Volume 65, Issue 6

The Brazil-Malvinas Confluence (BMC) is characterized by high environmental variability and represents a hotspot of phytoplankton biodiversity. This study has investigated the phytoplankton composition in the BMC and a Cold Core Eddy (CCE), with particular reference to the life forms and trophic modes of the species. Vertical hauls were performed between the maximum chlorophyll depth and the surface with a 20-μm mesh plankton net at six sampling points in the BMC (4 hauls) and CCE (2 hauls) during the austral spring (November 2019). Temperature and salinity were determined in situ . The Brazil Current and Malvinas Current in the BMC had different species compositions, and the CCE had greater similarity with the Malvinas Current. Autotrophic organisms (mainly diatoms) and marine planktonic oceanic and/or neritic life forms were predominant in the BMC and the CCE. Heterotrophic dinoflagellates were predominant in the Brazil Current and the CCE, while mixotrophic dinoflagellates in the Malvinas Current were associated with low temperatures and salinities. A high diversity of species was confirmed in the region, mainly associated with marine planktonic oceanic and/or neritic species, and there was a predominance of autotrophic organisms. The temperature conditions in the CCE promoted an increase in species richness in the region.

Macroalgae play a vital role in marine ecosystems, but human effects are threatening the composition and structure of algal communities. In the present investigation, the spatial and temporal variations of species composition, functional groups and percentage macroalgal cover were studied in relation to seasonal fluctuations of some physicochemical parameters, to determine the ecological status of macroalgae in coastal waters along the coast of the northwestern part of the Red Sea, from November 2020 to October 2021. Fifty-five species of macroalgae were collected and identified from the sites studied. Five functional groups of macroalgae were recognized. Among these were two turf-forming species, 34 species of upright fleshy algae, and three crustose algae. There was a large variation in the cover, as well as in the species richness and assemblage structure of the macroalgae in different sites and seasons. Seasonal changes, determined by environmental conditions, led to small changes in macroalgal cover at different sites, with the growth of some brown macroalgae suppressed by high sea temperatures, whereas some green and red macroalgae, increased in response to increasing temperature and salinity.

Sequencing of a mitochondrial intergenic spacer and 23S subunit was used to investigate the phylogeographic patterns in Fucus vesiculosus . Samples originated from 21 sites spanning six subbasins of the Baltic Sea. We identify a putative ancestral mitochondrial haplotype that entered the Baltic Sea from the Atlantic, colonising extensively throughout the species’ distribution. The dominance of this haplotype is seen in the low overall haplotype diversity ( H d  = 0.29). Moreover, there is indication of few spatially aggregated patterns in the deeper demographic time scales ( F ct  = 0.040; F st  = 0.049). Tajima’s D (−0.685, p-value 0.297) and Fu’s F S (0.267, p-value 0.591) showed no significant signals of extreme demographic changes. The Baltic Sea free-living Fucus is confirmed as  F. vesiculosus or a closely related species. Haplotype diversities are comparable between forms (attached H d  = 0.306; free-living H d  = 0.268). The relatively short temporal scale for colonisation alongside low variance in the Fucus mitochondrial genome results in a rather panmictic structure across the Baltic Sea. Our data suggest that the mitochondrial intergenic spacer and 23S poorly describe the evolutionary dynamics of Fucus spp. in such a young, postglacial environment, yet this concatenated-barcode advances our understanding of the colonisation dynamics of F. vesiculosus over deeper demographic timescales.

Digenea is a widely distributed genus in the Mexican Atlantic, and until a few years ago the only morphospecies D. simplex was recorded. Recent molecular research on this species from a locality in the Mexican Caribbean revealed the new species D. mexicana , whose morphological similarity with specimens from Gulf of Mexico suggests that its distribution range could extend to this area. The aim of this work was to characterize the molecular and morphological characters of Digenea specimens from different sites in the Mexican Atlantic, to confirm this hypothesis and even reveal the presence of new species or records for the country. Our phylogenetic analysis of COI-5P and rbc L markers revealed a new record of D. arenahauriens in Mexico and confirm the presence of D. mexicana in the southern Gulf of Mexico. The species delimitation methods showed potential new species for Australia, Japan, and Brazil. The true D. simplex was not recorded molecularly for Mexico. Morphological comparisons indicated an overlap among most of the species of the genus. Future studies about molecular and morphological characterization of Digenea specimens from around the world could help to clarify the problem of specific delimitation, and even reveal new species for the genus.

Kelp aquaculture is an emerging industry outside of Asia. To be successful, this industry requires a reliable production of seedstock, the optimisation of which greatly benefits from a detailed physiological understanding of the microscopic life-cycle stages of the cultured species. This study investigated the impact of six zoospore densities (10–278 mm −2 ) on the subsequent development of Ecklonia radiata gametophytes and sporophytes. The results showed that germination rates and sex ratio were unaffected by initial zoospore density, but there were significant effects on gametophyte size and sporophyte production. After two weeks, female gametophytes were largest at an initial zoospore density of 40 mm −2 while male gametophytes grew largest at densities below 40 mm −2 , but after four weeks gametophyte size showed a negative relationship with initial zoospore density. Significantly more sporophytes developed at initial zoospore densities below 40 individuals mm −2 and no sporophytes were observed at the highest density (271 zoospores mm −2 ). These results clearly show the importance of initial zoospore density in optimising the nursery stage of kelp aquaculture.