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

Abstract

OPSOMMINC'n Verslag word gegee van ons kennis van die strandslak, Bullia, op die Kaapse Skiereilandstrande. Dit is vernaamlik die twee soorte, B. digitalis and B. rhodostoma, albei soorte wat lief vir die branding is, wat behandel word. Die B. laevissima, 'n soort wat voorkeur het vir kalm water, word ook vermeld. Die voortplantingsgedrag word vir die eerste keer beskrywe. Heelwat van die werk gaan oor chemoresepsie en die reaksies wat tot voedselopname lei. Sommige gevolgtrekkings word gemaak in verband met groei en ouderdom. Die verspreiding van die drie soorte en die faktore wat 'n rol speel word bespreek. 'n Beskrywing word gegee van pogings om die aantal Bullia wat op die strand by Muizenberg voorkom, te skat. Die rol wat water en temperatuur in die lewe van hierdie diere speel, word vermeld, asook hulle verdedigingsmetodes en die organismes wat op hulle parasiteer. SUMMARYThis 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 chemoreception 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.

High population connectivity and Pleistocene range expansion in the direct-developing plough shellBullia rhodostomaalong the South African coast

“…The right inset shows the current distribution of B. rhodostoma. The major marine biogeographic regions (Griffiths et al 2010) are indicated at the bottom of the figure; abbreviations are as follows: NMB  Namaqua Bioregion, SWCB  South-Western Cape Bioregion, AB  Agulhas Bioregion, NB  Natal Bioregion, DB  Delagoa Bioregion Numerous egg capsules, each with at least 150 eggs, are deposited 4-12 cm below the sand surface or on the ventral surface of the foot of the females (Brown 1971;da Silva and Brown 1985). Owing to their direct developmental mode, and because sandy beaches are interspersed with rocky shores, Bullia species are expected to exhibit high genetic differentiation across their geographic range.…”

“…The two-phase life cycle of Bullia species involves benthic eggs that undergo up to five weeks of lecithotrophic development to hatch directly (i.e. no planktonic phase) into miniature snails (Brown 1971;da Silva and Brown 1985 Figure 1: Sampling localities, oceanic currents, biogeographic regions, and directionality of gene flow between adjacent localities for Bullia rhodostoma on the South African coast. Arrows indicate the direction of gene flow and the thickness of an arrow is proportional to relative migration rate.…”

Gametogenic activity in three internally fertilized prosobranchs from southern Africa, with notes on the egg capsules ofBurnupena lagenaria

“…Previous studies on the reproductive biology of rocky intertidal molluscs from southern Africa have been restricted to broadcast spawners (Newman 1967;Branch 1974;Griffiths 1977;Joska & Branch 1983;Lasiak 1986aLasiak & b, 1987a. With the exception of sandy beach whelks of the genus BuJlia (Brown 1971;McGwynne & van der Horst 1985) little is known of reproduction in gastropods which copulate and deposit egg capsules. The present study, based on gonadal histology, examines the gametogenic cycles of three numerically abundant internal fertilizers: the archaeogastropods Nerita albicilJa and Nerita plicata and the neogastropod Bumupena lagenaria.…”

Growth and Production ofBullia Rhodostomaon an Open Sandy Beach in Algoa Bay

“…Plough shells of the genus Bullia are well represented on South African sandy shores with five intertidal and eight subtidal species (Brown 1971). They are carnivorous scavengers and feed on stranded organisms, particularly coelenterate medusae and siphonophores.…”

“…They are carnivorous scavengers and feed on stranded organisms, particularly coelenterate medusae and siphonophores. Some aspects of the general biology and physiology of Bullia species in the Cape Peninsula have been studied by Brown (1961Brown ( , 1971. However, despite the quantitative importance of this group on South African sandy beaches (McLachlan 1977 b,c) there are no published data on population parameters such as growth and production.…”