Sundays River Estuary Research Articles

Occurrence and distribution of pharmaceuticals in surface water and sediment of Buffalo and Sundays River estuaries, South Africa and their ecological risk assessment

This study investigated the presence of pharmaceuticals in the water and sediment of Buffalo and Sundays River Estuary, South Africa. Extraction for water and sediment samples was achieved with solid-phase extraction and ultrasonic extraction methods, respectively. Quantification of the target analytes was done with UPLC-QTOF-MS. The pH of surface water in all the sampling sites (8.18–10.1) were above the WHO guideline (6.5). A good correlation was observed between the concentrations of analytes with organic matter and organic carbon. Results showed that carbamazepine exhibited the highest concentration (8.75 ± 1.45 μg/kg) of all the pharmaceuticals, while trimethoprim has the highest detection frequency with the highest concentration of 1.62 ± 0.83 μg/kg in the sediment samples. Sulfamethoxazole was below the detection limit in both estuaries. Calculated risk quotients revealed that carbamazepine and trimethoprim could be of potential risk, while caffeine may pose a very low risk to the aquatic organisms investigated. Proper monitoring of the runoff entering Buffalo Estuary is required, being the point of discharge of Buffalo River to the Indian Ocean. Also, the domestic waste discharge from residences in the surroundings of Sundays Estuary should be monitored.

Valuing user preferences for improvements in public nature trails around the Sundays River Estuary, Eastern Cape, South Africa

Many valuations have been made of changes to in-estuary attributes, but few have been made of out-of-estuary attributes. From a recreation perspective, an important type of out-of-estuary attribute is the availability of public paths by which to access attractive features of the estuary environment. This paper values an improvement in the level of public access in the form of an additional nature trail along the banks of the Sundays River Estuary in the Eastern Cape, but does not compare this value with the costs. By means of choice experiment modelling analyses it is estimated that in 2010 the marginal willingness to pay for an investment in a nature trail was R34 per user per annum. In order to determine whether the development of this trail is efficient, this benefit (R34 per user per annum) needs to be compared to the cost of the development, an analysis that remains to be done. However, this finding does serve to provide guidance on how much funding could efficiently be allocated to such a development – about ZAR1.22 million, assuming a social discount rate of 8.38%.

A demand-based management option to address boat congestion at the Sundays River Estuary, Eastern Cape, South Africa

The Sundays River Estuary situated in the Eastern Cape is an example of a South African Estuary experiencing congestion externalities, mainly vis-a-vis motorised boat use. This paper employs a choice model to estimate people’s preferences for less boat congestion on the Sundays River Estuary. The results show that visitors to the estuary are willing to trade off a levy of ZAR 35/a (in addition to what they already pay) for a reduction of boat congestion during peak periods (only). This paper proposes that this amount be set as a user charge to manage excess recreational boat use. Keywords : estuary, choice experiment, implicit prices, conditional logit, random parameter logit

A choice experiment application to estimate willingness to pay for controlling excessive recreational fishing demand at the Sundays River Estuary, South Africa

The Sundays River Estuary, situated in the Eastern Cape, South Africa, has excessive recreational demand for estuarine services, specifically recreational fishing. The estuary has been over-fished, putting its sustainability at risk. Various management interventions may be required in order to save it, but how is this to be done without reducing welfare? The main aim of this paper is twofold: first, to assess and comprehend the economic value of the estuarine resources at stake; and, second, to propose policy measures to redress the situation (excessive demand, specifically recreational fishing). An application of a choice experiment reveals that the physical size of fish stocks is a very important predictor of recreational choice at the Sundays River Estuary, and it is recommended that demand be curtailed through an increase in the boat license fee for using the estuary of ZAR174 per annum. Keywords : Estuary, demand management, recreational attributes, recreational fishery, choice experiment

Plankton distribution and abundance in the Sundays River estuary, South Africa, with comments on potential feeding interactions

Three mysid and three calanoid copepod species dominated the mesozooplankton in the Sundays River estuary, South Africa. Mid estuary, there was considerable overlap in the spatial and temporal distribution of species. Mesozooplankton abundance was lowest during winter. Microzooplankton, consisting of ciliates, zooflagellates and rotifers, was most abundant in the middle of the estuary. Rotifer abundance was lowest in winter and autumn. Other microzooplankton showed no seasonal variation. Phytoplankton was dominated by micro- and nanoflagellates, dinoflagellates and euglenoids, but diatoms were very abundant after a flood. Chlorophyll a concentrations were greatest in the middle and upper estuary, but there they showed no seasonal fluctuations.

Feeding of two mysid species on plankton in a temperate South African estuary

Two sympatric mysid species, Mesopodopsis wooldridgei and Rhopalophthalmus terranatalis, dominate mesozooplankton biomass in the Sundays River estuary, South Africa. This study aimed to investigate the food and feeding rates of the two mysids on naturally occurring phytoplankton and microzooplankton assemblages, and on copepod instars, using laboratory based feeding and predation experiments. Maximum clearance rates calculated for different size classes of M. wooldridgei on microplankton were on average 34.2, 15.8 and 18.6 ml ·. ind −1 ·. h −1 for adults, immatures and juveniles respectively. For the same R. terranatalis size classes clearance rates were 8.5, 13.0 and 13.5 ml ·. ind 1̄ ·. h −1 respectively. Thus, all size classes of the smaller M. wooldridgei had higher maximum clearance rates compared to any of the stages of the larger R. terranatalis, indicating that the former species fed more successfully on phyto- and microzooplankton and that these prey assemblages probably constitute the lower limit of the food particle size range consumed by the latter species. R. terranatalis is more successful in preying on larger plankton such as adult copepods and juvenile mysids. Microzooplankton was generally more important in mysid diet than phytoplankton. Apparent selection for microzooplankton species was probably due to an inability to feed efficiently on the smaller phytoplankton cells. Copepod nauplii were readily consumed by all mysid size classes. Predation rates, in terms of weight specific carbon ingestion, increased linearly with copepod instar prey concentration.

RELATIVELY NEGATIVE δ13C RATIOS OF MESOZOOPLANKTON IN THE SUNDAYS RIVER ESTUARY, COMMENTS ON POTENTIAL CARBON SOURCES

Summary Mesozooplankton, submergent and fringing macrophytes and particles suspended in the water column in the Sundays River estuary South Africa were analyzed for δ13C isotope ratios. Highly negative values (−28.3‰ to −32.0‰) for the mesozooplankton species suggest the possibility of phytoplankton rather than detritus derived from macrophytes as carbon source.

Comparative morphology of the feeding appendages of four mesozooplankton species in the Sundays River estuary

The morphology of feeding appendages of the coexisting estuarine copepods, Pseudodiaptomus hessei and Acartia longipatetla, and mysids, Rhopalophthalmus terranatalis and Mesopodopsis wooldridgei. were examined and compared as an aid in elucidating dietary differences. The robust mandibles of P. hessei copepodids compared to the more pointed and slender teeth with no molar region, of A. longipatella suggest that the latter species relies on more fragile food particles. Mandible edge indices indicate, however, omnivorous feeding by both species. No clear dietary differences could be deduced from the dimensions of the second maxillae of these copepods. Mandible edge indices calculated for the mysid species suggest a more herbivorous feeding mode in M. wooldridgei and a more carnivorous one in R. terranatalis, supporting previous studies on their diets. No interspecific differences between the mysid size classes were evident from edge indices. Significant increments in setae and setule lengths and spacing with increasing mysid size class were evident, reflecting differences in food particle sizes utilized. The morphological differences in the feeding apparatus could reflect differences in the diets between species and indicate differences in food particle sizes utilized by the various developmental stages within species. These differences in diet should reduce inter- and intraspecific competition.

Lunar influence on distribution of a calanoid copepod in the water column of a shallow, temperate estuary

Moonlight had a significant influence on the distribution of the copepodPseudodiaptomus hessei in the water column. Copepod samples were taken between March 1986 and March 1987 in the Sundays River estuary. South Africa. Late copepodid stages and adults showed vertical differences in abundance on moonlit nights, with more animals in bottom waters, but not on dark nights. Numbers of adults present in the water column were markedly lower on full moon nights compared with new moon nights. The strongest decrease in abundance was displayed by ovigerous females. These observed distribution patterns support published predation hypotheses.

Population dynamics and estimates of production for the calanoid copepod Pseudodiaptomus hessei in a warm temperate estuary

The copepod, Pseudodiaptomus hessie, was studied over 1 year in the Sundays River estuary. Maximum abundance occurred during summer in the upper half of the estuary. Nauplii and copepodid stages attained peak abundance higher up in the estuary compared with adults. Development time and body size were inversely related to temperature and varied between instars. Females took longer to reach maturity than males. Reproduction was continuous. Production estimates integrated over 1 year varied from 0·3 g dry mass m −3 at the estuary mouth to 4·3 g dry mass m −3 in the upper estuary. Annual P/B ratios varied between 78·5 and 100·2 for the same regions. High production estimates can be linked to high summer temperatures.

Mixing and circulation in the sundays river estuary, South Africa

In the winter of 1987, a field exercise of 6 weeks' duration was carried out to investigate tidal dynamics and circulation patterns in the Sundays River estuary, on the south-east coast of South Africa. Measurements included continuous monitoring of water levels inside and outside the estuary, salinity and temperature profiles along the estuary at slack tides, current velocity profiles and near-bottom currents. The estuary was found to be in a highly stratified state at neap tides, but became completely mixed at spring tides. Dynamically, it can be divided into four longitudinal sections, each with an essentially different circulation pattern. Stratification and mixing in the water column appears to depend on: (a) semidiurnal tides in the local coastal ocean; (b) the spring-neap tidal cycle; (c) freshwater input. Direct effects of wind mixing were not observed. Frequent visual observations of the phenomenon of axial convergence are supported by water temperature and current velocity data.

Covariance Analysis of Chlorophyll Distribution in the Sundays River Estuary, Eastern Cape

Summary An analysis of covariance performed on chlorophyll a distribution data from the Sundays River estuary identified five persistent water masses with significantly different chlorophyll a contents. These corresponded to different hydrodynamic regions within the estuary. The relationship between salinity and chlorophyll a was used to identify a transition zone between the low-salinity upper estuary and the brackish riverine inflow. Chlorophyll a concentrations ranged from <6 μg 1−1 near the mouth to >100 μg 1−1 in the middle and upper reaches. High variance of chlorophyll a data in this region was the result of temporal chlorophyll a fluctuations in two time scales. The first related to the daily ebb/tide and the second to the lunar spring/neap tidal cycle. Unlike its importance in larger and deeper estuaries, light played only a minor role in the horizontal distribution of chlorophyll a. The presence of a chlorophyll a maximum in the turbid low salinity region is explained in terms of the relatively constant photic depth/mixed depth ratio along the estuary and the high residence time of water in this region.

Composition, distribution and abundance of ichthyoplankton in the Sundays River Estuary

The species composition, distribution and seasonal abundance of ichthyoplankton in the Sundays River estuary was investigated at five stations from March 1986 to March 1987. Two estuarine taxa, the clupeid Gilchristella aestuaria and gobies Caffrogobius spp., accounted for 86% of the ichthyoplankton community, while the marine Mugilidae and sparid Rhabdosargus holubi together comprised 12% of the total catch. Ichthyoplankton densities were highest in the middle and upper reaches of the estuary where zooplankton stocks were greatest. Juvenile G. aestuaria predominated in the bottom waters throughout the system but the larvae were more evenly distributed (vertically) within the water column. In contrast, the mugilids were concentrated in surface waters throughout the estuary. Larvae were most abundant during spring and summer months, coinciding with the documented spawning period of most species and the peak in zooplankton biomass.

Two oncholaimid species from a South African estuary (Nematoda, Oncholaimidae)

Adoncholaimus papillatus Kreis, 1932 and Viscosia erasmi sp.nov. are described from an intertidal area of the Sundays River Estuary, South Africa. Adoncholaimus papillatus females have an, up to present, unknown organization of the demanian system: the main duct is connected with the two spermathecae by means of a strongly curved ductus uterinus. There is only one osmosium situated at the anterior part of the main duct (anteriad of the vagina). The uvette and the ductus entericus are absent. The main duct extends to the swollen part of the tail where it opens in one or two terminal pores. Viscosia erasmi sp.nov. is mainly characterized by the bifid apical part of the buccal cavity, three distinct teeth with the right ventrosublateral one the largest and by the setiform head sensilla.

The nutrient status of the Sundays River estuary South Africa

The nutrient status of the Sundays, an important estuarine system in the eastern Cape, South Africa, is described, together with other physico-chemical parameter and compared with two other local systems, namely the Swartkops and the Kromme. In the Sundays, significant nutrient gradients between the head and mouth of the estuary were found for nitrite, nitrate, phosphate, total phosphorus, silicate and faecal E. coli. Significant correlations were also found between riverflow/rainfall and some headwater nutrients. Highly significant correlations were similarly found between total inorganic nitrogen, total phosphorus and silica and salinity. In each case the relationship was linear indicating a conservative nutrient distribution along the estuary. An overall N:P ratio of 3.2:1 was obtained for the Sundays estuary (compared with 1.12:1 for Swartkops and 0.8:1 for Kromme). N:P ratios calculated separately for the head and mouth regions were 4.52:1 and 2.51:1, respectively, suggesting strong nitrogen enrichment in the headwaters from citrus fertilizer seepage upstream. Mean nitrate values for the Sundays, Swartkops and Kromme estuaries were 0.629, 0.516 and 0.064 mg l −1 respectively. Although phosphate values in the Sundays were double that of the Kromme (0.233 and 0.121 mg l −1 respectively), they were low compared to the Swartkops (1.320 mg l −1) which has phosphate enrichment due to urban sewage and industrial effluent. Faecal, E. coli was concomitantly higher in the Swartkops (640 per 100 ml −1) compared to the pollution free Sundays and Kromme (18 and 26 per 100 ml −1, respectively). Both the Swartkops and the Kromme displayed sink distributions for N and P. Both these estuaries are also rich in macrophytes with open Spartina marshes and intertidal Zostera beds. By contrast, the channel-like Sundays estuary is conservative for N, P and Si and has no saltmarshes. It is suggested therefore that the Sundays contributes nutrients to the adjacent, extremely productive Sundays beach surf zone system, which, despite nutrient recycling still requires large amounts of extrinsic nutrients in order to maintain high productivity.

Nitrogen regeneration by two surf-zone mysids,Mesopodopsis slabberi andGastrosaccus psammodytes

Nitrogen regeneration by two surf zone mysids,Mesopodopsis slabberi andGastrosaccus psammodytes, was determined under laboratory conditions. The mysids were collected from the lower Sundays River estuary, South Africa, from early spring 1984 to late summer 1985. The forms of nitrogen excreted and the effects of mass, temperature and feeding on excretion rate were determined for each species at three experimental temperatures. Comparison of the forms of nitrogen excreted revealed only slight differences between species, with ammonia the major form and urea and amino acids the secondary excretory products in both cases. Mass significantly influenced the rate of ammonia excretion at all experimental temperatures, with no significant difference in slope (common b=0.602) detected between species. During the day sediment deprivation resulted in a 15% and 20% increase in mean ammonia excretion rates of juvenile and adultG. psammodytes respectively, whereas no significant differences were found at night. The mean ammonia excretion rates of fedM. slabberi andG. psammodytes were 2 and 2.5 times higher than ‘starved’ excretion rates, respectively.G. psammodytes andM. slabberi recycle 139 to 150 g N per running meter of surf zone per year and 1 007 to 1 208 g N m-1 yr-1, respectively. Togehter this constitutes 10% of total phytoplankton nitrogen requirements in the surf zone.

Euryhaline zooplankton of the Sundays estuary and notes on trophic relationships

The euryhaline component of the Zooplankton in the Sundays River estuary was sampled monthly at 10 stations from August 1979 to April 1981. In deeper regions surface and near-bottom samples were taken (Stations 1-7) using WP2 nets. Shallow (< 2,0 m) stations were sampled in surface waters only. Water temperature ranged between 14-27 °C. A full salinity gradient was present and salinity stratification was well developed. Acartia longipatella was most abundant during winter and spring (maximum 73 300 m-3) in the lower estuary. The interaction of temperature and salinity as factors regulating temporal and spatial distribution was evident, these factors also interacting in the water column owing to stratification. The pioneer copepod species, seudodiaptomus hessei, attained high abundance following floods or increased river inflow. Three species of mysid shrimps were common in the plankton in summer, each species showing clear zones of maximum distribution. Zooplankton standing stock (dry mass) ranged from < 10 mg m-3 to 1 450 mg m-3 In surface samples and < 10 mg m -3 to 8 275 mg m -3 in bottom samples. Contribution of mysids to standing stock was rarely less than 70% and often exceeded 90%. Differences in standing stock between surface and bottom samples were owing to behavioural differences between the Zooplankton species, particularly the mysids. Behavioural adaptations play an important role in the retention of the indigenous Zooplankton in the estuary. Aspects of trophic relationships are discussed and demonstrate the significance of the Zooplankton in the transfer of energy to higher trophic levels In this estuary.

The utilization of tidal currents by the larvae of an estuarine fish

The mechanisms employed by Gilchristella aestuarius larvae to maintain their position in an estuary were investigated in the Sundays River estuary, South Africa. The larvae predominated in the bottom water on both the flood and ebb tides and by so doing, utilized the flood-tide bottom-water current and avoided the ebb-tide surface current, the net result being a transport of the larvae upstream. There was no evidence to suggest that the larvae migrate laterally toward favourable, or away from unfavourable, currents.