Estimation of the annual consumption of food by Cape hake Merluccius capensis and M. paradoxus off the South African west coast

Information on hake stomach contents collected during research cruises off the west coast of South Africa between 1988 and 1990 is analysed. Estimates of the annual consumption and daily ration of the Cape hakes Merluccius capensis and M. paradoxus are obtained. Coefficients of variation (CVs) for these estimates are estimated by a bootstrap variance-estimation procedure. Cape hakes are opportunistic feeders. Juveniles feed mainly on crustaceans and the diet becomes increasingly piscivorous with age. Anchovy were the dominant dietary item of juvenile M. capensis, although this may be a reflection of the fact that anchovy were readily available at the time of the surveys. The large number of anchovy found in the diet during this study highlights the dangers of extrapolating consumption estimates for opportunistic feeders to other time periods. Pooling of data across geographic and seasonal strata introduces substantial bias in estimates of consumption and daily ration for only the pelagic prey species. Estimates of annual consumption are highly sensitive to the cruise selected to provide the estimates of numbers-at-length, because these latter estimates vary substantially between cruises. Furthermore, estimates of annual consumption and daily ration by prey species are very imprecise due to the effects of small sample sizes, the opportunistic nature of and natural variability associated with feeding. This implies that it is unlikely that model-estimation procedures which utilize these data will be able to provide particularly precise predictions. Therefore, before any larger-scale stomach collection exercise is undertaken, it is advisable to perform simulation studies to assess the sampling intensity required to achieve the desired levels of accuracy and precision for predictions from multispecies model-estimation procedures which make use of such data.     

Estimation of size at first maturity in two South African coral species

The corals Acropora austera and Platygyra daedalea have been the subject of extensive reproductive and population genetic studies in the iSimangaliso Wetland Park (iSimangaliso), on the KwaZulu-Natal coast, eastern South Africa. Despite this, estimates of size at first maturity in these two species are lacking. This information could be used to provide a baseline to differentiate juveniles from adult sizes of corals, an important factor for assessing the condition of scleractinian communities in reefs. Here, we present the methods followed to provide such estimates for these two hard corals. Using generalised linear models and assuming knife-edge maturity (50% probability), it was estimated that A. austera from iSimangaliso matures at c. 15 cm mean colony diameter (MCD) (95% CI: 9.25–20.75 cm MCD) and P. daedalea matures at c. 7 cm MCD (95% CI: 4.55–8.39 cm MCD). These estimates were comparable to those for tropical species which is remarkable considering the high-latitude nature of the sampled reefs. It is expected that the findings from this study will assist in the assessment of reproduction, recruitment, survival and genetic variation in clonal organisms such as corals, and will provide a baseline to assess the effects of climate change on coral communities in the region.     

Trends and interventions in large whale entanglement along the South African coast

The major causes of large whale entanglement in South Africa are static fishing gear, especially the type associated with the West Coast rock lobster Jasus lalandii industry, and large-mesh gillnets that are set off the coast of KwaZulu-Natal (KZN) to reduce shark attacks (shark nets). The prevalence of entanglements is seasonal with the peaks in activity coinciding with the breeding migrations of humpback whales Megaptera novaeangliae and southern right whales Eubalaena australis, the two large whale species that are the most prone to entanglement. Generalised linear models with a Poisson or quasi-Poisson distribution were used to describe the relationship between the number of incidents and time. Taking into account the combined length of shark-net installations per year as an offset variable, entanglement of humpback whales in shark nets increased at 15.1% per year (95% CI = 9.5–21.6%) from 1990 to 2009. This is comparable to the rate of increase in the numbers of this species migrating past the KZN coast, between 1988 and 2002 (9–11%). The number of reported incidents of southern right whales entangled in gear other than shark nets also increased between 1990 and 2009. This was accounted for by the increase in numbers of this species in South Africa (7% per year), so in neither case are the two species at increasing risk of individual entanglement, and anthropogenic factors including entanglement do not seem to be affecting the recovery of these whale populations. Nevertheless, there is concern regarding the vulnerability to entanglement of a small assemblage of humpback whales that habitually visits the West Coast in spring and summer. The continued recovery of whale populations is likely to lead to greater levels of anthropogenic interaction and heighten the need for adequate mitigation measures. The KZN Sharks Board and the South African Whale Disentanglement Network (since 2006) have respectively released (disentangled) 81% and 23% of confirmed entangled individuals, and recorded relevant information on entanglement incidents. Such information is critical for developing mitigation measures and monitoring the prevalence of entanglement.     

The importance of cephalopods as prey for hake and other groundfish in South African waters

Literature on trophic relationships in the Benguela ecosystem has stressed the importance of cephalopods as prey of groundfish. The groundfish community of the shelf and upper slope of southern Africa is dominated by the Cape hakes, and the results presented (1984–1991) confirm that both species of hake are important predators of cephalopods, especially taking into consideration the abundance of hake in the ecosystem. However, geographic, seasonal and species variability are evident in the patterns observed. The main prey species are Sepia spp. (predominantly Sepia australis), Loligo vulgaris reynaudii, Todaropsis eblanae and Lycoteuthis ?diadema. The last-named is an important food organism for fish. Its systematic status needs revision, however. Qualitative results of studies of cephalopod predation are also provided for kingklip and monkfish.     

Age and growth of redeye round herring Etrumeus whiteheadi off the South African coast

Ages of redeye round herring Etrumeus whiteheadi were estimated with associated errors and used to infer life-history information, such as age composition, age-at-maturity and instantaneous mortality rate. Samples were collected in November 2005 during a research survey aimed at estimating the biomass of spawning pelagic fish off South Africa’s west and south coasts. Replicate age estimates obtained from sagittal otoliths were collected with slight bias and relatively high precision. A von Bertalanffy model describing growth of the combined sexes, including juveniles, was L_t = 20.41(1 ? e^{?0.41(t ? 1.92)}). Kimura’s likelihood ratio test revealed no statistically significant differences between growth parameters of males and females. Results suggested that otolith length is a better predictor of age than otolith weight. Maturity estimates for E. whiteheadi were similar to those previously documented.     

渤海湾西岸牡蛎壳体形态、生长速率与生长环境的关系

牡蛎壳体的尺寸、生长年龄和生长速率是其生命历史中一些最基本的生态信息,与礁体综合生长环境有关;通过对礁体中的壳体形态和壳体生长速率的对比研究,可以恢复礁体生长时期的综合环境。通过对取自黄港水库、大吴庄和岭头三个埋藏牡蛎礁体中保存完好的牡蛎壳体的形态统计分析,并对其中部分适合贝壳年轮研究的壳体进行生长年龄和死亡季节的分析研究;恢复了壳体记录的礁体生长环境,并探讨礁体生长环境对壳体形态的影响和塑造。结果表明,黄港水库礁体中的壳体具有最快的壳高生长速率和最短的生长寿命,礁体生长在距离河口较近的位置,礁体生长环境较动荡;大吴庄礁体中的壳体具有宽大肥厚的壳体外形和最快的壳重增长速率,礁体生长在潮间带或浅海区等稍远离河口的位置,生长环境相对稳定;岭头礁体中的壳体细窄扁平,壳重和壳高生长速率均最慢,礁体生长在如海湾或潟湖等相对封闭的环境中。     

Interactive effects of pH and temperature on native and alien mussels from the west coast of South Africa

Global warming and ocean acidification influence marine calcifying organisms, particularly those with external shells. Among these, mussels may compensate for environmental changes by phenotypic plasticity, but this may entail trade-offs between shell deposition, growth and reproduction. We assessed main and interactive effects of pH and temperature on four mussel species on the west coast of South Africa (33°48′ S, 18°27′ E) in October 2012 by comparing shell dissolution, shell growth, shell breaking force and condition index of two native species, the ribbed mussel Aulacomya atra and the black mussel Choromytilus meridionalis, and two aliens, the Mediterranean mussel Mytilus galloprovincialis and the bisexual mussel Semimytilus algosus. Live mussels and dead shells were exposed for 42 days to seawater of pH 7.5 or 8.0, at 14 °C or 20 °C. Low pH, high temperature and their combination increased shell dissolution of the two aliens but their growth rates and condition indices remained unchanged. Aulacomya atra also experienced greater shell dissolution at a low pH and high temperature, but grew faster in low-pH treatments. For C. meridionalis, shell dissolution was unaffected by pH or temperature; it also grew faster in low-pH treatments, but had a lower condition index in the higher temperature treatment. Shell strength was not determined by thickness alone. In most respects, all four species proved to be robust to short-term reduction of pH and elevation of temperature, but the native species compensated for greater shell dissolution at low pH by increasing growth rate, whereas the aliens did not, so their invasive success cannot be ascribed to benefits accruing from climate change.     

海洋动物营养生态位研究方法及其应用

食物资源对海洋动物的生存和繁衍至关重要。海洋动物的营养生态位描述了其在海洋生态系统中的生态地位及功能, 对分析种间关系和资源分配模式、了解群落结构与功能具有重要的指示作用。本文在整理近30年来国内外相关研究的基础上, 系统归纳了当前海洋动物营养生态位研究的主要方法(胃含物分析、整体组织稳定同位素分析、脂肪酸组成分析和特定化合物稳定同位素分析)及其应用领域, 着重归纳总结了量化营养生态位宽度和重叠的生态模型, 并分析了各营养生态位评估方法的优势和局限性。同时在此基础上, 对今后研究方向提出了展望, 以期为我国海洋动物摄食生态学相关研究工作提供参考。     

Genetic diversity and population connectivity of the sea urchin Tripneustes gratilla along the South African coast

The collector sea urchin Tripneustes gratilla has been identified as a species with potential for aquaculture production in South Africa. The species’ roe is considered a culinary delicacy in Asia and Europe. However, T. gratilla remains genetically uncharacterised in South Africa. Therefore, the purpose of this study was to provide baseline genetic information consisting of estimates of genetic diversity and population stratification, which may aid in future sustainable use of this urchin resource. A total of 22 species-specific microsatellite markers were used for the genetic characterisation of T. gratilla samples from along the South African coast, at Haga Haga, Coffee Bay, Hibberdene, Ballito Bay and Sodwana Bay. A moderate level of genetic diversity was observed, with an average number of alleles of 7.89 and an average effective number of alleles of 6.57, as well as an average observed heterozygosity of 0.55. Population differentiation tests suggest that the geographically representative samples form part of a single, large interbreeding population, with a global F_st estimate of 0.02 (p > 0.05). This finding is likely explained by high levels of gene flow between these locations caused by extensive larval dispersal during the planktonic larval stage. The panmixia observed within these natural populations of T. gratilla indicate that they could be managed as a single genetic stock.     

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.     

Fluxes of organic carbon in a fjord on the west coast of Ireland

The supply of particulate organic carbon (POC) via freshwater influx, and its exchange with the open sea, were estimated for a fjord-like coastal inlet (Killary Harbour, Ireland) during 1981. Biological production and destruction of organic matter within the inlet were also studied. POC levels in rivers feeding the system were correlated with rainfall. C : N ratios suggested an increased proportion of POC of terrestrial origin at stations influenced by freshwater inflow, and throughout the fjord in the non-productive season.A tentative annual carbon budget is presented.     

Valuing the health benefits of physical activities in the marine environment and their importance for marine spatial planning

The marine environment provides a number of services which contribute to human well-being including the provision of food, regulation of climate and the provision of settings for cultural gains. To ensure these services continue to be provided, effective management is required and is being strategically implemented through the development of marine spatial plans. These plans require an understanding of the costs and benefits associated with alternative marine uses and how they contribute to human well-being. One benefit which is often difficult to quantify is the health benefit of engaging with the marine environment. To address this, the research develops an approach which can estimate the contribution aquatic physical activities makes to quality adjusted life years (QALYs) in monetary and non-monetary terms. Using data from the Health Survey for England, the research estimates that physical activities undertaken in aquatic environments at a national level provides a total gain of 24,853 QALYs. A conservative estimate of the monetary value of a QALY gain of this magnitude is £176 million. This approach provides estimates of health benefits which can be used in more comprehensive impact assessments, such as cost-benefit analysis, to compare alternative marine spatial plans. The paper concludes by discussing future steps.     

基于稳定同位素技术的象山港海洋牧场区食物网基础与营养级的研究

本研究对2011年春季和秋季在象山港海洋牧场采集的生物消费者及其食物源样品的碳、氮稳定同位素组成进行了分析,通过IsoSource模型计算该海域生物的食物网基础并利用氮稳定同位素数据计算消费者的营养级.结果表明:该海域生物消费者食物源的δ13C值范围介于-13.75％～-24.29％之间;根据δ13 C值可以将其食物源分为4类:浮游植物、大型海藻、悬浮颗粒有机物(POM)、沉积相颗粒有机物(SOM).浮游植物和SOM是该海域生物食物网的基础,对消费者的碳源贡献率(50.27％)比较大,大型海藻也是消费者的重要碳源(贡献率为35.5％),POM对消费者的碳源贡献率为13.7％.消费者的δ15 N值则介于5.40％ ～ 11.85％之间,消费者的营养级介于2.0～3.7级之间,不同食性的鱼类处于食物网中不同的地位,浮游生物食性的鱼类位于食物网的底端,游泳生物食性的鱼类处于食物链的上层.     

Back to the future: reflections and directions of South African marine bioinvasion research

Biological invasions continue to increase around the world, with impacts on many coastal marine systems. Here we review the South African marine invasion literature which, despite the field being relatively new, has grown to have significant presence in both the local and international arenas. Of the 79 papers reviewed, 70% focused on the establishment and spread of alien species, with modes of transport and introduction largely overlooked. An emphasis was also apparent towards field studies, in particular survey work, with few experimental studies. The overwhelming majority of papers focused on a single species, the Mediterranean mussel Mytilus galloprovincialis, reflecting the scale of this invasion and the tractable nature of rocky shores as study systems. With the exception of this one species, the impacts of marine alien species have rarely been quantified. We suggest that future research extends the taxonomic coverage of present work and develops a better understanding of the mechanisms of introduction, establishment and spread of marine alien species. Through an experimental approach, the drivers of altered ecological patterns and processes resulting from invasions should be addressed, providing insight into associated impacts. This approach will maintain the local applicability and international relevance of South African marine invasion research.     

Energy budgets and predation impact of dominant epibenthic carnivores on a shallow soft bottom community at the Swedish west coast

The energy flow through the epibenthic community on a shallow soft bottom in Gullmar Fjord, Sweden, is evaluated. The interaction between the dominant epibenthic predators: brown shrimp Crangon crangon L., juvenile plaice Pleuronectes platessa L. and sand goby Pomatoschistus minutus (Pallas), and their food supply is examined, and the fate of the biomass produced within the shallow water ecosystem is described. A steady state model is presented which describes the amounts, pathways and annual rates of energy flowing through the shallow water community. Field and laboratory studies are performed in order to validate the consumption rates of the fish and shrimp species. The brown shrimp occupies a key position in this ecosystem. It represents food, consisting of newly settled juveniles, both to its conspecifics and to other epibenthic species in shallow water. Sixty to eighty per cent of the annual production of shrimps in shallow water is consumed by the epibenthic predators. The brown shrimp constitutes a main predator on other epibenthic species and, by providing such feedback loops, the shrimp constitutes a highly significant regulator of epibenthic carnivores in shallow water. A loss from the benthic community will occur due to predation, maximally amounting to 24–34% of the annual production, which is a high value compared to similar areas. A dynamic simulation is also performed in order to calculate the seasonal change of energy in the epibenthic community in shallow water. Based on mortality calculations, the total output from the shallow nursery should amount to 0·6 g m⁻² year⁻¹ (dry wt).     

Autonomous system for vertical profiling of the marine environment at a moored station

This paper presents new results of the research and development project on the moored profiler Aqualog aimed at multidisciplinary studies and ecological monitoring of the marine environment. The data on the profiler’s operation are summarized based upon the field experiments in the northeastern Black Sea in 2011. An important scientific result obtained by using the profiler during the experiments was the discovery of the countercurrent below the Black Sea Rim Current in the layer between the 500 m and 900 m depth.     

南黄海太阳沙西侧海域晚第四系地震层序和沉积环境演变

在南黄海太阳沙西侧潮流脊槽海域进行了密集网格的高分辨率浅地震勘探,测线间距主要为120 m和200 m。沉积物穿透厚度最大约80~90 m,划分为2个地震层序(SQ1和SQ2),细分为5个亚层(U1~U5)。位于下部的层序1(U1)为晚更新世陆相沉积,上部的层序2(U2~U5)以全新世海相沉积为主。根据地震相特征研究了各亚层的沉积环境,从晚更新世晚期以来,研究区经历了三角洲辫状河流—河流刻蚀—古河道充填—河口滨海—三角洲滨浅海—现代潮流脊槽的沉积环境演变过程。在早全新世中期,研究区发育了一条窄河口型潮流沙脊,并随海平面的快速上升而被掩埋。现代潮流沙脊形成于末次高海面后,与古潮流沙脊没有继承关系,与晚更新世古地形也没有关系,受控于潮流系统。