Seasonal and depth-driven changes in rhodolith bed structure and associated macroalgae off Arvoredo island (southeastern Brazil)

Rhodoliths are formed by coralline red algae and can form heterogeneous substrata with high biodiversity. Here we describe a rhodolith bed at the southern limit of the known distribution of this habitat in the western Atlantic. We characterized rhodolith and macroalgal assemblages at 5, 10 and 15. m depth during summer and winter. Lithothamnion crispatum was dominant amongst the six rhodolith-forming species present. Most rhodoliths were spheroidal in shape indicating high mobility due to water movement. Rhodolith density decreased with increasing depth and during winter. Turf-forming seaweeds accounted for 60% of the biomass growing on rhodoliths. Macroalgae increased abundance and richness in the summer, but was similar between 5 and 15. m depth. They were less abundant and diverse than that recorded in rhodolith beds further north in Brazil. Both, season and depth, affected the structure of the macroalgae assemblages. We conclude that Lithothamniom is the most representative genus of Brazilian rhodolith beds. Summer is responsible for increasing the diversity and richness of macroalgae, as well as increasing rhodolith density. © 2013 Elsevier B.V

Patterns of Spatial Variation of Assemblages Associated with Intertidal Rocky Shores: A Global Perspective

Assemblages associated with intertidal rocky shores were examined for large scale distribution patterns with specific emphasis on identifying latitudinal trends of species richness and taxonomic distinctiveness. Seventy-two sites distributed around the globe were evaluated following the standardized sampling protocol of the Census of Marine Life NaGISA project (www.nagisa.coml.org). There were no clear patterns of standardized estimators of species richness along latitudinal gradients or among Large Marine Ecosystems (LMEs); however, a strong latitudinal gradient in taxonomic composition (i.e., proportion of different taxonomic groups in a given sample) was observed. Environmental variables related to natural influences were strongly related to the distribution patterns of the assemblages on the LME scale, particularly photoperiod, sea surface temperature (SST) and rainfall. In contrast, no environmental variables directly associated with human influences (with the exception of the inorganic pollution index) were related to assemblage patterns among LMEs. Correlations of the natural assemblages with either latitudinal gradients or environmental variables were equally strong suggesting that neither neutral models nor models based solely on environmental variables sufficiently explain spatial variation of these assemblages at a global scale. Despite the data shortcomings in this study (e.g., unbalanced sample distribution), we show the importance of generating biological global databases for the use in large-scale diversity comparisons of rocky intertidal assemblages to stimulate continued sampling and analyses

Rhodolith bed structure along a depth gradient on the northern coast of bahia state, brazil

The aim of this study was to determine the structure of a rhodolith bed along a depth gradient of 5 to 25 m in the shelf in front of Salvador City, a region of northeastern Brazil. The dimensions, morphology and coralline algae composition of the rhodoliths were analyzed, as well as the vitality, density, and associated flora of the bed at three depths: 5, 15 and 25 m. Samples were obtained by SCUBA divers in summer 2007. Five rhodolith-forming taxa were identified: Sporolithon episporum, Lithothamnion brasiliense, Lithothamnion superpositum, Mesophyllum erubescens, and Lithophyllum sp. The encrusting growth form and the spherical shape were predominant at all depths. Rhodolith dimensions and vitality decreased and the density increased from the shallow to the deepest zones. Fifty-six macroalgal species were found as rhodolith-associated flora. The shallower depth presented higher values for macroalgal biomass and number of species. These results associated with other recent rhodolith bed descriptions indicate that the pattern of Brazilian rhodolith bed structure along depth gradients may be related to a combination of the extent and slope of the continental shelf.O objetivo deste estudo foi determinar a estrutura de um banco de rodolitos ao longo de um gradiente de profundidade na plataforma em frente à cidade de Salvador, nordeste brasileiro. Foram analisadas as dimensões, a forma e composição das algas calcárias dos rodolitos, bem como a vitalidade, densidade e flora associada ao banco, em três profundidades: 5, 15 e 25 m. As amostras foram obtidas por meio de mergulho autônomo no verão de 2007. Cinco espécies de algas calcárias formadoras de rodolito foram identificadas: Sporolithon episporum, Lithothamnion brasiliense, Lithothamnion superpositum, Mesophyllum erubescens e Lithophyllum sp. A forma de crescimento incrustante e a forma esférica foram predominantes em todas as profundidades. Houve uma redução da dimensão e vitalidade dos rodolitos e um aumento da densidade com a profundidade. Cinqüenta e seis espécies de macroalgas foram encontradas como flora associada aos rodolitos. A profundidade mais rasa apresentou os maiores valores de biomassa e número de espécies de macroalgas. Esses resultados, associados com outras descrições recentes de bancos de rodolitos, indicam que o padrão estrutural desses bancos no Brasil, ao longo de gradientes de profundidade, pode estar relacionado a uma combinação da extensão e da inclinação da plataforma continental

Morphology and distribution of Corallina vancouverensis (Corallinales, Rhodophyta) in Northwest Mexico

The morphology and distribution of Corallina vancouverensis Yendo was studied in order to determine its distribution limits and morphological variations in the northwestern coast of Mexico. Two hundred specimens were collected and analyzed, as well as samples from several herbaria, representing an overall total of 65 localities. The bibliographic records of this species in the Baja California Peninsula and mainland Mexico were also analyzed. Populations of C. vancouverensis are distributed from Alaska to Las Cabrillas, which is located South of Todos Santos, BCS. Several new localities are recorded for this species in the Gulf of California, and its southern limit in the Northeast Pacific is considered to lie within 23ºN on both sides of the Baja California Peninsula. Furthermore, the taxonomic relationship of this species with C. pinnatifolia and C. fiondescens is questioned based on morphological, ecological and distributional tendencies

Macroalgas epífitas de Zostera marina L. en Bahía Concepción, B.C.S., México

In order to understand the seaweeds epiphytes in Zostera marina beds in Bahía Concepción we determine the number of species, the overall percentage cover of epiphytes at dorsal or ventral position at three levels in the leaves every two weeks during the maximum growth of the plants between March 15 and May 14, 1992. Also, to understand if the presence of epiphytes have any relationship with the presence of the plant, fake leaves were installed in February 22 with the same periodicity of sampling. We find out that 8 species live as epiphytes, 1 green and 7 red algae were determined. Only two species have been previously cited as epiphytes of Z. marina. We found that the epiphytes can develop in both sides of the leaves and fakes with a relative abundance up to 80% of the area. The dominant component in the cover was a nongeniculate coralline algae while the fleshy species were more abundant in old portions. The species number associated with the leaves and fakes and the overall relative abundance increase and decline rapidly during the sampling, suggesting that there is not relation¬ship between epiphyte and the seagrass as suggested in other studies

Dynamics of epiphytism on Padina concrescens (Dictyotales: Phaeophyta) from the southwestern coast of the Baja California Peninsula, Mexico

The community dynamics of algal epiphytes was studied in relation to the area available on Padina concrescens at Los Cerritos, Baja California Sur (Mexico). Monthly surveys were conducted over ten months. Experimental structures were also deployed in order to assess epiphyte-host synchrony and affinity. The results rejected the hypothesis of a synchronous appearance, showing that epiphytes were present all the time and occupied the space available. By the end of the season they covered 60% of all the host´ s area. The environments from where samples were taken revealed differences in the structure of epiphytes, though their development trend over the host was similar. The exclusive colonization of the artificial substrate by coralline algae is attributed to the behavior of this type of epiphyte

Age and growth of Lithothamnion muelleri (Corallinales, Rhodophyta) in the southwestern Gulf of California, Mexico

 The nongeniculate coralline alga Lithothamnion muelleri Lenormand ex Rosanoff is commonly found as a free-living rhodolith in the wave-exposed shallow waters of the southwestern Gulf of California. This species has bands along the main branch axes suggesting that growth is periodic and that may be used to determine age and growth. As part of our ongoing research related to rhodoliths and their ecology, we have made observations on the nature of these bands based on their structure in entire plants and on field and laboratory growth experiments. Individual plants from different size classes were tagged, stained with alizarin and returned to the field, while another set was tested in the laboratory. Half of the plants were sampled after 6 months and the rest after 12 months. The data indicate that this species grew at a rate of 0.60 mm yr–1 in the field and 0.87 mm yr–1 in the laboratory. There were no significant differences among branches within a plant, or among plants of different size. Growth was seasonal, with high rates in winter and spring, and low rates in summer and fall. This may explain the observed alternating light-dark bands (up to 4) along branch axes. The growth rates suggest that larger plants (ca 15 cm diameter) may be over 100 years old