Summer biomass of a population of Iridaea cordata (Gigartinaceae,Rhodophyta) from Antarctica

Results of a seasonal study on biomass in an infralittoral population of Iridaea cordata from Terra Nova Bay (Ross Sea, Antarctica) are reported. Thalli were collected during the IX Italian Antarctic Expedition (austral summer 1993–94). The population studied is that living at depths of 4 to 6 m, where the highest density of plants occurred. The highest value of biomass (wet weight 3440 g m^–2) was found at the beginning of summer. In that period 72.5% of biomass was from 128 specimens belonging to weight classes 8 (>16 to 32 g) to 10 (>64 g), corresponding to 13.4% of the population in numbers. Small (<1 g) and medium (1 to 8 g) specimens provided the remaining biomass of 5% and 22.5%, respectively. During the month of January, the number of heavy specimens decreased. At the end of that month biomass reached a minimum of 2225 g m^–2. In February the biomass increased to 3169 g m ^–2, 72% of which was from 120 specimens belonging to weight classes 7 (>8 to 16 g) to 9 (>32 to 64 g), which numerically represented 18.5% of the population. Data showed that biomass depended mainly on the presence of large heavy specimens, even though they were always few in number. Moreover, the occurrence of such large thalli at the beginning of summer suggests that Iridaea cordata continues to grow during the long antarctic winter.     

DEFORMATIVE DISEASE IN IRIDAEA LAMINARIOIDES (RHODOPHYTA): GALL DEVELOMENT ASSOCIATED WITH AN ENDOPHYTIC CYANOBACTERIUM1

This study is the first report of an algal disease, developed in close association with an endophytic organism, documented for the southeastern Pacific. We describe a disease affecting wild populations of the red alga Iridaea laminarioides Bory in central Chile, characterized by gall development on the surface of sporophytic, cystocarpic, and immature thalli. These abnormal growths result in severe morphological alterations of the affected thalli. Diseased fronds display an aggregated spatial distribution and occur throughout the year, with a maximum in summer followed by a decline in winter. The presence of galls was not associated with broken or torn fronds. Although causality has not been unequivocally demonstrated, our field and laboratory observations indicate a strong association of the galls with infections by an endophytic cyanobacterium, probably belonging to the genus Pleurocapsa.     

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

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.     

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

Transmission 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.     

EFFECT OF ROCKY INTERTIDAL AMPHIPODS ON ALGAL RECRUITMENT: A FIELD STUDY1

Evidence about the potential of mobile marine invertebrates to act as algal spore dispersal agents is presently circumstantial. Using a field correlational and experimental protocol, our study tested the hypothesis that amphipods can increase the spore recruitment of the red alga Iridaea laminarioides Bory. Iridaea laminarioides spore recruitment onto glass slides was measured at a site with high amphipod abundance and a site with low density of amphipods. To evaluate the effect of an Ulva canopy on recruitment, replicated glass slides with and without a surrounding Ulva canopy were installed at both sites. The number of I. laminarioides spores recruited on the glass slides was four to eight times higher at the high amphipod abundance site than at the low density site. However, the presence of an Ulva canopy covering the glass slides did not significantly increase the recruitment of I. laminarioides. Because the abundance of I. laminarioides, the proportion of cystocarpic plants, and the percentage of open cystocarps only differed slightly between the low and high abundance amphipod sites, we suggest that the variation in recruitment between the sites is due to the differences in amphipod abundance (and their movements) and not to differences in spore production. Moreover, the presence of I. laminarioides cystocarps showing amphipod grazing scars was significantly higher at the high amphipod density site than at the low density site.     

DIFFERENTIATION OF LAMBDA CARRAGEENANS FROM RHODOPHYTA WITH IMMUNOLOGICAL AND SPECTROSCOPIC TECHNIQUES1

KCl soluble carrageenans from sporophytes of two Gigartina species were differentiated from those of Chondrus crispus Stackhouse, Iridaea cordata (Turner) Bory, Rhodoglossum californicum (J. Ag.) Abbott, and two Petrocelis species by their failure to precipitate on immunodiffusion against either of two absorbed anti-λ–carrageenan antisera. The carrageenans have been analyzed by infrared spectroscopy, and on this basis it is postulated that the antibody preparations recognize sulphate on C-6 of the carrageenans. The Gigartina carrageenans appear to lack sulfate at this position.     

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

The 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.     

INTERTIDAL AMPHIPODS AS POTENTIAL DISPERSAL AGENTS OF CARPOSPORES OF IRIDAEA LAMINARIOIDES (GIGARTINALES,RHODOPHYTA)1

Mid and late successional benthic algae have poor dispersal capacities. Mobile herbivores may increase dispersal of some algae because spores can survive digestion by grazers and stick to external body appendages. We show that carpospores are the only type of reproductive unit of the rhodophyte Iridaea laminarioides Bory that survive passage through the digestive tract of the amphipod Hyale sp. The spores also stick to the amphipods' legs and are thus carried by the amphipods in the field. Amphipods significantly increased (P < 0.01) the number of spores settling on artificial substrata in places where barriers prevented the normal ingress of algal propagules. The presence of artificial substrata that act as a refuge for the grazers also caused an increase (P < 0.01) in the number of settled spores. Amphipods also significantly increased (P < 0.01) the number of spores under an Ulva sp. canopy in laboratory experiments.     

THE RED ALGAL EPIPHYTES MICROCLADIA COULTERI AND M. CALIFORNICA (RHODOPHYCEAE,CERAMIACEAE). II. BASIPHYTE SPECIFICITY1

The phenomenon of basiphyte specificity in the settlement and growth of the red algal epiphytes Microcladia californica Farl. and M. coulteri Harv. was examined by studying the interface with their respective basiphytes and by cross-inoculation experiments. Microcladia californica attaches only to the surface of its single basiphyte Egregia menziesii (Aresch.) Turn. whereas M. coulteri penetrates the tissue of a wide range of basiphytes. The pattern of primary rhizoid development in both epiphytes determines the mode of attachment and may influence the range of basiphytes possible for each epiphyte. Cross-inoculation experiments show that Microcladia californica is not able to colonize the basiphytes of M. coulteri, Iridaea and Prionitis, or Ulva. The mechanisms by which these algae restrict the growth of epiphytes include short life-span, “cuticle peeling” and chemical defense. Microcladia coulteri, which naturally colonizes Iridaea and Prionitis, has evolved mechanisms to counteract the antifouling effects of those basiphytes. The question of why Egregia is the exclusive substratum for M. californica remains undetermined. However, Egregia may provide the appropriate ecological conditions and a surface topography conductive to M. californica spore settlement and growth.