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

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

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

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

Ocean acidification impacts mussel control on biomineralisation

Ocean acidification is altering the oceanic carbonate saturation state and threatening the survival of marine calcifying organisms. Production of their calcium carbonate exoskeletons is dependent not only on the environmental seawater carbonate chemistry but also the ability to produce biominerals through proteins. We present shell growth and structural responses by the economically important marine calcifier Mytilus edulis to ocean acidification scenarios (380, 550, 750, 1000&asymp; atm pCO 2). After six months of incubation at 750&asymp; atm pCO 2, reduced carbonic anhydrase protein activity and shell growth occurs in M. edulis. Beyond that, at 1000&asymp; atm pCO 2, biomineralisation continued but with compensated metabolism of proteins and increased calcite growth. Mussel growth occurs at a cost to the structural integrity of the shell due to structural disorientation of calcite crystals. This loss of structural integrity could impact mussel shell strength and reduce protection from predators and changing environments

Benthic oxygen exchange in a live coralline algal bed and an adjacent sandy habitat: an eddy covariance study

Coralline algal (maerl) beds are widespread, slow-growing, structurally complex perennial habitats that support high biodiversity, yet are significantly understudied compared to seagrass beds or kelp forests. We present the first eddy covariance (EC) study on a live maerl bed, assessing the community benthic gross primary productivity (GPP), respiration (R), and net ecosystem metabolism (NEM) derived from diel EC time series collected during 5 seasonal measurement campaigns in temperate Loch Sween, Scotland. Measurements were also carried out at an adjacent (~20 m distant) permeable sandy habitat. The O2 exchange rate was highly dynamic, driven by light availability and the ambient tidally-driven flow velocity. Linear relationships between the EC O2 fluxes and available light indicate that the benthic phototrophic communities were lightlimited. Compensation irradiance (Ec) varied seasonally and was typically ~1.8-fold lower at the maerl bed compared to the sand. Substantial GPP was evident at both sites; however, the maerl bed and the sand habitat were net heterotrophic during each sampling campaign. Additional inputs of ~4 and ~7 mol m-2 yr-1 of carbon at the maerl bed and sand site, respectively, were required to sustain the benthic O2 demand. Thus, the 2 benthic habitats efficiently entrap organic carbon and are sinks of organic material in the coastal zone. Parallel deployment of 0.1 m2 benthic chambers during nighttime revealed O2 uptake rates that varied by up to ~8-fold between replicate chambers (from -0.4 to -3.0 mmol O2 m-2 h-1; n = 4). However, despite extensive O2 flux variability on meter horizontal scales, mean rates of O2 uptake as resolved in parallel by chambers and EC were typically within 20% of one another

Red coralline algae assessed as marine pH proxies using 11B MAS NMR

Reconstructing pH from biogenic carbonates using boron isotopic compositions relies on the assumption that only borate, and no boric acid, is present. Red coralline algae are frequently used in palaeoenvironmental reconstruction due to their widespread distribution and regular banding frequency. Prior to undertaking pH reconstructions using red coralline algae we tested the boron composition of the red coralline alga Lithothamnion glaciale using high field NMR. In bulk analysed samples, thirty percent of boron was present as boric acid. We suggest that prior to reconstructing pH using coralline algae 1) species-specific boron compositions and 2) within-skeleton special distributions of boron are determined for multiple species. This will enable site selective boron analyses to be conducted validating coralline algae as palaeo-pH proxies based on boron isotopic compositions

Community-level sensitivity of a calcifying ecosystem to acute in situ CO2 enrichment

The rate of change in ocean carbonate chemistry is a vital determinant in the magnitude of effects observed. Benthic marine ecosystems are facing an increasing risk of acute CO2 exposure that may be natural or anthropogenically derived (e.g. engineering and industrial activities). However, our understanding of how acute CO2 events impact marine life is restricted to individual organisms, with little understanding for how this manifests at the community level. Here, we investigated in situ the effect of acute CO2 enrichment on the coralline algal ecosystem—a globally ubiquitous, ecologically and economically important habitat, but one which is likely to be sensitive to CO2 enrichment due to its highly calcified reef-like structures engineered by coralline algae. Most notably, we observed a rapid community-level shift to favour net dissolution rather than net calcification. Smaller changes from net respiration to net photosynthesis were also observed. There was no effect on the net flux of DMS/DMSP (algal secondary metabolites), nor on the nutrients nitrate and phosphate. Following return to ambient CO2 levels, only a partial recovery was seen within the monitoring timeframe. This study highlights the sensitivity of biogenic carbonate marine communities to acute CO2 enrichment and raises concerns over the capacity for the system to ‘bounce back’ if subjected to repeated acute high-CO2 events

Editorial: Coralline algae: Past, present, and future perspectives

Following the success of the Frontiers in Marine Science Research Topic on “Coralline Algae: Globally Distributed Ecosystem Engineers,” the Research Topic on “Coralline Algae: Past, Present and Future Perspectives” was launched to extend the opportunity for publishing further knowledge about these diverse ecosystem engineers across a broader time scale. In this Research Topic, an additional nine original research articles have been published, strengthening our understanding of coralline algae past, present, and future, including their biology, physiology and ecology. From reconstructing coralline algal assemblages during the Paleocene/Eocene thermal maximum, to understanding current trophodynamics and benthic-pelagic coupling in rhodolith beds, to assessing the adaptability of coralline algae to future warming, the original research articles in this Research Topic cover a time frame of 55.6 million years and span across an Atlantic biogeographical range from Brazil to the high Arctic.info:eu-repo/semantics/publishedVersio

The glacial geomorphology of upper Godthåbsfjord (Nuup Kangerlua) in south-west Greenland

© 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of Journal of Maps. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.The Greenland Ice Sheet (GrIS) is known to have experienced widespread retreat over the last century. Information on outlet glacier dynamics, prior to this, are limited due to both a lack of observations and a paucity of mapped or mappable deglacial evidence which restricts our understanding of centennial to millennial timescale dynamics of the GrIS. Here we present glacial geomorphological mapping, for upper Godthåbsfjord, covering 5800 km 2 at a scale of 1:92,000, using a combination of ASTER GDEM V2, a medium-resolution DEM (error < 10 m horizontal and < 6 m vertical accuracy), panchromatic orthophotographs and ground truthing. This work provides a detailed geomorphological assessment for the area, compiled as a single map, comprising of moraines, meltwater channels, streamlined bedrock, sediment lineations, ice-dammed lakes, trimlines, terraces, gullied sediment and marine limits. Whilst some of the landforms have been previously identified, the new information presented here improves our understanding of ice margin behaviour and can be used for future numerical modelling and landform dating programmes. Data also form the basis for palaeoglaciological reconstructions and contribute towards understanding of the centennial to millennial timescale record of this sector of the GrIS.Peer reviewedFinal Published versio