Temperature and salinity tolerance of adult hermit crabs,Diogenes brevirostris,Stimpson (Crustacea: Decapoda: Anomura)

Diogenes brevirostris was found to be tolerant to low salinities (0,5 - 4,0 %) at a wide range of temperatures (12 to 27°C). Tolerance to temperature and salinity were inversely related. At low salinities (0,5 and 1,0 %) the rate of mortality increased with temperature throughout the range, whereas at higher salinities (1,5 and 4,0 0/00) temperature had no effect on mortality. These results are discussed in relation to the distribution of D. brevirostris in estuaries. It appears that temperature and salinity tolerance are not solely responsible for limiting distribution of these crabs to estuary mouths.     

The fish community of the berg river estuary and an assessment of the likely effects of reduced freshwater inflows

Data concerning the species composition, abundance and distribution of fishes inhabiting the Berg River estuary are presented and used to assess the value of the estuary to fish, and the likely eflects of reduced freshwater inflows. A total of 31 species was recorded, eight of which were classified as estuarine residents, 11 as marine estuarine-opportunists, six as marine stragglers and six were freshwater species. Liza richard- sonii, an opportunist, was the most abundant (54% N) and widely distributed species encountered during the winter and summer seine-net surveys. Three other species (all residents) contributed more than 10% of the total catch; Atherina breviceps and Caffrogobius nudiceps occurring most abundantly in the lower estuary, and Gilchristella aestuaria in the middle estuary. The low number of species compared with estuaries in other regions of the South African coast reflect a well-established marine biogeographical trend. The higher proportions ol resident species, entirely dependent species and partially dependent species suggest, however, that west coast estuaries may be more important to the fish that inhabit them than are estuaries in other regions. It is concluded that the fish community of the estuary is already suffering the effects of habitat degradation and that further reductions in freshwater inllows are not desirable.     

Description and ecology of larvae of Glossogobius callidus and Redigobius dewaali (Gobiidae) from temperate South African estuaries

This paper describes the morphology and ecology of the larvae and early juveniles of two common gobiids in warm temperate South African estuaries. The early developmental stages of Glossogobius callidus and Redigobius dewaali were collected during plankton surveys in seven permanently open and five intermittently open estuaries along southeastern South Africa. Larval G. callidus have a characteristic ventral row of pigment that extends from the cleithral symphysis along the ventral midline of the tail to the end of the caudal peduncle; notochord flexion takes place at the yolk-sac stage, between 3 and 4 mm BL. Larval R. dewaali are characterized by having two very large stellate melanophores on the ventral surface of the trunk and tail, and internal pigment between the snout and hindgut; notochord flexion takes place between 4 and 6 mm. Body lengths at settlement for G. callidus and R. dewaali are 13 mm and 16 mm, respectively. G. callidus and R. dewaali dominate the larval gobiid catch in warm temperate estuaries. Estuary type and freshwater input played a defining role in the occurrence of larvae of these, often sympatric, species in temperate estuaries. Larval G. callidus occurred in both permanently open and intermittently open estuaries, and were most abundant in mesohaline regions over the spring/summer period. By contrast, larval R. dewaali occurred exclusively in permanently open estuaries and were more prevalent in the fresh and oligohaline regions in autumn. Larvae of both species were more prevalent in freshwater-rich estuaries. Densities of G. callidus and R. dewaali peaked at 101 and 3829 larvae per 100 m³respectively. The usefulness of using the early stages of these gobiids as indicators of estuarine health based on their specific and often prolific estuarine occurrence is discussed.     

The effect of temperature and salinity on oxygen consumption in the brachyuran crab Cyclograpsus punctatus (Crustacea: Decapoda: Grapsidae)

The aquatic oxygen consumption of the estuarine brachyuran crab, Cyclograpsus punctatus, was investigated after a 24-hour acclimation period at different temperature (12.5, 20, 30°C) and salinity (9, 17.5, 35, and 44°) combinations . Salinity had no significant effect on oxygen consumption at 12.5 and 20°C in both large and small crabs. At 30°C and 44°, however, the rate of oxygen consumption declined in large crabs (from 0.233 to 0.176 mg O₂ g wwt/h) and increased in small crabs (0.300 to 0.469 mg O₂ g wwt/h). There was also a significant increase in the oxygen consumption (0.300 to 0.536 mg O₂ g wwt/h) of small crabs at the high temperature/low salinity combination. Temperature had a significant effect on the rate of oxygen consumption at all salinities, with Q₁₀ values ranging from 1.16 to 2.85. In all cases the mass-specific oxygen consumption rate of small crabs was higher than that of large crabs. The results suggest that the confinement of this species to the lower reaches of estuaries may, in part, be due to physiological constraints on juveniles and small individuals.     

The ecology of two degraded estuaries on the north coast of Natal,South Africa

The biota of the Tongati and Mdloti estuaries were studied in relation to the environment and human interference. Results are compared with those obtained from a relatively undamaged estuary. The Tongati receives treated sewage effluent, is rarely closed from the sea, has low salinities and low oxygen tensions, but is rich in phosphorus and nitrogen. Energy values of benthic floe from Tongati were high and large quantities of water hyacinth (Eichomia crassipes) occurred. The zooplankton and zoobenthos were impoverished and dominated by freshwater species. The roots of Eichomia provided a habitat for many invertebrates, chiefly insect larvae and the crab Varuna iitterata. The fish fauna was poor and most species were confined to the lagoon near the mouth. Iliophagous species, mainly Mugilidae, were dominant. The Mdloti, frequently closed from the sea but often artificially opened, exhibited typical estuarine salinity patterns, was well oxygenated but relatively poor in phosphorus and nitrogen. Primary production and energy values of benthic floe were low. Zooplankton and zoobenthos were impoverished. The fish fauna, similar to that of Tongati, was dominated by Mugilidae.

The food chain from benthic floe to iliophagous fish remains viable in these degraded estuaries.     

A Comparative,Quantitative Study of the Micro-Arthropods in Different Types of Pasture Soil

The osmoregulatory abilities of the grapsoid crabs Cyclograpsus punctata*, Sesarma catenata andSesarma eulimene were studied comparatively in an attempt to explain, at least in part, their distribution in estuaries. Both survival and haemorymph osmotic pressure were used as indices of hyperosmotic regulatory ability.

All three species were shown to be capable of regulating their haemorymph osmotic pressure against lowered external salinities. S. eulimene was found to be better able to control its haemorymph concentration in very low salinities than S. catenata, which would account for the former's occurrence in the upper reaches of estuaries. C.punctatus was shown to be capable of roaintaining its haemorymph osmotic pressure above that of the environmental medium in lowered salinities, but without the degree of constancy characteristic of the two Sesarma species. It does, however, show a marked ability to tolerate lowered internal osmotic pressure, an ability which appears to develop in response to partial dilution of the haemorymph. These adaptations, together with its semi-terrestrial habit as a shore crab, suffice to enable C. punctata* to penetrate an estuary to almost the same extent as S. catenata.     

Species identification,distribution and abundance of Gerreidae (Teleostei) Bleeker,1859 in the estuaries of Natal

Comparison of published meristic and taxonomic data with measurements taken from specimens collected from Natal estuaries have provided information for an identification key to the Gerres of southern Africa. Body markings were different on each species of fry (< 40 mm S.L.) as well as immatures and adults (> 40 mm S.L.). A comparison of otoliths from the different species showed that they can be used to Identify specimens from a standard length of 20 mm. Turbidity may be a factor limiting the distribution of the genus in estuaries. The known distribution of Gerres species in the estuaries of southern Africa is given. The species of Gerres which is dominant in a particular locality depends on the salinity.     

The benthos of South Lake,St Lucia following a period of stable salinities

The invertebrate benthos of South Lake, St Lucia was monitored monthly from August 1981 to July 1982 following a period of stable salinities of approximately 35°/oo. The overall mean biomass for the year (dry mass) was 2,63 g m^-2 with mean values for muddy and sandy substrata of 4,19 g m^-2 and 1,07 g m^-2 respectively. The major contributors to standing stock were the bivalve Solen cytin-draceus and the polychaete Marphysa macintoshi. A total of 37 taxa were recorded compared with 23 in a previous survey in 1972-73. Present results are compared with those of 1972-73 and the differences discussed. The main changes were a decline in Assiminea, Nassarius and Prionospio and an increase in abundance of long-lived bivalves together with larger polychaetes. Species diversity at the sampling sites is analysed and discussed in terms of equitability of distribution.     

Recent records of megalopae of the crab Varuna litterata (Fabr.) entering Natal estuaries

An unusual occurrence Involving the stranding of many thousands of megalopae of the crab Varuna litterata on an outgoing tide is recorded. The locality was sandflats adjacent to the mouth of the Mgobezelenl estuary at Sodwana Bay, Natal, In mid-May 1985. Other records of recent local sightings are Included.     

The Zooplankton of Mgazana,A Mangrove Estuary in Transkei,Southern Africa

Mgazana, a mangrove estuary inTranskei, was investigated from May 1972 to March 1973 at six-week intervals. Salinities were consistently above 25 parts per thousand in the middle and lower estuary. In the upper estuary the salinity varied between 4 and 29 parts per thousand. Water temperatures varied between I5,5°C and 28°C. One hundred and fifteen taxa of zooplankton organisms were recorded in the samples. The copepods Acartia naialensis and Oithona brevicornis reached high population densities and numbers exceeding 100 000/m³ of water were recorded. Mysids were major contributors to zooplankton biomass. A maximum biomass of I 200 mg/m³ was recorded in February in the middle estuary and was attributed to the mysid Mesopodopsis africana. Species of mysids showed clear seasonal and spatial patterns of distribution in the estuary.     

Feeding ecology of major carnivorous fish from four eastern Cape estuaries

Stomach content analyses were performed on eight carnivorous fish from four eastern Cape estuaries. Dietary importance was assessed by using three unrelated methods and by combining them to determine the index of relative importance of each food item. It was attempted to relate the percentage of fish with food in the stomach and the feeding intensity to the abundance of the fish in a particular estuary. In general fish consumed more food in estuaries where they were more abundant. The few exceptions that occurred could indicate that a particular estuary was selected for purposes other than food availability eg. Tachysurus feliceps in the Krom estuary for spawning grounds or because of inter- or intraspecific competition for food eg. T. feliceps and Monodactylus falciform is in the Krom and Argyrosomus hololepidotus in the Gamtoos and Sundays estuaries. Similarity analyses showed resource partitioning. Predators such as A. hololepidotus, Elops machnata, Lichia amia and Platycephalus indicus preferred teleost fishes such as mullets and Gilchristella aestuarius, whereas the stomach content of Pomadasys commersonnl, T. feliceps and M. falciform is were dominated by Crustacea, particularly Upogebia africana. Most estuarine predators showed a diverse prey selection, but the food web was characterized by a high energy flow per pathway.     

Ecology of southern African estuaries: Part XIII. The Palmiet River estuary in the south-western Cape

The Palmiet estuary is only 1,67 km in length, but has a relatively large catchment of 539 km². Rain falls largely during winter when it scours the estuary and widens the mouth, but by late summer the mouth narrows and, in some years, may close. The estuary never closes for more than a few months, and salinities are normal. The entire estuary has clear bottom water and high bottom salinities, but the surface waters are usually fresh and darkly stained with humic acid. This permanent stratification allows many marine species to penetrate the estuary.

Owing to the scouring in winter, the sediments are coarse, >98% consisting of sand and gravel, with a low organic content. In situ primary production is low, contributing only about one fifth of the organic material in the system, the rest being imported from the river and the sea. Species richness is low, only 28 species of invertebrates being recorded, but many of these occur in enormous numbers. Callianassa kraussi plays a crucial role, trapping fine particles around its burrows and locally enhancing the organic content of the sediments. Its faeces are an important vehicle for the concentration and turnover of organic matter.

Four of the 19 species of fish recorded breed in the estuary, the rest being represented largely by juveniles or small adults. Only three species occurred in the estuary year-round, the other species being absent during the period that the estuary is in flood.

Floods and a relatively high flow of river water are critical to keeping the estuary open. If, as proposed, a dam is built on the river, steps will have to be taken to ensure that the mouth is kept open. A related problem will be the reduction of organic material entering the estuary from the river and the sea.     

The diet,food selectivity and niche of Rhabdosargus sarba (Teleostei: Sparidae) in Natal estuaries

The juveniles and subadults of Rhabdosargus sarba are one of the most common components of the benthic fish community of Natal estuaries. The diet consists mainly of aquatic macrophytes and filamentous algae although a significant proportion is made up of bivalves and the amphipod Grandidierella lignorum. The last two taxa are positively selected when little plant material is consumed. R. sarba feeds during daylight with a peak in the early afternoon. The relationship between R. sarba and the very similar sympatric R. holubi and R. auriventris are discussed in relation to their diet, divergence and distribution. Resource partitioning in Natal estuaries between R. sarba, the Gerreidae and Pomadasys commersonii is also discussed.     

Performance of cynodon species in the natal tall grassveld

A number of Cynodon lines were evaluated at two centres in the Natal Tall Grassveld. On a red clay soil in a relatively moist area good performance was recorded from several star grasses (Cynodon aethiopicus and C. nlemfuensis) and Cynodon hybrids, but herbage production was less satisfactory on a grey‐brown loamy soil at a drier site. Local C. dactylon strains did not compare well with the introduced Cynodon spp. Quality of the Cynodon herbage was good, and no problems were encountered with prussic acid poisoning,     

Blue sheep in the Annapurna Conservation Area,Nepal: habitat use,population biomass and their contribution to the carrying capacity of snow leopards

The Himalaya region of Nepal provides a habitat for the endangered snow leopard (Panthera uncia) and its principal prey species, the blue sheep (Pseudois nayaur). The aim of this study was to describe the habitat, the distribution and the population structure of blue sheep, and to estimate their contribution to the carrying capacity of snow leopard in the upper Mustang region of Nepal. Blue sheep were recorded at altitudes from 3209–5498 m on slopes with gradients of 16–60° and aspects of 40°NE to 140°SE. A total of 939 blue sheep were counted in the upper Mustang region, and 98 were counted in the Yak Kharka region of Manang district; however, upper Mustang had the lowest population density of blue sheep recorded within their distribution range in Nepal (0.86 blue sheep/km²). The results of the study show that a higher density of blue sheep is associated with greater plant species diversity. The most important species present in the blue sheep habitat were Kobresia pygmaea, Artemesia spp., Lonicera spp., Lancea tibetica, Poa spp., Astragalus spp. and Ephedra gerardiana. It is estimated that the existing blue sheep population biomass of approximately 38 925 kg in the upper Mustang region could support approximately 19 snow leopards (1.6 snow leopards/100 km²).     

The population dynamics of the estuarine isopod Exosphaeroma hylocoetes (Barnard, 1940) within three temporarily open/closed southern African estuaries

The population dynamics of the estuarine isopod, Exosphaeroma hylocoetes, was investigated monthly from February 2006 to August 2007 in three temporarily open/closed Eastern Cape estuaries, the East and West Kleinemonde and Kasouga Estuaries. Mean isopod abundances and biomasses ranged between 0 and 4791 ind/m² and 0 and 9.65 mg/dwt/m² in the West Kleinemonde Estuary and between 0 and 108 ind/m² and 0 and 0.318 mg/dwt/m² in the nearby East Kleinemonde Estuary. In the Kasouga Estuary, the values ranged between 0 and 3650 ind/m² and 0 and 5.105 mg/dwt/m². Temporal changes in the abundance and biomass of E. hylocoetes within the three systems was primarily linked to mouth phase, with populations crashing when the mouth was open and to a lesser extent, seasonality. In all three estuaries maximum abundance and biomass was recorded in the middle reaches, which could be ascribed to the presence of submerged macrophytes. E. hylocoetes demonstrates strong sexual dimorphism, with males being significantly larger than females (P < 0.05). Sex ratios were skewed in favour of females in all three estuaries. Females were encountered carrying young from an overall length of 2.5 mm throughout the year     

A survey of the fish fauna of Transkei estuaries Part Four: The Mntafufu and Mzamba River estuaries

The Mntafufu and Mzamba Rivers have small catchment areas (178 and 505 km², respectively) in the forested coastal belt of Transkei and have relatively small estuaries (5 and 2 km long, respectively). Although the annual rainfall is in excess of 1000 mm in this area, the mean annual runoff was less than 70 Mm³ in both cases. Serious floods were not observed during the survey period, while turbidity and sediment loads were usually very low. Salinities were usually high (x? = 30,0-38,0‰) in the bottom water and temperatures in the upper reaches were usually higher than in the lower reaches. The species composition, and seasonal and spatial abundance of the fish fauna of the two estuaries were determined by means of gill nets. A total of 1043 fish (385,8 kg) representing 42 species were caught in the Mntafufu estuary. The orangemouth glassnose Thryssa vitrirostris and V. cunnesius were the most abundant fish in the estuary. Numerically 42% of the catch (46% gravimetrically) belonged to the family Mugilidae (11 species) of which Mugil cephalus, Valamugil buchanani and V. cunnesius were the most important. A total of 389 fish (241,1 kg) were caught in the Mzamba estuary. Twenty-five species were obtained with Hilsa kelee dominating numerically. Seven species of mullet contributed 38,3% of the numbers or 54,2% of the fish biomass. The diamond mullet (Liza alata) and the flathead mullet (Mugil cephalus) were the most abundant in terms of biomass. The highest catches in the two estuaries were taken in the lower reaches. Mean number and biomass of fish taken per net was 20,5 fish and 7,2 kg, and 16,2 fish and 10,1 kg in the Mntafufu and Mzamba estuaries, respectively.     

Preliminary estimates of population size and capture rates of mature Acanthopagrus berda in the Kosi lakes system,South Africa,using mark-recapture methods

Population size estimates and capture rates by various fishing techniques of mature estuarine bream, Acanthopagrus berda, were determined in the Kosi lakes system using mark-recapture methods. The total population size of mature A. berda was estimated to be 45 257 (95% confidence interval: 31 589-74 429) based on fish recaptured in fish traps and 56 112 (95% confidence interval: 25 505-374 080) using recaptures from recreational anglers. Fish traps were estimated to catch about 5% of the mature population of A. berda annually, while recreational rod and line angling and traditional spearfishing accounted for about 1% and 0.2% of the mature population respectively. Limited mark-recapture data for other species of fishes in the lakes yielded annual capture rates by fish traps ranging from 2.4% to 5.8%. These levels of fishing appear low enough to be sustainable, but evidence from a long-term monitoring programme indicates an increase in overall fishing effort in the Kosi lakes between 1984 and 1996 and a three-fold increase in the proportion of the A, berda population caught annually. However, there is no evidence from available catch per unit effort (CPUE) data that current levels of harvesting of A. berda are unsustainable. This needs to be confirmed through modelling of the A. berda stocks and continued monitoring of CPUE in all components of the Kosi lakes fishery. In the meantime, an increase in fishing effort directed at this species is not recommended.     

>Utilization of shallow subtidal bays associated with warm temperate rocky shores by the late-stage larvae of some inshore fish species,South Africa

>This work describes the utilization of shallow, subtidal bays, associated with rocky shores, by the late-stage larvae and early juveniles of some common inshore fishes. Larval and early juvenile fishes were collected in seven small bays (30–50 m wide) between Port Alfred (33°36’S, 26°53’E) and Hamburg (33°17’S, 27°29’E), using a modified, beach seine net (500 µm mesh). Four bays were sampled weekly during peak fish spawning (September–November 2004) to firstly assess whether larval fishes occur in these previously-unstudiedhabitats and secondly, to assess the extent of this utilization in terms of species occurrence, abundance and potential nursery function. An additional three replicate bays, situated >50 km away near Bira were used for comparison. In total, 14 fish families represented by 26 taxa were recorded but the catch was dominated by a small suite of common species. Bays were extensively utilized by Sparidae (>Diplodus capensis >and >Sarpa salpa>), and to a lesser extent by Clinidae (>Clinus superciliosus>), Mugilidae (>Liza >spp.) and Kyphosidae (>Neoscorpis lithophilus>). Mean CPUE of larvae was high and exceeded 900 individuals per seine haul. Larval abundance peaked at 4000 larvae per haul and at these times, was dominated only by the two sparid species. Abundance of sparid larvae exceeds that recorded for these species in surf zones, estuaries or the shallow nearshore habitatssampled to date in temperate South Africa by an order of magnitude. Larval abundance was significantly higher during new moon sampling throughout the study period, but was not significantly different between repeated samples collected per site on each fieldtrip. The length-frequency of larvae utilizing the bays was dominated by postflexion stages ranging 7–14 mm SL. Length-frequency distribution of >Diplodus, Sarpa, Clinus, Sparodon, Neoscorpis >was indicativeof grow-out and use of bays as interim nurseries. The nursery function of these bays is supported by gut analysis of a sub-sample of the dominant species, >Diplodus capensis, >which showed that these larvae were actively feeding in the area, predominantly on copepods. This work prompts further research on shallow habitats associated with rocky shores particularly the shelter and feeding role that these under-studied habitats are playing in the early life history of coastal fishes.     

Inshore small-mesh trawling survey of the Cape south coast. Part 2. Occurrence of estuarine-associated fishes

Marine inshore trawl catches of 12 species of estuarineassociated fishes are reported together with their depth and length distributions. Underwater observations of four additional species, made during 122 SCUBA dives over rocky substrates, are also recorded. Species include Rhabdosargus holubi, R. globiceps, Pomadasys commersonii, Argyrosomus hololepidotus, Pomatomus saltatrix, Galeichthys sp. and Sarpa salpa. The data are related to published accounts of the occurrence of juveniles of estuarine-associated and inshore species in the Cape south coast region. This revealed three ecologically distinct groups of inshore fishes: typically marine species that only use marine inshore nursery grounds; an intermediate group that uses mainly marine inshore nurseries plus estuarine nurseries to a limited extent; and a specialized group that is dependent on estuarine nurseries. Possible reasons for this dependence on estuaries are suggested.