↓↓ Check out Facebook for some images from our latest survey at Dongsha Atoll, South China Sea. Image above shows the very high soft coral cover on the atoll’s eastern reef terrace ↑↑
Ecological and biogeochemical impacts of internal waves on mesophotic coral ecosystems: testing eddy correlation and isotope approaches, Iriomote, Japan
Alex S.J. Wyatt1*, Toshihiro Miyajima1, James J. Leichter2, Tohru Naruse3, Tomohiro Kuwae4, Shoji Yamamoto5, Naomi Satoh1, Toshi Nagata1
1Department of Chemical Oceanography, Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, JAPAN
2Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California, USA
3Tropical Biosphere Research Center, University of the Ryukyus, Taketomi, Japan
4Coastal and Estuarine Environment Research Group, Port and Airport Research Institute (PARI), Nagase, Yokosuka, JAPAN
5Department of Earth and Planetary Science, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
While mesophotic coral ecosystems (MCE) may be protected or damped from disturbances impacting shallower reefs insufficient information is available on the environmental conditions supporting these ‘deep water refugia’. Nutrient inputs and recycling have rarely been quantified over MCE but may differ fundamentally to that of shallow counterparts due to the reduction in light and increasing reliance on oceanic nutrients, leading to increased heterotrophy over autotrophy at species and ecosystem levels and stronger links to oceanic processes. For instance, due to the depth of MCE relative to typical water column density stratification, internal waves may be a highly significant process depending on community aspect and exposure. Preliminary observations of MCE along a continuum of oceanic exposure in Funauki Bay, Iriomote, Japan indicate that ocean-exposed MCE are subject to semi-diurnal temperature oscillations of up to 4 C during summer (range 23 – 29 deg C), while inner MCE occur shallower in more turbid but stable environments. Oceanic exposure along the bay may determine both the distribution and function of spatially extensive, but relatively homogenous, communities dominated by Leptoseris sp. or Acropora ?horrida. Combining bulk and compound-specific stable isotope analyses, depth-specific radioisotope markers such as radiocarbon, and eddy correlation experiments in these habitat promises a useful approach for elucidating the functional importance of internal waves in the development and persistence of MCE at local to regional scales.
Amino acid and radiocarbon insights from captive whale sharks
Alex S.J. WYATT1*, Rui Matsumoto2, Yoshito Chikaraishi3, Yosuke Miyari1, Yusuke Yokoyama1, Keiichi Sato2, Nao Ohkouchi3, Toshi Nagata1
1Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, JAPAN
2Okinawa Churaumi Aquarium, Motobu, Okinawa, JAPAN
3Japan Agency for Marine-Earth Science and Technology, Yokosuka, JAPAN
Stable isotope analyses (SIA) have the potential to provide novel insights into spatial and temporal patterns in the trophic ecology of poorly understood organisms like whale sharks Rhincodon typus. However, interpreting SIA depends on accurate diet-tissue discrimination factors (DTDF) to quantify diets and trophic positions, with experimental derivations of DTDF rare for such large-bodied organisms. Captive R. typus have provided a unique opportunity to validate a range of SIA, compound-specific isotope analyses (CSIA) and radioisotope approaches in the world’s largest fish and one of three planktivorous sharks. Diet records over the past five years revealed a diet dominated by North Pacific and Antarctic krill, 44% and 49% of weighted diet for Euphausia pacifica and E. superba, respectively. Despite the well-known diet, SIA of fin tissue from three captive R. typus (7.1, 7.2, and 8.4 m in length) proved hard to reconcile, especially for bulk carbon. In contrast, CSIA of amino acid (AA) nitrogen in the sharks’ tissue was relatively stable over time, despite evidence of variation in AA compositions and δ15N-AA of diet components. Tissue radiocarbon further suggested either long turnover in fin tissues (27 months), or the preferential assimilation of the smaller E. pacifica (Δ14C of 3 ‰ compared to -112 ‰ for E. superba). Daily-scale analysis of radiocarbon in R. typus faeces may support the preferential assimilation hypothesis, faeces generally being depleted relative to diet. Together, CSIA-AA and radiocarbon analyses add multiple addtional axes to our isotope space and may alleviate some of the complications involved in interpreting bulk SIA in ecological studies.
Dr Wyatt has been awarded the Dongsha Atoll Research Award (2016-2017) by the Dongsha Atoll Research Station (DARS), managed by Taiwan’s National Sun Yat-sen University (NSYU). The award will facilitate the implementation of a collaborative project with Professor Yu-Huai Wang (NSYU) examining the impact of internal waves on the biochemistry and ecology of Dongsha’s reef communities, focusing on ‘twilight zone’ mesophotic coral ecosystems around the atoll.
Dr Wyatt is excited to begin examining the reefs around Dongsha Atoll, which experiences some of the most energetic internal wave activity on the planet, and collaborating with Professor Wang’s group and NSYU. The support of the Dongsha Atoll Research Station is greatly appreciated.
Isotopic Tools for Assessing Oceanic Versus Reef-Scale Drivers of Planktivorous Megauna Aggregations
Alex S.J. WYATT1*, Rui Matsumoto2, Yoshito Chikaraishi3, Keiichi Sato2, Nao Ohkouchi3, Toshi Nagata1
1Marine Biogeochemistry Laboratory, Department of Chemical Oceanography, Atmosphere & Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, JAPAN.
2Okinawa Churaumi Aquarium, Motobu, Okinawa, JAPAN.
3Japan Agency for Marine-Earth Science and Technology, Yokosuka, JAPAN
Stable isotope analyses (SIA) have the potential to provide novel insights into spatial and temporal patterns in the trophic ecology of poorly understood planktivorous megafauna, especially the regional oceanic versus local reef-scale drivers of whale shark and manta ray aggregations that occur along coral reefs worldwide. However, interpreting SIA depends on accurate diet-tissue discrimination factors (DTDF) to quantify diets and trophic positions, with experimental derivations of DTDF rare for such large-bodied organisms. Captive whale sharks Rhincodon typus have provided a unique opportunity to validate a range of SIA, compound-specific isotope analyses (CSIA) and radioisotope approaches in the world’s largest fish and one of three planktivorous sharks. Combining SIA and CSIA with depth-specific radioisotope markers such as iodine ratios (129I/127I) are expected to offer a promising path towards elucidating the regional to local scale divers of planktivore aggregations Although I will focus on the implications of multi-tissue differences in DTDF and turnover times in three captive whale sharks (7.1, 7.2, and 8.4 m in length) the concepts and techniques are highly applicable to studying a wide range of species in diverse environments. An example will be provided of application to a wild caught (4.4 m) specimen of the smallest planktivorous shark, the rarely encountered megamouth shark Megachasma pelagios.
We are please to announce that we will be hosting The 10th International Conference on the Application of Isotopes to Ecological Studies (IsoEcol 2016) in Tokyo, Japan from April 3-8, 2016.
More information will be made available via the conference website: www.isoecol.com/2016
- Alex Wyatt, The University of Tokyo
- Ichiro Tayasu, Kyoto University
- Naohiro Yoshida, Tokyo Institute of Technology
- Naohiko Ohkouchi, JAMSTEC
- Toshi Nagata, The University of Tokyo