A. C. Brown

THE ECOLOGY OF THE SANDY BEACHES OF THE CAPE PENINSULA, SOUTH AFRICA PART 2: THE MODE OF LIFE OF BULLIA (GASTROPODA: PROSOBRANCHIATA)

Summary This paper gives an account of the present state of our knowledge of the sandy-beach snail, Bullia, on the beaches of the Cape Peninsula. The work deals mainly with the two surf-loving species, B. digitalis and B. rhodostoma, though mention is made of B. laevissima, a species found in quiet waters. Reproductive behaviour is described for the first time. Much of the work reported concerns chemo-reception and the responses which lead to feeding. Some conclusions are reached with regard to growth and life-span. The distribution of the three species is dealt with, and the factors responsible for this distribution are discussed. Attempts to estimate the numbers of Bullia on Muizenberg beach are described. Some mention is made of water- and heat-relationships, defence mechanisms and parasites.

THE ECOLOGY OF THE SANDY BEACHES OF THE CAPE PENINSULA, SOUTH AFRICA. PART 1: INTRODUCTION

Summary This is the first in a series of papers devoted to the ecology of the sandy beaches of the Cape Peninsula. Conditions on these beaches are described, with special reference to the beaches of Hout Bay, Llandudno, Milnerton and Muizenberg. Tidal conditions, wave-action, beach profiles and sand movements are discussed, while attention is also given to the particle-size distribution of the substrata forming the beaches. The organic content of the sand, its permeability and porosity, and the disposition of the water-tables are all discussed briefly and some data concerning salinities, temperature and pH are presented. Mention is made of the fauna and a list of the more important members of the resident fauna of the beaches accorded special attention is given. There is some attempt to show how the physical factors are interrelated.

THE ECOLOGY OF THE SANDY BEACHES OF THE CAPE PENINSULA, SOUTH AFRICA. PART 3: A STUDY OF GASTROSACCUS PSAMMODYTES TATTERSALL (CRUSTACEA: MYSIDACEA)

Summary The intertidal sandy-beach mysid, Gastrosaccus psammodytes, has been studied with respect to burrowing behaviour, substrate discrimination, reactions to water currents, responses to light, detection of changes in hydrostatic pressure, methods of feeding, reproduction and development, and distribution. Some mention is also made of the animals defence mechanisms, its tolerance of reduced salinities and certain other aspects of its ecology. Despite the success with which G. psammodytes has colonized the intertidal zone of surf-swept sandy beaches, it is concluded that this colonization has been achieved without drastic deviation from the usual mysid patterns of structure and behaviour.

THE ECOLOGY OF THE SANDY BEACHES OF THE CAPE PENINSULA, SOUTH AFRICA. PART 4: OBSERVATIONS ON TWO INTERTIDAL ISOPODA, EURYDICE LONGICORNIS (STÜDER) AND EXOSPHAEROMA TRUNCATITELSON BARNARD

Summary Two isopods, Eurydice longicornis and Exosphaeroma truncatitelson, have been studied in the field and in the laboratory with a view to elucidating aspects of their ecology. Particular attention has been given to factors which may be relevant to their distribution, as the two species are virtually segregated in the field. It is shown that both species favour some grades of sand over others, Exosphaeroma choosing finer substrates than Eurydice. Choice is made by trial burrowing. Studies of burrowing behaviour, depth of burrowing and reactions to water currents also demonstrate that Eurydice is better adapted to life on exposed sandy beaches than is Exosphaeroma. The food relationships of the animals, their reproduction, responses to light and hydrostatic pressure are dealt with briefly. In addition to a comparison between Eurydice and Exosphaeroma on Cape Peninsula beaches, an attempt is made to compare Eurydice longicornis with the European E. pulchra.

THE ECOLOGY OF SOUTH AFRICAN ESTUARIES PART IX: NOTES ON THE ESTUARY OF THE ORANGE RIVER

The Orange River presents a type of estuary previously undescribed for southern Africa. The estuarine fauna is extremely poor and lacks a true estuarine component. An analysis of the physical and chemical conditions indicates that the environment is particularly forbidding and it is suggested that the striking paucity of the fauna may be related to the short length of the estuary in winter and its complete disappearance in summer.

OBSERVATIONS ON THE EFFECTS OF CRUDE OIL POLLUTION ON THE SANDY-BEACH SNAIL, BULLIA (GASTROPODA: PROSOBRANCHIATA)

Summary The effect of crude oil on Bullia has been observed in the field, following an oil spill, and in the laboratory, using a light Arabian oil. Well-defined stress symptoms appear at sub-lethal concentrations; at higher doses these give way to paralysis before death ensues. Very low concentrations are fatal if there is contact between the animals and the oil, even if the oil has been weathered. If there is no direct contact much higher concentrations of fresh oil can be tolerated and weathering greatly reduces toxic effects. Mass mortality is unlikely to occur through eating oil-contaminated food.

EFFECTS OF CADMIUM AND ZINC ON OXYGEN UPTAKE IN THE WHELK BULLIA DIGITALIS (DILLWYN)

SUMMARY Solutions of both cadmium chloride and zinc chloride affect the oxygen intake of Bullia digitalis at 15 °C, the sensitivity to cadmium being about ten times greater than to zinc. Zinc concentrations above 1 ppm result in a lowering of oxygen consumption, uptake being reduced by some 40% at 2 ppm. Cadmium, on the other hand, increases respiration at levels between 0,1 and 0,7 ppm, there being an increase of 30% at 0,5 ppm. Above 0,6 ppm cadmium, oxygen uptake decreases rapidly and is 20% below normal at 0,75, 38% down at 1 ppm. Altering the temperature within the range 10–20 °C has little effect on these responses, while the length of the exposure period has a greater effect. Low concentrations of zinc do not alter the responses to cadmium but at higher concentrations of zinc the effect is additive.

OBSERVATIONS ON THE EFFECT OF AMMONIUM NITRATE SOLUTIONS ON SOME COMMON MARINE ANIMALS FROM TABLE BAY

Summary The toxicity of ammonium nitrate in natural sea water has been studied with respect to a number of sandy-beach animals, to the rock lobster, Jasus llalandii, and to the isolated heart of Ciona intestinalis. Results are integrated with previous findings on other species.

THE EFFECT OF AMMONIUM NITRATE SOLUTIONS ON SOME ASPECTS OF THE BIOLOGY OF THE BLACK MUSSEL, CHOROMYTILUS MERIDIONALIS

Summary The effects of low concentrations of ammonium nitrate on the fertilization and early development of Choromytilus meridionalis have been studied in the laboratory at 14°C. Concentrations up to 10 p.p.m. have no significant effect on fertilization, though concentrations as low as 0,5 p.p.m. retard early development. Spontaneous recovery takes place unless the pollutant is repeatedly renewed. At 10 p.p.m. a high proportion of the larvae achieving the veliger stage show abnormal shell growth. At 100 p.p.m. ammonium nitrate there is complete failure to pass beyond the trochophore stage, development tending to terminate at gastrulation. These results contrast with the tolerance of the adults, solutions of 1 000 p.p.m. having no significant effect on either the tendency to shell adduction or the ciliary beat of the gills.