Anatomical structure overrides temperature controls on magnesium uptake – calcification in the Arctic/subarctic coralline algae <i>Leptophytum laeve</i> and <i>Kvaleya epilaeve</i> (Rhodophyta; Corallinales)

Abstract

Abstract. Calcified coralline red algae are ecologically key organisms in photic benthic environments. In recent decades they have become important climate proxies, especially in the Arctic and subarctic. It has been widely accepted that magnesium content in coralline tissues is directly a function of ambient temperature, and this is a primary basis for their value as a climate archive. In this paper we show for two genera of Arctic/subarctic corallines, Leptophytum laeve and Kvaleya epilaeve, that previously unrecognised complex tissue and cell wall anatomy bears a variety of basal signatures for Mg content, with the accepted temperature relationship being secondary. The interfilament carbonate has lower Mg than adjacent cell walls and the hypothallial cell walls have the highest Mg content. The internal structure of the hypothallial cell walls can differ substantially from the perithallial radial cell wall structure. Using highmagnification scanning electron microscopy and etching we expose the nanometre-scale structures within the cell walls and interfilament. Fibrils concentrate at the internal and external edges of the cell walls. Fibrils ∼ 10 nm thick appear to thread through the radial Mg-calcite grains and form concentric bands within the cell wall. This banding may control Mg distribution within the cell. Similar fibril banding is present in the hypothallial cell walls but not the interfilament. Climate archiving with corallines can achieve greater precision with recognition of these parameters.

Multiple phases of mg‐calcite in crustose coralline algae suggest caution for temperature proxy and ocean acidification assessment: lessons from the ultrastructure and biomineralization in Phymatolithon (Rhodophyta, Corallinales)1

“…The IAPs were derived from experiments that explicitly assumed there was only one Mg-calcite phase present in their experimental corallines (Plummer andMackenzie 1974, Mackenzie et al 1987). As this study and others (Ragazzola et al 2016, Nash andAdey 2017) show, this premise of only one phase is not supported. We have shown that within one coralline crust there are at least three distinct phases of Mg-calcite with a large range of Mg content.…”

“…The individual data for cell wall and interfilament for the Boreal Phymatolithon species in this study do not extend to the higher and lower temperatures needed to provide significance in a regression curve. However, by adding data collected similarly by EDS for Leptophytum laeve and Kvaleya epilaeve (Nash and Adey 2017) in the Labrador Sea and for tropical P. onkodes (Table 3), the temperature range can be extended. In that case, a positive linear correlation from a least squares regression is seen for both carbonate components ( Fig.…”

Phymatolithon (Melobesioideae, Hapalidiales) in the Boreal–Subarctic Transition Zone of the North Atlantic

“…Although this may not generally be applicable to cold-water corallines, dolomite has been described in a Clathromorphum crust from Greenland (Nash and Adey, 2017b). These Mg variations are in agreement with the Mg offsets obtained for the cell wall, IF, and hypothallial cells in Leptophytum laeve and Kvaleya epilaeve from Arctic Labrador (Nash and Adey, 2017a). The elevated Mg in perithallial cell walls compared to IF (called interstitial) has also been noted for Lithothamnion glaciale (Ragazzola et al, 2016).…”

“…Most critically, we know, from experimental and field studies , that Clathromorphum does not require light to calcify, although ultimately stored energy from photosynthesis is required. Also, there are non-photosynthetic coralline parasites, such as Kvaleya in the North Atlantic and Arctic (Adey and Sperapani, 1971; also Ezo on Lithophyllum; Adey et al, 1974) that show the same basic calcified wall structure as free-living corallines; in these cases the calcified walls are developed using photosynthate derived from their hosts (Nash and Adey, 2017a). Thus, calcification is almost certainly metabolically driven (Adey, 1998) rather than supported by pH elevation during photosynthesis.…”

Effects of light and temperature on Mg uptake, growth, and calcification in the proxy climate archive <i>Clathromorphum</i> <i>compactum</i>

“…distribution becomes severely limited at temperatures above 11-13 • C (Adey, 1965). The precise mode of calcification in coralline algae has been long debated (Adey, 1998;Nash et al, 2018), and the role of photosynthesis in influencing calcification has not yet been fully established. The shape of Mg content curves from subarctic/Arctic Clathromorphum sp.…”