Langebaan Lagoon Research Articles

Energy budgets of curlew sandpipers at Langebaan Lagoon, South Africa

The energy requirements and energy consumption of curlew sandpipers Calidris ferruginea at Langebaan Lagoon, South Africa, are described. The paper also includes estimates of the net annual production of the benthic invertebrates potentially available to the birds, and of the birds' impact on this. Mean estimated energy requirement of a free-living curlew sandpiper was 125 kJ day −1 . Mean energy intake was 180 kJ day −1 , with 144 kJ assimilated at an assumed assimilation efficiency of 80%. Overwintering immature birds had a negative energy balance. A substantial positive balance existed in late summer and autumn, when adult birds moult and lay in fat reserves for migration. The estimated mean net annual production of benthic invertebrates potentially available to curlew sandpipers was 705±444 kJ m −2 yr −1 . The birds took 12·3% of this or 86·7 kJ m −2 yr −1 . It appears that the carrying capacity of Langebaan Lagoon for curlew sandpipers has not been reached with respect to food, but food is unlikely to be the only limiting factor.

Breeding biology of the White-fronted Plover (Charadrius marginatus) in the south-western cape, South Africa

Summary A small breeding population of White-fronted Plovers Charadrius marginatus was studied at Langebaan Lagoon, South Africa, between 1974 and 1977. Adults maintained territories throughout the year though territory holders sometimes joined flocks of non-territorial birds, usually outside the breeding season. Territories included sections of sand dune and beach where nests were located, and an area of intertidal sand flat where the birds fed. The species is monogamous and mates are usually faithful to each other for long periods. Divorce was recorded and two birds whose mates disappeared, presumed dead, did not lose their territories. Eggs were found between June and January (eight months). A minimum of two to four days elapsed between the laying of the first and second egg. The mean clutch size was 2·1 eggs and the most frequent clutch was two. Incubating birds moulted some tertials, tail and body feathers. Incubation was shared by the sexes and lasted 26 or 27 days (one record). Breeding success was...

South African populations of Littorina rudis

Littorina rudis was collected from stands of Spartina capensis in saltmarsh habitats within Langebaan and knysna lagoon, Cape Province. It was absent from rocky sores and from saltmarshes east of Knysna. The shell, radular and penial morphology are described. L. rudis from both localities bore tessellated colour patterns similar to those of British saltmarsh ecotypes. The Knysna population contained individuals with a unique amber background colour. The shells from Knysna and Langebaan were very thin in accordance with the sheltered habitats. The number of embryos carried in the brood puch was similar in both countries. Sexual maturity was attained at about 4 mm shell length; the male and female modal sizes were 4.9 mm and 5.1 mm respectively at Langebaan. No. published records were found for L. rudis in South West Africa. Some possible origins of the South African L. rudis populations are discussed.

A PRELIMINARY ANALYSIS OF BACTERIAL NUMBERS AND BIOMASS IN LANGEBAAN LAGOON

Summary Water samples taken down the length of Langebaan lagoon reveal a decline in bacterial numbers from Saldanha Bay to the head of the lagoon, with a parallel decline in suspended particles. Bacterial biomass (x 43, 27 mg.m−3) was comparable to zooplankton biomass. Intertidal samples from different sediment types showed an increase of bacteria towards the southern tip of the lagoon, with decrease in particle size and increases in percentage mud and percentage organic material. Bacteria comprise only a small percentage of the organic pool, but their biomass ranges from 16 to 232 mg (dry weight) per kg of wet sediment. This approximates a mean of 14,2 g (dry weight) per m2 (range 1,32 to 25,74): comparable to the biomass of benthic macrofauna. Considerable seasonal variation occurs in the organic pool.

THE DIET OF THE CURLEW SANDPIPER AT LANGEBAAN LAGOON, SOUTH AFRICA

Summary Puttick, G. M. 1978. The diet of the Curlew Sandpiper at Langebaan Lagoon, South Africa. Ostrich 49:158-167. Nereid worms (mainly Ceratonereis erythraensis) and the hydrobiid gastropod Assiminea globulus were the most important prey items throughout the year for Curlew Sandpipers Calidris ferruginea feeding at Langebaan Lagoon. Other important items were the amphipod Urothoe grimaldi, the crabs Hymenosoma orbiculare and Cleistostoma edwardsii and dipteran larvae (Stratiomyidae). Immature Curlew Sandpipers took smaller prey items than adult birds. The diet of male and female birds differed in the proportion, sue and range of prey items taken.

DISTRIBUTION AND NUMBERS OF COASTAL WADERS (CHARADRII) IN THE SOUTHWESTERN CAPE, SOUTH AFRICA, SUMMER 1975–76

Summary Summers, R. W., Cooper, J. & Pringle, J. S. 1970. Distribution and numbers of coastal waders (Charadrii) in the southwestern Cape, South Africa, summer 1975–76. Ostrich 48: 85–97. A survey of the distribution and numbers of waders (suborder Charadrii) in the coastal regions of the southwestern Cape was conducted from November 1975 to February 1976. Forty-four coastal wetlands and 49 sections of coastline were visited between the Olifants and Groot-Brak rivers. The estimated total wader population was 119 008 of which 102 841 (86,4%) were Palaearctic migrants. Langebaan Lagoon and the Berg estuary supported the largest numbers. The Curlew Sandpiper Calidris ferruginea and Sanderling Calidris alba were the most numerous species. The abundance of waders was greater on west coast shores than along the south coast.

Langebaan lagoon: a mixed carbonate-siliciclastic tidal environment in a semi-arid climate

Langebaan Lagoon is a mixed siliciclastic-carbonate tidal environment in a hot, semi-arid climate about 100 km north of Cape Town. The tidal range reaches 1.8 m at spring tide. Peak current velocities of 1.3 m/sec are recorded at the inlet. The tidal ellipse is characterized by a significant time-velocity asymmetry with ebb-current dominance. Absence of open mud flats is attributed to low freshwater drainage into the lagoon. Salt marshes are well developed in the south. The lagoon divides physiographically into a north-south sequence following the modern energy gradient. In contrast sediment distribution is east-west aligned, dividing the lagoon into two major provinces that reflect a different, relict energy regime. The sediments consist predominantly of a quartz-carbonate mixture. Both sedimentary components are in hydraulic equilibrium although concentration levels are diametrically opposed. The carbonate content decreases from over 40% in the north to less than 5% in the south. This differential concentration is explained by selective separation of the carbonate component during the transportation phase of the sediment. The modern sand banks and intertidal flats are underlain by large fossil oyster reefs dating between 6000 and 2000 years B.P. Primary sedimentary structures are environmentally sensitive. Large underwater dunes occur in the channels. The upper intertidal flats, close to the lagoonal beaches, are characterized by a distinct association of primary structures. Evaporites are not forming under present climatic conditions and the lack of such deposits, together with the absence of open mud flats, could be a good indicator for a semi-arid climate with marked seasonal changes. The modern lagoon originated by flooding and scouring of a late Pleistocene fossil dune landscape during the early Flandrian transgression that reached about 3 m above present sea level. Regression to present sea level terminated about 2000 years B.P.

PHYSICAL AND CHEMICAL CHARACTERISTICS OF WATER IN SALDANHA BAY AND LANGEBAAN LAGOON

Summary In April 1974 the Sea Fisheries Branch commenced a detailed survey of the physical and chemical characteristics of the water in Saldanha Bay and Langebaan Lagoon to establish base-line conditions in the region prior to the development of the bay as a major port and industrial centre. The thermohaline characteristics of the water resemble those of the Benguela Current, although in summer surface heating and evaporation tend to raise the temperature and salinity somewhat. This is most marked in the Langebaan Lagoon where surface temperatures and salinities in excess of 24 °C and 37 %0 were recorded during the latter part of summer. A variety of chemical parameters were determined. These include a number of heavy and transition elements, dissolved oxygen, nitrate/nitrite, inorganic phosphorus, total phosphorus, reactive silica, pH, chlorophylls, chemical oxygen demand and oxygen absorbed. Data for some of these parameters are tabulated, and indicate that the bay is at present relatively unpolluted. Prior to 1974 organic pollution from the fish factories in Hoedjies Bay was serious, but the situation has shown a marked improvement since the installation of the dry off-loading systems for fish. The circulation pattern in Saldanha Bay is complex. The bay and lagoon are tidal and currents in the upper 5 m are highly dependent on wind speed and direction. Surface currents in the region have a magnitude typically in the range 10–20 cm/sec. Currents in the mouth of the bay are tidal and are not appreciably influenced by wind. Tidal currents of up to 1 m/sec were recorded at the entrance to Langebaan Lagoon. The construction of the jetty and breakwater is altering the circulation pattern. The physical and chemical data indicate the existence of three systems, viz. Bay System, Lagoon System and Benguela System. The interchange between the bay and the open sea is small and on the basis of a simple model the removal time of pollutants from the bay was calculated as 20 days. The available data indicate that the discharge of noxious and toxic effluents into the bay should be discouraged. The beach near the residential area of Saldanha Bay and the Donkergat peninsula will probably be polluted on occasions once the harbour comes into operation, and it is not impossible that Langebaan Lagoon will also become polluted.

THE ZOOPLANKTON OF LANGEBAAN LAGOON AND SALDANHA BAY

Summary The zooplankton of Langebaan Lagoon and Saldanha Bay are described on the basis of 127 plankton samples taken between 1946 and 1976. Hydrological conditions are described indicating a range from marine conditions in Saldanha Bay to hypersaline conditions at the head of the Langebaan Lagoon. Different zooplankton communities occur in different parts of the Saldanha-Langebaan system. In Saldanha Bay the plankton is composed predominantly of species which occur in the neritic plankton of the west coast. The plankton of Langebaan Lagoon is distinct but elements of the Saldanha Bay plankton community penetrate the lagoon to various extents. At the head of the lagoon the plankton community is estuarine in character which is remarkable as Langebaan Lagoon is not an estuary. The significance of this is discussed. Zooplankton biomass was highest in the middle reaches of Langebaan Lagoon ([xbar] = 41,80 mg/m3) and lowest at the head of the lagoon ([xbar] = 16,84 mg/m3) where the lowest diversity index also was recorded. Studies of diurnal variations indicate that the distribution of plankton in Langebaan Lagoon is essentially dynamic resulting from a complex interaction between vertical migration and tidal transport.

DISTRIBUTION OF RECENT SEDIMENTS IN SALDANHA BAY AND LANGEBAAN LAGOON

Summary Sediment distribution in Saldanha Bay is wave controlled and can be related to the energy levels created by the refraction pattern. Four energy zones are distinguished in the inner bay: a centrally exposed zone, two marginal semi-exposed zones, a sheltered zone in the north and a bay/lagoon transitional zone in the south. Sediment is supplied on the abrasion platform of the exposed zone and along the rocky shoreline of the North Channel. These areas display the coarsest sediments. In North Bay medium sands dominate, whereas the South Channel is characterized by very fine sands. Both semi-exposed zones as well as the sheltered zone consist of very fine sand. The bay/lagoon transitional zone is constructed of a tidal delta made of fine sand. Sediment distribution seems to be in equilibrium with the prevailing hydrodynamic regime. In contrast, Langebaan Lagoon is a current controlled regime. Four physiographic units can be separated: tidal channels, subtidal flats and sandbanks, intertidal flats, and salt marshes. These units reflect the major energy levels of the tidal system. Texturally the lagoon divides into two major zones separated roughly by the central channel. East of the channel fine sands dominate, whereas west of the channel medium sands are more frequent. Coarse sediments occur as lag deposits in the northern outflow channels. In contrast to the dominating presence of very fine sand in Saldanha Bay this size fraction is surprisingly deficient in Langebaan Lagoon. There is evidence for a Holocene high stand of the sea between 6 000 and 2 000 y B.P. The modern sediment distribution is the result of the subsequent regression and stabilization of the sea-level about 1 800 y B.P., and is therefore essentially a relict feature.

PHYTOPLANKTON PRODUCTION IN LANGEBAAN LAGOON AND SALDANHA BAY

Summary Between February 1971 and February 1972 monthly measurements of phytoplankton primary production were made at six stations in Langebaan Lagoon. The gross primary production rates obtained showed a marked seasonal variation. They increased from 261,6 mgC/m3/day in winter to 675,4 mgC/m3/day in spring and to a maximum of 885,3 mgC/m3/day in summer. Production rates ranged from 611,0 mgC/m3.day at the entrance of the lagoon to 162,6 mgC/m3/day at the station nearest to the head of the lagoon. A correlation between total chlorophyll and gross primary production was established for the lagoon, and was used in conjunction with chlorophyll concentrations and water transparency measurements from Saldanha Bay to estimate the gross primary production for the bay. The estimates ranged from 864,9 mgC/m2/day to 3 301,2 mgC/m2/day.

DISTRIBUTION OF BENTHIC MACROFAUNA IN LANGEBAAN LAGOON

Summary Fifteen stations were sampled in Langebaan Lagoon using a diver-operated suction sampler. The macrofauna was analysed using numerical methods, by the rarefaction technique, to define relative species richness and by ash-free dry-weight biomass determinations. Three basic groups were defined which were the channel, island and sandbank groups. The channel and island groups had the greatest biomass and the highest species richness values respectively. In contrast the sandbank group had the lowest biomass values, intermediate species richness values and the highest density of individual animals per m2 The availability of food, water current velocity and hence sediment texture, water temperatures and salinity apparently were most important factors in determining the distribution of the macrofauna.

DISTRIBUTION, ABUNDANCE AND ENERGY RELATIONSHIPS OF WADERS (AVES: CHARADRII) AT LANGEBAAN LAGOON

Summary The distribution and numbers of waders on the low-tide sandflats and at high-tide roosts at Langebaan Lagoon during the austral summer of 1975–6 are described. The sandflats in Rietbaai, and at the lower and upper sections of the lagoon supported the highest densities of waders. Several species were restricted in their distribution. The majority of the high-tide roosts, incorporating some 30 000 waders, were situated on Arthrocnemum saltmarsh, especially between Bottelary and Geelbek. Approximately 1 000 waders (3 % of the lagoon's population) roosted on the beaches along the Atlantic coastline at high tide. Many thousands roosted on the beach north of Langebaan village at night. The wader community consumed an estimated quantity of food equivalent to 20,8 kcal/m2 per year. Between 2,1 and 6,2 kcal/m2 per year are returned as faeces to the lagoon system. Feather material deposited in the lagoon was equivalent to 0,06 kcal/m2 per year.

A PRELIMINARY REPORT ON THE GEOCHEMISTRY OF RECENT SEDIMENTS IN SALDANHA BAY AND LANGEBAAN LAGOON

Summary Average major and trace element data are reported for recent sediments from Saldanha Bay and Langebaan Lagoon. Chemically, the sediments are composed mainly of SiO2 and CaCO3 (SiO2 + CaCO3 > 93 %). The sediments are considered to be a three-component mix of quartz, calcite and a granitic fraction presumed to be derived from local granitic rocks.

SPATIAL AND TEMPORAL VARIATIONS IN INTER-TIDAL ANIMAL DISTRIBUTION AT LANGEBAAN LAGOON, SOUTH AFRICA

Summary Spatial and temporal changes in the distribution of food organisms potentially available to curlew sandpipers Calidris ferruginea at Langebaan Lagoon (33 °S, 18 °E) are described for the period February 1974—March 1975. The inter-tidal benthic fauna at sandy sites showed spring and autumn peaks in biomass and numbers. The fauna was dominated by the gastropod Assiminea globulus, which comprised 62,5% of the total biomass. A Production: Biomass ratio of 4,96 was found for this species, and 1,36 for the amphipod Urothoe grimaldi. The fauna at sites containing macrophytes (Spartina, Zostera, Arthrocnemum) showed winter peaks in biomass and numbers. Classification and ordination confirmed the discreteness of macrophyte and non-macrophyte sites, each having its own characteristic benthos. There was a positive correlation between the distribution of benthos and sediment parameters at the different sites, macrophyte sites having a higher fine fraction and organic content.

THE VEGETATION OF THE LANGEBAAN AREA, SOUTH AFRICA

Summary An account, with illustrations, is given of 20 terrestrial plant communities found in the vicinity of Langebaan Lagoon. A map is included which is based on the Braun-Blanquet method of vegetation sampling and data synthesis, and on the photo interpretation of 1:10 000 scale colour aerial photographs. Known rare and endangered plants occurring in the Saldanha—Langebaan area are listed. Recommendations are made for the establishment of a nature reserve which includes the marsh communities around the lagoon and the varied West Coast Strandveld vegetation on the Langebaan Peninsula.

THE PALAEARCTIC WADER POPULATION OF LANGEBAAN LAGOON

Summary Pringle, J. S. & Cooper, J. 1975. The Palaearctic wader population of Langebaan Lagoon. Ostrich 46:213-218. Monthly counts of Palaearctic waders were made at high tide in three areas of Langebaan Lagoon, southwestern Cape, during 1973 and 1974. A total of sixteen species was observed. The five commonest species, in order of abundance, were Curlew Sandpiper Calidris ferruginea, Grey Plover Squalarola squatarola, Turnstone Arenaria interpres, Knot C. canutus and Sanderling C. alba. Together they formed 95,7% of the population counted. Waders arrived in September and departed in March and April. Overwintering populations of the commoner species were observed. Estimates of the total population size of the lagoon were 41 000–55 000 in summer and 10 500 in winter. These figures are of value for nature conservation and show that the lagoon is a wetland of international importance.

An assessment of the role of the sand sharkRhinobatos annulatusas a predator in Langebaan Lagoon

The possible impact of predation on benthic invertebrates by the sand shark Rhinobatos annulatus in Langebaan Lagoon was investigated. Studies on the population dynamics and the feeding biology of the sand sharks indicated temporal and spatial changes in the intensity of predation. Temporal changes were seasonal, numbers and biomass increasing during summer. The sand sharks were concentrated in specific areas of the lagoon, and their distribution appeared to be correlated with that of prey biomass. Crustaceans constituted the major portion (88,12%) of the diet. Calculations suggest that 26–77 per cent of the annual invertebrate production is consumed by sand sharks, so it is evident that R. annulatus has a substantial impact on the macrofauna and thereby plays an important role as a predator in Langebaan Lagoon.

Report on the Tanaidacean Crustacea of Langebaan lagoon and Saldanha bay, on the West Coast of South Africa

Report on the Tanaidacean Crustacea of Langebaan lagoon and Saldanha bay, on the West Coast of South Africa