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Marine heatwaves (MHWs), or prolonged periods of anomalously warm sea water temperature, have been increasing in duration and intensity globally for decades. However, there are many coastal, oceanic, polar, and sub-surface regions where our ability to detect MHWs is uncertain due to limited high quality data. Here, we investigate the effect that short time series length, missing data, or linear long-term temperature trends may have on the detection of MHWs. We show that MHWs detected in time series as short as 10 years did not have durations or intensities appreciably different from events detected in a standard 30 year long time series. We also show that the output of our MHW algorithm for time series missing less than 25% data did not differ appreciably from a complete time series, and that the level of allowable missing data could cautiously be increased to 50% when gaps were filled by linear interpolation. Finally, linear long-term trends of 0.10°C/decade or greater added to a time series caused larger changes (increases) to the count and duration of detected MHWs than shortening a time series to 10 years or missing more than 25% of the data. The long-term trend in a time series has the largest effect on the detection of MHWs and has the largest range in added uncertainty in the results. Time series length has less of an effect on MHW detection than missing data, but adds a larger range of uncertainty to the results. We provide suggestions for best practices to improve the accuracy of MHW detection with sub-optimal time series and show how the accuracy of these corrections may change regionally.

Marine bioregional planning requires a meaningful classification and spatial delineation of the ocean environment using biological and physical characteristics. The relative inaccessibility of much of the ocean and the paucity of directly measured data spanning entire planning regions mean that surrogate data, such as satellite imagery, are frequently used to develop spatial classifications. However, due to a lack of appropriate biological data, these classifications often rely on abiotic variables, which act as surrogates for biodiversity. The aim of this study was to produce a fine-scale bioregional classification, using multivariate clustering, for the inshore and offshore marine environment off the east coast of South Africa, adjacent to the province of KwaZulu-Natal and out to the boundary of the exclusive economic zone (EEZ), 200 nautical miles offshore. We used remotely sensed data of sea surface temperature, chlorophyll a and turbidity, together with interpolated bathymetry and continental-slope data, as well as additional inshore data on sediments, seabed oxygen and bottom temperature. A multivariate k-means analysis was used to produce a fine-scale marine bioregionalisation, with three bioregions subdivided into 12 biozones. The offshore classification was primarily a pelagic bioregionalisation, whereas the inshore classification (on the continental shelf) was a coupled benthopelagic bioregionalisation, owing to the availability of benthic data for this area. The resulting classification was used as a base layer for a systematic conservation plan developed for the province, and provided the methods for subsequent planning conducted for the entire South African EEZ. Validation of the classification is currently being conducted in marine research programmes that are sampling benthic biota and habitats in a sampling design stratified according to the biozones delineated in this study.

The importance of coastal upwelling systems is widely recognized. However, several aspects of the current and future behaviors of these systems remain uncertain. Fluctuations in temperature because of anthropogenic climate change are hypothesized to affect upwelling-favorable winds and coastal upwelling is expected to intensify across all Eastern Boundary Upwelling Systems. To better understand how upwelling may change in the future, it is necessary to develop a more rigorous method of quantifying this phenomenon. In this paper, we use SST data and wind data in a novel method of detecting upwelling signals and quantifying metrics of upwelling intensity, duration, and frequency at four sites within the Benguela Upwelling System. We found that indicators of upwelling are uniformly detected across five SST products for each of the four sites and that the duration of those signals is longer in SST products with higher spatial resolutions. Moreover, the high-resolution SST products are significantly more likely to display upwelling signals at 25 km away from the coast when signals were also detected at the coast. Our findings promote the viability of using SST and wind time series data to detect upwelling signals within coastal upwelling systems. We highlight the importance of high-resolution data products to improve the reliability of such estimates. This study represents an important step towards the development of an objective method for describing the behavior of coastal upwelling systems.

A changing global climate places shallow water ecosystems at more risk than those in the open ocean as their temperatures may change more rapidly and dramatically. To this end, it is necessary to identify the occurrence of extreme ocean temperature events – marine heatwaves (MHWs) and marine cold-spells (MCSs) – in the nearshore ( 1 4 ° NOAA Optimally Interpolated sea surface temperatures. Regional drivers due to nearshore influences (local-scale) and the forcing of two offshore ocean currents (broad-scale) on MHWs and MCSs were taken into account when the events detected in these two datasets were used to infer the links between offshore and nearshore temperatures in time and space. We show that MHWs and MCSs occur at least once a year on average but that proportions of co-occurrence of events between the broad- and local scales are low (0.20–0.50), with MHWs having greater proportions of co-occurrence than MCSs. The low rates of co-occurrence between the nearshore and offshore datasets show that drivers other than mesoscale ocean temperatures play a role in the occurrence of at least half of nearshore events. Significant differences in the duration and intensity of events between different coastal sections may be attributed to the effects of the interaction of oceanographic processes offshore, as well as with local features of the coast. The decadal trends in the occurrence of MHWs and MCSs in the offshore dataset show that generally MHWs are increasing there while MCSs are decreasing. This study represents an important first step in the analysis of the dynamics of events in nearshore environments, and their relationship with broad-scale influences.

One of the paradigms underlying sandy beach ecology is the overriding control by physical processes; thus, biological interactions (i.e. food availability, competition and predation) are believed to play a role structuring macrofaunal communities only in benign habitats such as dissipative beaches. Moreover, sandy beaches are characterized by low in-situ productivity, so their food webs rely heavily on marine inputs. Studies have shown that estuarine organic matter plays a key role in influencing the dynamics of marine ecosystems. However, very few studies have tested the role of estuarine input on sandy beaches. Here, we aim to determine the impact of estuarine input on the food web of a sandy beach macrobenthic community. To this end, particulate organic matter (POM) samples from the marine environment and the estuary, as well as macrobenthic samples from the beach, were analysed for their stable isotope (SI) signature. Our results indicated that the POM SI signatures were not different along the beach, but differences were recorded between marine and estuarine sources. Bayesian mixing models indicated that the organisms did not make use of the estuarine POM at the beginning of the wet season, but relied more heavily on this resource towards the end of the wet season. This leads to the conclusion that changes in estuarine flow throughout the wet season can impact the trophic structure of macrobenthos communities, confirming a link between lotic and marine communities. Moreover, SI signatures suggest that the species collected here exhibit overlapping trophic niches, indicating high level of inter-specific competition. This highlights that species in low-productivity areas, such as the one studied here, can experience high levels of competition even in physically controlled environments such as sandy beaches.

In South Africa, 129 in situ temperature time series of up to 43 years are used for investigations of the thermal characteristics of coastal seawater. They are collected with handheld thermometers or underwater temperature recorders (UTRs) and are recorded at precisions from 0.5° to 0.001°C. Using the natural range of seasonal signals and variability for 84 of these time series, their length, decadal trend, and data precision were systematically varied before fitting generalized least squares (GLS) models to study the effect these variables have on trend detection. The variables that contributed most to accurate trend detection, in decreasing order, were time series length, decadal trend, variance, percentage of missing data (% NA), and measurement precision. Time series greater than 30 years in length are preferred and although larger decadal trends are modeled more accurately, modeled significance (p value) is largely affected by the variance present. The risk of committing both type-1 and type-2 errors increases when ≥5% NA is present. There is no appreciable effect on model accuracy between measurement precision of 0.1°–0.001°C. Measurement precisions of 0.5°C require longer time series to give equally accurate model results. The implication is that the thermometer time series in this dataset, and others around the world, must be at least two years longer than their UTR counterparts to be useful for decadal-scale climate change studies. Furthermore, adding older lower-precision UTR data to newer higher-precision UTR data within the same time series will increase their usefulness for this purpose.

Salt marshes are highly productive and biologically diverse coastal wetlands that are threatened by rising sea-level. Salt marsh habitats within the Swartkops Estuary were examined to determine their structure along an elevation gradient and how this structure has changed over the past seven decades, what the primary drivers of this structure were and whether the salt marsh surface is stable, rising or declining relative to current and future sea-level rise. Relative sea-level has been rising by 1.82 mm·year − 1 over the past 36 years, with a short-term trend of 7.48 mm·year − 1 measured during the study period. GIS analyses showed that during the last 70 years, losses of floodplain, intertidal and supratidal salt marsh are mainly attributed to developmental pressure. The main environmental drivers influencing salt marsh distribution were soil moisture and elevation. Elevation dictates tidal inundation periodicity and frequency, and thus acts to influence all edaphic factors influencing vegetation distribution. Rod Surface Elevation Table results for the past six years indicate that the salt marsh surface elevation is keeping pace (2.98 ± 2.34 mm·year − 1 ) with historic relative sea-level rise (RSLR), but at an accelerated RSLR, only two of the eight RSET stations show an elevation rate surplus. These results should be interpreted with caution though because of the short time-series (RSET and RSL) and the high likelihood that the current ratio of sediment elevation change will be accelerated in response to the increased sea-level rise.

Kelp forests are believed to host a large biomass of epiphytic fauna and flora, including diatoms, which constitute the base of aquatic food webs and play an important role in the transfer of energy to higher trophic levels. Epiphytic diatom assemblages associated with two common species of South African kelps, Ecklonia maxima and Laminaria pallida, were investigated in this study. Primary blades of adult and juvenile thalli of both kelp species were sampled at False Bay in July 2017 and analysed using scanning electron microscopy. Our findings showed that both kelp species hosted relatively low densities of diatoms (ranging from 7 [SD 5] cells mm–2 on adult specimens of L. pallida to 43 [SD 66] cells mm–2 on blades of juvenile E. maxima), with Amphora and Gomphoseptatum reaching the highest absolute abundances. Although non-metric multidimensional scaling showed overlapping and largely scattered sample sets, a significant relationship between the diatom communities and the species and age of the host macroalga was detected by two-way PERMANOVA. In general, more abundant and diverse diatom communities were observed on juvenile thalli than on adult thalli, with species belonging to Navicula and Rhoicosphenia contributing significantly to the observed dissimilarity. Due to a significant interaction between species and age effects, however, the overall ability of kelp species, their age, and their interaction to explain the variation in diatom community structure was limited. We suggest that the low densities of epiphytic diatoms were directly related to the sloughing of epithelial cells observed in both kelp species. We further speculate that on such unstable substrata some diatom taxa might adapt to an endophytic life to avoid the antifouling mechanisms developed by their hosts.Keywords: Bacillariophyceae, diatom abundance, endophytic diatoms, epiphytes, False Bay, macroalgae, Phaeophyceae, seaweeds

The Thukela Bank, KwaZulu-Natal, supports a diverse ecosystem and South Africa’s only prawn fishery. Oceanographic studies suggest riverine input is not important for the biology of this system, whereas biological studies suggest the contrary, with prawn catches increasing with increased fluvial run-off. The aim of this study was to determine (i) the importance of riverine and marine organic matter for the Thukela Bank food web; and (ii) whether there are seasonal changes in the Thukela River stable isotope values, and, if so, whether these are reflected in the isotope values of demersal organisms. Estuarine organic matter, sediments and demersal organisms were collected from several sites across the bank in the wet and dry seasons of 2008, 2009 and 2010. Marine particulate organic matter was also collected in 2010 and analysed for δ13C and δ15N, as well as C/N ratios. There were strong seasonal changes in isotopic values of organic matter and fauna, especially faunal δ13C. There was an apparent time-lag in organisms assimilating riverine organic matter isotopic values, with the isotopic signature of demersal organisms reflecting that of riverine organic matter from the previous season, which is likely the result of tissue turnover time. In 2010, Thukela Bank sediment organic matter was of riverine origin and this maintained the demersal food web. We conclude that Thukela River organic matter is an important input to the food web of the Thukela Bank, indicating that any future damming of the catchment area could have serious consequences for this ecosystem.Keywords: demersal fauna, organic matter, riverine input, seasonality, stable isotopes, Thukela Bank, total suspended solids

Coastal urban environments have high plastic pollution levels, and hence interactions between plastic debris and marine life are frequent. We report on plastic ingestion by mullet Mugil cephalus in Durban Harbour, KwaZulu-Natal, South Africa. Of 70 mullet (13.0–19.5 cm total length), 73% had plastic particles in their guts, with a mean of 3.8 particles per fish (SD 4.7). Plastic ingestion showed no relation to digestive tract content or fish length. White and clear plastic fibres were ingested most commonly. This urban population of M. cephalus had a higher incidence of plastic ingestion than has been reported in studies on fish from other coastal areas or the oceanic environment.

Monitoring plastic concentrations in estuaries is vital in assessing the magnitude of terrestrial inputs to oceanic environments. Data on plastics ≤ 5 mm in estuaries are scant. This study determined microplastic levels within five estuaries along the Durban coastline and on intervening beaches. Plastics were isolated from estuarine sediment, beach sediment and the surface water of each estuary and characterised. Sediment at the Bayhead area of Durban harbour had the highest average plastic concentrations (745.4 ± 129.7 particles per 500 ml) and an attenuating concentration trend away from the city centre was found. Prevailing south to north longshore drift was hypothesised to result in plastic accumulation on the northern shores of beaches with estuarine effluents, however, this was not found. Fragments composed the largest percent of plastics (59%) found in Bayhead, whereas fibres dominated other estuaries with proportions ranging from 38% of total plastics in the uMgeni estuary to 66% in the Mdloti.

The knowledge on the composition and spatial distribution of marine benthic diatoms around the coast of South Africa remains limited. Epilithic diatom assemblages from natural intertidal rocky substrate and physico-chemical variables were investigated during July–August in 2016 and 2017 along the South African coastline. A total of 85 diatom taxa from 31 genera were observed at 15 sites along the coast. Taxa with the highest contribution included Nitzschia (9 species), Cocconeis (7 species) and Achnanthes (6 species) and the observed Shannon–Wiener diversity (H’) during the study varied from 0.44 (Kraalbaai) to 2.09 (Bird Island). Non-metric multidimensional scaling ordination (nMDS) separated the diatom assemblages into three groups with 20% similarity among sites (grouped according to coastal sections) and PERMANOVA analysis revealed a significant difference between the coastal sections. The observed diatom composition was shown to be influenced by both nutrient concentrations along the west coast and temperature along the east coast. This study provides insights on the abundance and distribution patterns of marine littoral diatoms along the coastline and the potential environmental drivers. The observed variations in diatom composition and distribution warrant further investigations if they are to be considered as potential indicator species of change.

SARS-CoV-2 virus infections in humans were first reported in December 2019, the boreal winter. The resulting COVID-19 pandemic was declared by the WHO in March 2020. By July 2020 COVID-19 is present in 213 countries and territories, with over 12 million confirmed cases and over half a million attributed deaths. Knowledge of other viral respiratory diseases suggests that the transmission of SARS-CoV-2 could be modulated by seasonally-varying environmental factors such as temperature and humidity. Many studies on the environmental sensitivity of COVID-19 are appearing online, and some have been published in peer-reviewed journals. Initially, these studies raised the hypothesis that climatic conditions would subdue the viral transmission rate in places entering the boreal summer and that southern hemisphere countries would experience enhanced disease. For the latter, the COVID-19 peak would coincide with the peak of the influenza season, increasing misdiagnosis and placing an additional burden on health systems. In this review, we assess the evidence that environmental drivers are a significant factor in the trajectory of the COVID-19 pandemic, globally and regionally. We critically assessed 42 peer-reviewed and 80 preprint publications that met qualifying criteria. Since the disease has been prevalent for only half a year in the northern, and a quarter of a year in the southern hemisphere, datasets capturing a full seasonal cycle in one locality are not yet available. Analyses based on space-for-time substitutions, i.e. using data from climatically distinct locations as a surrogate for seasonal progression, have been inconclusive. The reported studies present a strong northern bias. Socio-economic conditions peculiar to the ‘Global South’ have been omitted as confounding variables, thereby weakening evidence of environmental signals. We explore why research to date has failed to show convincing evidence for environmental modulation of COVID-19, and discuss directions for future research. We conclude that the evidence thus far suggests a weak modulation effect, currently overwhelmed by the scale and rate of the spread of COVID-19. Seasonally-modulated transmission, if it exists, will be more evident in 2021 and subsequent years.

As the mean temperatures of the worlds oceans increase, it is predicted that marine heatwaves (MHWs) will occur more frequently and with increased severity. However, it has been shown that variables other than increases in sea water temperature have been responsible for MHWs. To better understand these mechanisms driving MHWs we have utilized atmospheric (ERA-Interim) and oceanic (OISST, AVISO) data to examine the patterns around southern Africa during coastal (

Historical and recent evidence is documented to demonstrate that the eastern limit of the major kelp-bed forming seaweed Ecklonia maxima has moved c. 73 km eastward along the south coast of South Africa since 2006, after remaining unchanged for almost 70 years. A significant population has established at Koppie Alleen, De Hoop Nature Reserve, which has been monitored from 2008 to 2011. It is hypothesised that the eastward spread is limited by aspects of the inshore water temperature regime, and recent evidence suggests that gradual cooling along this coast may have caused the change in distribution. It seems likely that if a cooling trend continues along the South African south coast, kelp beds and their associated species will move farther eastward in future decades, affecting the ecology and livelihoods along this coast.

The seaweed flora of Angola is relatively poorly known. Most of the 124 records listed for the country come from a 1974 British Natural History Museum expedition to the central and southern parts of that country. Previous biogeographic studies treated the Angolan seaweed flora as a whole and grouped it with those of certain West African islands as transitional between a Tropical West African seaweed flora (essentially extending from Senegal to Gabon) and temperate floras to the north and south of this truly tropical region. In the present study a total of 99 species and subspecies of seaweeds was collected from the intertidal zone and shallow sublittoral zones at five sites in the north of Angola and four sites in the south. The biogeographic distributions of our records were examined and compared with the temperate flora of Namibia to the south and the flora of Ghana to the north (as an example of a well-studied Tropical West African flora). Multivariate analyses of our presence/absence records showed differences between northern and southern sites (cluster analysis [Jaccard, average linkage] and detrended correspondence analysis). All Angolan sites were clearly different from floras of south, central and northern Namibia, which are considered to be strictly temperate in nature. Northern Angolan sites grouped more closely with Ghana than with southern Angolan sites. Distribution patterns within Angola are discussed in relation to monthly sea surface temperature data that were processed for this region. We conclude that the overall affinities of the Angolan seaweed flora, as represented by our collections, are Tropical West African, but with a well-developed temperate element in southern Angola (from about 13° S) comprising mainly cooler-water species from the Benguela Marine Province of Namibia and western South Africa. Our collections add about 45 species to the Angolan seaweed flora, raising the total number of species to around 169. This total approaches that of Ghana which, with about 200 species, is considered to have the richest seaweed flora in Tropical West Africa.Keywords: Benguela Marine Province, biogeography, Ghana, Gulf of Guinea Marine Province, Namibia, seaweed diversity, West AfricaAfrican Journal of Marine Science 2012, 34(1): 1–13

The propagation and growth of scleractinian corals under aquaculture conditions could reduce the pressure of extractive fishing for ornamental species. To fulfil their growth requirements, corals rely on a combination of photosynthetic products translocated from symbiotic zooxanthellae, and particulate heterotrophic sources. In aquaculture, the latter is provided by Artemia sp. nauplii as they provide adequate nutrition and promote optimal growth and survival. In this study, we evaluated feeding rates and estimated growth rates of cultured scleractinian corals. Polyp and colonial nubbins of the coral Galaxea fascicularis were randomly assigned to each of three tanks within three naturally lit systems under standard conditions. Corals were subjected to three feeding treatments: i) fed once or ii) three times weekly, or iii) unfed until the end of the trial (two months). The survival rates were 98.7% and 100% for the colonial and polyp forms, respectively. Ingestion rates of Artemia salina nauplii between the three feeding treatments were significantly higher for specimens fed 3-times a week compared to those two treatments involving a lower feeding frequency (individual prey items polyp − 1 20 min − 1 : 8 vs. ≤ 4, respectively), but growth rates of colonial and polyp forms were not significantly different with respect to feeding frequency. Mean rate of new polyp growth was ca . 4 polyps nubbin − 1 week − 1 for colonial form and ca . 1 polyp polyp − 1 week − 1 for the polyp form. The high survival and growth rates of G . fascicularis , coupled with an apparent low heterotrophic prey requirement, make this species an ideal candidate for commercial propagation in aquaculture.

The IPCC AR5 provided an overview of the likely effects of climate change on Eastern Boundary Upwelling Systems (EBUS), stimulating increased interest in research examining the issue. We use these recent studies to develop a new synthesis describing climate change impacts on EBUS. We find that model and observational data suggest coastal upwelling-favorable winds in poleward portions of EBUS have intensified and will continue to do so in the future. Although evidence is weak in data that are presently available, future projections show that this pattern might be driven by changes in the positioning of the oceanic high-pressure systems rather than by deepening of the continental low-pressure systems, as previously proposed. There is low confidence regarding the future effects of climate change on coastal temperatures and biogeochemistry due to uncertainty in the countervailing responses to increasing upwelling and coastal warming, the latter of which could increase thermal stratification and render upwelling less effective in lifting nutrient-rich deep waters into the photic zone. Although predictions of ecosystem responses are uncertain, EBUS experience considerable natural variability and may be inherently resilient. However, multi-trophic level, end-to-end (i.e., winds to whales) studies are needed to resolve the resilience of EBUS to climate change, especially their response to long-term trends or extremes that exceed pre-industrial ranges.

Stable isotopes are an increasingly important tool in trophic linkage ecological studies. In studies of large marine animals, isotopic sampling is often given secondary priority to sampling for diversity and biomass aspects. Consequently, isotopic samples are frequently collected subsequent to repeated freezing and thawing of animals, and the results of these studies are often based on the assumption that this pre-treatment does not affect the isotopic values. Our study tested this assumption and examined the difference between oven- and freeze-drying on isotopic values and elemental carbon-to-nitrogen (C:N) ratios. The values for δ(15)N and δ(13)C, percentage nitrogen and carbon, and the C:N ratios were determined from the tissues of six marine species, including invertebrates and fish, as (1) fresh samples, (2) samples thawed once, and (3) samples thawed twice. The drying method, thawing treatment and their interaction did significantly affect the δ(15)N and δ(13)C isotope values for all species. Oven-dried samples had slightly higher δ(13)C and δ(15)N values than freeze-dried samples, although not significant in most instances. For most species, oven-drying produced lower carbon and nitrogen percentage than freeze-drying for samples that had been thawed once, but the C:N ratio was unaffected by the drying method. Repeated freezing and thawing did not affect the isotope values, but it did decrease the percentage carbon and nitrogen for both desiccation methods. We recommend drying samples from fresh wherever possible, and careful choice of desiccation method in light of the fact that most lipid models are based on oven-dried samples and oven-drying could cause enrichment of (15)N or (13)C through evaporation of volatile compounds richer in lighter isotopes such as some lipids. Finally, we recommend that further studies on the specific effects of freezing and desiccation on elasmobranchs is needed. Overall we recommend the use of freeze-drying when possible and to use the samples from freshly caught organisms.

The St. Lucia Estuary is Africa’s largest estuarine system and is currently experiencing the stress of prolonged freshwater deprivation, manifested by extremely low water levels and hypersalinity. These unprecedented conditions have raised questions regarding the trophic functioning of the ecosystem. Despite the substantial amount of research previously undertaken within this system, no studies of food web structure and function have yet been documented. This study therefore aimed to examine the food web structure of the St. Lucia estuary system through the use of carbon and nitrogen stable isotope analysis. Analysis of carbon isotope ratios indicates that benthic carbon sources are most utilised at sites with low water levels and generally higher salinity (Catalina Bay, Charter’s Creek). Conversely, the estuarine region of the mouth and Narrows, with its elevated water levels and lower salinity, still sustains a viable pelagic food web. Analysis of δ15N ratios indicates that the number of trophic transfers (food chain length) might be related to water levels. Overall, the study provides a greater understanding of the ecological processes of this complex estuarine lake, which may allow for future comparisons of trophic functioning under drought and normal/wet conditions to be made.

Sensory quality often determines the market value of seafood and may be affected by the feeding regime during the product’s grow-out phase, processing, the release of volatile compounds or various cultural expectations. Here, we related the abalone diet during the grow-out phase to the sensory quality of the product as a function of abalone diet and the tasters’ preference. A quantitative descriptive analysis of the flavour and texture of abalone raised on Ulva sp., kelp, a mixed diet of various macroalgae, and a formulated compound feed, as well as of wild-collected abalone, was undertaken. Raw and cooked samples of abalone meat from each of four feed categories (Ulva spp., kelp, manufactured pellets and mixed diets) and of wild-caught abalone were offered to a taste panel (comprising abalone farmers, abalone buyers and local consumers) which was asked to score each sample for 20 sensory attributes; the sensory attributes responsible for differentiating between the samples were then identified. Complex interactions among the sensory variables were identified as important drivers of the ability of panellists to distinguish between samples. For the raw samples, visual characteristics were particularly important. Conversely, taste became generally more important in the cooked samples. The experience of the tasters (e.g. producers, local consumers or buyers) also influenced how the panellists perceived the sensory quality, with the abalone buyers having a more discerning palate.

Macroalgae, some of which produce dimethylsulfoniopropionate (DMSP), are important feeds for aquacultured abalone Haliotis midae Linnaeus. DMSP levels were high in Ulva lactuca Linnaeus (up to 6977 ± 1161 μg g− 1, mean ± 1 SD) but low in Gracilaria gracilis (Stackhouse) Steentoft et Farnham and the kelp Ecklonia maxima (Osbeck) Papenfuss (0.8 ± 0.3 to 26.8 ± 20.6 μg g− 1), and increased in abalone tissue after feeding on these algae. A volatile breakdown product of DMSP, dimethylsulfide (DMS), was formed in abalone during canning, causing repellent tastes and odours in some batches of canned meat. Abalone adductor muscle displayed high DMSP concentrations compared to other tissues. Further, the feeding regime determined the level to which DMSP accumulated: abalone previously fed Ulva accumulated DMSP to 16162 ± 3408 μg g− 1. This was higher than in wild-collected abalone (471 ±339 μg g− 1) or those fed with manufactured feeds (up to 46.2 ± 9.6 μg g− 1) or Ecklonia (198 ± 73 μg g− 1). A depuration phase prior to processing allowed for the reduction of tissue DMSP levels to those seen in wild abalone. Knowing the DMSP levels in feeds and its behaviour in abalone tissue will lead to the development of new strategies for controlling abalone taste characteristics.

Ecklonia maxima is an economically important kelp in South Africa. The harvested kelp is used mainly as feed for cultured Haliotis midae (abalone) on farms all along the South African South and West Coast. The effects that different harvesting methods have on the growth of sub-canopy kelps, kelp population structure and kelp recruitment were tested in a kelp bed at Bordjies Rif near Cape Town. Two 30 × 10 m sites were set up, about 100m apart, in near monoculture stands of E. maxima. Each 30 × 10m area was subdivided into three treatments. In treatment 1 (T1) the whole ‘head’ of each kelp sporophyte that reached the surface was cut off between the bulb and the primary blade (‘lethal’ method). In treatment 2 (T2) (‘non-lethal’ method), the secondary fronds of all sporophytes that reached the surface were cut 20–30 cm from their junction with the primary blade, and removed. In the control plot, the kelp plants were not treated. Harvesting treatments were done approximately every four months, at low spring tide, from 3 March 2003 to 3 November 2003 (three treatments). The effects of harvesting on the kelps depend largely on the size of plant and the time the fronds were removed; however, no seasonal pattern could be observed. The different treatments had no effect on the growth rate, population structure or recruitment of the kelp. This means that factors other than light play an important role in the growth, structure and recruitment of the kelp beds in False Bay. Results are discussed in relation to current commercial harvesting practices.

Potential food sources and dominant invertebrates and fishes were collected for the examination of variability in 13 C/ 12 C and 15 N/ 14 N to determine the sources of carbon available to consumers within a Western Australian Posidonia sinuosa -dominated seagrass bed. Autotrophs showed a wide distribution of δ 13 C values, with P. sinuosa at −11.3 ± 0.8‰ and macroalgae ranging from −16.6 to −31.7‰. This variation allowed us to successfully identify macroalgae as the main contributor of carbon to the trophic structure, although no distinction could be made between epiphytic macroalgae on seagrass, or allochthonous macroalgal sources. The range in δ 15 N ratios among potential food items at the trophic base was too small to make it useful as tracer of nitrogen flow pathways, but it consistently increased from macrophytes and detritus (4.1–6.8‰), to invertebrates (5.7–7.4‰) located near the middle of the food web, to fishes (8.3–11.9‰), with piscivorous species such as Leviprora inops generally having a higher 15 N. δ 13 C of seston (−12.8‰) and sedimentary organic matter (−8.7‰) indicate that seagrass material is the main contributor to these two carbon pools, and that very little of it contributes to animal biomass.

Three species of sea urchin regularly co-occur in high abundances on subtidal rocky reefs in south-western Australia. We used two lines of evidence (stable isotope analysis and gut contents analysis), to test whether these species occupy different trophic positions. We looked at five discrete populations to test whether patterns were consistent. The gut contents of Heliocidaris erythrogramma contained almost exclusively fragments of macroalgae, and the δ 15 N of muscle was consistent with that expected for a herbivore. In contrast, the gut contents of Phyllacanthus irregularis and Centrostephanus tenuispinus contained a greater proportion of animal tissue, and the δ 15 N of muscle suggested that animal tissue was an important source of nutrition. Of the three co-occurring sea urchin species, one ( H. erythrogramma ) was ecologically dissimilar to the others and occupied a lower trophic position. This pattern was consistent among populations separated by up to 270 km in south-western Australia. Food resource partitioning might be one way in which these species are able to coexist.

In the last three decades the discovery of metabolites with biological activities from macroalgae has increased significantly. However, despite the intense research effort by academic and corporate institutions, very few products with real potential have been identified or developed. Based on Silverplatter MEDLINE and Aquatic Biology, Aquaculture & Fisheries Resources databases, the literature was searched for natural products from marine macroalgae in the Rhodophyta, Phaeophyta and Chlorophyta with biological and pharmacological activity. Substances that currently receive most attention from pharmaceutical companies for use in drug development, or from researchers in the field of medicine-related research include: sulphated polysaccharides as antiviral substances, halogenated furanones from Delisea pulchra as antifouling compounds, and kahalalide F from a species of Bryopsis as a possible treatment of lung cancer, tumours and AIDS. Other substances such as macroalgal lectins, fucoidans, kainoids and aplysiatoxins are routinely used in biomedical research and a multitude of other substances have known biological activities. The potential pharmaceutical, medicinal and research applications of these compounds are discussed.

Toxic algal blooms are common world-wide and pose a serious problem to the aquaculture and fishing industries. Dinoflagellate species such as Karenia brevis, Karenia mikimotoi, Heterosigma akashiwo and Chatonella cf. antiqua are recognised toxic species implicated in various faunal mortalities. Toxic blooms of Karenia cristata were observed on the south coast of South Africa for the first time in 1988 and were responsible for mortalities of wild and farmed abalone. K. cristata and various other dinoflagellate species common along the South African coast, as well as K. mikimotoi (Isolation site: Norway, Univ. of Copenhagen) and K. brevis (Isolation site: Florida, BIGELOW), were tested for toxicity by means of a bioassay involving Artemia larvae as well as abalone larvae and spat. K. cristata, like K. brevis, contains an aerosol toxin; however, the toxin present in K. cristata has not yet been isolated and remains unknown. K. brevis was, therefore, used to determine which developmental phase of the bloom would affect abalone farms most, and whether ozone could be used as an effective mitigating agent. Of the 17 dinoflagellate species tested, K. cristata, Akashiwo sanguinea, K. mikimotoi and K. brevis pose the greatest threat to the abalone mariculture industry. K. brevis was most toxic during its exponential and stationary phases. Results suggest that ozone is an effective mitigation agent but its economic viability for use on abalone farms must still be investigated.

The feeding activity of macroalgal grazers such as amphipods and isopods may be responsible for decreased productivity of cultivated macroalgae. This could have potentially disastrous consequences to the well-being of the seaweed cultures, especially in land-based aquaculture systems where the natural predators of the herbivores are absent. Generally, losses due to herbivores grazing on seaweed cultures are small or even beneficial due to their preference for epiphytes on the main seaweed species, but it can be significant when the number of grazers is high. A large population of the herbivorous isopod Paridotea reticulata (approximately 616±116 isopods per 100 g dry seaweed), became established in outdoor Gracilaria gracilis tanks at a commercial abalone farm on the south coast of South Africa. It was found that a freshwater treatment could eliminate the isopods: when G. gracilis cultures containing isopods were placed in freshwater for 3 h, the isopods were killed with no lasting or significant damage to the seaweed resource.

We examined whether δ 15 N levels of marine biota with different nutrient uptake character- istics can be used to trace the dispersal of sewage effluent in highly mixed, nitrogen-limited waters, and whether they can reveal the dispersal of sewage over different timescales. We hypothesised that macro- algal species with fast uptake rates would display a spatial pattern in δ 15 N levels reflecting recent sewage dispersal while those with slower rates would provide a signal integrated over a longer time period. Filter- feeding sponges and ascidians were also sampled to see if they reflected patterns in the dispersal of sewage particulate organic matter (POM). A laboratory experiment was performed to test whether the δ 15 N level of 3 macroalgal species (Ulva australis, Vidalia sp. and Ecklonia radiata) and 2 filter-feeding species (Clathria sp. and Pyura australis) was altered after cultivation in sewage nitrogen. We then sampled each organism along transects radiating away from the outlet of a wastewater treatment plant north of Perth, Western Australia, to determine spatial patterns in δ 15 N. U. australis and Vidalia sp. developed higher iso- topic signatures when exposed to low concentrations of sewage nitrogen (1:500 dilution in seawater) for 7 d in the laboratory. U. australis and Vidalia sp. showed an increase of 1.7 and 1.4‰ in treatments respectively. In the field, macroalgae sampled north and south of the sewage outlet generally had higher δ 15 N levels than those sampled west of the outlet and at the reference site, and algae within 500 m of the outfall tended to have lower values than at 1000 m or more from the outfall. These trends are consistent with our current knowledge of plume dynamics: a predominantly northerly drift of effluent as a buoyant plume that tends not to be fully mixed in the water column for the first 500 m. The results confirmed that the δ 15 N signature of macroalgae could be used to trace sewage disposed in well-mixed waters. The strength of the spatial trends varied between algae, with E. radiata, the species with the lowest nutrient uptake rates and affin- ity, having the least spatial variability. We interpret this as reflecting a wider regional dispersal of sewage in the longer time frame, but a strong northerly drift in the short term, which was reflected in the δ 15 N values of the species with the fastest nitrogen uptake rates. The results were consistent with our hypothesis and are suggestive of a relationship between algal functional form and isotopic signatures that can be applied to determine the dispersal of sewage over different timescales. The δ 15 N values of benthic filter feeders did not provide strong evidence to suggest that they can be used to represent the dispersal of sewage POM, but trends found in the field experiment for Clathria sp. warrant further investigation.

Worldwide, persistent cyanobacterial blooms are becoming more frequent and are often associated with effects of global climate change. In June 2009, a widespread bloom of the unicellular cyanobacterium, Cyanothece sp., appeared in North Lake and False Bay of Lake St Lucia – a large (360 km2) estuarine lake system in KwaZulu-Natal, South Africa – and persisted for 18 months. It remains unclear how the bloom status was maintained for so long. This study investigates aspects of the nutrient uptake dynamics of Cyanothece sp. and how this process may relate to maintaining a persistent bloom state during hypersaline conditions. 15N nutrient uptake experiments were performed to evaluate the effect of the most important environmental variables on the nutrient uptake rate of Cyanothece sp. Highest 15N uptake rates were during salinities of 35 and temperatures of 30 °C for both N sources (43.9 [SE 18.3] and 85.5 [SE 42.9] μg atom N l–1 h–1 for 15NH4+ and 15NO3 − respectively). In contrast, at high salinities of 160 and low temperatures of 10 °C, 15NH4 + and 15NO3− uptake rates were low (3.76 [SE 0.23] and 14.5 [SE 6.40] μg atom N l–1 h–1 respectively). Hence nutrient uptake was significantly influenced by environmental variables, particularly salinity, which suppressed uptake rates, and temperature, which facilitated them. The long-term bloom maintenance appears to be attributed to efficient nutrient uptake rates, absence of grazers during the hypersaline phase, and the ability of Cyanothece sp. to outcompete other microalgae at temperatures >25 °C.Keywords: 15N isotope pairing technique, cyanobacteria, estuarine lake, hypersalinity, iSimangaliso, unicellularAfrican Journal of Marine Science 2014, 36(2): 155–161

The growth of Gracilaria gracilis (Stackhouse) Steentoft, Irvine et Farnham was examined by studying the effect of organismic determinants such as thallus length, position along the thallus and branching. Knowledge of these factors is essential in order to increase production from suspended seaweed rafts seeded with vegetative G. gracilis fragments. Seeding netlons with seaweed material freshly collected from subtidal populations provided up to 30% higher relative growth rates than seaweed maintained on the netlons for successive months. Initial seedstock length greatly affected growth rates and yields such that 30-cm thalli fragments resulted in growth rates 14% higher than for 10-cm fragments. This difference is suggested to be due to the higher contribution to overall biomass by growth of lateral branches. Comparisons of the growth of apical and basal fragments suggest that growth takes place over the entire length of the thallus, but that the apex contributes more to overall elongation than does the proximal part. The removal of apical meristems resulted in an enhanced branching frequency with production of four times as many branches as intact fragments. Evidence is also provided for extensive morphological differentiation following long periods of rapid growth. These thalli have very high frequency of branching, are hollow due to the disintegration of medullary cells and are considered to be completely senescent. These factors have implications for the successful cultivation of G. gracilis on commercial mariculture systems.

Large populations of epiphytic Ceramium diaphanum and the isopod Paridotea reticulata are found in association with commercially farmed Gracilaria gracilis . When given a choice, P. reticulata consumed C. diaphanum rather than G. gracilis . Feeding rate experiments indicate that small isopods could consume 0.060±0.040 mg (dry) C. diaphanum per gram (dry) of isopod per day and that large isopods consumed 0.043±0.007 mg (dry) C. diaphanum per gram (dry) of isopod per day. In contrast, the amount of G. gracilis consumed was negligible. One year's population data indicated that P. reticulata populations increased as C. diaphanum populations increased. However, P. reticulata 's influence on C. diaphanum was only significant when C. diaphanum populations were low. Using the consumption rate of 0.060±0.040 g (dry) C. diaphanum consumed per gram (dry) of isopod per day and biomass values obtained in the field, it was calculated that during some months P. reticulata is capable of consuming 7.8% of the total C. diaphanum population per day.

Gridded SST products developed particularly for offshore regions are increasingly being applied close to the coast for biogeographical applications. The purpose of this paper is to demonstrate the dangers of doing so through a comparison of reprocessed MODIS Terra and Pathfinder v5.2 SSTs, both at 4 km resolution, with instrumental in situ temperatures taken within 400 m from the coast. We report large biases of up to +6°C in places between satellite-derived and in situ climatological temperatures for 87 sites spanning the entire ca . 2 700 km of the South African coastline. Although biases are predominantly warm (i.e. the satellite SSTs being higher), smaller or even cold biases also appear in places, especially along the southern and western coasts of the country. We also demonstrate the presence of gradients in temperature biases along shore-normal transects -- generally SSTs extracted close to the shore demonstrate a smaller bias with respect to the in situ temperatures. Contributing towards the magnitude of the biases are factors such as SST data source, proximity to the shore, the presence/absence of upwelling cells or coastal embayments. Despite the generally large biases, from a biogeographical perspective, species distribution retains a correlative relationship with underlying spatial patterns in SST, but in order to arrive at a causal understanding of the determinants of biogeographical patterns we suggest that in shallow, inshore marine habitats, temperature is best measured directly.

The growth rate ofGracilaria gracilis maintained in tanks at an abalone farm near Port Elizabeth, South Africa, was examined under various tank conditions and NH4-N pulse frequencies and concentrations. This was accompanied by analyses of the components of the internal nitrogen pool. A maximum growth rate of ca. 35% wk−1 was obtained at 1200 μM NH4-N. The alga was able to grow at non-nitrogen limited rates using only internal stored nitrogen to sustain growth for one week before the growth rate decreased to ca. 17% per week. NH4-N pulse frequency did not affect growth rate but one pulse per week led to a marked decrease in total-N, protein, phycoerythrin and chlorophyll-a content. An increase in pulse frequency to two pulses per week doubled the protein content from 2.351 ± 0.143 to 4.453 ± 0.090% (per unit dry mass). Carbohydrate content was inversely related to nitrogen storage. The growth rate in fouled tanks was always lower than in clean tanks. It seems likely that seaweeds and diatoms colonising the tank sides reduced light reflected off the inside of a tank, thereby reducing the growth rate.