We suggest that relatively few species attributes are of overriding importance to the structure of benthic marine algal communities and that these are often shared among taxonomically distant species. Data from the western North Atlantic, eastern North Pacific and Caribbean suggest that patterns in algal biomass, diversity and dominance are strikingly convergent when examined at a functional group level relative to the productivity and herbivore-induced disturbance potentials of the environment. We present a simple graphical model that provides a way to predict algal community composition based on these two environmental axes. This predictability stems from algal functional groups having characteristic rates of mass-specific productivity, thallus longevity and canopy height that cause them to «behave» in similar ways (...)

http://www.vliz.be/imisdocs/publications/131003.pdf

A functional group approach to the structure of algal-dominated communities

The seasonal development of the endemic Antarctic Desmarestiales Himantothallus grandifolius, Phaeurus antarcticus, Desmarestia anceps, of a ligulate Desmarestia sp., of the Antarctic cold-temperate Adenocystis utricularis (Dictyosiphonales) and of the endemic Antarctic Ascoseira mirabilis (Ascoseirales) was monitored in a 2-year culture study under fluctuating daylengths mimicking the daylength conditions on King George Island (Antarctica). Temperature was kept constant at 0° C and nutrient levels were maintained at 0.6 moles m−3 nitrate and 0.025 moles m −3 phosphate. Sporophytes were initiated between (April-) June and July in all Desmarestiales. This event was controlled either by induction of gametophyte fertility (in H. grandifolius and D. anceps) or by induction of spore formation (in Desmarestia sp. and P. antarcticus). Young sporophytes of all species showed a growth optimum from September to December (-February). Desmarestia sp. and P. antarcticus produced spores and degenerated subsequently after one year of culture at ≥3 μmol photons m−2 s−1 or after 22 months of culture at 2 μmol m−2 s−1. In D. anceps spores were released without degeneration of the mother plants after 20 and 19 months of culture at 3 and 10 μolm−2 s−1, respectively. In H. grandifolius spore formation was not observed. Adult one year old plants of the latter two perennial species showed growth optima between September and November. Microthalli of A. utricularis were the dominant life phase of this alga in winter. Macrothalli started to develop from June onwards at ≥3 μmol m−2 s−1 or from August to September at 2 μmol m−2 s−1. Growth rates of macrothalli cultivated at ≥9 μmol m−2 s−1 showed a growth optimum from September to November. The macrothalli released spores from January to February. Macrothalli cultivated at ≥3 μmol m−2 s−1 maximally grew in January. They became fertile after almost 2 years of culture at 3 μmol m−2 s−1 and remained vegetative at 2 μmol m−2 s−1. A. mirabilis exhibited a prominent growth optimum from August to October, at photon fluence rates between 2 and 47 μmol m−2 s−1. A second optimum was evident from January to March in plants cultivated at ≥9 μmol m−2 s−1. The results closely correspond to available field data and indicate that the phenology of the studied species can be controlled in the laboratory solely by simulating Antarctic daylengths conditions. The light requirements for growth were very low in microthalli and in juvenile macrothalli and growth was mostly light saturated at 4–12 μmol m−2 s−1. Few-celled sporophytes of H. grandifolius and D. anceps tolerated at least 8 and 11 months of darkness. The minimum light demands for completion of the life cycle are 31.4 mol m−2 year−1 in Desmarestia sp., P. antarcticus and probably also in the 2 perennial Desmarestiales; 47.1 mol m−2 year−1 are needed in A. utricularis and probably also in A. mirabilis. These values predict a lower distribution limit of the investigated species at 53±23 m or 48±21 m in clear offshore waters and at 28±5 m or 26±5 m, respectively, in inshore fjords of the Antarctic Peninsula region.

Seasonality of red and green macroalgae from Antarctica—a long-term culture study under fluctuating Antarctic daylengths

This study tests the hypothesis that species traditionally characterized as isomorphic exhibit similar physiological and ecological responses to different environmental factors, by comparing the ecological and ecophysiological responses of reproductive phases of 2 isomorphic species of Iridaea. Results indicate that although the tetrasporic and cystocarpic phases of I. laminarioides and I. ciliafa have similar morphology, they do not have identical responses to ecological variables. In the field, the reproductive stages d~ffer in their relative abundances and in their patterns of spatial and temporal distribution. In laboratory experiments, the reproductive phases showed intraspecific differences in growth rates under conditions of varying temperature, light intensity, water movement and salinity. Differences in susceptibility to grazing vary from juvenile to adult frond and from one grazer to another. The degree of ecological divergence between phases found was greater in the upper intertidal I. laminarioides and smaller in the low intertidal-shallow subtidal I. ciliata. Cystocarpic thalli of I. laminarioides dominated the upper margin of species distribution and grew faster than tetrasporic thalli under several laboratory conditions. In both species the cystocarpic phase was more abundant in the field than the tetrasporic phase. These results call into question the general belief of increased adaptivity of diploidy over haploidy in the algae.

/pdf/ecological-differences-between-the-isomorphic-reproductive-3yoypfovsm.pdf

Ecological differences between the isomorphic reproductive phases of two species of Indaea (Rhodophyta. Gigartinales)

/pdf/temperature-requirements-for-growth-and-survival-of-42sombtj1t.pdf

Temperature requirements for growth and survival of macroalgae from Antarctica and southern Chile

Colonisation of patches disturbed at different times of the year and at d~fferent locations was investigated from November 1995 to August 1997 in subtidal, rocky-shore, algal assemblages (Mediterranean Sea. Italy). A field experiment tested specifically: (1) whether and how the success of turf-forming, encrusting and erect algae are influenced by the timing of disturbance and (2) whether recovery of these species is cons~stent across space (from about 1 m to 100s of metres). Clearings were made at 8 different times within 1 year, in order to identify possible temporal trends in responses of algae to disturbance. Reproductive traits of the most abundant algae were also investigated. Encrusting, turf-forming and erect algae responded differently to spatial and temporal variation in disturbance, depending on their varylng abilities to colonise available space and on spatlal and temporal differences in rates of recruitment and growth. Turf-forming algae colonised space by vegetative propagation and quickly regained spatial dominance in patches cleared at all times of the year and at all locations. Conversely, encrusting and erect species occupied space mostly by colonisation of propagules; their recruitment was influenced by the timing and location of disturbance, probably depending on the concomitant availabil~ty of bare rock, viable propagules and favourable environmental conditions. A regime of d~sturbance adverse to recruitment of erect algae was identified as the probable cause of their low abundance in the study area. Overall, results suggested that while recruitment by sexual propagules can be highly variable through space and time, recovery by vegetative propagation can be constant and highly predictable over a range of environmental conditions, and that vegetative reproduction is likely to be fundamental to spatial dominance in a variety of habitats.

https://www.int-res.com/articles/meps/195/m195p081.pdf

Responses of algae with different life histories to temporal and spatial variability of disturbance in subtidal reefs

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.

Ecology and natural history of iridaea cordata (rhodophyta; gigartinaceae): population structure1

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.

Ecology and natural history of iridaea cordata (gigartinales, rhodophyta) growth1

Algal mariculture research at Hopkins Marine Station (Stanford University) and Marine Bioassay Laboratories (Watsonville, Calif.) led to the development of a critical pathway approach: ecological studies, strain selection, physiological experimentation, and cultivation trials. Initial ecological studies focused on seasonal growth and life history patterns of Gelidium and Gracilaria. The results provided the clues for selection of experimental tolerance ranges for key physical and chemical parameters to be studies. Plant vigor and the algal products of interest were the primary criteria in the strain selection program. The metabolic response patterns for net photosynthesis of the species were then studied to characterize the presumptive environmental optima and tolerance ranges for these red algal cultures. The results from these shortterm physiological experiments are tested in algal cultivation trials. The results from this critical pathway approach were: 1) selected, vigorous strains; 2) basic requirements for cultivation of the species; 3) predictions of how the species will respond in culture; 4) production estimates for use in mariculture feasibility models; and 5) a definition of conditions which must be met by a specific culture technique. This research, which takes place primarily in the laboratory, provides the foundation for development of the capital-intensive, pilot mariculture system for a specific red algal species.

Judith E. Hansen

Papers

Ecology and natural history of iridaea cordata (rhodophyta; gigartinaceae): population structure1

Ecology and natural history of iridaea cordata (gigartinales, rhodophyta) growth1

A physiological approach to mariculture of red algae