Sporolithon molle (Heydrich) Heydrich has previously only been reported from the Red Sea, Arabian Gulf, Indonesia, and eastern Australia. The species is reported for the first time from the Atlantic Ocean where it was found in the remote oceanic island of Trindade, Brazil. This study provides a comparative account of tetrasporic plants from the Atlantic Ocean against those from the other known locations and from other well-described species of the genus Sporolithon. The specimens reported here, presented all the features of the genus, namely: flared epithallial cells, cells of adjacent filaments joined by both cell fusions and secondary pit connections, cruciately divided tetrasporangia formed within sori; and tetrasporangia bearing apical pore plugs and formed on a single stalk cell. Sporolithon molle differs from other species of Sporolithon mainly by the absence of a layer of elongate cells at the base of tetrasporangial sori. Samples from Trindade differ slightly from the type collection and from specimens from other known locations by the tetrasporangial sori which can be flush to slightly raised (to 3 cells) above the surrounding vegetative thallus surface as opposed to being flush only in all material reported previously.

Fertile gametangial plants of Phymatolithon calcareum, which are seldom reported in the Atlantic European coasts, were collected as encrusting, epilithic plants in a subtidal maerl bed in Brittany (France). Based on their morphological features, the plants were identified as P. calcareum. This identification was further confirmed by DNA barcodes using as a reference COI-5P sequences obtained from the neotype together with recent collections from the Atlantic European maerl beds. The reproductive structures were empty but they were regarded as mature female conceptacles. Compared to the two previous records of gametangial plants of P. calcareum for the Atlantic European waters, the uniporate conceptacles observed in this study are larger, and were collected at a different time of the year. To our knowledge, this is the first time that the occurrence of gametangial plants of P. calcareum is corroborated with molecular tools (DNA barcodes).

The macroalgal flora associated with rhodolith beds in the Bay of Islands, northeastern North Island, was investigated as part of the first detailed study of subtidal rhodoliths in New Zealand. The rhodolith beds differed in their physical characteristics and in the dominant rhodolith-forming species present, one bed with clear water and predominantly Lithothamnion crispatum rhodoliths, and the other bed with turbid water, and Sporolithon durum rhodoliths covered by fine sediments. One hundred and three taxa were identified (12 green, 24 brown and 67 red algae), with similar numbers of taxa found in the two seasons sampled. The floral composition at the two beds differed significantly. The flora included range extensions for species previously reported within New Zealand (e.g. Cutleria multifida), new records for the New Zealand region (at family, genus and species levels — e.g. Dumontiaceae, Cutleria, Dictyota, Peyssonnelia spp), and new discoveries (e.g. Halymenia sp., Grateloupia sp., Tsengia sp.). Two species with a partially prostrate growth habit, Caulerpa flexilis and Chondracanthus chapmanii, were present in both beds consolidating rhodoliths and shell debris.

Bahía Concepción was once recognized as a very productive coastal lagoon not only for the Peninsula of Baja California but also for all Mexico. However, lack of proper management has resulted in the closure of various fisheries, such as the Calico scallop, Argopecten ventricosus, in 1994. One of the main challenges for the management of coastal resources is the selection of critical habitats for conservation considering the economic activities of the communities associated with them. This study used Geographic Information Systems (GIS) and remote sensing to assess the roll of rhodoliths and Sargassum spp. as critical habitats in Bahía Concepción for endangered and commercial species. Underwater surveys, on 72 randomly selected sites within the bay, were conducted to characterize the shallow benthic habitats, fish and invertebrate species abundance and richness during the spring of 2011. Analyses show that rhodoliths are important for the invertebrate assemblages and for at least 4 species protected under the Mexican law, NOM-059, for threatened species. Sargassum spp. and seagrass beds are also relevant for diversity but their annual life cycle limits the time when these are available as habitat for other species. GIS tools proved an innovative and effective method to provide essential information to protect critical habitats such as rhodoliths, Sargassum spp. and seagrasses, for the recovery and conservation of diversity.

A dense rhodolith bed on deep-water soft bottoms in the Peregrino oil field in Campos Basin, Brazil was recently described. This critical habitat is increasingly subjected to disturbances that promote massive sediment dislodgment. This study aimed to test the combined effects of sediment burial and light attenuation on two main rhodolith-forming coralline algae. Experiments were conducted using the dominant algae Mesophyllum engelhartii and Lithothamnion sp. Color changes were measured as a response to burial with a thin layer of fine and coarse sediments compared to uncovered samples at two natural light levels. A mesocosm system exposed species to combined treatments of light and burial by sediments that mimic drill cuttings. M. engelhartii bleached after 75 days and Lithothamnion sp. earlier than that, at 41 days, when buried by fine sediments. Sediments had a strong negative effect on the photosynthesis of coralline algae species within two weeks. Low light levels are not a problem for these deep-water coralline species, but fine sediments have a negative effect after a relatively short time. Lithothamnion was more sensitive than M. engelhartii in terms of color changes but less sensitive in terms of their fluorescence responses to burial.

In the northwestern Gulf of Mexico, beds of rhodoliths and unconsolidated rubble at 55–70 m depth are associated with unique offshore deep bank habitats known as salt domes or diapirs. Prior to the 2010 BP Deepwater Horizon oil spill these harbored the highest known seaweed diversity in the northern Gulf of Mexico. Six post-spill cruises led offshore Louisiana to two sites previously documented with rich algal assemblages (i.e. prespill) revealed a dramatic post-spill die-off of seaweeds at both sites, with dredged rhodoliths appearing bleached and mostly denuded of fleshy algae, or “bare” (with a few crustose genera only, e.g. Corallinales and Peyssonneliales). This rubble, brought to the laboratory and maintained in a series of ∼75 liter microcosm tanks, gradually became covered by a suite of red, green and brown seaweed germlings that to this day continue to grow to adult size, reproduce, disappear and re-emerge, and whose species composition reflects pre-spill assemblages. These experiments revealed the expression of biodiversity from alternative life stages or resting stages apparently repressed in the Gulf at the time of sampling, including new, previously overlooked diversity. The rate of algal succession was documented by biweekly photography, and species taxonomic identity is being confirmed by ongoing molecular and morphological evidence. The implications of these exciting results, namely that undetected propagules, spores and endolithic filaments collected along with the “bare” substrata and in situ seawater have been triggered to germinate, grow, and reproduce under laboratory conditions are far-reaching. We hypothesize the function of rhodoliths and rubble as marine seedbanks for biological diversity and explore the role of this ecosystem for community resilience following a major anthropogenic disaster. This is a speculative paper since we currently lack many rigorous, quantitative data. The paper is envisioned as a “first step” in approaching the dynamics of rhodoliths and associated diversity following a catastrophic anthropogenic event, from which the algal and invertebrate diversity has not recovered, as of October 2013, our last collecting expedition to Ewing Bank in the NW Gulf of Mexico.