ECOLOGY AND NATURAL HISTORY OF IRIDAEA CORDATA (RHODOPHYTA; GIGARTINACEAE): POPULATION STRUCTURE¹

Abstract

SUMMARY The population structure of 4 California Iridaea cordata (Turner) Bory populations was studied. Random sampling procedures were used to measure seasonal variations in standing crops, density and size‐class distribution of life history stages. The results describe aspects of the in situ life history; a prerequisite to realistically considering the distribution, ecology or life history expressions of an alga. Seasonal fluctuations in density occur only in the juvenile stage, which is initiated during the winter (November to January) predominantly from the basal perennial crusts. Both the gametangial and tetrasporangial stages are present throughout the year. The tetrasporangial stage is dominant in relation to the sexual stages in both density and biomass during most of the year, except spring when the new crop in just maturing and all stages are abundant. Density in nearly constant and observable changes in the populations are due to biomass fluctuations. Seasonal lows in biomass occur during the winter with the majority of thalli in the smaller size‐classes. Growth and maturation culminate in peak summer crops and dominance of the tetrasporangial stage, followed by autumnal senescence and die‐back in winter. Carrageenans analyzed from immature thalli showed a predominance of lambda‐type, previously determined as specific for tetrasporangial plants. This indirect evidence for the tetrasporangial nature of immature plants suggests that dominance of the diploid stage occurred prior to blade development and most likely at the spore level. Alternatively, field results indicate a major contribution and possible replacement of alternation of gametangial and tetrasporangial stage by thallus perennation and vegetative reproduction.

Clump structure, population structure and non-destructive biomass estimation of the New Zealand carrageenophyte Sarcothalia lanceata (Gigartinaceae, Rhodophyta)

“…This stability may be attributable to S. lanceata blades eroding or tearing rather than completely detaching. A similar phenomenon has been observed in other species (Hansen and Doyle 1976, Klein 1987, Santos 1994, and may act as a dispersal mechanism in some species (Gomez and Westermeier 1991).…”

“…A lack of seasonality has been reported in total population densities (e.g. Hansen and Doyle 1976) and standing crop . Santelices et al (1989) suggested that this lack of variation resulted from stability in population densities.…”

“…The commercial value of carrageenans means that many gigartinacean species have been the subject of ecological investigations (e.g. Hansen and Doyle 1976, Hansen 1977, Dyck et al 1985, Levitt et al 1995, Avila et al 1996, Otaiza et al 2001, Scrosati 2001. Information on the biology and ecology of natural populations is critical for determining whether a species is a suitable candidate for sustainable wild harvest, and also whether or not the species has potential as a candidate for aquaculture.…”

Photoperiodic and temperature responses in the growth and tetrasporogenesis ofGigartina acicularis (Rhodophyta) from Ireland

“…This study * Previously known as Gigartina stellata (see frequency of tetrasporophytes than gametophytes in the wild (Hansen & Doyle, 1976) whereas Iridaea flaccida has a very low frequency of tetrasporophytes (20 %) {Abbott, 1980). These differences in frequency of phases may, of course, be due to factors other than photoregime and/or temperature limitations; such environmental parameters as differential grazing pressure, growth rates, survival abilities and spore production and germination all may be involved in preferentially selecting one phase or another {West & Hommersand, 1982).…”

Life history bias in endophyte infection of the Antarctic rhodophyte, Iridaea cordata

“…Densities of asexually reproducing organisms are known to increase towards margins of a population, in what is termed geographic parthenogenesis (Craigie andPringle 1978, De Wreede andKlinger 1988). Populations under adverse conditions, such as the cold temperatures or high disturbance levels characterizing the western Antarctic Peninsula, are hypothesized to be sporophyte dominated (Hansen and Doyle 1976) because diploid individuals have the ability to mask mutations (increased genetic variability; Sosa and Garcia-Reina 1992) and adapt quickly to environmental variation (Bell 1982). Still, there is no pattern describing every species population (De Wreede and Green 1990).…”