Structural integrity and skeletal trace elements in intertidal coralline algae across the Northeast Atlantic reveal a distinct separation of the leading and the trailing edge populations.

Intertidal macroalgae, such as coralline algae, represent an essential structural element and substrate in rocky coastal zones. They have a high degree of flexibility allowing their survival in environments with severe mechanical stress during tidal cycles. This study characterised the genicula and intergenicula of the calcifying red algae Corallina officinalis across its geographic distribution in the Northeast Atlantic. Poleward populations have constructed more sturdy cell walls compared to equatorward populations, potentially due to greater local adaptations to higher frequency and intensity of environmental factors like storms and wave action. Southern populations showed a lack of local adaptation culminating in survival rather than thriving within their current environment, hence, they are located at the margin of this species' favourable conditions. Results clarify significant differences between latitudes and indicate a north-to-south gradient in this species' skeletal elemental composition. Northern populations were dominated by cadmium, whereas chromium was the major trace element found in southern populations. In the future, these characteristics could lead to a permanent decline and a decrease in the ecosystem functions of C. officinalis in the southern locations in the Northeast Atlantic, which may be accelerated by predicted future climatic changes.

An intertidal life: Combined effects of acidification and winter heatwaves on a coralline alga (Ellisolandia elongata) and its associated invertebrate community.

In coastal marine ecosystems coralline algae often create biogenic reefs. These calcareous algal reefs affect their associated invertebrate communities via diurnal oscillations in photosynthesis, respiration and calcification processes. Little is known about how these biogenic reefs function and how they will be affected by climate change. We investigated the winter response of a Mediterranean intertidal biogenic reef, Ellissolandia elongata exposed in the laboratory to reduced pH conditions (i.e. ambient pH - 0.3, RCP 8.5) together with an extreme heatwave event (+1.4 °C for 15 days). Response variables considered both the algal physiology (calcification and photosynthetic rates) and community structure of the associated invertebrates (at taxonomic and functional level). The combination of a reduced pH with a heatwave event caused Ellisolandia elongata to significantly increase photosynthetic activity. The high variability of calcification that occurred during simulated night time conditions, indicates that there is not a simple, linear relationship between these two and may indicate that it will be resilient to future conditions of climate change. In contrast, the associated fauna were particularly negatively affected by the heatwave event, which impoverished the communities as opportunistic taxa became dominant. Local increases in oxygen and pH driven by the algae can buffer the microhabitat in the algal fronds, thus favouring the survival of small invertebrates.

Structural and Elemental Analysis of the Freshwater, Low-Mg Calcite Coralline Alga Pneophyllum cetinaensis.

Coralline algae are one of the most diversified groups of red algae and represent a major component of marine benthic habitats from the poles to the tropics. This group was believed to be exclusively marine until 2016, when the first freshwater coralline algae Pneophyllum cetinaensis was discovered in the Cetina River, southern Croatia. While several studies investigated the element compositions of marine coralline algal thalli, no information is yet available for the freshwater species. Using XRD, LA-ICP-MS and nano indentation, this study presents the first living low-Mg calcite coralline algae with Mg concentrations ten times lower than is common for the average marine species. Despite the lower Mg concentrations, hardness and elastic modulus (1.71 ± 1.58 GPa and 29.7 ± 18.0 GPa, respectively) are in the same range as other marine coralline algae, possibly due to other biogenic impurities. When compared to marine species, Ba/Ca values were unusually low, even though Ba concentrations are generally higher in rivers than in seawater. These low values might be linked to different physical and chemical characteristics of the Cetina River.

Physiological response of the coralline alga Corallina officinalis L. to both predicted long-term increases in temperature and short-term heatwave events.

Climate change is leading to an increase of mean sea surface temperatures and extreme heat events. There is an urgent need to better understand the capabilities of marine macroalgae to adapt to these rapid changes. In this study, the responses of photosynthesis, respiration, and calcification to elevated temperature in a global warming scenario were investigated in the coralline alga Corallina officinalis. Algae were cultured for 7 weeks under 4 temperature treatments: (1) control under ambient-summer conditions (C, ~20 °C), (2) simulating a one-week heatwave of 1 °C (HW, Tcontrol+1 °C), (3) elevated temperature (+3, Tcontrol +3 °C), (4) combination of the two previous treatments (HW+3, T+3+1 °C). After exposure at T+3 (up to a Tmax of ~23 °C), respiration and photosynthesis increased significantly. After 5 weeks, calcification rates were higher at elevated temperatures (T+3 and THW+3) compared to Tcontrol, but at the end of the experiment (7 weeks) calcification decreased significantly at those temperatures beyond the thermal optimum (six-fold at T+3, and three-fold at THW+3, respectively). The same trend was noted for all the physiological processes, suggesting that a prolonged exposure to high temperatures (7 weeks up to T+3) negatively affect the physiology of C. officinalis, as a possible consequence of thermal stress. A one-week heatwave of +1 °C with respect to Tcontrol (at THW) did not affect respiration, photosynthesis, or calcification rates. Conversely, a heatwave of 1 °C, when combined with the 3 °C increase predicted by the end of the century (at THW+3), induced a reduction of physiological rates. Continued increases in both the intensity and frequency of heatwaves under anthropogenic climate change may lead to reduced growth and survival of primary producers such as C. officinalis.

Understanding the margin squeeze: Differentiation in fitness-related traits between central and trailing edge populations of Corallina officinalis.

ABSTRACT: Assessing population responses to climate-related environmental change is key to understanding the adaptive potential of the species as a whole. Coralline algae are critical components of marine shallow water ecosystems where they function as important ecosystem engineers. Populations of the calcifying algae Corallina officinalis from the center (southern UK) and periphery (northern Spain) of the North Atlantic species natural distribution were selected to test for functional differentiation in thermal stress response. Physiological measurements of calcification, photosynthesis, respiration, growth rates, oxygen, and calcification evolution curves were performed using closed cell respirometry methods. Species identity was genetically confirmed via DNA barcoding. Through a common garden approach, we identified distinct vulnerability to thermal stress of central and peripheral populations. Southern populations showed a decrease in photosynthetic rate under environmental conditions of central locations, and central populations showed a decline in calcification rates under southern conditions. This shows that the two processes of calcification and photosynthesis are not as tightly coupled as previously assumed. How the species as whole will react to future climatic changes will be determined by the interplay of local environmental conditions and these distinct population adaptive traits. OPEN RESEARCH BADGES: This article has earned an Open Materials Badge for making publicly available the components of the research methodology needed to reproduce the reported procedure and analysis. All materials are available at https://doi.pangaea.de/10.1594/PANGAEA.899568.

Isolation and characterization of nine microsatellite markers for the red alga Corallina officinalis.

We report the development of nine polymorphic microsatellite markers for Corallina officinalis (Linnaeus, 1758), a calcifying intertidal red alga and important ecosystem engineer spread along the North East Atlantic. Characterization and analysis of loci were made using 15 individuals of C. officinalis from populations in Iceland and the UK. The average number of alleles per locus was 3.78 (range 2-6) and mean of gene diversity was 0.58 (range 0.38-0.77). The set of microsatellites developed here will provide a useful molecular tool for population genetic and conservation studies.