The Sargasso Sea, named due to the floating presence of Sargassum fluitans and S. natans, is usually reported for the tropical region of the Northern Hemisphere. On 14 July 2011, at 02°45’ N and 48°28’ W, samples of pelagic seaweed masses were collected by the Patrol Ship Bracuí of the Brazilian Navy. The seaweed was identified as S. natans, previously considered as of doubtful occurrence in Brazil.

Sargassum is an important primary producer of rocky bottom communities in coastal ecosystems. Like other parts of the planet, benthic populations of S. natans from Ilha Grande Bay (IGB), southeastern Brazil, have been suffering from different forms of natural and anthropogenic disturbances, in particular increasing seawater temperatures. The aim of this study was to understand the effects of temperature on the photosynthetic performance of S. natans using the pulse amplitude modulated (PAM) fluorometry. In the field experiments, the occurrence of photoprotection resulted in a difference between the effective and maximum quantum yields [(ΔF (F’_m − F_s)/F’_m and F_v/F_m, respectively) that was maximized at noon. The stress induced by incubation at 32–35 °C caused a decrease in F_v/F_m by 33% on the first day and approximately 20% on subsequent days. In the laboratory, using two co-occurred species of S. natans and Padina gymnospora, we verified that the photosynthetic apparatus of S. natans collapses at 34 °C. The fate of the energy absorbed by photosystem II (PSII) antenna showed that, in S. natans, photochemical activity and non-photochemical quenching of chlorophyll fluorescence (NPQ) drastically decrease, and only the passive dissipation in the form of heat and fluorescence remains. Our results indicate the disappearance of the NPQ photoprotection at 34 °C before the decline of F_v/F_m as the reason for the collapse of photochemistry of Sargassum.

Caulerpa scalpelliformis grows on rocky and sandy bottoms at different depths in Jacuacanga Cove, Ilha Grande Bay, where it can form dense patches. The invasive behavior of this and other species of Caulerpa is well documented in the literature. This study analyzed the variation of the vegetative development of C. scalpelliformis from Baleia Beach (23º01'63''S and 44º14'18''W) in Jacuacanga Cove, from June 2003 to September 2004, including plants from rocky and sandy substrates. Morphometric and dry weight data from the erect and prostrate portions were used. Plants were collected from 20 x 20 cm² plots (n=3), randomly positioned on the rocky boulders (≅1.5 m depth) and on contiguous sandy bottom (≅3.0 m depth). During the study period, C. scalpelliformis occurred on both substrates as a pseudo-perennial species, showing partial loss of the erect portions from winter to spring; the height and dry weight of the erect portions increased from summer to autumn on both substrates. The temporal variation of C. scalpelliformis vegetative development in Baleia Beach was similar to that described for the invasive C. racemosa and C. taxifolia from different geographical regions of the world. Caulerpa scalpelliformis cresce sobre substrato rochoso e arenoso a diferentes profundidades na Enseada de Jacuacanga, Baía da Ilha Grande, onde pode formar bancos densos. O comportamento invasor desta e de outras espécies de Caulerpa é bem documentado na literatura. Este estudo analisou a variação do desenvolvimento vegetativo de C. scalpelliformis da Praia da Baleia (23º01'63''S e 44º14'18''W), Enseada de Jacuacanga, de junho de 2003 a setembro de 2004, considerando plantas do substrato rochoso e do fundo de areia. Dados morfométricos e de peso seco das porções prostrada e ereta foram usados. Plantas foram coletadas em quadrados de 20 cm de lado (n=3), posicionados aleatoriamente sobre o substrato rochoso (profundidade ≅ 1,5 m) e sobre o substrato arenoso (profundidade ≅ 3,0 m). Durante o período de estudo, C. scalpelliformis ocorreu nos dois substratos como espécie pseudo-perene, mostrando perda parcial das porções eretas do talo do inverno para a primavera; altura e massa seca das porções eretas mostraram tendência de aumento do verão para o outono nos dois substratos. A variação temporal do desenvolvimento vegetativo de C. scalpelliformis na Praia da Baleia foi similar à descrita para C. racemosa e C. taxifolia, espécies invasoras em diferentes regiões do mundo

Em unidades de conservação da zona costeira, o conhecimento das macroalgas marinhas é essencial para monitoramento e manejo. Para o Núcleo Picinguaba do Parque Estadual da Serra do Mar (PESM), Ubatuba, norte do Estado de São Paulo, estudos pretéritos realizados na Enseada da Fazenda listam espécies de macroalgas, coletadas em costões rochosos e manguezais. O presente estudo visou complementar o levantamento taxonômico da flora ficológica marinha do Núcleo Picinguaba, avaliando também a adequação da metodologia para amostragens de suas comunidades de costões rochosos. Foram selecionados 13 pontos de coleta, entre a Ponta da Almada e a Ponta do Cambury, área de maior interferência antropogênica na zona costeira do PESM. No verão de 2007, foram efetuadas coletas de macroalgas, desde a franja da região sublitorânea até o limite do substrato rochoso com a areia. Para uniformizar o esforço amostral, estas buscas foram efetuadas, em cada ponto de coleta, pelo mesmo especialista, durante uma hora de mergulho em apnéia, em uma extensão horizontal do costão rochoso de cerca de 20 m. Foram identificados 128 táxons de categoria infragenérica (80 Rhodophyta, 22 Ochrophyta e 26 Chlorophyta). Callithamniella flexilis Baardseth, Cryptonemia seminervis (C. Agardh) J. Agardh, Cladophora pseudorupestris C. Hoek e Cladophora cf. pygmaea Reinke são ocorrências novas para o litoral do Estado de São Paulo, tendo sido descritas e ilustradas. Foram acrescentadas 64 espécies de macroalgas para os costões rochosos do PESM. O esforço amostral foi considerado adequado, resultando na identificação de número de espécies de macroalgas similar ao de outros estudos realizados no litoral norte do estado de São Paulo e no extremo sul do estado do Rio de Janeiro. Para o monitoramento da zona costeira desta unidade de conservação, recomenda-se o levantamento taxonômico das macroalgas dos costões rochosos de modo continuado, durante o período de verão de anos sucessivos, seguindo a mesma metodologia aqui descrita.

Sargassum is an important primary producer of rocky bottom communities in coastal ecosystems. Like other parts of the planet, benthic populations of S. natans from Ilha Grande Bay, southeastern Brazil, have been suffering from different forms of natural and anthropogenic disturbances, in particular increasing seawater temperatures. In this study, we focused on understanding the effects of temperature on the photosynthetic performance of S. natans using PAM fluorometry. Measurements in the field revealed the dynamics of effective and maximum quantum yields (ΔF/F’m and Fv/Fm, respectively), as well as the dynamics of photoprotection mechanisms. The stress induced by incubation at 32-35°C, caused a decrease in Fv/Fm by 33% on the first day and approximately 20% on subsequent days. Additionally, direct estimates of the net photosynthesis of S. natans by measurements of dissolved oxygen concentration showed that an increase in temperature inhibited photosynthesis. In the laboratory, using specimens of S. natans and Padina gymnospora, we verified the effect of temperature on the fate of the energy absorbed by the PSII antenna using complementary quantum yields. Exclusively in Sargassum, temperatures in the range of 32 to 35ºC promoted a decline of non-photochemical quenching of chlorophyll fluorescence before the decline of Fv/Fm, indicating that PSII is destroyed in the absence of the NPQ photoprotection.