Dissepiments, density bands and signatures of thermal stress in Porites skeletons
The skeletons of many reef-building corals are accreted with rhythmic structural patterns that serve as valuable sclerochronometers. Annual high- and low-density band couplets, visible in X-radiographs or computed tomography scans, are used to construct age models for paleoclimate reconstructions and to track variability in coral growth over time. In some corals, discrete, anomalously high-density bands, called “stress bands,” preserve information about coral bleaching. However, the mechanisms underlying the formation of coral skeletal density banding remain unclear. Dissepiments—thin, horizontal sheets of calcium carbonate accreted by the coral to support the living polyp—play a key role in the upward growth of the colony. Here, we first conducted a vital staining experiment to test whether dissepiments were accreted with lunar periodicity in Porites coral skeleton, as previously hypothesized. Over 6, 15, and 21 months, dissepiments consistently formed in a 1:1 ratio to the number of full moons elapsed over each study period. We measured dissepiment spacing to reconstruct multiple years of monthly skeletal extension rates in two Porites colonies from Palmyra Atoll and in another from Palau that bleached in 1998 under anomalously high sea temperatures. Spacing between successive dissepiments exhibited strong seasonality in corals containing annual density bands, with narrow (wide) spacing associated with high (low) density, respectively. A high-density “stress band” accreted during the 1998 bleaching event was associated with anomalously low dissepiment spacing and missed dissepiments, implying that thermal stress disrupts skeletal extension. Further, uranium/calcium ratios increased within stress bands, indicating a reduction in the carbonate ion concentration of the coral’s calcifying fluid under stress. Our study verifies the lunar periodicity of dissepiments, provides a mechanistic basis for the formation of annual density bands in Porites, and reveals the underlying cause of high-density stress bands.
KeywordsCoral Calcification Density banding Sclerochronology Stress bands Bleaching
We thank Yimnang Golbuu (Palau International Coral Reef Center) for assistance with permits and hosting us at PICRC, Hannah Barkley, G.P. Lohmann, Chip Young, and Kathryn Pietro for help with fieldwork, Burnham Petrographics for mounting and polishing sections, and Horst Marschall for assistance with microscope analyses. We thank two anonymous reviewers for their helpful comments. This work was supported by NSF Grants OCE 1220529 and OCE 1605365 awarded to A.L. Cohen, a WHOI Ocean Ventures Fund award to T.M. DeCarlo, a WHOI Coastal Ocean Institute award to T.M. DeCarlo, and an NSF Graduate Research Fellowship to T.M. DeCarlo.
- Abe N (1937) Postlarval development of the coral Fungia actiniformis var. palawensis Doderlein. Palao Tropical Biological Station Studies 1:73–93Google Scholar
- Buddemeier RW (1974) Environmental controls over annual and lunar monthly cycles in hermatypic coral calcification. Proc 2nd Int Coral Reef Symp 2:259–267Google Scholar
- Buddemeier RW, Kinzie RA (1975) The chronometric reliability of contemporary corals. In: Rosenberg G, Runcorn S (eds) Growth rhythms and the history of the earth’s rotation. Wiley, London, pp 135–147Google Scholar
- Cai W-J, Ma Y, Hopkinson BM, Grottoli AG, Warner ME, Ding Q, Hu X, Yuan X, Schoepf V, Xu H, Han C, Melman T, Hoadley KD, Pettay DT, Matsui Y, Baumann JH, Levas S, Ying Y, Wang Y (2016) Microelectrode characterization of coral daytime interior pH and carbonate chemistry. Nat Commun 7:11144CrossRefPubMedPubMedCentralGoogle Scholar
- Dodge RE, Szmant AM, Garcia R, Swart PK, Forester A, Leder JJ (1993) Skeletal structural basis of density banding in the reef coral Montastrea annularis. In: Proc 7th Int Coral Reef Symp 1: 186–195Google Scholar
- Hoegh-Guldberg O, Mumby PJ, Hooten AJ, Steneck RS, Greenfield P, Gomez E, Harvell CD, Sale PF, Edwards AJ, Caldeira K, Knowlton N, Eakin CM, Iglesias-Prieto R, Muthiga N, Bradbury RH, Dubi A, Hatziolos ME (2007) Coral reefs under rapid climate change and ocean acidification. Science 318:1737–1742CrossRefPubMedGoogle Scholar
- Hudson JH (1981a) Response of Montastrea annularis to environmental change in the Florida Keys. Proc 4th Int Coral Reef Symp 2: 233–240Google Scholar
- Hudson JH (1981b) Growth rates in Montastrea annularis: a record of environmental change in Key Largo Coral Reef Marine Sanctuary, Florida. Bull Mar Sci 31:444–459Google Scholar
- Sorauf J (1970) Microstructure and formation of dissepiments in the skeleton of the recent Scleractinia (hexacorals). Biomineralization 2:1–22Google Scholar
- Veron JEN (1986) Corals of Australia and the Indo-Pacific. Angus & Robertson, Sydney, AustraliaGoogle Scholar
- Winter A, Sammarco PW (2010) Lunar banding in the scleractinian coral Montastraea faveolata: fine-scale structure and influence of temperature. J Geophys Res 115:G04007Google Scholar