i) to describe the successional development of subtidal hard- and soft-bottom communities over 27 months and a two year period, respectively; (ii) to estimate the time necessary for the developing communities to resemble the surrounding natural community, and (iii) to evaluate the effect of the seasonal starting point of community succession over a one year period of development. Succession in hard-bottom habitats showed a progressive change in community structure and competition for space, which was identified as the most important factor during succession. After 27 months, the developing communities contained the same species as the natural community but did not yet fully resemble their surroundings. Seasonality had an effect on successful species settlement, but the final stages of the developing community were influenced by interspecific competition for space (i.e. hierarchical competition). Succession followed a non-rigid, but deterministic pattern, in which colonial suspension-feeding species were hierarchically dominant over solitary species. This dominance of suspension feeders appears to be favoured by high levels of primary production associated with upwelling. On hidden surfaces of the hard substratum early successional species survive better and can laterally spread over exposed habitats as strong interactions for space among species are alleviated in hidden habitats.Succession in soft-bottom habitats supported the "tolerance succession model" where components of the later successional stages can colonize at the same time with species generally associated to the early successional stages. Resemblance to natural sediment communities occurred after eighteen months. Seasonality had no evident effect on the resulting community composition and all communities starting in different seasons converged into a similar composition after one year of exposure. These results support the notion that benthic community can return to an almost identical faunal structure with the same dominants after disturbance events. Both, hard- and soft- bottom communities showed a high capability to return and to converge towards natural surrounding communities, which highlights the resistance of the benthic system to small scale disturbances. Furthermore, the finding of new species in both study locations suggest that the components and their potential colonizing role need to be surveyed in detail tounderstand the species turnover during succession. My results demonstrate that benthic communities from northern Chile present a high resistance capacity to small scale disturbance during cold conditions with hard bottoms responding slower compared to the relatively quick recovery detected in soft bottoms. The question to be resolved in the future is whether or not this resistance capacity is also valid during strong El Nino events. Enhancing the temporal and spatial scale of this type of experiments is therefore recommended not only for the understanding resistance and succession, but also other ecosystem stability properties such as resilience, persistence and elasticity.Dissertation238 149 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Bacterial community patterns along small- and large-scale environmental radients in Arctic deep-sea sediments(2008-10-28); ; ; One focus of this study was to detect local coherences between deep-sea benthic bacterial community patterns and an ice-edge related input of organic material (Fram Strait, Arctic Ocean) as well as physical disturbances (Ardencaple Canyon, Greenland Sea). Such large-scale patterns along a depth-dependent gradient were compared to small scales patterns within the sediment column. A further aim was to assess the local impact of small biogenic structures (Macrofaunal crawling and feeding tracks, burrows, plough traces, faeces, Tentorium semisuberites) on benthic bacterial communities by increasing microhabitat heterogeneity through the modification of near-bottom flows and hence deposition patterns in deep-sea surface sediments. As the retrieval and incubation procedures of all deep-sea sediments sampled for this study were performed in absence of pressure-retaining gears, bacterial viability and activity has been assessed by different approaches to estimate bulk metabolic pathways.Dissertation376 146 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Die Lebensgemeinschaften des Seegats der Otzumer Balje in Abhängigkeit von morphodynamischen Prozessen(2000-02-15); ; ; Tidal Inlets are the links between the Wadden Sea and the open shore. So their benthic communities are influenced by both sides. Export- and import processes along tidal inlets were discussed on specific species by e.g. BOSSELMANN (1989), HERTWECK (1995), and SMTDT (1951). Additionally DÖRJES&HOWARD 1992, DÖRJES et al. 1970, DÖRJES&REINECK 1977, PARKE&HAUSMANN 1971, SCHUSTER 1951, STECHER&DÖRJES 1993a,b. They show main differences between benthic communities of tidal flats and shore faces of the open sea. Investigations of the links, the tidal inlets, are still missing. The benthos- and the according driftfauna of Tidal Inlet of the Otzumer Balje were investigated in close relationship with the hydrographical investigations (KRÖGEL 1995) to answer following questions: Are the benthic associations of Tidal Inlets a mix of Wadden Sea and Shore Face communities ? Are the Tidal Inlets a reservoir of species, which will settle on the Tidal Flats ? Can exchange processes be documented between the Wadden Sea and the Open Sea ? In which way are benthic associations of Tidal Inlets influenced by morphodynamic processes ?Dissertation357 183 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Shallow-water mega-epibenthic communities in the high Antarctic (Weddell Sea) and the west coast of the Antarctic Peninsula (Bellingshausen Sea)(2004-04-08); ; ; Continental shelves around Antarctica are unusual in being deep, and consequently shallow habitats at depths <150 m are scarce. In the Weddell Sea, only two shallow sites with water depths between 55 and 160 m are known (Atka Bay and a shallow bank off Four Seasons Inlet NE of Kapp Norvegia). In contrast, the Antarctic Peninsula has a true coast and thus, true littoral areas are common. This study (1) characterises and describes the distribution and spatial patterns of shallow-water mega-epibenthic fauna in the Antarctic Peninsula (Bellingshausen Sea) and at two sites in the high Antarctic (Weddell Sea), (2) analyses community structures and (3) compares benthic biodiversity in these areas at different spatial scales and with additional data from deep Antarctic shelf sites and corresponding shallow and deep areas in the Arctic. Multivariate analyses revealed significant faunal differences between Marguerite Bay (Bellingshausen Sea) and the Weddell Sea stations, Atka Bay and Four Seasons Bank. Echinoderms, especially ophiuroids, dominated Marguerite Bay, bryozoans and ascidians were abundant at Atka Bay, and hydroids and gorgonians were well represented at Four Seasons Bank. These differences can mainly be explained by the influence of local environmental conditions that are probably the primary factor shaping the Antarctic shallow-water epifauna, and not an intensive exchange with larger depths or limited dispersion due to scarce and isolated shallow areas. Spatial patterns of Antarctic benthic shelf communities were analysed and different patterns are identifiable: a locally limited typical fauna, a patchwork of assemblages as well as continuous faunistic gradients. Combinations of these three scenarios can be considered as the rule in Antarctic mega-epibenthic communities. A faunistic and environmental parallelism with the Arctic in terms of biodiversity was also studied.Dissertation396 412 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Spatial and temporal variability of North Sea mega-epibenthos assessed by seabed photography.(2008-06-23); ; ; Spatial and temporal variability of mega-epibenthic assemblages (including invertebrates and demersal fish) of the German Bight were investigated at different spatial and temporal scales using seabed photography.A methodological comparison between seabed photography (UWP) and parallely taken beam trawl (BT) data showed that dominance patterns recorded by the two methods were similar. Abundances recorded by UWP were generally higher than those yielded by beam trawls, while taxa numbers were lower by UWP than by BT.For spatial and temporal variability of mega-epibenthic assemblages and taxa, seabed photographs were analysed for abundances and distribution patterns of solitary mega-epibenthic organisms and occurrences of biotope features. Correlations of taxa and assemblage distribution patterns with environmental factors were found at the different spatial and temporal scales.It was shown that UWP data contribute to the knowledge on ecology of the mega-epibenthos of the German Bight.Dissertation311 175 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Demography, Reproductive Biology and Trophic Ecology of Red Coral (Corallium rubrum L.) at the Costa Brava (NW Mediterranean): Ecological Data as a Tool for Management(2005-04-14); ; ; The precious Mediterranean red coral (Corallium rubrum, L. 1758) is an overexploited gorgonian coral whoose red calcium carbonate skeleton is used in the jewelery industry. This work studies the demography, reproductive ecology and trophic ecology of red coral, and used the data to provide recomendations for its fishery managment and conservation. Five harvested populations at the Costa Brava, Spain, showed a population structure that is significantly shifted towards small/young colonies, compared to a protected population at the Medas Islands Marine Park. Average size and age of colonies in the harvested populations were estimated at 5 cm height and 7.5 years, whereas the species is capable of reaching 50 cm and 100 years. Only a small part of the colonies found show a well developed branching pattern, indicating overexploitation. The reproductive output significantly depends on colony size, with 100 % fertility being reached by colonies of 4 � 6 cm height. Mesoscale geographic variation however had no significant effect on reproductive output. Colonies in deep water spawned slightly earlier than shallow ones, when temperature stratification in summer was particularly pronounced. The main proportion of the diet of corallium rubrum is particulate organic matter (POM), while crustaceans such as copepods played a smaller role due to their infrequent capture. No clear seasonal pattern of the ingestion rate was found, due to the high variablity that may be linked to variability in watermovement. It appears that red coral is a flexible omnivore, able to exploit various trophic situations. Maximum sustainable yield, calculated using the Beverton and Holt model, show an optimal age at first capture of 98 years, while current fishing regulations permit harvesting of colonies that are 11 years old. This results in only a fraction of the calculated maximum yield. Poaching and illegal capture of small colonies appear to be a major problem at the Costa Brava.Dissertation297 162