North Atlantic Rhodolith Beds

Aggregations of living unattached corallines, previously often referred to as nodules, were given the name rhodoliths by Bosselini and Ginsburg ( 1971 ). Adey and MacIntyre ( 1973 ) provided an early discussion of their genesis and distribution. Such aggregations have long been known as maerl in the North East Atlantic, a Breton term for unattached thalli that lack a shell or pebble core (Irvine and Chamberlain 1994 ). Here, we provide an overview of rhodolith/maerl occurrence in the colder/temperate waters of the North Atlantic and summarize the distribution, species composition, biodiversity and ecological importance of these habitats

Influences of salinity on the physiology and distribution of the Arctic coralline algae, Lithothamnion glaciale (Corallinales, Rhodophyta)

In Greenland, free-living red coralline algae contribute to and dominate marine habitats along the coastline. Lithothamnion glaciale dominates coralline algae beds in many regions of the Arctic, but never in Godthåbsfjord, Greenland, where Clathromorphum sp. is dominant. To investigate environmental impacts on coralline algae distribution, calcification and primary productivity were measured in situ during summers of 2015 and 2016, and annual patterns of productivity in L. glaciale were monitored in laboratory-based mesocosm experiments where temperature and salinity were manipulated to mimic high glacial melt. The results of field and cold-room measurements indicate that both L. glaciale and Clathromorphum sp. had low calcification and photosynthetic rates during the Greenland summer (2015 and 2016), with maximum of 1.225 ± 0.17 or 0.002 ± 0.023 μmol CaCO3 · g-1 · h-1 and -0.007 ±0.003 or -0.004 ± 0.001 mg O2 · L-1 · h-1 in each species respectively. Mesocosm experiments indicate L. glaciale is a seasonal responder; photosynthetic and calcification rates increase with annual light cycles. Furthermore, metabolic processes in L. glaciale were negatively influenced by low salinity; positive growth rates only occurred in marine treatments where individuals accumulated an average of 1.85 ± 1.73 mg · d-1 of biomass through summer. These results indicate high freshwater input to the Godthåbsfjord region may drive the low abundance of L. glaciale, and could decrease species distribution as climate change increases freshwater input to the Arctic marine system via enhanced ice sheet runoff and glacier calving.Peer reviewedFinal Accepted Versio

Coralline Algae in a Changing Mediterranean Sea: How Can We Predict Their Future, if We Do Not Know Their Present?

In this review we assess the state of knowledge for the coralline algae of the Mediterranean Sea, a group of calcareous seaweeds imperfectly known and considered highly vulnerable to long-term climate change. Corallines have occurred in the Mediterranean area for ∼140 My and are well-represented in the subsequent fossil record; for some species currently common the fossil documentation dates back to the Oligocene, with a major role in the sedimentary record of some areas. Some Mediterranean corallines are key ecosystem engineers that produce or consolidate biogenic habitats (e.g., coralligenous concretions, Lithophyllum byssoides rims, rims of articulated corallines, maerl/rhodolith beds). Although bioconstructions built by corallines exist virtually in every sea, in the Mediterranean they reach a particularly high spatial and bathymetric extent (coralligenous concretions alone are estimated to exceed 2,700 km2 in surface). Overall, composition, dynamics and responses to human disturbances of coralline-dominated communities have been well-studied; except for a few species, however, the biology of Mediterranean corallines is poorly known. In terms of diversity, 60 species of corallines are currently reported from the Mediterranean. This number, however, is based on morphological assessments and recent studies incorporating molecular data suggest that the correct estimate is probably much higher. The responses of Mediterranean corallines to climate change have been the subject of several recent studies that documented their tolerance/sensitivity to elevated temperatures and pCO2. These investigations have focused on a few species and should be extended to a wider taxonomic set

Taxonomy, molecular biodiversity and ecology of coralline algae (Corallinales: Rhodophyta), with special emphasis on maerl-forming species

Coralline algae are important biological and ecological components in coastal environments around the world, and in this study a comprehensive molecular and ecological analysis of the group was performed. Questions related to molecular diversity, species delimitation and the diagnosis of morphological features were investigated. In Chapter 2, the inclusion of rhodolith-forming species for the first time in the phylogeny of the order Corallinales showed that a monophyletic group of samples within the genus Neogoniolithon was associated with this feature. So, there is a possibility that the rhodolith habit is a combination of environmental conditions and genotypic control. In Chapter 3 it was shown that there are three common species of Lithophyllum distributed in Europe, which were identified as Lithophyllum incrustans, L. dentatum and L. hibernicum using sequences obtained from type specimens. Morphological characteristics were observed and described for each of the three species. Nine other species were found and the names for the entities will require additional studies. In Chapter 4 the new genus Chamberlainia was described using molecular affinities and morphological features; it was separated from Phymatolithon using sequence data. The phylogenetic position and taxonomy of Chamberlainia are discussed in context with representatives of related genera in the family Hapalidiaceae. In Chapter 5 the cox 2-3 marker was shown to be useful to separate taxa in the order Corallinales. Nevertheless, in some cases the taxonomic level at which the separation is established is not clear (e.g., species? Populations? Genus?). This marker was also useful for population level diversity in Phymatolithon calcareum, Chamberlainia purpurea and Lithothamnion corallioides. In Chapter 6 three maerl beds of the western Irish coast were examined and it was found that rhodoliths forming the three beds studied (Mukinish Inlet, Carraroe Bay and Mannin Bay) differed in sizes, coverage, reproduction and shape. Observations conducted over a year at Mukinish Inlet showed differences only in the reproductive phenology of the species forming the bed (Chamberlainia purpurea). Even the composition in coralline species was different in the three sites. The information acquired herein is useful for conservation strategies, ecological monitoring or even to study further questions related with molecular diversity in the group

Analysis of the cox2-3 spacer region for population diversity and taxonomic implications in rhodolith-forming species (Rhodophyta: Corallinales)

Coralline red algae demonstrate phenotypic plasticity related to environmental factors, rendering their identification difficult. The cox2-3 spacer is a mitochondrial marker widely used for phylogeographic studies and discrimination between closely related species in red algae; however, cox2-3 spacer sequence data for coralline algae are still limited. In this study we substantially increase the number of cox2-3 spacer sequences available for coralline algae, exploring their usefulness for different types of molecular investigations in coralline algae (DNA barcoding and phylogeography), with emphasis on rhodolith-forming species. Specimens from North Atlantic Europe, the Caribbean region and the Gulf of California (Mexico) were sequenced and two datasets were built, one for the subfamily Lithophylloideae and one for the Melobesioideae. Our results suggest the utility of cox2-3 spacer as barcoding marker for coralline algae with a slight variation in the barcode gap depending in the way gaps in the alignment are treated. Analyses on both datasets found a barcode gap or separation between intra and interspecific divergence (p distance and ABGD analysis) while some inconsistencies were evident when the results were compared with morphology-based classification. Using the cox2-3 spacer region, the morphospecies Lithophyllum margaritae from the Gulf of California revealed the existence of two well-supported clades, with the possibility of respectively five and two additional species; haplotype networks for Phymatolithon calcareum and P. purpureum revealed similar patterns when Mediterranean and NW Europe specimens were analysed, and P. calcareum was shown to consist of a single population in NW Europe. Based on our analyses the marker cox2-3 spacer has strong potential applications for studies of phylogeography and DNA barcoding in coralline algae after understanding its variation

Genetic and morphological variation in an ecosystem engineer, Lithophyllum byssoides (Corallinales, Rhodophyta)

Lithophyllum byssoides is a common coralline alga in the intertidal zone of Mediterranean coasts, where it produces biogenic concretions housing a high algal and invertebrate biodiversity. This species is an ecosystem engineer and is considered a target for conservation efforts, but designing effective conservation strategies currently is impossible due to lack of information about its population structure. The morphological and molecular variation of L. byssoides was investigated using morphoanatomy and DNA sequences (psbA and cox2,3) obtained from populations at 15 localities on the Italian and Croatian coasts. Lithophyllum byssoides exhibited a high number of haplotypes (31 psbA haplotypes and 24 cox2,3 haplotypes) in the central Mediterranean. The psbA and cox2,3 phylogenies were congruent and showed seven lineages. For most of these clades, the distribution was limited to one or a few localities, but one of them (clade 7) was widespread across the central Mediterranean, spanning the main biogeographic boundaries recognized in this area. The central Mediterranean populations formed a lineage separate from Atlantic samples; psbA pair-wise divergences suggested that recognition of Atlantic and Mediterranean L. byssoides as different species may be appropriate. The central Mediterranean haplotype patterns of L. byssoides were interpreted as resulting from past climatic events in the hydrogeological history of the Mediterranean Sea. The high haplotype diversity and the restricted spatial distribution of the seven lineages suggest that individual populations should be managed as independent units