Skeletal carbonate mineralogy of Scottish bryozoans

This paper describes the skeletal carbonate mineralogy of 156 bryozoan species collected from Scotland (sourced both from museum collections and from waters around Scotland) and collated from literature. This collection represents 79% of the species which inhabit Scottish waters and is a greater number and proportion of extant species than any previous regional study. The study is also of significance globally where the data augment the growing database of mineralogical analyses and offers first analyses for 26 genera and four families. Specimens were collated through a combination of field sampling and existing collections and were analysed by X-ray diffraction (XRD) and micro-XRD to determine wt% MgCO3 in calcite and wt% aragonite. Species distribution data and phylogenetic organisation were applied to understand distributional, taxonomic and phylo-mineralogical patterns. Analysis of the skeletal composition of Scottish bryozoans shows that the group is statistically different from neighbouring Arctic fauna but features a range of mineralogy comparable to other temperate regions. As has been previously reported, cyclostomes feature low Mg in calcite and very little aragonite, whereas cheilostomes show much more variability, including bimineralic species. Scotland is a highly variable region, open to biological and environmental influx from all directions, and bryozoans exhibit this in the wide range of within-species mineralogical variability they present. This plasticity in skeletal composition may be driven by a combination of environmentally-induced phenotypic variation, or physiological factors. A flexible response to environment, as manifested in a wide range of skeletal mineralogy within a species, may be one characteristic of successful invasive bryozoans

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

Supplemental Information 3: Raw data from this study

Although the existence of coral-reef habitats at depths to 165 m in tropical regions has been known for decades, the richness, diversity, and ecological importance of mesophotic coral ecosystems (MCEs) has only recently become widely acknowledged. During an interdisciplinary effort spanning more than two decades, we characterized the most expansive MCEs ever recorded, with vast macroalgal communities and areas of 100% coral cover between depths of 50–90 m extending for tens of km2 in the Hawaiian Archipelago. We used a variety of sensors and techniques to establish geophysical characteristics. Biodiversity patterns were established from visual and video observations and collected specimens obtained from submersible, remotely operated vehicles and mixed-gas SCUBA and rebreather dives. Population dynamics based on age, growth and fecundity estimates of selected fish species were obtained from laser-videogrammetry, specimens, and otolith preparations. Trophic dynamics were determined using carbon and nitrogen stable isotopic analyses on more than 750 reef fishes. MCEs are associated with clear water and suitable substrate. In comparison to shallow reefs in the Hawaiian Archipelago, inhabitants of MCEs have lower total diversity, harbor new and unique species, and have higher rates of endemism in fishes. Fish species present in shallow and mesophotic depths have similar population and trophic (except benthic invertivores) structures and high genetic connectivity with lower fecundity at mesophotic depths. MCEs in Hawai‘i are widespread but associated with specific geophysical characteristics. High genetic, ecological and trophic connectivity establish the potential for MCEs to serve as refugia for some species, but our results question the premise that MCEs are more resilient than shallow reefs. We found that endemism within MCEs increases with depth, and our results do not support suggestions of a global faunal break at 60 m. Our findings enhance the scientific foundations for conservation and management of MCEs, and provide a template for future interdisciplinary research on MCEs worldwide

Calcareous Organisms and Sediment Mineralogy on a Mid-Depth Bank in the Hawaiian Archipelago

The dominant calcareous organisms on Penguin Bank, a middepth bank (40-100 m) off the southwestern tip of the island of Molokai, Hawaii, are red and green algae, benthic foraminifera, and bryozoans. The sediments on Penguin Bank are a mixed mineralogic assemblage of benthically derived magnesian calcite and aragonite. A low pelagic input of foraminifera and coccolithophorids to the sediments was indicated by the small percentage of low magnesian calcite found only in the smallest size fractions and the lack of recognizable particles of these organisms in these size fractions. The benthic community on Penguin Bank, composed ofcoralline algae, benthic foraminifera, and bryozoans, produces magnesian calcite with a range in magnesium content of about 6-16 mole % MgC03. Calcareous green algae (predominantly Halimeda) are the dominant producers of aragonite. Sediments on Penguin Bank are dominated by magnesian calcite particles in all size fractions (<45-3962 mm). The ratio of the percentage of high magnesian calcite (>5 mole %) to aragonite increases in the smaller size fractions and with increasing water depth from 40 to 93 m. The magnesium content of the sediments decreases within the same depth range. Mid-depth banks may be potential sources of highly chemically reactive carbonate particles to the open ocean. The magnitude of this input has not been quantitatively assessed but may be important in global biogeochemical cycles of calcium and carbon in the ocean reservoir

Callidictyon abyssorum, gen. et sp. nov. (Rhodophyta), A New Deep-water Net-forming Alga from Hawai'i

Callidictyon abyssorum, gen. et sp. nov., an unusual, net-forming red alga, is described from deep-water Pacific collections made from the research submersible Makati'i at 80-m depths on Penguin Bank, off the island of Moloka'i, Hawai'i. Though no reproductive structures were found, the new genus shares vegetative similarities with three tribes of the Ceramiaceae. The vegetative structure of C. abyssorum is similar to that of genera of the tribe Antithamnieae in having: (1) distinct basal cells on all primary lateral branches that are isodiametric and smaller than other cells of the primary laterals; (2) a central axis that is prostrate except for the portions near the apices of branches; and (3) axes that are completely without cortication. Some characters of C. abyssorum also suggest affinities to genera of the Callithamnieae, including: (1) the oblique apical cell division resulting in a strictly alternate branching pattern; (2) the absence of gland cells; and, (3) the presence of short, branching rhizoids on the basal cells of the primary lateral branches and long slender rhizoids on the main axial cells. Finally, the regularly alternate branching pattern, blunt apices, formation of anastomoses, and different .types of rhizoidal filaments, all characteristics of C. abyssorum, are also features present in members of the Compsothamnieae. Based on vegetative features, Callidictyon is tentatively placed in the Ceramiaceae until reproductive structures are found

Global community breaks at 60 m on mesophotic coral reefs

Aim: Mesophotic coral ecosystems (MCEs) are unique communities that support a high proportion of depth-endemic species distinct from shallow-water coral reefs. However, there is currently little consensus on the boundaries between shallow and mesophotic coral reefs and between upper versus lower MCEs because studies of these communities are often site specific. Here, we examine the ecological evidence for community breaks, defined here as species loss, in fish and benthic taxa between shallow reefs and MCEs globally. Location: Global MCEs. Time period: 1973–2017. Major taxa studied: Macrophytes, Porifera, Scleractinia, Hydrozoa, Octocorallia, Antipatharia and teleost fishes. Methods: We used random-effects models and breakpoint analyses on presence/absence data to identify regions of higher than expected species loss along a depth gradient of 1–69 m, based on a meta-analysis of 26 studies spanning diverse photoautotrophic and heterotrophic taxa. We then investigated the extent to which points of high faunal turnover can be explained by environmental factors, including light, temperature and nutrient availability. Results: We found evidence for a community break, indicated by a significant loss of shallow-water taxa, at ~ 60 m across several taxonomically and functionally diverse benthic groups and geographical regions. The breakpoint in benthic composition is best explained by decreasing light, which is correlated with the optical depths between 10 and 1% of surface irradiance. A concurrent shift in the availability of nutrients, both dissolved and particulate organic matter, and a shift from photoautotroph to heterotroph-dominated assemblages also occurs at ~ 60 m depth. Main conclusions: We found evidence for global community breaks across multiple benthic taxa at ~ 60 m depth, indicative of distinct community transitions between shallow and mesophotic coral ecosystems. Changes in the underwater light environment and the availability of trophic resources along the depth gradient are the most parsimonious explanations for the observed patterns