Iridaea Cordata Research Articles

ECOLOGY AND NATURAL HISTORY OF IRIDAEA CORDATA (GIGARTINALES, RHODOPHYTA) GROWTH1

ABSTRACTThe in situ growth, maturation and senescence, of central California Iridaea cordata (Turner) Bory was studied. This ontogenetic progression was quantified by measuring development and growth of: i) individually tagged blades, and ii) populations of blades within cumulative (1‐yr duration) and seasonal experimental plots. Greatest growth and longest life span were exhibited by winter‐spring initiated blades, and were correlated with a rapid increase, in irradiance, but not with either seawater temperature or nutrients. Tagging studies showed that reproductive maturation and senescence of blades occurred throughout the year, irrespective of date tagged, growth rate or size. Moreover, the majority of blades continued to elongate following maturation, and some matured within 3 mo of initiation at all seasons but winter. At the population level maturation took place primarily during summer‐autumn when 90 ±2% of the population was mature. The majority of the population senesces or “dies back” during autumn‐winter. It is concluded that in situ, the blades are derived almost totally via vegetative means involving perennation. This indirectly suggests that sexual reproduction or the success of sporeling development are marginal. Additionally, the species is perennial with annually deciduous blades, characterized by both rapid growth and maturation.

STRUCTURAL, CHEMICAL AND ECOLOGICAL STUDIES ON IRIDESCENCE IN IRIDAEA (RHODOPHYTA)1

ABSTRACTTransmission electron microscopy of the iridescent algae Iridaea flaccida (S & G) Silva, Iridaea cordata (Turn.) Bory var. cordata and I. cordata var. splendens (S & G) Abbott reveals a multilaminated cuticle covering the thallus. Experimental results show the cuticle: a) can be isolated intact by mechanical scraping or NaOH treatment; b) is iridescent by itself and the denuded thallus is not; and, c) is isolated without any subtending polysaccharide layer, cell walls, or cells. This cuticle acts as a thin layer producing the constructive and destructive light interference which is seen as iridescence. It is formed of alternating electron opaque and translucent layers with a total thickness of 0.5–1.6 μm. Analysis of mechanically isolated cuticle shows that it is composed of protein (50%), carbohydrate (ca. 40%), inorganic salts (5%) and some fatty acids (less than 1.0%). The electron opaque layers may correspond to protein‐rich regions and the electron translucent ones to regions rich in carbohydrates. The cuticle does not appear to affect photosynthesis or respiration, but rather, may protect the alga from physical factors such as desiccation and from predator injury. It is likely that the iridescence in other foliaceous red algae is caused by a similar structure.

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

SUMMARYThe 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.

Growth of the red alga Iridaea cordata (Turner) Bory in semi-closed culture

The marine red alga Iridaea cordata (Turner) Bory, a carrageenan producer, was grown in a semi-closed culture system in which agitation was provided by aeration. Factors regulating the growth and conditions favoring optimum productivity in such a culture system were studied. The factors studied included plant size, rate of flow of sea water, ratio of biomass to surface area, and light intensity. Yield/surface area in such a culture system (5700 kcal/m 2/yr or 1950 g ash free dry matter/m 2/yr) can exceed that of natural populations by six-fold. Such a culture system also provides a novel means of assessing the growth and potential productivity of large benthic seaweeds.

Observations of algal zonation resulting from competition

In the coastal waters of the Pacific Northwest Region it was found that Iridaea cordata is excluded from areas below its normal distribution by a competitive interaction with more rapidly growing kelps, especially Laminaria saccharina. In areas cleared of kelps, I. cordata grew to cover 20% of the bottom from a natural settlement of spores.

Seasonal changes in calorific value of three pacific coast seaweeds, and their significance to some marine invertebrate herbivores

Samples of three intertidal seaweeds, Iridaea cordata (Turner) Bory, Hedophyllum sessile (C. Agardh) Setchell and Lessoniopsis littoralis (Farlow and Setchell) Reinke, collected at nine intervals over the period May 1971–May 1972, showed statistically significant seasonal fluctuations in percentage dry weight, percentage ash content, and calorific value. Percentage dry matter was generally highest in late summer through winter, whereas ash content was low. All three species showed a distinct annual cycle in calorific value of live (damp-dried) material, being highest during August–February for Hedophyllum and Iridaea, and during August–December for Lessoniopsis. Calorific values of dry material similarly varied seasonally for all species, but the differences were not significant for Iridaea. On an ash-free basis, the calorific values of Hedophyllum and Iridaea were variable during the year and only Lessoniopsis showed significantly higher values in late summer and autumn. The seasonal variability in calorific value of seaweeds has important implications in the feeding ecology of certain invertebrate herbivores. For example, while the chiton, Katherina tunicata Wood, consumed less Hedophyllum in the autumn than during the spring and summer, caloric intake did not decrease proportionately due to an inverse cycle in calorific value of Hedophyllum. In addition, we discuss for a number of invertebrate herbivores their feeding preferences, and the importance of calorific value of seaweeds and other factors which may have been involved in the evolution of these preferences.

Studies on HCO3− ion uptake during photosynthesis in benthic marine algae

Carbon uptake was recorded in the light for species of the following marine algae: Alaria, Costaria, Desmarestia, Enteromorpha, Gigartina, Nereocystis, Porphyra, and Ulva. The change in total inorganic carbon in the experimental water was determined by acid release from 1 ml samples and measured by infrared gas analysis. With the exceptions of Porphyra and Desmarestia, the algae were concluded to use HCO3− ion as a substrate for photosynthesis.The relationship of rate of photosynthesis to total inorganic carbon present in seawater was determined for Ulva fenestrata, Iridaea cordata, and Sargassum muticum.