Carlos Sangil

Sargassum species play a key role in habitat formation in tropical and subtropical regions; however, species identification has been hampered by the phenological plasticity exhibited in response to environmental conditions and life history. Molecular phylogenetics has challenged taxa circumscriptions and proven critical in delimiting species in this genus. Yet, the Atlantic species of Sargassum remain poorly understood, and recent studies have shown low molecular diversity between the species in the NW Atlantic. Here, we expand the taxon sampling to the NE Atlantic to assess the diversity of Sargassum in the Atlantic basin, based on a comprehensive morphological and multigene approach. We selected genes commonly used in delineating species in this genus (ITS2, rbcLS, cox3, mtsp) and explored additional markers (cox2, nad6, psbC, clpC, atpB) to infer the phylogenetic relationships between the morphospecies observed in the NE Atlantic. Phylogenetic analyses using single‐gene and multigene alignments including 185 new sequences confirmed the low molecular diversity and supported the distinction of a single clade in Sargassum section Sargassum of N Atlantic benthic species. In contrast, morphological analysis resulted in the identification of 10 species and three new morphospecies that we described here but opt not to equate to species until further molecular evidence is available. Our results were congruent with previous findings from the NW Atlantic and highlight the morphological and ecological diversity of Sargassum in the Atlantic. These results suggest a recent colonization and incipient speciation of Sargassum in the Atlantic basin and showcase the need of further high‐throughput analyses.

We studied the primary succession of benthic communities in the lava flows of the Tajogaite volcano at 2, 4.5, and 7 months after the eruption ended. The lava from the Tajogaite created several lava flows and sterile rocky reefs that were monitored in both intertidal and subtidal areas up to 20 m depth. Sampling included macroinvertebrates and algae in the intertidal, and fishes, macroinvertebrates, and algae in the subtidal. A control zone was selected to compare the early colonisation of lava flows with that of a mature ecosystem. Colonisation of the lava flow was swift, with numerous species arriving and proliferating soon after the eruption ended. After 7 months, the total number of species recorded in the lava flows was 70, representing 64% of those found in the control zone. thus, communities were gradually becoming increasingly complex owing to the continuous incorporation of species. The number of fishes, and macroinvertebrates in both the intertidal and subtidal, lava flows increased progressively, approaching the values of the control zone. However, algae, in terms of total cover, presented values similar to the control zone from the beginning of the monitoring. All the communities have followed the same trajectory to converge towards communities like those in the control zone, although the rate at which they have changed with time differs. After seven months, differences in fishes between lava flows and the control zone were small, but they were still large with respect to macroinvertebrates and algae. Thus, according to each community of organisms, the benthic ecosystem of the lava flows was found at different stages of succession.

Populations inhabiting the periphery of a species’ distribution suffer the immediate pressure of the environmental changes. Studying their physiology under stressful conditions is essential in the context of climate change. We characterized two morphotypes with measurements of length, thickness and width of the thallus of the macroalga Fucus guiryi in two localities (north and south) in Tenerife (Canary Islands), the southern limit of distribution of the species. We hypothesized that the individuals from the north locality, especially the large morphotype, would be more vulnerable to desiccation and high temperatures than those from the south. Tolerance to desiccation was tested through two long desiccation experiments and by comparing the vegetative and reproductive blades. Tolerance to high temperatures was tested by keeping the individuals in seawater (26–32 °C) for 24 h. The recovery of physiological functions after the stressful conditions was estimated through maximal photochemical efficiency of PSII. Results indicate that both of the two morphometrically differentiated morphotypes were tolerant to prolonged desiccation; however, the small one was more affected, particularly in the northern locality. The reproductive blades were hardly affected, indicating greater tolerance to desiccation than the vegetative blades. Fucus guiryi showed tolerance to high temperatures (32 °C) suggesting plasticity to future warming scenarios.

Relationships between sea urchins and noncrustose macroalgae are typically nonlinear, and an abrupt phase shift from a barren to a macroalgae‐dominated state and vice versa happens when the sea urchin abundance exceeds a critical threshold. Here, we have used two mass mortality events as a natural experiment to study progressive changes and dynamics between these stable states. In 2009–2010 and 2018, two mass mortalities decimated the populations of the sea urchin Diadema africanum in the Canary Islands (Eastern Subtropical Atlantic). In these islands, this sea urchin is a key‐herbivore controlling the growth of macroalgae, and sea urchin barrens have persisted for more 60 yr. Mass mortality events differed in intensity both in space and time, and two phase shifts from sea urchin barrens to macroalgal beds were detected in both when sea urchin density declined below a critical threshold of 4 indv. · m⁻². The first mass mortality was greater in La Palma Island, consequently in this island a long‐lasting alternative state dominated by noncrustose macroalgae has been established. Subsequently, a recurrent mass mortality also favored the transition from the sea urchin barrens to noncrustose macroalgal beds in Tenerife Island. After mass mortalities, D. africanum populations were reduced by 94–98% in both islands. No signs of recovery of these populations have been identified after phase shifts; ecosystem feedbacks may be the cause of the low population density of D. africanum.

Is a canopy-forming endemic macroalga from the Canary Islands. Vegetative and reproductive characteristics of all phases in its life cycle are examined. Key macromorphological features are its blackish color and the corymbose-to-subfastigiate branching pattern that differentiates

Four species of marine algae are reported from the Canary Islands for the first time. Our report of the western Atlantic Gelidiella setacea (Gelidiales, Rhodophyta) is the first from the eastern Atlantic Ocean. Pseudotetraspora marina (Tetrasporales, Chlorophyta) previously known on the eastern side of the Atlantic Ocean from temperate saltmarshes only, is now reported growing in the shallow sublittoral zone, the habitat in which tropical western Atlantic populations also occur. The presence of Lomentaria chylocladiella (Rhodymeniales, Rhodophyta) represents the first report in the Atlantic Ocean of a species previously thought to be endemic to the Mediterranean Sea. The record of the widely distributed Acrochaetium hallandicum (Acrochaetiales, Rhodophyta) was not unexpected. Specimens of A. hallandicum have vegetative cells with a single lobate parietal chloroplast with a single pyrenoid, a feature that among acrochaetioid algae occurs exclusively in the genus Colaconema (Colaconematales), and consequently the species is transferred to this genus. Fertile sporophytes are described for Gelidiella setacea, a species previously known only in its vegetative condition. Cruciately to irregularly divided sporangia are regularly arranged in transverse rows in stichidia laterally formed on the axes. The species is transferred to the genus Parviphycus on the basis of the morphology of the stichidia and the distichous pattern of apical division exhibited by the axes, both exclusive features of this genus.