Research ArticleECOLOGY

Living evidence of a fossil survival strategy raises hope for warming-affected corals

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Science Advances  09 Oct 2019:
Vol. 5, no. 10, eaax2950
DOI: 10.1126/sciadv.aax2950
  • Fig. 1 Rejuvenescence-mediated recovery at the polyp and colony levels in Cladocora caespitosa.

    Summer heat waves trigger polyp contraction and tissue necrosis. Most of the warming-affected polyps die during the necrosis events, but some survive via rejuvenescence, characterized by a drastic reduction in polyp size and the partial retreat of the polyp from the original skeletal structures (detailed information is provided in Figs. 2 and 3). Rejuvenated polyps regrow and undergo budding, eventually recolonizing dead colony areas. The right panel shows the death and recovery of a colony affected by warming in 2006 (the white color of the colony is given by the denuded coral skeleton after the death of the polyps, not by bleaching). After the necrosis event, dead colony areas are eventually overgrown by algae (2009). By 2017, the colony shows a recovery of ca. 80%, together with a recently necrosed area to the right. Scale in 2006: 25 cm (photo credit: D. K. Kersting, Freie Universität Berlin).

  • Fig. 2 Rejuvenated Cladocora caespitosa polyps and related skeletal structures.

    (A) C. caespitosa polyp showing a drastic size reduction shortly after a necrosis event. (B) Rejuvenated polyp regrowing its skeleton inside a partially abandoned calix. (C) Calix showing the first stages of rejuvenation, with the contracted polyp retreated to the center-left portion of the calix; note how some septa show continuity inside the new external wall. (D) Rejuvenated calix growing over the abandoned calix. Scale bars, 0.5 cm (photo credit: D. K. Kersting, Freie Universität Berlin).

  • Fig. 3 3D computed tomography sections in C. caespitosa calices showing rejuvenation.

    Septa and columnella partially connect through the abandoned and rejuvenated calices [arrows in (A) to (F)], while a new external wall is built [asterisks in (A) to (G)], leaving the rest of the skeletal structures and a portion of the original external wall outside the rejuvenated calix and characteristically marking the inner corallite structure. The new calix eventually recovers its original diameter, and the polyp starts budding (C to H). The partially abandoned calix, exposed to surrounding water, eventually fills with debris and foraminifera [arrows in (I), zoomed-in white rectangle of (H)]. Scale bars, 0.25 cm. Note that the sections belong to three corallites; (A) and (B) show two sections of two different corallites, while (C) to (I) belong to the same one.

  • Fig. 4 3D computed tomography sections of a C. caespitosa calix showing three new calices.

    (A) Photograph of the scanned corallite. (B and C) Arrows point to the new calices, which show connections to the skeletal structures of the original polyp. Scale bars: 0.15 cm (photo credit: D. K. Kersting, Freie Universität Berlin).

  • Fig. 5 Rejuvenescence marks at the corallite and colony levels.

    (A) External rejuvenescence scar in a corallite. (B and C) 3D computed tomography sections showing rejuvenescence scars (arrows) in corallites grown many centimeters after the rejuvenescence process. (D) 3D computed tomography section of a rejuvenated calix in a C. caespitosa fossil corallite (Holocene) from Menorca (NW Mediterranean Sea). (E) Inner recovery interface or discontinuity (arrows) in a colony fragment. Scale bars, 0.25 cm (photo credit: D. K. Kersting, Freie Universität Berlin).

Supplementary Materials

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Long-term rejuvenescence-mediated recoveries of warming-affected C. caespitosa colonies.
    • Table S1. Recovery data and annual recovery rates in transect colonies showing rejuvenation processes.

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