THE REPRODUCTIVE CYCLES OF THREE TROCHID GASTROPODS FROM THE TRANSKEI COAST, SOUTHERN AFRICA

Changes in gonadal histology were used to determine the reproductivecycles of three trochid gastropods commonly found along theTranskei coast. They were dioecious, the sexes being evenlydistributed both in terms of numbers and size. Despite someasynchrony, Monodonta australis had a distinct reproductivecycle with a short inactive period during the winter, gonadaldevelopment coincided with increasing sea temperatures and spawningtook place from late summer to autumn. Both Oxystele tabularisand O. variegata exhibited asynchronous intermittent spawningthroughout the study period. However, intensified spawning activityby O. tabularis was noted between April and September. The reproductivecycles and mechanisms of these trochids are compared with thoseelsewhere. (Received 20 January 1986;     

TEMPORAL AND SPATIAL VARIATIONS IN EXPLOITED AND NON- EXPLOITED POPULATIONS OF THE INTERTIDAL LIMPET CELLANA CAPENSIS

Temporal and spatial variations in the density, size compostionand growth of exploited and non-exdploited populations of theintertidal limpet Cellana capensis from the Transkei coast ofsouthern Africa, between 1989 and 1991, are described. The timingand intensity of recruitment varied between shores and amongstsites within shores. Recruitment success was relatively poorand, in fact, at some of the protected sites no recruitmentwas recorded until July 1991. Juvenile and adult limpets wereboth significantly more abundant at the exploited than at theprotected sites. The gradual decline in density of limpets observedat the latter sites reflected poor recruitament as well as senescenceof older individuals. The extent of variations in density amongstshores was also found to vary from censius to census. Limpetsat the exploited sites tended to be much smaller than thosefound at the protected sites. Although there were initiallyno differences in the size of limpets amongst sites withingshores marked differences became apparent during the courseof the study. This finding, together with the observation ofmarked annual differences in population size compostion at severalof the study sites highlighted the temporal instability of thesepopulations. Such results have profound implications for comparativestudies of population size composition. The absence of significant differences in growth rate amongstshores suggests that differences in the intensity of competitiveinteractions may have been offset by the higher microalgal productionat the exploited shore. It is also suggested that upshore migrationof largter individuals may counter the intense competition experiencedat mid-tidal levels on the exploited shore. Differences in therate of recritment could also account for some of the observeddifferences in population characteristics. Both of these explanationsare viable alternatives to an earlier proposal which attributeddifferences solely to the effects of size-selective predationby man. (Received 30 May 1992; accepted 10 December 1992)     

SPATIAL VARIATION IN DENSITY AND BIOMASS OF PATELLID LIMPETS INSIDE AND OUTSIDE A MARINE PROTECTED AREA

Although differences in the mean density, biomass and size ofrocky intertidal biota inside and outside MPAs have been welldocumented, little is known about the variability in these attributesat different spatial scales. This topic merits investigationbecause it can influence the outcome of reproduction, competitionand predation, and thereby affect the viability of populations.In this study, a nested sampling design was used to assess differencesin density and biomass of seven species of patellid limpetsat the scales of plots, sites and shores inside and outsidea marine protected area (MPA) on the southeast coast of SouthAfrica. At the scale of plots, significant variation was morecommon inside than outside the MPA. This probably reflects differencesin the general pattern of space occupancy and quality of habitatsavailable to limpets inside and outside the MPA. Significantvariation at the scale of sites was rare. This suggests thateither the processes contributing to variability at this scalecounteract each other or that the sites were similar in termsof habitats and ecological processes. At the scale of shores,significant variation was more common in densities than in biomass,but both occurred with equal frequency inside and outside theMPA. Variation at this scale is probably driven by a combinationof recruitment and/or mortality. Five species exhibited greaterspatial variability inside than outside the MPA. The spatialpatterns observed did not appear to be linked with differencesin the mobility, habitat requirements or susceptibility of thesespecies to exploitation. The lack of consistent patterns suggeststhat each species probably responds in a different way to theecological processes operating at these spatial scales. (Received 1 February 2005; accepted 29 July 2005)     

ASYNCHRONOUS REPRODUCTIVE ACTIVITY IN THE BROADCAST SPAWNER CELLANA CAPENSIS (GMELIN, 1791) (GASTROPODA: PATELLIDAE)

Short-term fluctuations in the reproductive condition of thelimpet Cellana capensis are described. Gravimetric and histologicalanalyses of gonadal development were carried out on samplescollected at 4 day intervals over a 3 month period from theMkambati Nature Reserve, Transkei. The results indicate a distinctlack of reproductive synchrony within the population, whichapplied not only to gametogenic development per se but alsoto spawning activity. Some of the spawning events identifiedduring the study period were more marked than others, thesemay reflect a greater degree of synchronization in activity.Results presented suggest that C. capensis is probably a ‘partial’rather than a ‘complete’ spawner. The implicationsof asynchronous spawning activity for the reproductive successof broadcast spawners are also discussed. (Received 6 December 1988; accepted 15 February 1989)     

BUCEPHALID TREMATODE INFECTIONS IN MYTILID BIVALVES FROM THE ROCKY INTERTIDAL OF SOUTHERN CHILE

Bucephalid trematode sporocysts were found embedded amidst themantle tissue and viseral mass of intertidal mytilid bivalvesfrom Southern Chile. An investigation into the prevalence ofinfection revealed that <1% of Perumytilus purpuratus wereinfected whereas 20–32% of the Semimytilus algosus examinedharboured sporocysts. No sporocysts were found in an adjacentpopulation of Choromytilus chorus. Prevalence of infection wasrelated to size of S. algosus present at a particular site,and generally increased with host size. The majority of parasitizedmussels appeared to be at an advanced stage of infection, inthese animals destruction of the host's gonadal tissue was evident.Such parasitic castration combined with high prevalence of infectionsuggests that the reproductive potential of this mytilid maybe severely impaired. The implications of these results forthe mariculture industry are also discussed. (Received 19 February 1991; accepted 11 June 1991)     

BEHAVIOURAL ADAPTATIONS OF THE MANGROVE WHELK, TELESCOPIUM TELESCOPIUM (L.), TO LIFE IN A SEMI-TERRESTRIAL ENVIRONMENT

The movements of individually marked Telescopium telescopiumin the upper intertidal zone at Bowling Green Bay, N.E. Queenslandwere followed over a five week period. During their inactivephase these snails were found clustered together in refuge micro-habitatswhere the harsh physical conditions were ameliorated relativeto those on the exposed mud surface. The timing of activitywas related to the tital regime, with movement initiated bytidal inundation. There was no evidence of an endogenous componentto the activity rhythm. Synchronization of movements with thetidal regime is of vital importance to survival; animals leftexposed succumbed to heat stress. (Received 17 October 1985;