The structure of rocky intertidal communities may be influenced by large-scale patterns of productivity. In this study we examine the in situ rates of production by intertidal epilithic microalgae (chlorophyll a production per unit area per month), intertidal nutrient concentrations (nitrates, nitrites, phosphates and silicates), and standing stocks of different functional-form groups of macroalgae around the South African coast, and their relationships to consumer biomass. Clear gradients of in situ intertidal primary production and nutrient concentrations were recorded around the South African coast, values being highest on the west coast, intermediate on the south and lowest on the east coast. Primary production by intertidal epilithic microalgae was correlated with nutrient availability and could also be related to nearshore phytoplankton production. The dominance patterns of different functional forms of macroalgae changed around the coast, with foliose algae prevalent on the west coast and coralline algae on the east coast. However, overall macroalgal standing stocks did not reflect the productivity gradient, being equally high on the east and west coasts, and low in the south. Positive relationships existed between the average biomass of intertidal intertebrate consumers (grazers and filter-feeders) and intertidal productivity, although only the grazers were directly "connected" to in situ production by epilithic intertidal microalgae. The maximum body size of a widely distributed limpet, Patella granularis, was also positively correlated with level of in situ primary production. The maximal values of biomass attained by intertidal filter-feeders were not related to intertidal primary production, and were relatively constant around the coast. At a local scale, filter-feeder biomass is known to be strongly influenced by wave action. This implies that the local-scale water movements over-ride any effects that large-scale gradients of primary production may have on filter-feeders. The large-scale gradient in intertidal productivity around the coast is thus strongly linked with grazer biomass and individual body size, but any effect it has on filter-feeder biomass seems subsidiary to the local effects of wave action.

The autocology of the intertidal brown alga, Fucus spiralis was studied at Ketch Harbour, Canada. In particular, aspects investigated included fecimdity, reproductive allocation (R. A.), recruitment and changes in canopy structure which result from reproduction.Peak fertility occurred in September, at which time strong positive correlations exist between frond mass and both receptacle mass and number. A mean fecundity of 284.6 eggs m~2 was estimated, but correlations between frond mass and fecundity are Iow. R. A., which is dependent on frond mass, reaches a maximum of 30% in September in fronds with a mass of more than 4g. A significant decrease in R. A. occurred after September.During September to November, attrition of receptacles and old fertile blades occurs. These changes result not only in the reduction of biomass, but more importantly, in a significant change in biomass distribution within the canopy. Concomitantly, a rapid recruitment of fronds occurs. It is postulated that this recruitment is partially, if not largely due to a reduction in shading by the overstorey of the canopy.The aims of this study were thus a) to determine the total reproductive proportion (R. A.) of the Standing crop of F. spiralis, rather than just the biomass of gametes äs reported by Vernet and Harper (1980); b) to determine the fecundity of this species; Botanica Marina / Vol. 30 / 1987 / Fase. 6

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Different processes shape ecological communities at different physical scales. Their relative importance is central to ecology, particularly in the case of foundational species like mussels. For 5 yr at 8 locations across 5 bioregions spanning 3200 km of the southern African coast, we monitored recruitment and adult populations of 4 intertidal mussel species. At most locations, mussel bed width and percent cover were surprisingly constant, but declines did occur at 3 locations. Recruitment rates displayed a strong geographic gradient: exceptionally high on the West Coast, low on the South Coast and intermediate on the East Coast. At a regional scale, significant positive relationships existed between the magnitude of annual recruitment maxima and (1) adult abundance, (2) intertidal primary productivity and (3) the magnitude of upwelling. Recruitment was highest at locations with large adult populations, high productivity and more upwelling. Within locations, recruitment varied inconsistently among sites, years and seasons. Sea temperature and recruitment were seasonal at all locations except in the southern Benguela, suggesting they are linked. At the medium scale (<1 km), at which local hydrology is believed to be important, relationships between recruitment and adult abundance were observed at only 2 locations, while at the smallest scale (<1 m), significant positive relationships were more common. Two of the 3 locations with lowest recruitment were recruitlimited. This has important management implications because low-recruitment and recruit-limited locations in southern Africa occur where human exploitation is most intense.

Megagametophyte development in barley (Hordeum vulgare 'Atsel') was studied using Nomarski-interference optics and transmission electron microscopy. Stages described include the functional megaspore to cell wall formation. Aspects of the transition from the free nuclear stage of the embryo sac to the cellular embryo sac indicate involvement of elongate cell plates associated with clusters of microtubules. Initial cell walls among micropylar and chalazal nuclei are composed of beads derived from dictyosome vesicles. Fusion of growing cell plates occurs, especially within the antipodal apparatus.