Sponge and coral zooxanthellae in heat and light: preliminary results of photochemical efficiency monitored with pulse amplitude modulated fluorometry

Authors

  • Christine H. L. Schönberg,

    1.  Centre for Marine Studies, The University of Queensland, St Lucia, Qld, Australia
    2.  Present address: Carl von Ossietzky University Oldenburg, Faculty 5, Institute of Biology and Environmental Sciences, Department of Animal Biodiversity and Evolution, Oldenburg, Germany
    Search for more papers by this author
  • Ryota Suwa,

    1.  Department of Marine and Environmental Science, Graduate School of Engineering and Science, University of the Ryukyus, Nishihara, Okinawa, Japan
    Search for more papers by this author
  • Michio Hidaka,

    1.  Department of Marine and Environmental Science, Graduate School of Engineering and Science, University of the Ryukyus, Nishihara, Okinawa, Japan
    Search for more papers by this author
  • William Kok Weng Loh

    1.  Centre for Marine Studies, The University of Queensland, St Lucia, Qld, Australia
    2.  Marine Biology Australia, St Lucia, Qld, Australia
    Search for more papers by this author

Christine H. L. Schönberg, Department of Animal Biodiversity and Evolution, Institute of Biology and Environmental Sciences, Faculty 5, Carl von Ossietzky University Oldenburg, 26111 Oldenburg, Germany. E-mail: christine.schoenberg@uni-oldenburg.de

Abstract

Photochemical efficiency (Fv/Fm) was compared between a common symbiotic bioeroding sponge, Cliona cf. orientalis, and a common reef-builder, Acropora palifera using pulse amplitude modulated fluorescence (PAM). The study was conducted on Sesoko Island, Okinawa, where reefs were severely damaged during previous bleaching episodes. Sponge and coral dinoflagellate symbionts were treated with heat and light in a tank experiment, both in hospite (=still within their host) and isolated from their hosts. We found significant differences for photochemical efficiency of holobionts (=host and symbiont together) compared to the isolate symbionts and over time. All symbionts suffered in isolation and displayed stronger reactions to the treatments, and there was evidence for increasing damage despite returning to control conditions. However, because of large variability of the bi-symbiont coral samples and restrictions of the experimental design, our main results remained inconclusive, with no significant differences between sponge and coral samples and between the different stress treatments. Judging the results based on the uniform trends in the subsets of data, the G-clade sponge symbionts appeared to be more stress tolerant than the C- and D-clade coral symbionts, with no treatment effects in hospite and less damage in isolation compared to the coral symbionts, but this is an unconfirmed assumption. Isolated sponge symbionts were very resistant against heat stress, but may have suffered from light stress. In hospite, the latter risk can be countered by the sponge’s 3-dimensional morphology, the endolithic life style that affords shading, and by behavioural adaptation, i.e. the ability to move symbionts away from the source of stress. Overall, C. cf. orientalis symbionts displayed a more stable photochemical efficiency during and after stress than those of A. palifera. Results of this study suggest that with climate change C. cf. orientalis might have a better survival potential than A. palifera, but further investigations are necessary.

Ancillary