Volume 65, Issue 5

Extreme warming events have diminished kelp ecosystems around the world, but few reports exist about their impacts on invasive species. Warming events along the coast of Baja California from 2014 to 2016 negatively affected kelp forest communities historically dominated by Macrocystis pyrifera . We measured changes in the macroalgal community at Todos Santos Islands, Baja California, Mexico between 2018 and 2019. Our results documented a dramatic reduction of M. pyrifera , and a concurrent structural shift to invasive kelps dominance, with Sargassum horneri and Undaria pinnatifida being highly abundant in 2019. This study provides insights about impacts of invasive kelp species on macroalgal community structure under future climate scenarios.

We provide the first documented case of the black mangrove, Avicennia germinans , producing multiple seedlings from a single propagule, a phenomenon called polyembryony, on several occasions. There is a lack of knowledge about polyembryony in mangroves, as it is an extremely rare phenomenon previously observed in only three other mangrove species. A higher weight of mature propagules may indicate polyembryony, thus enabling early detection. A. germinans may make use of mixed reproductive strategies to ensure the continued survival of the species, or to increase its expansion under favourable environmental conditions. Potential causes and implications of polyembryony in A. germinans are discussed.

During midday low tides, tropical intertidal seagrasses are challenged by high irradiance and high temperature. This study assessed photosynthetic and oxidative stress responses of Thalassia hemprichii and Halophila ovalis exposed to 150 and 1000 μmol photons m −2  s −1 and 30 and 40 °C for 3 h. High temperature (40 °C) significantly decreased the maximum quantum yield of both seagrasses and this heat-induced photoinhibition was exacerbated by high irradiance (1000 μmol photons m −2  s −1 ). High irradiance also aggravated the effects of high temperature on the effective quantum yield of T. hemprichii . Non-photochemical quenching (NPQ) of  T. hemprichii was induced by both stressors with no additive effects. In contrast, NPQ of H. ovalis was induced under high irradiance at 30 °C but was inhibited at 40 °C. Nevertheless, antioxidant enzyme activity and reactive oxygen species content did not differ among treatments in either seagrass. Monitoring chloroplast distribution in  H. ovalis revealed a partial inhibitory effect of high temperature on chloroplast avoidance movement under high irradiance. Our results suggest that warming events may cause detrimental impacts on shallow water seagrasses. Halophila ovalis may be more vulnerable than T. hemprichii as its photoprotection, i.e. NPQ and chloroplast avoidance movement, was hindered at high temperature.

Codium cylindricum is a large green alga distributed along the temperate Northeast Pacific coasts. Although the species is edible and contains pharmaceutical substances, little is known about its ecology. In this study, we characterized the phenology of C. cylindricum by monthly observations in Tateyama on the central Pacific coast of Japan from March 2018 to February 2019. The average length of attached thalli in three quadrats (2 × 2 m) was 5 cm from April to July. After disappearing in August, recruits appeared in November and the maximum density (1.08 ± 3.5 inds·m −2 ) was reached in February. On the sea bottom, detached thalli were present from April to October; the biomass monitored in a single quadrat (2 × 20 m) was high from June to August. Based on monthly observations of 50–100 utricles in each of 18–25 thalli, gametangium formation started in June and reached a peak (i.e., gametangia detected in 75% of thalli and 63.4% of utricles) in September, before the disappearance of the detached thalli. These results strongly suggest that C. cylindricum is annual and reproduces mainly while they are drifting. Therefore, growth during detached stage is critically important to increase biomass and dispersal.

The effects of ocean acidification on macroalgae have been extensively studied. However, most studies focused on the adult stages, while other life cycle stages have been overlooked. To better understand the influence of the marine environment on macroalgae, their whole life cycle should be considered, especially the juvenile stage. In this study, Ulva prolifera was cultured under two CO 2 concentrations (400 and 1000 ppmv) and at 10, 18, 30, and 55% of incident sunlight to assess the photosynthetic performance. Our results showed that the acidification treatment had a negative effect on growth at the juvenile stage, but a positive effect at the adult stage. The relative growth rate and effective quantum yield of PSII increased with decreased light levels, irrespective of the CO 2 concentration. At the adult stage, the Chlorophyll (Chl) a , Chl b , and carotenoid contents declined under the high CO 2 concentration. The protein content significantly increased at 18, 30%, and full sunlight levels under the high CO 2 but not under the low CO 2 concentration. Our results suggest that juveniles were less tolerant of the acidic stress compared with the adult stage, although the alga was able to increase cellular proteins in response to the acidic stress.

Most of the archipelagos of the Russian Arctic are still extremely poorly studied. New data have been obtained using SCUBA diving and on-shore sampling during the “Open Ocean: Arctic Archipelagos – 2019. Severnaya Zemlya” expedition, which provided a significant update to scarce information on the seaweeds of the Severnaya Zemlya Archipelago. The list of macroalgae of the archipelago includes 48 species to date, belonging to Chlorophyta (17 species), Rhodophyta (18), and Phaeophyceae (13). Twenty-eight species are recorded for the first time in the study area; three species are new for the entire Russian Arctic. The taxonomic status of some observed species is discussed. For the first time, a wide distribution of kelps is described in the sub-tidal zone in the high-Arctic areas of the Siberian shelf, which is severely affected by ice disturbance and glacial processes. The highest population densities of the kelp communities have been observed near the Krasnoflotskie Islands (the Kara Sea) and in the Akhmatov and Mikoyan bays (the Laptev Sea). Further studies of the flora and vegetation of both the Severnaya Zemlya Archipelago shelf and other Arctic archipelagos are required.

Biecheleriopsis adriatica is a brittle dinoflagellate first described from the Adriatic Sea. In the present study, not only the presence of this species, but also the order Suessiales, is recorded for the first time in the Eastern Pacific Ocean, specifically in Todos Santos Bay, northwestern Mexico. The specimens found were collected at three sampling stations in November 2020. A molecular analysis was carried out based on the amplification of the 28 s rDNA gene, and cell morphology was examined using light microscopy. The analyses confirmed the identity and the first record of Biecheleriopsis adriatica in the area. Phylogenetically, the sequences formed a monophyletic group with those from GenBank for the Adriatic Sea and the Indo-Pacific; the morphology was consistent with the original and later descriptions. These results suggest that the diversity of the Suessiales in Mexico had been underestimated and the potential presence of a greater number of species of this group in the region.

The genus Gayralia has a complex taxonomy, often with morphological and ontogenetic characteristics that overlap with those of other monostromatic green algae, mainly Monostroma . Molecular studies of monostromatic green algae are still rare, especially in Brazil, where G. brasiliensis was described originally. Considering the difficulties in delimiting genera and species based on morphological criteria, we investigated the genus Gayralia through ITS sequencing of field collections in the tropical northeastern region of Brazil. Our 14 newly generated sequences formed a fully supported clade with G. brasiliensis showing low intraspecific divergence (0–0.6%). The distribution of G. brasiliensis in Brazil was expanded to the northeastern Brazilian coast, with the first record for the states of Rio Grande do Norte, Paraíba, Alagoas, and Sergipe. In addition, two sequences from India identified as G. “ oxysperma ” were grouped in the G. brasiliensis clade, indicating that they correspond to the same genetic species. This finding extends the geographical distribution of G. brasiliensis to India. Our results place Monostroma kuroshiense within the Gayralia clade, which warrants a new combination – Gayralia kuroshiensis (F.Bast) comb. nov.