Trevor A. Probyn

Brown tides and mariculture in Saldanha Bay, South Africa.

In 1997, the brown tide organism, Aureococcus anophageffens, was detected for the first time in Saldanha Bay, South Africa. Its presence was limited to an isolated, tidal dam that was similarly impacted during the late summer of the following two years but not in 2000. Bloom concentrations are typically of the order of 10(-9) cells l-1. This is one of the few reported occurrences of these nuisance blooms outside the north-eastern United States. A small oyster grow-out facility based in the dam has been severely affected by the reduced growth of oysters during these blooms. Reduced flushing of this culture site is a possible explanation for bloom initiation and persistence. However, Aureococcus blooms can be considerably more extensive as was evident during 1998 when the whole of the bay system, including Langebaan Lagoon, was affected for 6-8 weeks during late summer.

Nitrogen dynamics in the Bellingshausen Sea during the Austral spring of 1992

Abstract A series of 15N experiments were conducted in the early summer of 1992 during the course of cruise 198 of R.R.S. Discovery, with a focus on the seasonal ice zone (SIZ) of the Bellingshausen Sea. Nitrogen (NO3, NH4 and urea) uptake was measured over the nominal euphotic zone, and size fractionation experiments of a similar nature were conducted on surface waters. The most productive zone during this study was not associated with stable ice-melt water but with a west-east oriented, haline dominated density front centred around 67.3°S. The pelagic bloom coincident with the area south of the front had a banded structure with chlorophyll a concentrations up to 5 mg m 3. Integrated N uptake rates within the bloom varied between 56 and 34 mmol N m −2 day − , with a decreasing trend from north to south. A similar trend was evident in the |-ratios, where values decreased from 0.6 to 0.3. From size fractionated experiments in the bloom it was found that 82–87% of the chlorophyll a was in the netplankton fraction, which also accounted for 28 to 95% of the N uptake. The bloom was dominated by Porosira glacialis, Coscinodiscus bouvet, Thalassiosira antarctica and Phaeocystis spp. North of the front, integrated N uptake was 25 mmol N m −2 day − (f-ratio 0.28) and 60 to 69% of the uptake in surface waters was in the netplankton fraction. Waters adjacent to the ice-edge exhibited a lower rate of N uptake than the frontal stations (19 mmol N m −2 day −1 ) with an f-ratio of 0.1. Specific rates on N uptake indicated strong bloom viability in an Antarctic context but a lack of response of VN0P 3 to [N0 3 ]. The cross-frontal trends may provide an explanation of bloom development and persistence in the SIZ of the Bellingshausen Sea. Rates of new production in mature waters of the SIZ were comparable to those of previous studies in other regions, but rates measured within the bloom were higher. The rates of new production presented here are the first to have been made in the Bellingshausen Sea and as such can be incorporated in regional and global models relating to the sink of carbon.

Nitrogen utilization by phytoplankton in the Namibian upwelling region during an austral spring

Abstract The uptake of NO 3 − , NH 4 + and urea by phytoplankton populations was investigated off the Namibian coastline between 20° and 26°30′S during the spring, 1985. The region was characterized by intense upwelling with resultant penetration of high nutrient concentrations into adjacent oceanic waters. In spite of the high ambient NO 3 − concentrations, nitrogen was taken up primarily as NH 4 + and urea in accordance with phytoplankton preference. Measured f -ratios (NO 3 − uptake/total nitrogen uptake) were correspondingly lower than expected, with a mean value of 0.32. Ratios calculated from integrated data for the photic zone ( f ′-ratio) proved to be positively correlated with phytoplankton biomass (Chl α) and production. Factors such as NO 3 − concentration, light, temperature and recycled nutrient concentration were considered as potential influences on the f -ratio. No obvious relationship was evident between f -ratios and either NO 3 − concentrations or concentration ratios. Temperature (mean upper mixed layer) was well correlated with nutrient uptake but not with the f -ratio. Temperature coefficients θ 10 ) were considerably larger than expected, suggesting control of nutrient uptake by factors other than temperature. Light limitation, though probably influencing individual depth profiles of f -ratios, could not explain inter-station variability in f ′-ratio, however, was negatively affected by increasing concentrations of recycled nutrients both for discrete depths and for depth-integrated values. It is proposed that the high nutrient and low chlorophyll conditions that prevailed over much of the region were the result of an inhibition of phytoplankton bloom development by zooplankton grazing and deep mixing. The nitrogen excretory products of zooplankton (NH 4 + and urea) in turn were preferentially utilized by phytoplankton with the resultant suppression of NO 3 − uptake, explaining the low measured f -ratios.

Production and standing stocks of the kelp Macrocystis laevis Hay at the Prince Edward Islands, Subantarctic

SummaryThe recently described species Macrocystis laevis Hay is endemic to the Prince Edward Islands. Aerial photographs of Marion Island were used to outline the distribution of the kelp and to assess its cover. M. laevis occurs along the lee shore of the island, between the 5 and 20 m isobaths. Plant densities and gross plant morphology were measured by divers during April/May 1988. Net production was estimated from growth measurements taken in April/May 1988 and 1989 and again during August 1989. The mean biomass of kelp was 0.67 kgC·m−2 within the kelp beds. Net production was estimated at 7.7 gC·m−2·d−1 and 11.5 gC·m−2d−1 during the months of April and August respectively. M. laevis had a uniform frond-length frequency distribution, which suggests that only the oldest fronds are lost by wave action or senescence. Based on calculations for M. laevis and Durvillaea antarctica (the two species making up most of the macrophyte biomass) macrophytes are more productive per unit area than the phytoplankton but contribute less to the seas around the Prince Edward Islands by virtue of their small spatial coverage. Neither of the kelps lose much material as particulate or dissolved organic carbon through fragmentation. The extent of grazing on live M. laevis fronds is unknown, and only D. antarctica contributes to a macrofaunal detrital community. The contribution of M. laevis production to the nearshore ecology of the islands seems limited, as we suspect that almost all of its production is exported to the open ocean pelagic system.

Dynamics of oxygen depletion in the nearshore of a coastal embayment of the southern Benguela upwelling system

Acquisition of high resolution time series of water column and bottom dissolved oxygen (DO) concentrations inform the dynamics of oxygen depletion in St Helena Bay in the southern Benguela upwelling system at several scales of variability. The bay is characterized by seasonally recurrent hypoxia (<1.42 ml l−1) associated with a deep pool of oxygen-depleted water and episodic anoxia (<0.02 ml l−1) driven by the nearshore (<20 m isobath) decay of red tide. Coastal wind forcing influences DO concentrations in the nearshore through its influence on bay productivity and the development of red tides; through shoreward advection of the bottom pool of oxygen-depleted water as determined by the upwelling-downwelling cycle; and through its control of water column stratification and mixing. A seasonal decline in bottom DO concentrations of ∼1.2 ml l−1 occurs with a concurrent expansion of the bottom pool of oxygen depleted water in St Helena Bay. Upwelling of this water into the nearshore causes severe drops in DO concentration (<0.2 ml l−1), particularly during end-of-season upwelling, resulting in a significant narrowing of the habitable zone. Episodic anoxia through the entire water column is caused by localized degradation of red tides within the confines of the shallow nearshore environment. Oxygenation of the nearshore is achieved by ventilation of the water column particularly with the onset of winter mixing. No notable changes are evident in comparing recent measures of bottom DO concentrations in St Helena Bay to data collected in the late 1950s and early 1960s.

Sensitivity in reflectance attributed to phytoplankton cell size: forward and inverse modelling approaches

Synoptic scale knowledge of the size structure of phytoplankton communities can offer insight in to primary ecosystem diversity and biogeochemical variability from operational to the decadal scales. Accordingly, obtaining estimates of size and other phytoplankton functional type descriptors within known confidence limits from remotely sensed data has become a major objective to extend the use of ocean colour data beyond chlorophyll a retrievals. Here, a new forward and inverse modelling structure is proposed to determine information about the cell size of phytoplankton communities using Standard size distributions of two layered spheres to derive a full suite of algal inherent optical properties for a coupled radiative transfer model. This new capability allows explicit quantification of the remote sensing reflectance signal attributable to changes in phytoplankton cell size. Inversion of this model reveals regions within the parameter space where ambiguity may limit potential of inversion algorithms. Validation of the algorithm within the Benguela upwelling system using independent data shows promise for ecosystem applications and further investigation of the interaction between phytoplankton functional types and optical signals. The results here suggest that the utility of assemblage related signals in spectral reflectance is highly sensitive to algal biomass, the presence of other absorbing and scattering constituents and the resultant constituent-specific inherent optical property budget. As such, optimal methods for determining phytoplankton size from (in situ or satellite) ocean colour data will likely rely on appropriately spectrally dense and optimised sensors, well characterised measurement errors including those from atmospheric correction, and an ability to appropriately limit ambiguity within the context of regional inherent optical properties.

Real-time monitoring of harmful algal blooms in the southern Benguela

The southern Benguela Current region off South Africa is subject to frequent harmful algal blooms (HABs), which can have serious impacts — both through the introduction of toxins into the ecosystem and the collapse of high-biomass blooms leading to anoxia. As part of the Benguela Current Large Marine Ecosystem Programme, a bio-optical buoy has been developed for monitoring HABs in the region, providing both real-time and time-series data. Considerations in developing the buoy were that it should be small, cost effective and robust, allowing for field calibration of the sensors and servicing from a small boat. The instrument package on the buoy consists of two hyperspectral radiometers (providing remote sensing reflectance), a thermistor chain, a fluorometer and an Acoustic Doppler Current Profiler. A half-hourly acquisition regime collects data from the instruments, which are transmitted in real time using cellular phone telemetry. A website is updated with these data, when available, along with satellite data and shellfish warnings, to provide near real-time information on conditions in the area. Demonstration data from the buoy, related to observed blooms of dinoflagellates and the ciliate Mesodinium rubrum, are presented.

Determination of Urinary Calcium Oxalate Crystallization Mechanisms and Kinetics Using Flow Cytometry

This paper describes the application of flow cytometry to the determination of calcium oxalate crystallization kinetics and mechanisms in real urine. The technique has the unique advantage of simultaneously providing quantitative particle number-size distributions and qualitative data concerning particle structure and morphology. Twenty-four-hour urines from 10 healthy male subjects were treated with sodium oxalate and the ensuing crystallization of calcium oxalate was monitored by flow cytometry. In 7 specimens crystallization was accompanied by increasing size and by a fundamental change in particle morphology. This suggests that nucleation and aggregation occurred in these specimens. In the remaining 3 samples, increasing particle numbers occurred without any changes in size or morphology, indicating that nucleation was the sole mechanism in these specimens. These results demonstrate that flow cytometry is able to differentiate between nucleation, growth and aggregation mechanisms thereby making it an extremely useful analytical tool for stone researchers.

Suffocating Phytoplankton, Suffocating Waters—Red Tides and Anoxia

The dynamics of O2 depletion in exceptional dinoflagellate blooms, often referred to as red tides or harmful algal blooms (HABs), was investigated in St Helena Bay in the southern Benguela upwelling system in 2013. The transition to bloom decay and anoxia was examined through determination of O2-based productivity and respiration rates. Changes in O2 concentrations in relation to bloom metabolism were tracked by fast response optical sensors following incubation of red tide waters in large volume light-and-dark polycarbonate carboys. Concurrent measurements of nutrients and nutrient uptake rates served to assess the role of nutrient stressors in community metabolism and bloom mortality. The estimates of community productivity and respiration are among the highest values recorded. Nutrient concentrations were found to be low and were unlikely to meet the demands of the bloom as dictated by the rates of nutrient uptake. Ratios of community respiration to gross production were particularly high ranging from 0.6 – 0.73 and are considered to be a function of the inherently high cellular respiration rates of dinoflagellates. Nighttime community respiration was shown to be capable of removing as much as 17.34 ml O2 l-1 from surface waters. These exceptional rates of O2 utilization are likely in some cases to exceed the rate of O2 replenishment via air-water exchange thereby leading overnight to conditions of anoxia. These conditions of nighttime anoxia and nutrient starvation are likely triggers of cell death and bloom mortality further fueling the microbial foodweb and consumption of O2.

Identification of the marine diatom Pseudo-nitzschia multiseries (Bacillariophyceae) as a source of the toxin domoic acid in Algoa Bay, South Africa

A unialgal culture of a Pseudo-nitzschia species dominant in the plankton of Algoa Bay in the spring of 2012 was established by isolation of clonal chains of cells. Identification of the species as Pseudo-nitzschia multiseries was based on frustule morphometrics provided by light and scanning electron microscopy, and confirmed by phylogenetic analysis of the LSU rDNA gene. Cultures were shown to produce domoic acid (DA) as measured by ELISA and LC/MS-MS methods, and levels of cellular DA were ∼0.1 pg cell–1. Although it is recognised as a cosmopolitan species, these observations provide the first account of this toxic diatom in the coastal waters of South Africa.