Limonium procerum (Large Sea-lavender) and storm damage resilience Ivor Rees

Calcareous concretion associated with Limonium procerum (Large Sea-lavender) and storm damage resilience

IVOR REES

Colonies of Limonium binervosum agg. (Rock Sealavender) have been known for many years on the rocky coast of Anglesey (v.c.52) near Aberffraw (Roberts, 1986). From descriptions by Sell & Murrell (2018) they have been determined as L. procerum (C.E. Salmon) Ingr. (Large Sea-lavender). In early March 2014, shortly after the particularly stormy winter of 2013/14, several of the sites for this species were revisited. Storm surges that winter had resulted in some extremely high tides on Irish Sea coasts; the highest tide for 21 years being recorded at Liverpool on 5 December 2013, followed by another major storm surge on 3–6 January 2014 (Duigan et al, 2014). Wave swash during these events caused considerable erosion to foredunes on the south-west coast of Anglesey and damage to infrastructure. Plants in the supra-littoral zone on nearby rocky shores would also have been subject to the same abnormal wave conditions.

Observations

At Porth Lleidiog (SH 3483 6783) it was apparent that large parts of some L. procerum colonies had been torn away. Less expected, was the exposure of patches of cemented sand overlying the bedrock where L. procerum rosettes had been. Discrete pits in the concretions also indicated where the tap roots had been pulled out. The concretions also seemed to be associated specifically with Sea-lavender colonies and not with clumps of other vascular plants which had also suffered storm damage.

In case the observation might be of wider ecological or geological interest, several photographs were taken (Plates 1–6). Subsequently, one of the more easily relocated concretion patches was photographed from above at intervals over six years. The images were taken on an opportunistic basis so

Rock Sea-lavender (Limonium binervosum agg.), Penmon Point, Anglesey. Photographs by the author.

not all originally had the same alignment. Rotating them using identifiable rock cracks as markers has allowed both the regrowth of the plant and the persistence of the concretion to be compared. A photograph of the same colony also happened to be available from six years before the storms.

The colony is located on an outcrop of PreCambrian rock at a level only reached by wave runup when storms coincide with the biggest tides. It is towards the rear of a small south-facing beach backed by a low cliff of glacial till. Adjoining the rock most of the beach has poorly sorted medium–coarse sand in the zone from high water springs down to high water neaps with extensive intertidal rock

platforms to seaward. The beach material includes much shell hash derived from limpets (Patella spp.) and other marine organisms.

Plate 1 shows the L. procerum colony in summer 2007. It may have been derived from a single very long-

established plant. That summer it had many closely spaced rosettes and many flowering stems. It is not known whether it expanded significantly or not during the six years before the storm damage occurred. The image in Plate 2 shows the situation in early March 2014, two months after the second storm surge. The sand seen on the photo was solidly cemented. Some remains of apparently dead sections of the plant with bleached and decaying leaves were still present. A few surviving rosettes still with partly green leaves, can also be seen on the left edge of the concretion. In most L. binervosum agg. taxa the leaves from a previous year normally remain through the winter, even if not in pristine condition. Later in the summer old leaves may be found decaying but still attached under the subsequent ones on the rosette. In this trait, they differ from L. vulgare and L. humile Mill (Lax-flowered Sea-lavender), where the leaves wither and are lost during the winter. Plate 3 shows the situation in August 2014, the first summer after the storm damage. The concretion had apparently lost Plates 1–6. Porth Lleidiog L. procerum colony showing concretion and little and the tap root pits were still stages in regrowth following storm damage (bottom edge of images is orientated towards the sea). 1 & 2 (top): 20 June 2007 (left); 3 March sharply defined. Rosettes that had 2014 (right), two months after storm damage. 3 & 4 (middle): 16 survived the storms of the winter August 2014 (left), in first summer after storm damage; 8 August 2019 did not all put up flowering stems (right). 5 & 6 (bottom): 13 March 2020 (left); 1 August 2020 (right). that summer. Plate 4 shows that five years later in August 2019 the plant had spread so that the rosettes now covered about half the extent of the concretion as seen in March 2014. An apparently normal proportion of the rosettes put up flowering stalks. Some reduction of the extent of the concretion around the edges

was apparent, but the remains of old tap root pits confirmed that much of the cement bonding was still strong.

Plate 5 shows the colony in mid-March 2020. It shows signs of leaf damage, probably having been washed over again during winter storms, but without enough force from wave run-up to tear rosettes away. In August 2020 (Plate 6) there were again multiple well grown rosettes and many flowering stems. It was noticed in 2020 that the flowering stems had a length distribution that was bimodal, with short ones as well as the normal tall ones. Some of the original concretion could still be seen but more of it appeared to have been lost from the edges and it was breaking down where there had been a concentration of tap root pits.

Discussion

Carbonate cementation around plant roots, sometimes termed ‘rhizocretion’ (Tucker & Wright, 1990), has more commonly been found in semi-arid climates. In the geological context, concretion by calcite or dolomite was considered indicative of fluctuating pore water chemistry. Experimental studies and electron-microscopy have also demonstrated the importance of microbially induced calcite precipitation (MICP). Fungi and bacteria have been shown to interact in this process (Martin, et al, 2012). At the Porth Lleidiog site there would have been a ready source of calcium carbonate from the shell hash fragments washed or blown over the rock. A proportion of these could become trapped in depressions in the rock surface and under L. procerum rosettes. Large temporal fluctuations in pore water salinity would occur in this type of situation due to salt deposition from spray and aerosols, evaporation due to solar heating of the rock and transpiration of the plant versus dilution by rain. The concretion was slightly darker in colour than loose sand nearby, implying some incorporation of organic matter. Possible sources of this would be fragments of stranded marine algae, decaying rosette leaves and exudates from the salt glands of the plant. Salt glands feature in descriptions by Sell & Murrell (2018) of many Limonium taxa.

Taken together, the above indirect evidence suggests that the concretion described here was partly due to MICP. Concreted shell hash has also been seen in the crevices occupied by the rhizomes of the atypical rock living L. vulgare (Common Sealavender) on this part of the Anglesey coast (Rees, 2016). Where an abundance of shell is available, concretion may provide additional anchorage for Limonium plants in locations subject to intermittent splash or swash from storm waves. Such concretions have not been noticed at other rocky places where there is less shell available and where L. binervosum agg occurs in the ecotone fringe between sandy saltmarshes and low dunes. The observation of slow regrowth in a harsh environment supports the contention that individual plants in some L.binervosum agg. colonies may have maintained themselves by vegetative means for very many years.

References

Duigan, C., Rimmington, N. & Howe, M. (Eds.). 2016. Welsh coastal storms, December 2013 & January 2014 – an assessment of environmental damage. Natural Resources

Wales Evidence Report No. 33. Martin, G., Guggiari, M., Bravo, D., Zopfi, J., Cailleau, G.,

Aragno. M., Job, D., Verrechia, E. & Junier, P. 2012. Fungi, bacteria and soil pH: the oxalate – carbonate pathway as a model for metabolic interaction. Environmental Microbiology, 14: 2960–2970. Rees, E.I.S. 2016. The conundrum of Limonium vulgare (Common Sea-lavender) on rocky shores in Anglesey v.c.52. BSBI News 132: 7–10. Roberts, R.H. 1982. The Flowering Plants and Ferns of Anglesey.

National Museum of Wales, Cardiff. Sell, P. & Murrell, G. 2018. Flora of Great Britain and Ireland.

Volume 1, Lycopodiaceae – Salicaceae. Cambridge University

Press, Cambridge. Tucker, M.E. & Wright, V.P. 1990. Carbonate Sedimentology.

Blackwell Scientific Publications, London.

E. Ivor S. Rees

Lahti, Mount Street, Menai Bridge, Anglesey LL59 5BW

ivorerees@hotmail.com