M. Cecilia Gauna

Epi-endophytic symbiosis between Laminariocolax aecidioides (Ectocarpales, Phaeophyceae) and Undaria pinnatifida (Laminariales, Phaeophyceae) growing on Argentinian coasts

The present is the first study on epi-endophytic algae on thalli of Undaria pinnatifida growing along Argentinian coasts. The main goal is to describe the nature and the morphology of this symbiosis. Individuals of Laminariocolax aecidioides were detected in both June and December 2004, growing on U. pinnatifida sporophytes. In nature, the epi-endophyte were macroscopically observed as dark zones that partially covered the hosts’ fronds. L. aecidioides vegetative thalli were irregularly branched uniseriate filaments. The life cycle is described from laboratory cultures started from Patagonian populations. Caryology revealed that the sporophytic diploid phase presented 16 chromosomes whereas the gametophytic haploid phase presented 8 chromosomes. Isolates made from thalli growing in the interior of infected hosts developed into filamentous, branched sporophytes that reproduced by both unispores and plurispores that were produced in unilocular and plurilocular sporangia, respectively. The results of this paper also allowed us to conclude that L. aecidioides uses the thalli of U. pinnatifida as a proper substrate. The penetration of endophitic filaments among the host´s cortical cells produced a lateral compression and, finally, their thalli development generated perforations in the host tissues. The effects of the epi-endophytic infection of L. aecidioides on U. pinnatifida are neither severe nor deleterious.

Green epi-endophytes in Hymenena falklandica (Rhodophyta) from the Patagonian coasts of Argentina: Preliminary observations

The occurrence of epi‐endophyte algae in Hymenena falklandica J. G. Ag. Ex Kylin (Rhodophyta) is reported in Argentina. Epicladia heterotricha (Yarish) Nielsen (Chlorophyceae) revealed a 100% prevalence of occurrence, particularly in the basal region of the host. Low (14%), moderate (28%) and high (58%) severity degrees of infection were also registered for E. heterotricha. Pseudendoclonium submarinum Wille (Chlorophyceae) exhibited a lower frequency of occurrence, close to 3%. The developmental morphology and dynamics of E. heterotricha and P. submarinum were investigated under unialgal as well as bialgal culture conditions. The experimental infection of H. falklandica by E. heterotricha demonstrated that E.  heterotricha initially behaves as epiphytic but with endophytic filaments growing into the cortex of the host during late infection. P. submarinum was found to be exclusively epiphytic, with no development of endophytic filamentous systems. The present study reports the first lines of evidence of an epidemiological study conducted with the purpose of comparing both the prevalence and effects of algal epi‐endophytic organisms in H. falklandica in the southern coasts of Argentina.

Temporal variations of vegetative features, sex ratios and reproductive phenology in a Dictyota dichotoma (Dictyotales, Phaeophyceae) population of Argentina

This paper addresses the phenology of a Dictyota dichotoma population from the North Patagonian coasts of Argentina. The morphology of the individuals was characterized, and analyses of the temporal variations of vegetative features, diploid and haploid life cycle generations and sex ratios are provided. Individuals, represented by growing sporophytes and gametophytes, occurred simultaneously throughout the year. Morphological variables showed temporal variation, except the width and height of medullary cells, which did not vary between seasons. All vegetative variables were significantly correlated with daylength. Besides, frond length, frond dry mass and apical and basal branching angles were significantly correlated with seawater temperatures. Vegetative thalli were less abundant than haploid and diploid thalli. Sporophytes were less abundant than male and female gametophytes. Male gametophytes dominated in May, August, October and January, and female gametophytes were more abundant in September, November, December, February and March. The formation of female gametangia showed a significant correlation with daylength, and the highest number of gametangia was registered in spring. In general, the male/female sex ratio varied between 1:2 and 1:1. Apical regions were more fertile than basal regions. Our data about frequency in the formation of reproductive structures and male/female ratios are the first recorded in the Dictyota genus and thus could not be compared with populations from other regions of the world. Significant morphological variation was observed in thalli of both life cycle generations, regarding length and dry mass, number of primary branches and branching basal angle. In general, all variables analyzed varied seasonally except cortical cell width.

Epiphytic relationships of Pseudendoclonium submarinum Wille (Ulvophyceae) and Rhodymenia pseudopalmata (Rhodophyta) from the Patagonian coast of Argentina

The occurrence of the epiphyte alga Pseudendoclonium submarinum Wille (Ulvophyceae) on Rhodymenia pseudopalmata (Lamouroux) Silva (Rhodophyta) is reported. The present study describes a first line of evidence of an epidemiological study conducted with the purpose of comparing both the prevalence and effects of algal epiphytic organisms in R. pseudopalmata in the Patagonian coasts of Argentina. P. submarinum infected approximately 80% of R. pseudopalmata thalli and the frequency of infection was variable in connection with different areas of the hosts thalli: 42% of R. pseudopalmata fronds presented P. submarinum thalli in the basal region, which presented a severity degree of infection from low to high. The median region presented an average frequency of infection of 30% and minor susceptibility to colonization. The covering varied from 1% to 70% representing a low to moderate degree of colonization. The apical region presented a cover frequency of 28% and the level of infection varied between low to moderate. The developmental morphology and the growth dynamics of the epiphyte were also investigated under unialgal as well as bialgal culture conditions. In nature, thalli of P. submarinum on R. pseudopalmata never invaded internal tissues of the host. Vegetative thalli of P. submarinum were inoculated on fronds R. pseudopalmata. Experimental infections confirmed that P. submarinum thalli did not penetrate the hosts fronds. P. submarinum swarmers showed the capacity of settlement on a hosts fronds and developed an epiphytic monostromatic thallus. The results allowed us to suggest that P. submarinum uses the R. pseudopalmata thalli as a proper substrate, since Pseudendoclonium thalli complete the entire life cycle. Culture experiments revealed that P. submarinum could develop without the presence of the host and evidenced the nutritional independence, being the relationship in nature, probably triggered by an ecological advantage since fronds of R. pseudopalmata offer a suitable substratum.

The Occurrence of Laminarionema elsbetiae (Phaeophyceae) on Rhodymenia pseudopalmata (Rhodophyta) from the Patagonian Coasts of Argentina: Characteristics of the Relationship in Natural and Experimental Infections, and Morphology of the Epi-endophyte in Unialgal Free Cultures

The occurrence of Laminarionema elsbetiae (Ectocarpaceae, Phaeophyceae), as epi-endophyte of Rhodymenia pseudopalmata (Rhodymeniales, Rhodophyta), described from Santa Isabel, Rawson, Argentina. L. elsbetiae grows in the host tissues forming epi-endophytic relationship in the epidermal, cortical and medullar layers. Epiphytic thalli of L. elsbetiae were unbranched filaments emerging from hostis surface. Reproductive structures of L. elsbetiae on the host were absent. On the contrary, free cultured individuals formed different reproductive structures. Macrozoosporangia containing a single large motile zoospore originated from vegetative cells, they were conical to cylindrical in shape, 30-50 μm in length and 18-20 μm in wide. Uniseriate plurilocular zoosporangia were cylindrical shape, 40 μm in length and 10-13 μm in wide. Sexual fusion was not seen. In mixed cultures of L. elsbetiae with R. pseudopalmata fronds, L. elsbetiae infected the host, grew as in natural host and, formed macrosporangia between host subcortical cells. Gametophytes of L. elsbetiae were filaments with diffuse growth, branched with a branch pattern alternate or opposite. Gametangia were plurilocular, uni or biseriate and lateral. When mature they contained 2 to 6 isogametes. The presence L. elsbetiae on R. pseudopalmata could be defined as an epi-endophytic relationship. The percentage of infection of R. pseudopalmata thalli by L. elsbetiae was 34%.A25% of the infected thalli presented a low, non-symptomatic level infection, whereas a 62% and a 13% of them exhibited respectively moderate and high indexes of infection.

Temporal dynamics of algal epiphytes on Leathesia marina and Colpomenia sinuosa macrothalli (Phaeophyceae)

ABSTRACT This is the first study on the temporal dynamics of the epiphyte communities of Leathesia marina and Colpomenia sinuosa, in terms of richness, diversity and abundance, and their relationships between the hosts and the environmental factors. A total of 31 epiphyte taxa were recorded, with the two hosts sharing 64.5% of the epiphytic species found. The red algal epiphytic group had the highest abundance on both hosts and the diatoms presented the highest species richness. The epiphyte species on L. marina showed a progressive increase in abundance during the warm seasons that was related to the end of the macroscopic life stage of the host. They also showed a greater specific richness on L. marina than on C. sinuosa, but a lower diversity and evenness, and a clear dominance of the species Urospora penicilliformis and Erythrotrichia carnea. Low abundance of epiphytes was found on C. sinuosa, without temporal variation, but high diversity and evenness and without any dominant species. In addition, a clear zonation was observed on this host, where epiphytic abundance decreased on the lateral and upper part of the thallus.

Heteromorphic phases of Leathesia marina (Ectocarpales, Ochrophyta) over time from northern Patagonia, Argentina

Abstract: The emergence and evolution of the heteromorphic life history in algae has been considered as a response to the selective pressures of changing environments. The brown alga Leathesia marina has a typical heteromorphic life history, alternating between microscopic branched filaments (gametophytic phase) and a macroscopic erect stage (sporophytic phase). The first aim of this study was to describe vegetative and reproductive morphologies of sporophytes (macrothalli and diploid phase) of L. marina and their relationship with environmental factors in an annual cycle. The second aim was to report the discovery of gametophytes (microthalli and haploid phase) in the natural environment on northern Patagonian coasts, and to describe their morphology, abundance and reproductive output. The macroscopic phase was observed over 8 months, from September to April during the warm season. The microscopic phase was observed in two periods, March–April and September–October. A temporal overlap was observed between the microscopic and macroscopic phases. The population of macrothalli had a type III survivorship curve. The cover, density and size of macrothalli were associated with warmer months, but the abundance of microthalli and reproductive output of both phases were higher in temperate periods. Demographic parameters, including mortality rate, survivorship, reproductive output and the morphological characteristics of L. marina are used to evaluate the adaptation of this species to a changing environment, typical of the temperate coasts of northern Patagonia in Argentina.

Molecular evidence of the presence of Dictyota dichotoma (Dictyotales: Phaeophyceae) in Argentina based on sequences from mtDNA and cpDNA and a discussion of its possible origin

ABSTRACT Dictyota is a brown algae genus inhabiting tropical to warm temperate environments where it is an important food source, shelter and substrate to several species of invertebrates and other algae. The taxonomy of this genus is troublesome, with poor species delimitation and doubtful records in the literature. Dictyota dichotoma, the type species of the genus, was commonly accepted as a cosmopolitan species because of the inaccurate geographical distributional range as a consequence of misidentification in several parts of the world. Recent studies with molecular data revealed new species and a new understanding of the evolution and biogeography of the genus Dictyota. These studies confined natural populations of D. dichotoma to Europe (Atlantic and Mediterranean coasts) and Macaronesian islands (Azores, Madeira and Canary archipelagos). Also, they confirmed its presence in South Africa, but whether the species was native or introduced in South Africa could not be verified. In the present study two regions of cpDNA (psbA, rbcL) and one region of mtDNA (nad1) from Argentinian samples, identified morphologically as D. dichotoma, were analysed and compared to other Dictyota species. The identity of these samples as D. dichotoma was confirmed. A haplotype network analysis using all available psbA sequences distinguished seven haplotypes divided into two geographic groups: Atlantic–Mediterranean and Canarian. In Argentina and South Africa only the most common haplotype of the Atlantic–Mediterranean group was observed. According to the paleoceanographic currents and the presence of a European haplotype, the introduced nature of D. dichotoma is indicated.

Spatial and temporal variation in algal epiphyte distribution on Ulva sp. (Ulvales, Chlorophyta) from northern Patagonia in Argentina

Abstract: In this study of northern Patagonia in Argentina, we examined the annual cycle of the epiphyte composition and abundance on Ulva sp. with respect to intertidal elevation, season and position on host. We found spatial segregation in most environmental gradients. Local environmental conditions, intertidal levels, seasons and portion of host thalli had specific patterns of algal epiphytic community. The host population exhibited seasonality and differential morphological attributes according to the intertidal elevation. Thalli of Ulva sp. had the highest maximum diameters and were heavier in spring and summer at the upper elevation. Epiphytes were more abundant growing on host thalli at middle elevations. Epiphytic Dinophyceae, Chlorophyceae and Cyanophyceae presented clear seasonality. Epiphyte abundances were related to periods with high seawater temperature, long days and high radiation. Lyngbya sp., Cocconeis sp., Navicula spp., Rhabdonema arcuatum, Stylonema alsidii and Myrionema strangulans had the highest frequency. The highest epiphyte abundance was observed in holdfasts, with M. strangulans having the highest frequency and cover. These results are relevant to commercial aquaculture ventures for food and feed sources and application in bioremediation.