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. 2023 Jun 29;13(1):10577.
doi: 10.1038/s41598-023-37110-3.

Impact of sea level rise on the Mediterranean Lithophyllum byssoides rims

Aurélie Blanfuné  1 , Charles-François Boudouresque  2 , Marc Verlaque  2 , Antoine Minne  3 , Fanny Noisette  4 , Thierry Thibaut  2
Affiliations

Impact of sea level rise on the Mediterranean Lithophyllum byssoides rims

Aurélie Blanfuné et al. Sci Rep. .

Abstract

The calcified red macroalga Lithophyllum byssoides, a very common midlittoral species in the western Mediterranean Sea, is a significant ecosystem engineer capable, under exposed and dim light conditions, of building wide and solid endemic bioconstructions near the mean sea level: the L. byssoides rims or 'trottoirs à L. byssoides'. Although the growth of the species is relatively rapid for a calcified alga, the construction of a large rim requires several centuries of near stable or slowly rising sea level. As the time scale of their formation is measured in centuries, L. byssoides bioconstructions constitute valuable and sensitive sea level markers. The health status of L. byssoides rims has been studied at two sites located far apart from each other (Marseille and Corsica), both in areas heavily impacted by humans and in areas with little impact (MPAs and unprotected areas). A health index is proposed: Lithophylum byssoides Rims Health Index. The main and inevitable threat is the rise in the sea level. This ecosystem would be the first case worldwide of marine ecosystem collapse resulting, indirectly, from man-induced global change.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
(A) Live (pink) and dead (white) L. byssoides. (B) Dead and eroded L. byssoides. (C) Live individuals of L. byssoides, with well-developed cristae, articulated corallines and Ulvophyceae. (D) Soft Rhodophyta. (E) Live crustose corallines and a hole. (F) Heavily bio-eroded L. byssoides rim, with many holes. Photos © Aurélie Blanfuné and Thierry Thibaut.
Figure 2
Figure 2
Location of studied sites for the assessment of the status of Lithophyllum byssoides rims during 2014 in Corsica and during 2015 in Marseille.
Figure 3
Figure 3
The Lithophyllum byssoides rim of Cala Litizia (SNR, Corsica), seen from the sea. Photo @Thierry Thibaut.
Figure 4
Figure 4
(A) MDS (MultiDimensional Scaling) of the different studied rims in Corsica and at Marseille, according to the protection level (WR, within reserve—red dots; outside reserve—black dots) and the circle of correlations of the different descriptors (categories). The rims with the name in pink are located near the mean sea level, those in green are a few tens of centimeters above the sea level and those in blue are far above sea level, 50 to 100 cm). Processing: Square root; Similarity Matrix: S17 Bray Curtis; 2D Stress: 0.09. (B) dbRDA (Distance-based redundancy analysis) of the different studied rims in Corsica and at Marseille, according to the LBRHI index (in yellow LBRHI index > 0.25, in orange: index between 0.25 and 0.5, and in green: LBRHI index > 0.5) and correlations of the different descriptors (categories). The rims with the name in pink are located near the mean sea level, those in green are a few tens of centimeters above the sea level and those in blue are far above sea level, 50 to 100 cm). Processing: Square root; Similarity Matrix: S17 Bray Curtis.
Figure 5
Figure 5
Height of the Lithophyllum byssoides rim above the mean sea level. (A) Low (Site C1, Palazzu cave). (B) high (Site C3, Punta Palazzu). (C) very high (site M2, Calanque de l’Oule). Photos © Aurélie Blanfuné and Thierry Thibaut.
Figure 6
Figure 6
Profile of a cliff showing the structure of the present Lithophyllum byssoides rim (LIA—Little Ice Age—and post-LIA; DACP—Dark Ages Cold Period) and the remains of the previous submerged rims that are gradually disappearing under the influence of infralittoral bioerosion. From Laborel & Laborel-Deguen, redrawn and simplified.
See this image and copyright information in PMC

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