Physiological differences among cryptic species of the Mediterranean crustose coralline alga Lithophyllum stictiforme (Corallinales, Rhodophyta)

ABSTRACT

The crustose coralline alga Lithophyllum stictiforme is an important reef builder, forming coralligenous concretions in the Mediterranean Sea. This algal species complex is composed of eight cryptic species (or clades). The objective of our study was to compare light-dependent physiological processes within and between the two most abundant cryptic species (C1 and C4) of L. stictiforme from the Bay of Marseille (France). Physiological rates of respiration, photosynthesis and calcification were measured using incubation chambers under various irradiance levels and in the dark during the summer period. We compared the physiology of the C1 and C4 cryptic species of L. stictiforme among three algal groups: C1 (the most common in the Marseille area) from 28 m depth, C4 from the same site and depth, and C1 from a deeper site at 45 m depth. We found both interspecific (between C1 and C4) and intraspecific (within C1) physiological differences. Photosynthetic parameters showed acclimation to light (or depth) with higher values of initial slope of photosynthetic light response curve (α) and lower values of saturating irradiance (E_k) and compensating irradiance (E_c) for C1 from 45 m than for C1 and C4 from 28 m depth. At the shallower depth, significant physiological differences were observed between C1 and C4 with a higher value of maximum rate of gross photosynthesis (P_{g max}) in C4, suggesting better ability to grow under high irradiance. Light and dark calcification rates differed only between C4 from 28 m and C1 from 45 m depth, being intermediate in C1 from 28 m depth. On a 24 h basis, diel net calcification rates were significantly higher in specimens from the shallower waters than from the deeper waters. Physiological differences suggest physiological plasticity within the regionally dominant cryptic species C1 and species-specific physiological traits between the cryptic species C1 and C4.

Highlights

• Photosynthesis and calcification rates differ among Lithophyllum stictiforme cryptic species.

• The regionally dominant cryptic species exhibits light-dependent physiological plasticity.

• Physiological differences occur between cryptic species found in similar environments.

KEYWORDS:

• Calcification
• coralline algae
• cryptic species
• depth
• light
• Lithophyllum
• photo-acclimation
• photosynthesis
• physiology

Acknowledgements

We thank Dorian Guillemain from the diving service of the Observatory of Sciences of the Universe (OSU) Pytheas Institute and Bruno Belloni, Pascal Mirleau and Sandrine Ruitton for their help in sample collection by scuba diving. We also thank Sacha Molinari for technical help during lyophilization and Térence Legrand for providing a map image file he has previously built. Data used in this work were partly produced through the technical facilities of the Molecular laboratory facility (SCBM) and the Experimental Aquaria facility (SCDE) of the IMBE (Marseille).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2023.2281484.

Supplementary table S1: Abundances of the eight cryptic species (or clades, C1 to C8) of the Lithophyllum stictiforme complex found (a) along the French Mediterranean coastline and (b) along the Marseille coastline according to depth (data from Fig. 2 and Fig. 3 of De Jode et al., 2019).

Supplementary fig. S1: Morphological characteristics of the three algal groups (LC-C4, LC-C1, and RM-C1) of the Lithophyllum sticitiforme species complex: (a) surface area to volume ratios and (b) surface area to weight ratios. LC = 28 m depth and RM = 45 m depth.

Supplementary fig. S2: Photosynthetic parameters of the P_n-E curves in the three algal groups (LC-C4, LC-C1, and RM-C1) of the Lithophyllum sticitiforme species complex: (a) respiration rates (R_d), (b) maximal rate of gross photosynthesis (P_{g max}), (c) saturating irradiance (E_k), and (d) initial slope of the photosynthesis-irradiance curve (α). LC = 28 m depth and RM = 45 m depth.

Author contributions

S. Martin: original concept, designed and performed the experiment, physiological measurements, data analyses, drafting and editing manuscript; V. Calvert: set up and performed the experiment; A. Chenuil: original concept, molecular analyses, editing manuscript.

Additional information

Funding

This work was funded by the CNRS-INEE initiative ‘Projets Exploratoires Premier Soutien (PEPS Adaptation 2017)’.