Seagrass and submerged aquatic vegetation (VAS) habitats off the Coast of Brazil: state of knowledge, conservation and main threats

Seagrass meadows are among the most threatened ecosystems on earth, raising concerns about the equilibrium of coastal ecosystems and the sustainability of local fisheries. The present review evaluated the current status of the research on seagrasses and submerged aquatic vegetation (SAV) habitats off the coast of Brazil in terms of plant responses to environmental conditions, changes in distribution and abundance, and the possible role of climate change and variability. Despite an increase in the number of studies, the communication of the results is still relatively limited and is mainly addressed to a national or regional public; thus, South American seagrasses are rarely included or cited in global reviews and models. The scarcity of large-scale and long-term studies allowing the detection of changes in the structure, abundance and composition of seagrass habitats and associated species still hinders the investigation of such communities with respect to the potential effects of climate change. Seagrass meadows and SAV occur all along the Brazilian coast, with species distribution and abundance being strongly influenced by regional oceanography, coastal water masses, river runoff and coastal geomorphology. Based on these geomorphological, hydrological and ecological features, we characterised the distribution of seagrass habitats and abundances within the major coastal compartments. The current conservation status of Brazilian seagrasses and SAV is critical. The unsustainable exploitation and occupation of coastal areas and the multifold anthropogenic footprints left during the last 100 years led to the loss and degradation of shoreline habitats potentially suitable for seagrass occupation. Knowledge of the prevailing patterns and processes governing seagrass structure and functioning along the Brazilian coast is necessary for the global discussion on climate change. Our review is a first and much-needed step toward a more integrated and inclusive approach to understanding the diversity of coastal plant formations along the Southwestern Atlantic coast as well as a regional alert the projected or predicted effects of global changes on the goods and services provided by regional seagrasses and SAV

Effect of seed mass on germination and growth in three dominant species in southern Brazilian coastal dunes

The effect of seed mass on germination and growth was tested in fresh-seeds of Blutaparon portulacoides, Panicum racemosum, and Spartina ciliata, selected at random in southern Brazilian populations. The seed mass varied within a population of the three species. Both B. portulacoides and P. racemosum showed normal frequency distribution of seed mass, while S. ciliata did not. Significant differences were observed in seed germination between large and small seeds of all species. In all species the capacity of seedling elongation was greater in seedlings of large seeds than those of small ones. Relative growth rate of seedlings of P. racemosum and S. ciliata decreased with time in all seed mass size-classes. On the other hand, the relative growth rate of B. portulacoides seedlings increased during the first 40 days. Seed mass is an important biological factor, affecting seed germination, seedling elongation, and growth of these species, and favoring large seeds, specially in areas of active sand accretion like coastal dunes

Effects of salinity on seed germination, seedling growth and survival of Spartina ciliata Brong Efeitos da salinidade sobre a germinação, crescimento e sobrevivência das plântulas de Spartina ciliata Brong

The effects of different salinities on the germination of Spartina ciliata seeds were tested during 40 days in the laboratory, using six concentrations of NaCl (0,45, 80, 130, 170 and 215 mM) besides three concentrations of seawater (25,30 and 35&#8240;). In addition, the survival and growth of seedlings were tested in five constant salinity regimes (0,45, 80 and 170 mM NaCl) as well as in five regimes of simulating seawater overwash. The results showed that seeds possed a high germination capacity over a wide range of salinities (0 to 215 mM NaCl). Although concentrations close to full-strength seawater completely inhibited seed germination, the transfer of the ungerminated seeds to freshwater immediately stimulated this. The effects of salinity on seedling growth showed that shoot height and root length were the variables most sensitive to salt stress. Frequent overwash with seawater significantly reduced the survival and growth of Spartina ciliata seedlings. The success in seed germination, survival, and growth of Spartina ciliata in salinities above those normally found in the natural environment could explain the species being distributed throughout salt-stressed foredune habitats in southern Brazil.<br>O efeito de diferentes salinidades sobre a germinação das sementes de Spartina ciliata foi testado em laboratório ao longo de 40 dias, usando seis concentrações de NaCl (0,45, 80, 130, 170 e 215 mM NaCl) e em três concentrações de água do mar (25, 30 e 35&#8240;). Adicionalmente a sobrevivência e crescimento das plântulas foram testados em cinco regimes de salinidade (0,45,80,130 e 170 mM NaCl) assim como, em cinco regimes de inundação com água do mar. Os resultados mostraram que as sementes apresentam alta capacidade germinativa numa grande amplitude de salinidades (0 a 215 mM NaCl). Apesar de concentrações próximas as da água do mar terem inibido completamente a germinação, a transferencia das sementes que não germinaram para água doce, estimulou, imediatamente, a germinação. O efeito da salinidade no crescimento das plântulas mostrou que a altura das hastes e comprimento das raízes foram as variáveis mais sensíveis ao estresse salino. Frequentes alagamentos com água do mar reduziram significativamente a sobrevivência e o crescimento das plântulas de Spartina ciliata. O sucesso na germinação, sobrevivência e crescimento de Spartina ciliata em salinidades acimas daquelas normalmente encontradas no ambiente natural poderiam explicar a distribuição da espécie ao longo dos hábitats estressados por sal nas dunas costeiras no extremo sul do Brasil