Wucherungen von Cyanophyceen an den Ufern des Zürichsees und deren Ursachen

Ohne Zusammenfassung Nach einem Referat, gehalten am I. Internationalen Cyanophyceen-Symposium in Luzern, Kastanienbaum, 29.8.-3.9. 60.     

Reflection on the first five years of South Africa’s Acoustic Tracking Array Platform (ATAP): status,challenges and opportunities

The Acoustic Tracking Array Platform (ATAP) is a marine science programme that monitors the movements and migrations of inshore marine animals along the South African coastline. Acoustically tagged animals are monitored by an expanded network of approximately 100 automated data-logging acoustic receivers moored at strategic node sites, from Cape Point in the west to the South Africa–Mozambique border in the east. During five years since its inception, in 2011, the ATAP has achieved outstanding progress in terms of the numbers of animals and the variety of species tagged. To date, the ATAP has yielded over 2.6 million detections from more than 700 acoustically tagged animals, representing 27 different species from 20 families, including the African penguin Spheniscus demersus, fishery-at-risk species (e.g. dusky kob Argyrosomus japonicus) and iconic elasmobranchs (e.g. white shark Carcharodon carcharias). Following a period of considerable equipment loss in 2014, refinement of the receiver network was required and the deeper receivers at each site were decommissioned without influencing the integrity of the nationwide array. The platform, managed by the South African Institute for Aquatic Biodiversity, ultimately represents a low-cost method of collecting long-term data that currently benefits approximately 25 researchers from 14 organisations. Case studies are presented to expose the opportunities provided by the ATAP, which will undoubtedly yield new discoveries and provide a greater understanding of the movement patterns and migrations of a wide variety of inshore marine and estuary-associated species.     

Ein Beitrag zur Vulkanologie Süd-Perus

The Nevado Coropuna (6400 m/19 500 ft) is the largest and highest volcano of Peru and is situated 150 km NW of the town of Arequipa at a distance of 110 km from the Pacific coast. Results of a thorough petrographic study are presented including microprobe and radiometric measurements.

1. The constituent rocks building up the Coropuna volcano are lavas and rhyodacitic ash flows intercalated between older and younger lavas at the foot of the cone. The volcanic edifice rests on older ignimbrite sheets (14 m. y.) exposed only in the surrounding valleys.
2. The lavas are typically latite-andesites which contain some normative quartz in the groundmass. Plagioclase has 37–47% An. The depth of the phenocryst crystallization is calculated at 8–12 km based on the equilibrium between plagioclase, clinopyroxene and groundmass.
3. The Coropuna volcano has existed since the Late Miocene (5 m. y.). Approximately 2 m. y. ago a catastrophic explosion produced large rhyodacitic ignimbrite deposits around the foot of the mountain. Thereafter the effusion of lavas was dominant through Holocene times with the latest lavas becoming slightly more acidic (62% SiO₂).
4. 30–40 km to the W and SW of the Coropuna some outliers of the coastal batholites are exposed. Both their radiometric age (Cretaceous, 97 m. y.) and their chemical composition are in disagreement with the notion of these granodioritic to gabbroic rocks as the intrusive equivalents of the young volcanics.

     

Gastric lavage as a non-lethal method for stingray (Myliobatiformes) diet sampling

Understanding the trophic interactions of ecologically important mesopredators such as Myliobatiformes (stingrays) is vital, but, given their susceptibility to overexploitation, the collection of stomach contents for dietary analysis necessitates the use of non-lethal methods. We provide a detailed method of using gastric lavage to collect stomach contents from the ‘Vulnerable’ porcupine ray Urogymnus asperrimus at the St Joseph Atoll of the Amirantes Group, Seychelles. Rays were captured by hand, inverted and restrained while a plastic hose, connected to a bilge pump, was inserted into the stomach to flush out the contents. A high percentage (94.5%) of gastric lavage attempts resulted in the collection of stomach contents. There was no visual evidence of stress or short-term, post-release mortality and, given the success and relative ease of this technique, we conclude that the described method of gastric lavage is an effective, non-lethal means of obtaining stomach contents from stingrays.     

Genetic stock structure of white steenbras Lithognathus lithognathus (Cuvier, 1829), an overexploited fishery species in South African waters

White steenbras Lithognathus lithognathus (Teleostei: Sparidae) is an overexploited marine fish species endemic to South Africa. Overexploitation in recreational, subsistence and commercial fisheries has resulted in stock collapse and the need for improved management of the species. Adults are thought to undertake large-scale annual spawning migrations, yet studies of their movement indicate low levels of connectivity among coastal regions. To address this, mitochondrial DNA sequencing and genotyping of microsatellite loci in the nuclear genome were conducted to determine the genetic stock structure and level of gene flow in this species. Genetic diversity was high throughout the species’ core distribution, with no evidence of isolation by way of distance or localised spawning. Low, non-significant pairwise fixation indices (F_ST, R_ST and Jost’s D_est) indicated low genetic differentiation and high levels of gene flow. The observed results, and agreement between mitochondrial and microsatellite DNA, confirm that white steenbras exists as a single genetic stock with high levels of gene flow throughout its distribution.     

Growth rate of speckled snapper Lutjanus rivulatus (Teleostei: Lutjanidae) based on tag-recapture data from the iSimangaliso Wetland Park,South Africa

The growth rate of speckled snapper Lutjanus rivulatus was investigated using data from a long-term tag-recapture study conducted in the St Lucia Marine Reserve within the iSimangaliso Wetland Park, a World Heritage Site in northern KwaZulu-Natal, South Africa. A total of 1 429 L. rivulatus were tagged and 453 (31.7%) individual fish were recaptured one or more times. Growth rates were modelled from the tag-recapture data using a maximum-likelihood approach. It is shown that L. rivulatus is a slow-growing species with L_∞ = 918?mm FL, K = 0.06 and phi-prime (Ø, the growth index) = 2.69. The effects of deep-hooking and multiple captures were tested and this revealed that there was no significant impact on the growth of L. rivulatus. The growth index was lower than that recorded in many other similar congeneric species. Slow growth, coupled with high levels of residency and site fidelity, suggest that this species is vulnerable to exploitation and that a precautionary approach towards future management is appropriate.     

Orographical modification and large scale forcing of a cold front

Summary The development of a cold front influenced by orography and large scale forcing is examined with a two-dimensional meso-scale model. The model is based on the primitive equations and uses the hydrostatic and anelastic approximations. Gradients of the basic flow and temperature field in the third dimension are taken into account during the simulations. Low diffusive numerical schemes and radiation boundary conditions reduce the numerical errors to an acceptable minimum for a two day simulation and avoid reflections at the upper and lateral boundaries. Frontogenetical forcing is included in the simulations by specifying either a vertically sheared or horizontally convergent basic zonal flow field. Model runs with an idealized cold front were carried out over flat terrain and in the presence of a bell shaped mountain ridge.The simulations show a weakening of the cold front on the windward side of the mountain ridge and a strong reintensification on the leeward side relative to the control runs without topography. Analysis of frontogenesis terms demonstrates the importance of convergence in the ageostrophic circulation and of along-front temperature advection for the development of the cold front. The strong intensification of the cold front on the leeward side of the mountain ridge can only partly be explained by superposition with the mountain induced wave. It is mainly caused by ageostrophic deformation forcing in the strong downward flow of this wave.The results also show that the cold front passage over the mountain ridge is not a continuous process. The formation of a new frontal structure on the leeward side of the mountain ridge, well separated from the primary one, is observed while the initial cold front still exists in the upslope region. Generally nonlinear interactions between the mountain wave and the cold front are the important mechanisms to explain these phenomena.With 18 Figures     

Movement patterns of surf-zone fish species in a subtropical marine protected area on the east coast of South Africa

A long-term mark-recapture study was used to assess the movement patterns of surf-zone fishes in the St Lucia Marine Reserve, a marine protected area within the iSimangaliso Wetland Park, a World Heritage Site on the east coast of South Africa. Between 2001 and 2013, 6 613 fish from 71 species, caught by hook and line, were tagged at four sites within and adjacent to a no-take marine sanctuary area. A total of 1 004 (15.2%) recaptures were made from 17 species. The majority (82.4%) of these species displayed station-keeping behaviour, whereas only three were classified as wider-ranging species, and no species with discernible migratory behaviour was observed. Findings for five species with the highest recapture rates, namely Pomadasys furcatus, Epinephelus andersoni, E. marginatus, Dinoperca petersi and Lutjanus rivulatus, are presented in greater detail. Recapture rates ranged from 7% to 50% and time at liberty from 0 to 3 163 days. Individuals of all five species displayed station-keeping behaviour, with the 95th percentile of intra-study-site movements varying between 200 and 1 025 m (linear distance). However, four of the five species also displayed some ranging behaviour and made exploratory excursions ranging from 3.5 to 125 km, in both northerly and southerly directions. The dominance of station-keeping behaviour suggests that the St Lucia Marine Reserve sanctuary zone provides an important refuge for these species, with some export to adjacent areas.     

Beta diversity of pelagic assemblages at fish aggregating devices in the open ocean

Owing to difficulties in accessing the vast open ocean, the beta (β) diversity of pelagic fish assemblages remains poorly studied. We investigated the relationship between assemblage similarity and geographical distance between anchored fish aggregating devices (FADs), sampled by standardised underwater visual censuses in three anchored FAD arrays in the Indian Ocean—at the Maldives, the Seychelles and Mauritius. The use of two complementary indices of β-diversity, based on presence/absence data (Jaccard similarity coefficient) and abundance data (Bray–Curtis index), revealed that geographical distance between sampling sites (from 4 to 257 km) appeared to have no effect on the similarity of fish assemblages associated with FADs within each array. The results of this preliminary study question the generalisation of the paradigm of an increase in β-diversity with geographic distance to the open-ocean fish community. Large-scale studies using a variety of datasets should be conducted to further investigate patterns of β-diversity in the open ocean.