Calculating the global contribution of coralline algae to carbon burial

The ongoing increase in anthropogenic carbon dioxide (CO2) emissions is changing the global marine environment and is causing warming and acidification of the oceans. Reduction of CO2 to a sustainable level is required to avoid further marine change. Many studies investigate the potential of marine carbon sinks (e.g. seagrass) to mitigate anthropogenic emissions, however, information on storage by coralline algae and the beds they create is scant. Calcifying photosynthetic organisms, including coralline algae, can act as a CO2 sink via photosynthesis and CaCO3 dissolution and act as a CO2 source during respiration and CaCO3 production on short-term time scales. Long-term carbon storage potential might come from the accumulation of coralline algae deposits over geological time scales. Here, the carbon storage potential of coralline algae is assessed using meta-analysis of their global organic and inorganic carbon production and the processes involved in this metabolism. Organic and inorganic production were estimated at 330 g C m−2 yr−1 and 880 g CaCO3 m−2 yr−1 respectively giving global organic/inorganic C production of 0.7/1.8 × 109 t C yr−1. Calcium carbonate production by free-living/crustose coralline algae (CCA) corresponded to a sediment accretion of 70/450 mm kyr−1. Using this potential carbon storage by coralline algae, the global production of free-living algae/CCA was 0.4/1.2 × 109 t C yr−1 suggesting a total potential carbon sink of 1.6 × 109 t C yr−1. Coralline algae therefore have production rates similar to mangroves, saltmarshes and seagrasses representing an as yet unquantified but significant carbon store, however, further empirical investigations are needed to determine the dynamics and stability of that store

Common lizards break Dollo’s law of irreversibility: genome-wide phylogenomics support a single origin of viviparity and re-evolution of oviparity

Dollo’s law of irreversibility states that once a complex trait has been lost in evolution, it cannot be regained. It is thought that complex epistatic interactions and developmental constraints impede the re-emergence of such a trait. Oviparous reproduction (egg-laying) requires the formation of an eggshell and represents an example of such a complex trait. In reptiles, viviparity (live-bearing) has evolved repeatedly but it is highly disputed if oviparity has re-evolved. Here, using up to 194,358 SNP loci and 1,334,760 bp of sequence, we reconstruct the phylogeny of viviparous and oviparous lineages of common lizards and infer the evolutionary history of parity modes. Our phylogeny supports six main common lizard lineages that have been previously identified. We find strong statistical support for a topological arrangement that suggests a reversal to oviparity from viviparity. Our topology is consistent with highly differentiated chromosomal configurations between lineages, but disagrees with previous phylogenetic studies in some nodes. While we find high support for a reversal to oviparity, more genomic and developmental data are needed to robustly test this and assess the mechanism by which a reversal might have occurred

Coralline algal Mg-O bond strength as a marine <i>p</i>CO₂ proxy

Past ocean acidification recorded in the geological record facilitates the understanding of rates and influences of contemporary &lt;i&gt;p&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt; enrichment. Most pH reconstructions are made using boron, however there is some uncertainty associated with vital effects and isotopic fractionation. Here we present a new structural proxy for carbonate chemistry; Mg-O bond strength in coralline algae. Coralline algae were incubated in control (380 μatm &lt;i&gt;p&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt;), moderate (750 μatm&lt;i&gt;p&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt;), and high (1000 μatm &lt;i&gt;p&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt;) acidification conditions for 24 months. Raman spectroscopy was used to determine skeletal Mg-O bond strength. There was a positive linear relationship between &lt;i&gt;p&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt; concentration and bond strength mediated by positional disorder in the calcite lattice when accounting for seasonal temperature. The structural preservation of the carbonate chemistry system in coralline algal high-Mg calcite represents an alternative approach to reconstructing marine carbonate chemistry. Significantly, it also provides an important mechanism for reconstructing historic atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentrations

Coralline algae in a naturally acidified ecosystem persist by maintaining control of skeletal mineralogy and size

To understand the effects of ocean acidification (OA) on marine calcifiers, the trade-offs among different sublethal responses within individual species and the emergent effects of these trade-offs must be determined in an ecosystem setting. Crustose coralline algae (CCA) provide a model to test the ecological consequences of such sublethal effects as they are important in ecosystem functioning, service provision, carbon cycling and use dissolved inorganic carbon to calcify and photosynthesize. Settlement tiles were placed in ambient pH, low pH and extremely low pH conditions for 14 months at a natural CO2 vent. The size, magnesium (Mg) content and molecular-scale skeletal disorder of CCA patches were assessed at 3.5, 6.5 and 14 months from tile deployment. Despite reductions in their abundance in low pH, the largest CCA from ambient and low pH zones were of similar sizes and had similar Mg content and skeletal disorder. This suggests that the most resilient CCA in low pH did not trade-off skeletal structure to maintain growth. CCA that settled in the extremely low pH, however, were significantly smaller and exhibited altered skeletal mineralogy (high Mg calcite to gypsum (hydrated calcium sulfate)), although at present it is unclear if these mineralogical changes offered any fitness benefits in extreme low pH. This field assessment of biological effects of OA provides endpoint information needed to generate an ecosystem relevant understanding of calcifying system persistence

The future of marine biodiversity and marine ecosystem functioning in UK coastal and territorial waters (including UK Overseas Territories) – with an emphasis on marine macrophyte communities

Funding from the UK Natural Environment Research Council (NERC) through Oceans 2025 (WP4.5), Funder Id: 10.13039/501100000270, Grant Number: Oceans 2025 – WP 4.5 and the MASTS pooling initiative (Marine Alliance for Science and Technology for Scotland, funded by the Scottish Funding Council and contributing institutions; grant reference HR09011) is gratefully acknowledged.Peer reviewedPublisher PD

Rhodoliths and rhodolith beds

Rhodolith (maërl) beds, communities dominated by free living coralline algae, are a common feature of subtidal environments worldwide. Well preserved as fossils, they have long been recognized as important carbonate producers and paleoenvironmental indicators. Coralline algae produce growth bands with a morphology and chemistry that record environmental variation. Rhodoliths are hard but often fragile, and growth rates are only on the order of mm/yr. The hard, complex structure of living beds provides habitats for numerous associated species not found on otherwise entirely sedimentary bottoms. Beds are degraded locally by dredging and other anthropogenic disturbances, and recovery is slow. They will likely suffer severe impacts worldwide from the increasing acidity of the ocean. Investigations of rhodolith beds with scuba have enabled precise stratified sampling that has shown the importance of individual rhodoliths as hot spots of diversity. Observations, collections, and experiments by divers have revolutionized taxonomic studies by allowing comprehensive, detailed collection and by showing the large effects of the environment on rhodolith morphology. Facilitated by in situ collection and calibrations, corallines are now contributing to paleoclimatic reconstructions over a broad range of temporal and spatial scales. Beds are particularly abundant in the mesophotic zone of the Brazilian shelf where technical diving has revealed new associations and species. This paper reviews selected past and present research on rhodoliths and rhodolith beds that has been greatly facilitated by the use of scuba

Coralline algal skeletal mineralogy affects grazer impacts

In macroalgal‐dominated systems, herbivory is a major driver in controlling ecosystem structure. However, the role of altered plant–herbivore interactions and effects of changes to trophic control under global change are poorly understood. This is because both macroalgae and grazers themselves may be affected by global change, making changes in plant–herbivore interactions hard to predict. Coralline algae lay down a calcium carbonate skeleton, which serves as protection from grazing and is preserved in archival samples. Here, we compare grazing damage and intensity to coralline algae in situ over 4 decades characterized by changing seawater acidity. While grazing intensity, herbivore abundance and identity remained constant over time, grazing wound width increased together with Mg content of the skeleton and variability in its mineral organization. In one species, decreases in skeletal organization were found concurrent with deeper skeletal damage by grazers over time since the 1980s. Thus, in a future characterized by acidification, we suggest coralline algae may be more prone to grazing damage, mediated by effects of variability between individuals and species

Reviews and syntheses: Calculating the global contribution of coralline algae to total carbon burial

The ongoing increase in anthropogenic carbon dioxide (CO2) emissions is changing the global marine environment and is causing warming and acidification of the oceans. Reduction of CO2 to a sustainable level is required to avoid further marine change. Many studies investigate the potential of marine carbon sinks (e.g. seagrass) to mitigate anthropogenic emissions, however, information on storage by coralline algae and the beds they create is scant. Calcifying photosynthetic organisms, including coralline algae, can act as a CO2 sink via photosynthesis and CaCO3 dissolution and act as a CO2 source during respiration and CaCO3 production on short-term timescales. Long-term carbon storage potential might come from the accumulation of coralline algae deposits over geological timescales. Here, the carbon storage potential of coralline algae is assessed using meta-analysis of their global organic and inorganic carbon production and the processes involved in this metabolism. Net organic and inorganic production were estimated at 330 g C m−2 yr−1 and 900 g CaCO3 m−2 yr−1 respectively giving global organic/inorganic C production of 0.7/1.8 × 109 t C yr−1. Calcium carbonate production by free-living/crustose coralline algae (CCA) corresponded to a sediment accretion of 70/450 mm kyr−1. Using this potential carbon storage for coralline algae, the global production of free-living algae/CCA was 0.4/1.2 × 109 t C yr−1 suggesting a total potential carbon sink of 1.6 × 109 tonnes per year. Coralline algae therefore have production rates similar to mangroves, salt marshes and seagrasses representing an as yet unquantified but significant carbon store, however, further empirical investigations are needed to determine the dynamics and stability of that store