Volume 64, Issue 2

Controlling the life cycle of the green macroalga Ulva (Chlorophyta) is essential to maintain its efficient aquaculture. A fundamental shift in cultivation occurs by transforming the thallus cells into gametangia and sporangia (sporulation), with the subsequent release of gametes and zoids. Sporulation occurrence depends on algal age and abiotic stimuli and is controlled by sporulation inhibitors. Thus, quantification of sporulation intensity is critical for identifying the biotic and abiotic factors that influence the transition to reproductive growth. Here, we propose to determine the sporulation index by measuring the number of released gametes using flow cytometry, in proportion to the total number of thallus cells present before the occurrence of the sporulation event. The flow cytometric measurements were validated by manually counting the number of released gametes. We observed a variation in the autofluorescence levels of the gametes which were released from the gametangia. High autofluorescence level correlated to phototactically active behaviour of the gametes. As autofluorescence levels varied between different groups of gametes related to their mobility, flow cytometry can also determine the physiological status of the gametes used as feedstock in seaweed cultivation.

To investigate the effects of river waters on estuarine seagrass, the tropical seagrass Halophila ovalis was collected at Brunei Bay, Borneo, and was cultured under laboratory conditions for 18 days. Three treatments were set up in the experiment: natural seawater with a salinity 30 (S30), estuarine river water with a salinity 10 (S10), and the intermediate water that was composed of the seawater and river water with a salinity 20 (S20). New leaf production, the average length of new leaves, rhizome elongation, and photosynthetic rate of H. ovalis were significantly higher in S20 than S10. Chlorophyll a (chl a ) and carotenoid content in H. ovalis were significantly lower in S10 than S20 and S30. Though the tropical river waters could potentially cause both positive and negative effects on seagrass, the present results suggested that low salinity would be the most influential factor to hinder the growth and metabolism of H. ovalis, and the salinity threshold was observed between 10 and 20. These results suggested that H. ovalis may be able to extend its present distribution to the upper estuary at this study site in the future.

Cymodocea nodosa , a typical marine angiosperm species in the Mediterranean Sea, hosts a range of epiphytic algae. Epiphyte abundance varies at different spatial scales, yet epiphyte diversity and community composition are poorly understood. This study explores the epiphytes on C. nodosa from two reference meadows (Thasos, Vrasidas) and one anthropogenically stressed meadow (Nea Karvali) in the northern Aegean Sea (Kavala Gulf, Greece). A nested destructive sampling design at three spatial scales (metres, hundreds of metres, kilometres) and stereoscopic/microscopic observations were used. Light microscopy revealed a total of 19 taxa of macroalgae populating the leaves of C. nodosa . The most commonly encountered taxa with highest cover (%) were Hydrolithon cruciatum and Feldmannia mitchelliae . DNA sequencing (18S rDNA) confirms the presence of a number of dinoflagellate and red algal epiphytes, and this represents the first application of DNA metabarcoding to study the diversity of seagrass epiphytes. Epiphytic communities studied at species/taxon and functional (Ecological Status Groups) levels separated the reference low-stressed meadows from the degraded one, with the functional approach having higher success. The ecological evaluation index classified the studied meadows into different Ecological Status Classes according to anthropogenic stress.

Rhodoliths are important foundation species of the benthic photic zone but are poorly known and rarely studied in Alaska. A bed of Lithothamnion soriferum rhodoliths was discovered in 2008 in Kinzarof Lagoon, Alaska, a shallow-water embayment dominated by eelgrass ( Zostera marina ). Rhodolith spatial extent and biomass were estimated to assess trends and environmental factors that may influence rhodolith distribution and abundance during four years spread over a 12-year period (2008–2010, and 2019). Presence and biomass of rhodoliths were negatively associated with percent eelgrass cover. Biomass of rhodoliths also decreased with increased water temperature. Rhodoliths occurred in two primary areas of the lagoon, a 182 ha core area in a shallow water (mean tide depth of −0.03 m MLLW) tidal channel with low eelgrass density, and a 22 ha outlying area at shallower water depths (>0.2 m MLLW) with moderate to high eelgrass cover. There was no apparent trend in rhodolith biomass over the study period despite wide variation in mean annual estimates. This study establishes a baseline for continued investigations and monitoring of this important benthic resource in Alaska.

Introductions of macroalgae are becoming more common with increased surveillance and the use of molecular tools to unequivocally identify invaders. We here report two non-indigenous macroalgal species newly confirmed to be present in New Zealand. Pachymeniopsis lanceolata is an irregularly divided foliose blade, first detected in Lyttleton Harbour/Whakaraupō, South Island but here also reported from the North Island. It has known introductions from its native range in Pacific Asia to the Mediterranean, Atlantic and the eastern Pacific. The introduced cox 3 haplotype was also found in New Zealand, suggesting a secondary introduction from a previous introduced area, but we also found a novel haplotype in the North Island suggesting a case of multiple introductions. Fushitsunagia catenata , a recent segregate from Lomentaria, was also first detected in Whakaraupō and was initially identified as a species of Champia . Rbc L data shows that it belongs to F. catenata . This species is also of Asian origin and has been known to have been introduced to Spain, Mexico, and Australia. We provide morphological and reproductive descriptions of the species in New Zealand. Continued surveillance, and follow up monitoring, are needed to track the expansion and effects of these macroalgae on native biotas.

We used three molecular markers (COI-5P, rbc L and UPA) to investigate the diversity of Hypnea spp., an economically important red algal genus, collected from India. Our concatenated tree (COI-5P and rbc L) supported the monophyly of two new species, Hypnea indica sp. nov. and Hypnea bullata sp. nov. H. indica diverged from its closest two sister species, Hypnea cervicornis and Hypnea tenuis (by 15.9 and 11.2%, respectively, in COI-5P; and 3.4 and 3.2% in rbc L). We describe H. indica as a new species characterised by an erect, percurrent main axis with spine-like branchlets in acute angles, straight and forked apices, axial cells surrounded by large periaxial cells or two cells similar in size to the axial cell, and the presence of lenticular thickening in the cross-section of the thallus. H. bullata diverged from its closest sister species, Hypnea brasiliensis (by 10.9% in COI-5P and 3.3% in rbc L). H. bullata is characterized by a prostrate thallus up to 1.5 cm in height, highly anastomosed, with an axial cell surrounded by similar sized, or smaller, periaxial cells, tetrasporangia present near the base of branchlets, and the presence of lenticular thickening.

Dinoflagellates in the genus Gambierdiscus are known to produce potent neurotoxins known as ciguatoxins. These toxins vector through the food web and can reach sufficiently high levels to cause ciguatera fish poisoning (CFP). In many regions of the Caribbean, little is known about the occurrence of CFP-causing species or the incidence of CFP, despite its apparent regional increase over the last few decades. Given the intraspecific variability in content and potencies of these toxins among Gambierdiscus species, the precise identification of local species of this genus is crucial. In this study we confirm the presence of the epibenthic dinoflagellate Gambierdiscus caribaeus in the Colombian continental Caribbean. Cells were collected in seagrass beds of Thalassia testudinum in Bonito Gordo, a site located on the western side of Bahía Concha, Tayrona National Natural Park, near the city of Santa Marta, Colombia. Subsequently, a single strain of Gambierdiscus could be established for further identification. Morphological (light and scanning electron microscopy), and molecular results (partial LSU and ITS rDNA sequencing) were consistent with the original description of G. caribaeus, as well as with the morphological characteristics shown by other authors in organisms obtained near the sampling area.