Browsing by Author "Reed, Cecile"

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    Distribution of epifauna in offshore benthic environments along the west and south coast of South Africa
    (2018) Shah, Aliya; Atkinson, Lara; Sink, Kerry; Reed, Cecile
    Marine unconsolidated sediments, such as sand, gravel and muds, constitute the most extensive benthic ecosystems globally. Biological data for these ecosystems are frequently sparse which can hinder the success and implementation of marine management strategies for benthic ecosystems. There are limited studies in South Africa on benthic epifauna. This study investigates the composition and distribution of epibenthic invertebrate assemblages along the west and south coast of South Africa (sampled using depth-stratified demersal trawls) to inform marine environmental management. Sample depth varied from 36m to 899m. Multivariate tools (PRIMER and PERMANOVA+) were used to analyse spatial (west vs south coast) and temporal (2011 vs 2017) patterns in epifauna. This study also investigated an overlap region between the west and south coast. A group average linkage cluster analysis defined biotopes using significant branching (p< 0.05). Biotopes were compared against the 2012 National Biodiversity Assessment (NBA) benthic habitat map to investigate whether epifaunal biotopes identified, align with the existing classification. A significant difference among epifauna between region and depth was found, where the west coast had a higher average number of individuals and species per station. Sympagarus dimorphus and Pelagia noctiluca were characteristic species for west and south coast respectively. Epifauna was found to be significantly different between 2011 and 2017, with a notable increase in the abundance of Crossaster penicillatus in 2017. The majority of the biotopes aligned with the current NBA classification, in particular the Agulhas Sandy Shelf Edge ecosystem type on the south coast and South Atlantic Upper Bathyal and Namaqua Muddy Inner Shelf ecosystem types on the west coast. This thesis contributes to the mapping and description of offshore ecosystem types to inform marine environmental impact assessments, marine spatial planning and marine protected area expansion.
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    Entanglement of Cape Fur Seals (Arctocephalus pusillus pusillus) in South Africa
    (2022) Henry, Maguiña Ramilo; Gridley, Tess; Reed, Cecile
    Global pollution is increasing, and marine mammals are commonly affected by the waste in the ocean. Endemic to the African continent, the pinniped species, Cape fur seal (Arctocephalus pusillus pusillus), are vulnerable to entanglement due to their curious nature and thick fur. Entanglement data were available from systematic photographic surveys of six colonies in South Africa (2019-2022) as well as opportunistic and citizen science records, photographs, aerial images and historical records from 1997 onwards. Overall, 314 cases of entangled seals were identified. As calculated from the systematic surveys, Baboon Point in Elands Bay (0.24% ± 0.78%, n = 7, with a 95% confidence interval) had the highest entanglement incidence. Seal Island in False Bay had the highest overall number of entanglements (50) and the highest mean number per survey (5.10 ± 0.46 number of entangled seals, n = 10), but this was also the largest colony assessed. Entanglement was observed the most in adults (61%, n = 189), with fishing materials being the primary cause of entanglements (40%, n = 59), specifically monofilament fishing lines (33%, n = 103). Although most entanglements were deemed ‘sight' (67%, n = 100), 28 cases (19%) were considered ‘severe,' likely impacting the health and welfare of affected individuals. Random Forest classification analysis identified the item of entangling material as an important predictor variable in terms of the severity level of the entanglement. The most common entangling material color was white (35%, n=82) followed by green (13%, n=30) and clear (7%, n=17) which may reflect the proportion of materials seals are exposed to, how they perceive them underwater, or their attraction to such colors. Aerial photographs showed higher efficiency in detecting entanglement cases than boat-based data where comparisons were possible. This is the first study to investigate entanglements of Cape fur seals in South Africa and highlights the need for correct disposal of waste, particularly that derived from the fishing industry, to mitigate its impacts on the welfare and conservation of marine fauna.
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    Examining the trophic ecology of five myctophid genera in the southern Benguela using morphological, stomach content and stable isotope analyses
    (2022) Maré, Charné; Reed, Cecile
    Myctophids, mesopelagic fishes commonly known as lanternfish, are a vital component of the oceanic food web. However, significant uncertainties about the feeding habits of co-occurring and potentially competing myctophid genera still exist. This study examined the trophic ecology of five genera of myctophid fishes from the southern Benguela, namely Diaphus spp., Gymnoscopelus spp., Lampanyctodes hectoris, Lampanyctus spp. and Symbolophorus spp. Fishes were collected during DFFE research surveys conducted in 2019 and were processed for morphological (M), stomach content (SC), and stable isotope (SI) analyses. The morphological analysis determined the relationship between gape and fish size for each genus and compared these between genera. The stomach content analysis evaluated the relative importance of prey items using percent frequency of occurrence (%F), percent numerical abundance (%N) and percentage contribution to dietary carbon (%C), and combined these into an index of relative importance (%IRI). Owing to the high concentration of lipids within the muscle tissue of myctophids, samples were run in duplicate (one lipidextracted and one untreated sample) to obtain accurate δ13C (to infer source production) and δ 15N (to infer trophic level) values. Significant linear relationships between gape and fish standard length (SL) were found for all genera, and average gape size relative to SL differed significantly between genera, with Symbolophorus spp. having the smallest and Lampanyctodes hectoris the largest values. Myctophids within the southern Benguela were generalist and opportunistic secondary and tertiary consumers. They consumed an array of macro- and meso-zooplankton with euphausiids being the principal prey item in terms of %IRI for all five genera. Significant differences in average prey length were observed between the genera and the positive sizerelated shift in average prey length noted for Symbolophorus spp. provided evidence of interand intrageneric dietary segregation. Although the differences in δ15N do not fully reflect the results obtained from the stomach content analysis, the hypothesis of inter- and intrageneric dietary segregation is further supported by Diaphus spp. and L. hectoris which both had significantly higher δ15N values compared to the other three genera, as well as by the positive (Diaphus spp., L. hectoris and Symbolophorus spp.), negative (Gymnoscopelus spp.) and nonsignificant (Lampanyctus spp.) size-related shifts in δ15N. Significant variation in δ13C values were found, with some genera showing complete segregation (e.g. Lampanyctus spp. and Symbolophorus spp.) or overlap (e.g. Diaphus spp., Gymnoscopelus spp. and Lampanyctus spp.) in their foraging habitats, resource use or source production. Furthermore, both positive (i.e. Diaphus spp. and L. hectoris) and negative (Gymnoscopelus spp.) size-related shifts in δ13C were observed, possibly indicating differential habitat use within each of these genera. However, the relationship between δ13C and SL for Diaphus spp. was significantly influenced by outliers, possibly indicating opportunistic feeding by some individuals. Myctophids are still largely understudied within this system. Therefore, despite the small sample size for each of the five genera, this study serves as a baseline for better understanding the role that these genera play within the southern Benguela food web. This knowledge is important for developing an ecosystem approach to fisheries management of mesopelagic fishes in the southern Benguela, should commercial exploitation of these resources begin as seems likely. Although the results of this study provide a glimpse into the trophic ecology of local myctophid genera, future studies should include increased sampling in terms of the numbers of individuals and genera examined and in spatial and temporal coverage through-out the entire southern Benguela.
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    Fish parasites as bio-indicators of heavy metals in two South African embayments
    (2015) Morris, Thomas Colin; Reed, Cecile; Lamberth, Stephen Justin; Avenant-Oldewage, Annemarie
    The Cape Elephant fish (Callorhinchus capensis) and two common sand shark species (Rhinobatos annulatus and Rhinobatos blochii) were caught off False Bay and Saldanha Bay and surveyed for their parasite community in 2013 and 2014. The surveys were used to build species accumulation curves (SAC) and calculate biodiversity indices, particularly, rarefied species richness, Shannon Weiner's diversity index, Simpson's index and Pielou's J index. The biodiversity indices were correlated with the host's biological data and parasite infection data, to determine the parasite community structure and provide insight into the host's community structure. The parasites identified in C. capensis (n=19) include a cestode (Gyrocotyle plana), two monogeneans (Callorhynchicotyle callorhynchi and Callorhinchicola multitesticulatus) and an isopod (Anilocra sp.). The cestode was the most prevalent at 68.4 % and the monogenean, C. callorhynchi was the most abundant (1.68 ±0.78) and had the highest infection intensity (4.00 ±1.45). The SAC and biodiversity measures indicate a uniform parasite community across the host population, suggesting a highly interactive shark community. Conversely, Rhinobatos annulatus (n=19) and R. blochii (n=17) had very limited parasite infection with two species of nematode found infecting the stomach (Proleptus obtusus) and encysted in the kidneys (Ascaris sp.) and a copepod species (Clavelottis sp.) found infecting the gills. Proleptus obtusus was the most prevalent (31.6 % and 29.4%), the most abundant (1 ±0.37 and 3.68 ±2.76) and had the highest mean infection intensity (3.17 ±0.4 and 14 ±1.5). A cestode (Trilocularia sp.) was found infecting three specimens of R. annulatus from False Bay. The SAC and biodiversity indices combined with the limited parasite infection indicate a non-uniform parasite community across the host population, suggesting an isolationist population. Within the parasite community discovered, a potential biological indicator for heavy metal accumulation was identified to determine the levels of heavy metal pollution within these two anthropogenically impacted bays. Gyrocotyle plana and Proleptus obtusus were chosen as potential indicators due to their high prevalence and the close relationship they have with their hosts. The results support the use of higher trophic level animals as biological indicators. The results also indicate that G. plana is an incredibly good accumulator of certain metals, particularly As (4073.52 ± 5561.54 μg/g), Mn (522.16 ± 578.21 μg/g), Pb (64.87 ± 101.7 μg/g), Ti (1821.42 ± 1348.16 μg/g), and Zn (12439.57 ± 9743.60 μg/g). Unfortunately water and sediment samples were not tested, however, concentrations were compared to baseline values, and the accumulation of these metals are orders of magnitude above the surrounding environment. Proleptus obtusus did not significantly accumulate metals from its surrounding environment. These results show that parasites can be used to infer their own and their host's community structure and confirm their usefulness as indicators of pollution in marine ecosystems.
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    Population crash of an endemic South African cyprinid: the role of non-native fish, drought and other environmental factors
    (2020) Cerrilla, Cecilia; Shelton, Jeremy; Paxton, Bruce; Schumann, Mandy; Reed, Cecile
    Native freshwater fish are in decline worldwide due to human impacts including impoundment, changes to water quality, over-abstraction, climate change and the introduction of non-native species. South Africa's Cape Fold Ecoregion (CFE) harbours exceptionally high freshwater fish endemism, yet the majority of these species are threatened with extinction. The Clanwilliam sandfish (Labeo seeberi), an endangered cyprinid, has declined across its range in the CFE and currently exists in only a handful of tributaries of the Doring River in severely fragmented populations. The last remaining recruiting sandfish population occurs in the Oorlogskloof River, making this tributary one of critical conservation value. In this study, I analysed a six-year dataset comprising fish survey data from 38 sites along 25 km of the Oorlogskloof River to characterise spatio-temporal variation in sandfish abundance and size structure and evaluate the relative influence of different environmental factors on sandfish population trends. The environmental factors considered included other fish in the system, especially three non-native fishes (banded tilapia Tilapia sparrmanii, smallmouth bass Micropterus dolomieu and bluegill sunfish Lepomis macrochirus), temperature, precipitation, habitat characteristics and a range of physicochemical factors. The results show that sandfish have experienced a 93% decline in the sampled stretch of the Oorlogskloof River since 2013 and that the ongoing drought may be preventing recovery. They also suggest that banded tilapia do not adversely affect the Oorlogskloof River sandfish population, while predation of juveniles by smallmouth bass and/or bluegill sunfish apparently reduces the abundance of sandfish, especially of juveniles, where these non-native fish are present. Future studies should attempt to isolate the relative impacts of the different invasive fish species and examine habitat requirements of different sandfish life stages. Management of the river's sandfish population should focus on precautionary actions such as continued monitoring and landowner engagement, as well as clearing dams of non-native species high in the catchment, to prevent the further upstream invasion of smallmouth bass and bluegill sunfish. Proactive measures, such as eradicating smallmouth bass and bluegill sunfish from the Oorlogskloof River, are also necessary to restore connectivity of suitable sandfish habitat in the Doring River system.
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    Sexual segregation and abundance trend of whale sharks in southern Mozambique
    (2022) Auditore, Lisa-Marie; Pierce, Simon; Rohner, Chris; Reed, Cecile
    Coastal aggregations of endangered whale sharks (Rhincodon typus) consist mainly of juveniles, and most have a strong male bias. Generalised additive models were constructed on a 15-year dataset (2005–2019), from Praia do Tofo, Mozambique, to investigate sexual segregation in relation to environmental conditions. Temporal (year, day of year), and biophysical (sea surface temperature, time from high tide, moon illumination, Indian Ocean dipole index, wind, and chlorophyll a concentration) predictors were modelled in relation to the total, male, and female sightings. Encounter histories of individual sharks were then used in three capture-markrecapture model parameterisations to test for sex-specific demographic variables, and evaluate trends within the constellation. No differences in selected environmental variables were found between males and females, and demographic parameters were similar. Segregation does not occur from a preference for localised habitat conditions; while fewer females are present, they make use of the area similarly to males. Declining annual sighting trends corroborate trends in the seasonal abundance from multi-state open robust design models. Total abundance decreased over the study period (89%), with females (92%) declining at a greater rate than males (81%) suggesting exposure to different conditions or threats. The rapid decline indicates a need for a detailed threat assessment to assess potential causes.
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    The biology of Boopsoidea inornata (Castelnau, 1861) and life history comparisons within the Sparidae
    (2019) Ensair, Hend Assiad M; Attwood, Colin; Reed, Cecile
    South African marine ichthyofauna has remarkable diversity across a range of biogeographic zones from cold-temperate to subtropical. Two families stand out here, both with high diversity and high rates of endemism to the region, namely Sparidae and Clinidae. The Sparidae are of greater interest because of their commercial importance, and conversely, their conservation status. Several are listed as threatened by the IUCN. The Sparidae is also the family with the greatest plasticity in life history characteristics of any vertebrate family, as they include gonochorism, rudimentary hermaphrodites, and both kinds of sequential hermaphrodites. Life history characteristics are known determinants of the resilience of fish species to fishing, and more generally of their response, either positive or negative, to any form of disturbance. Life history characteristics of most of the species of Sparidae, in South Africa and worldwide, have been studied, particularly those of commercial and conservation importance. Omissions include those that are small, with little commercial importance. This is an oversight, as there is much to be learned about life history strategies by studying the full spectrum of variation in the family, and particularly those variants which produce numerically, and therefore ecologically, significant population sizes. In this thesis, I study the life history and parasite community of one of South Africa’s most abundant seabreams in separate chapters. In the last chapter I take a fresh perspective on life history variation among fishes, by comparing four sympatric seabreams to describe the several dimensions along which life history trade-offs can occur without the confounding influences of environment and phylogeny. Boopsoidea inornata (Castelnau, 1861) is endemic to South Africa. Eight hundred and seventeen fishes were sampled from four locations: False Bay, Struisbaai, Goukamma and Port Elizabeth from 2012 to 2014. They ranged in size from 130 to 310 mm fork length. The diet of B. inornata was investigated in False Bay and Struisbaai using Prey-Specific Index of Relative Importance (%PSIRI). B. inornata is an omnivore, with a preference towards small sand- and reef-dwelling prey and has only limited intake of algae and small fish. Age and growth were assessed using sectioned otoliths. A clear seasonal pattern of band formations deduced from the frequency of opaque margins show that B. inornata lay down one opaque and one transparent band per year. B. inornata is a small species (L∞= 222.7 mm) with high longevity (tmax= 37). It is a rudimentary hermaphrodite. The ovaries hold up to 8000 vitellogenic eggs, which equates to an average 19 eggs per gram of body mass. This value is low compared with other seabream species. B. inornata females spawn repeatedly during the year, although there is more spawning activity in spring, than in other months. The sex ratio is heavily skewed towards females (1:3.35). The presence of post-ovulatory follicles together with hydrated oocytes indicates that the species is an indeterminate batch spawner. Length at 50% maturity was calculated based on gonads collected throughout the spawning season. Females mature at 178 mm FL, compared to 185 mm FL for males. Female GSI greatly exceeds male GSI, and, together with the sex ratio, suggests a polygamous mating system. One hundred and fifty B. inornata were collected from False Bay, Struisbaai, Goukamma and Port Elizabeth to investigate associated parasite assemblages. Eighty six percent of the sample was infected by parasites. Parasites infecting B. inornata have never before been recorded. Nineteen parasite taxa were found infecting B. inornata across all localities and included myxozoan, monogenean, digenean, cestode, nematode, copepod and isopod representatives. Three species of digenean metacercaria showed high prevalence of infection in B. inornata across all four localities. These included a Stephanostomum sp. infecting the gill arches of 61%, and two unidentified digeneans. The unidentified digenean metacercariae- 2 was found in the kidneys and musculature of 59% of the total sample and the unidentified digenean metacercariae-1 was found infecting the hearts of 47% of the total sample. Overall parasite assemblages were significantly different amongst all localities, with no significant difference in parasite assemblages among size classes, age classes or sex within localities. Fish life history is affected by environmental and biological factors but is also constrained by phylogenetic influences on morphology and physiology. In an attempt to expose the nature and extent of life history trade-offs, I compared four closely related and sympatric seabreams, namely Spondyliosoma emarginatum, Pachymetopon blochii, Rhabdosargus globiceps and Boopsoidea inornata. I contend that only by eliminating or reducing as far as possible the effect of environment, habitat and phylogeny can we expose real trade-offs. Samples of each species were obtained in every season from the south-western Cape, South Africa, to obtain measures of total length, mass, gonadosomatic index and condition. S. emarginatum is a nest-guarding, short-lived, protogynous hermaphrodite. P. blochii is a resident, group-spawner, engaging in sperm competition. R. globiceps is a moderately long-lived migrant with a sex ratio of 1:1, that also engages in sperm competition over a short spawning season. B. inornata is a polygamous, long-lived resident with low annual fecundity, but a protracted spawning season. Although all four species are periodic strategists, life history trade-offs exist between several sets of variables, namely semelparity vs iteroparity, age-at-maturity vs maximum size, annual fecundity vs longevity, length of spawning season vs parental care, and length of spawning season vs migration. The efficiency of the sequential hermaphrodite strategy which allows every fish to spawn as a female until they are large enough to act as a male makes one question the rarity of this strategy. I argue that halving of the female life-span compromises the periodic strategy, and that hermaphroditism is at odds with migration. The latter rests on the assumption that the migrant social structure is based on cooperation, for feeding, defence and navigating in schools, whereas the hermaphrodite social structure is based on aggression and dominance hierarchies which requires residency and territoriality. No clear adaptive reason for the divergence among the sympatric species can be identified, although competition among the young is a candidate. This comparison reveals a wide range of options available to seabreams and shows how disparate life histories can be equally adaptive under identical conditions. More generally I have shown how a variety of life-history traits, such as migration, sex-ratio, reproductive strategy and somatic growth form interact to define a life-history.
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    The effects of an unidentified pathogen, ‘Frill on Gill’, on body condition of Cape hake Merluccius capensis, on the south coast of South Africa
    (2019) Hunt, Kim-Kelly; Reed, Cecile; Attwood, Colin; Singh, Larvika
    The unidentified pathogen, known as 'Frill on Gill’ (FOG), infects the shallow-water Cape hake Merluccius capensis off the south and west coast of South Africa. This pathogen, a parasitic castrator, occurs on the gill filaments of infected fish. This study investigates the effects of this pathogen on the body condition of M. capensis on the south coast of South Africa, through the use of two body condition measures, condition factor and hepatosomatic index (HSI). A total of 24275 M. capensis were sampled, of which 825 (3.4%) were infected with the FOG pathogen. The smallest M. capensis infected with FOG was 10 cm, and the largest was 84 cm. The smallest uninfected M. capensissampled was 6 cm and the largest was 106 cm. The presence of FOG had a significant impact on the condition factor and HSI of M. capensis (three-way analysis of variance (ANOVA): p-value = 0.002, and p-value = 5.13e-09 respectively), with the effect of the pathogen varying with length. For fish with a total length smaller than 26 cm, infected M. capensis were in poorer condition than uninfected fish at the same length, with lower condition factors and HSI values. However, for M. capensis with lengths between 30 and 34 cm, 42 and 46 cm, 54 and 62 cm, and 78 and 82 cm, the condition factors of FOG infected fish were higher than uninfected fish. The HSI values of M. capensis infected with FOG also steadily increase above those of uninfected fish, for lengths greater than 42 cm. The lower body condition measures of uninfected M. capensis could be linked to the large amounts of energy that these fish expend during reproduction and gonad maturation. In contrast, M. capensis infected with FOG do not partake in the energy intensive task of reproduction. Merluccius capensis infected with FOG don’t contribute to reproduction, but still compete with uninfected M. capensis for resources. The effect of FOG as a type of parasitic castrator on the regulation of M. capensis populations could become a concern for fishery managers, as they reduce reproductive output and impact fish body condition.
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    The parasite assemblage of Scomber japonicus (Houttyun, 1782) off South Africa
    (2019) Hendricks, Joshua Paul; Reed, Cecile; van der Lingen, Carl
    In South Africa, knowledge of marine parasite diversity is lacking and is often ignored or underutilised. Parasitology has several potential applications in fisheries management, pollution monitoring, aquaculture and general community ecology. With increased knowledge and understanding, the role that parasites play in the marine ecosystems of South Africa is gradually being exposed. This study aimed to document the parasite assemblage of Scomber japonicus (commonly known as chub mackerel) off South Africa, and to determine which host characteristics (size, sex and region) influenced parasite infection indices. This species is a small to medium sized, pelagic fish, that has a cosmopolitan, anti-tropical distribution and with populations showing large-scale, environmentally dependant migratory behaviours. It is found off South Africa throughout the year but is most abundant between austral spring and summer. Thanks to their diverse diet and wide array of predators, S. japonicus is an ecologically important species, and although it was historically important in the South African purse-seine fishery with large catches taken in the 1960’s and 1970’s it is no longer, although small amounts are taken as bycatch. A total of 152 fish ranging between 99 and 514 mm (FL) were sampled in this study and were found to host a total of 16 parasite taxa, 9 of which were identified to species level and 6 to genus level, as well as cysts that were not identified. The parasite assemblage was made up of two nematode species [Anisakis simplex (Rudolphi, 1809) and Contracaecum sp. (Railliet & Henry, 1912)], six digenean species [Lecithocladium sp. (Lühe, 1901), Opechona bacillaris (Molin, 1859), Nematobothrium faciale (Baylis, 1938), Halvorsenius sp. (Gibson, MacKenzie & Cottle, 1981), Didymocystis sp. (Ariola, 1902) and a metacercarean], three monogenean species [Pseudokuhnia minor (Goto, 1984), Kuhnia sp. (Sproston, 1945) and Grubea cochlear (Diesing, 1858)], one acanthocephalan species [Rhadinorhynchus pristis (Rudolphi, 1802)], one cestode species [Tentacularia coryphaenae (Bosc, 1802)], two myxozporan species [Kudoa thyrsites (Gilchrist, 1924) and Ceratomyxa sp. (Thélohan, 1892)], one copepod species [Clavellisa scombri (Kurz, 1877)] and one unidentified cyst species [Cyst 1]. Whilst no new host records were recorded in this study, N. faciale and Halvorsenius sp. are new locality records. Generalized linear models were used to determine which host characteristics most influence the prevalence and infection intensity of the six most prevalent parasite taxa (A. simplex, Lecithocladium sp., O. bacillaris, P. minor, R. pristis and Cyst 1). All showed significant relationships between size and either prevalence or infection intensity or both. This was attributed to the fact that larger, older fish have had more opportunities to get infected than smaller, younger fish, as well as the different diets of adult and juvenile S. japonicus which, along with the fact that adults and juveniles tend to school separately, means that the level and diversity of parasites that they are exposed to are different. Three parasites, A. simplex, P. minor and R. pristis also showed significant spatial variation in either prevalence or infection intensity. The prevalence of A. simplex and the infection intensity of P. minor decreased with in an eastward direction, while the prevalence of R. pristis increased eastwards. The spatial trends in the prevalence of A. simplex and R. pristis were predicted to be driven by the diet of the fish, and the intensity spatial trend observed in P. minor infections was predicted to be driven by environmental factors. An analysis of the gill preference of P. minor revealed that the outermost gills, furthest from the spinal cord were favoured sites of infection. The driver behind this trend was not definitively identified, however space availability was removed through standardization and water flow is suspected to be the main factor affecting gill arch selection. Using data from Oliva et al. (2008), the parasite assemblage of S. japonicus off South Africa was compared to the parasite assemblages of populations of this species in Brazil, Peru, Chile and Portugal using Nonmetric Multidimensional Scaling modelling (NMDS) and an ANOSIM. The NMDS plot showed that all populations were unique. The South African and Portuguese populations (R statistic = 0.28) as well as the Chilean and Peruvian populations (R statistic = 0.32) were the most similar, while the Brazilian population was the most dissimilar from the other populations analysed. The SIMPER analysis revealed that 16 parasite taxa account for 80% of the dissimilarity between the six populations of S. japonicus. This result supports the conclusions made by Oliva et al. (2008) that extended separation is the main driver of interspecific differences in the parasite assemblages of this species. This study has increased our knowledge of South African marine biodiversity and of the ecology of South African chub mackerel, and further demonstrated how parasites can be used to elucidate the taxonomic status of their hosts.
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    Tolerating climate change: a study on the influence of thermal history on thermal tolerance of Galaxias zebratus in rivers of the Cape Peninsula, South Africa
    (2018) Olsen, Toni; Dallas, Helen; Shelton, Jeremy; Reed, Cecile
    Global climate change models predict a reduction in rainfall and rise in air temperature for the Cape Peninsula of South Africa’s Cape Floristic Region (CFR). The CFR is a biodiversity hotspot renowned for its high level of floral endemism, but the high level of endemism also applies to the region’s freshwater fish assemblage. Whereas the current threats to endemic freshwater fish include habitat modification, water abstraction, pollution and impacts of non-native species, climate change is predicted to further exacerbate negative impacts on fish communities. The endemic CFR fish species, Cape Galaxias, Galaxias zebratus Castelnau, 1861, is widespread throughout the region, and occurs in both non-perennial and perennial rivers, and wetlands. The species is thought to be a relict group of ancient species originating from the break up of Gondwanaland 180 – 135 million years ago. Endemic CFR freshwater fish, like G. zebratus, may be sensitive to the thermal regime of their environment and may thus be influenced by climate warming. The most commonly used experimental approach for determining the effect of elevated temperature on freshwater biota is the Critical Thermal Method (CTM). The CTM determines the upper thermal tolerance limit or critical thermal maximum (CTmax) of a species. Thermal history is the range of temperatures experienced by an organism in its natural habitat over time and this may be an important factor determining the thermal tolerance of species. The aim of this study was to evaluate the influence of thermal history, reflecting a stream’s thermal profile, on upper thermal tolerance limits of G. zebratus. We hypothesised that G. zebratus from warmer sites would have a higher CTmax than individuals at cooler sites. To examine the influence thermal history has on the thermal tolerance of G. zebratus, hourly water temperature data were collected and the CTmax values were determined for fish (n=30 per site) from 10 different sites in rivers of the Cape Peninsula. The CTmax values from all sites for the November-December experimental period ranged from 30.00°C to 32.45°C. CTmax values for all sites from the JanuaryFebruary experimental period ranged from 31.29°C to 33.42°C. Upper thermal tolerance limits of G. zebratus increased from the November-December experiments to the January-February experiments. Regression analyses show that G. zebratus upper thermal tolerance limits are significantly influenced by its thermal history as characterised by the seven day moving average of daily mean (Mean_7) two weeks preceding the experiments, implying that changes to the thermal regime will influence the thermal tolerance of G. zebratus. The resultant regression equation allows G. zebratus CTmax to be predicted by thermal history based on Mean_7, providing valuable information to set thermal limits of G. zebratus and guide future research. This is the first study on the thermal ecology of G. zebratus in the CFR and in Africa. The data not only enhance understanding of the thermal ecology of the species, but also further our understanding of their potential vulnerability to climate change.