Population studies on a South African carrageenophyte: Iridaea capensis (Gigartinaceae, Rhodophyta)

Abstract

An intertidal population of Iridaea capensis in the south-western Cape Province of South Africa has been studied in detail for a year. The species is generally restricted to sand-inundated rocky shores, which appears not to be the case for Iridaea species in the Pacific. In early winter (June) biomass, plant density and plant size were at a minimum. A small increase in these parameters occurred in August, but there was a massive increase in plant numbers and biomass in October. The largest plants were recorded in summer (February). The population was over 70% sporophytes in April, but switched to almost 80% gametophytes following heavy recruitment between August and October, and remained significantly gametophyte-dominated through April of the following year. Carrageenan levels were high (ca 42% of dry weight) in late winter-spring, and lowest (ca 30-35%) in summer-autumn. Strong offshore wind conditions in early summer caused a reduction in biomass, and it is hypothesized that the associated upwelling of nutrient rich water may be implicated in the lower carrageenan levels at this time.

Seasonal and spatial patterns of population density in the marine macroalga Mazzaella splendens (Gigartinales, Rhodophyta)

“…High density in summer and low in winter is often observed in populations of Mazzaella . It has been observed for Mazzaella capensis (J. Agardh) Fredericq (Bolton & Joska 1993, as I. capensis ) on the Cape Peninsula in South Africa and for M. laminarioides and Mazzaella ciliata in central Chile (Hannach & Santelices 1985 , as I. laminarioides and I. ciliata ). This pattern was variable, however, for Mazzaella flaccida (Setchell et Gardner) Fredericq in central California (Thornber 2001), where high summer and low winter density was present in certain years and locations but the reverse in others.…”