Isotopic tools for planktivorous megafauna @ ASLO 2015 (Dr Wyatt)

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
*Presenting author

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.

Ecosystem inputs and recycling over coral reefs @ 3rd APCRS, 2014 (Dr Wyatt)

Functional understanding of ecosystem-scale inputs and recycling over coral reef communities from stable isotope analyses of organic matter

Alex S.J. Wyatt1*, James J. Leichter2, Benoit Thibodeau1, Toshihiro Miyajima1, Craig A. Carlson3, Craig E. Nelson4, Toshi Nagata1

1Marine Biogeochemistry Laboratory, Department of Chemical Oceanography, Atmosphere & Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, JAPAN
2Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California, USA
3University of California at Santa Barbara, Santa Barbara, California, USA
4Center for Microbial Oceanography: Research and Education, University of Hawai’i, USA

Stable isotope analyses (SIA) are an increasingly useful tool for understanding functional links between water flow and nutrient cycling over coral reefs, including relative fluxes of oceanic and reef-derived material. SIA have suggested that oceanic particulate organic matter (POM) flowing over reefs can be rapidly metabolized, with the subsequent release of remineralized inorganic nutrients, as well reef-derived POM, representing a significant resource for downstream communities. High oceanic concentrations of dissolved organic matter (DOM) relative to POM suggests DOM may be an even more significant resource, especially around low-POM reefs such as mid-ocean islands and atolls. However, DOM fluxes have rarely been quantified, perhaps due to the refractory nature of oceanic DOM and difficulties linking small concentration changes with spatial changes in both hydrodynamics and macro- and microbial communities. Our Lagrangian studies of DOM around Moorea, French Polynesia and Ishigaki Island, Japan suggest that DOM changes occurring over short spatial scales reflect a balance between uptake and release. SIA further suggest that the release of reef-derived DOM (i.e. enriched in 13C), perhaps relatively labile and from nitrogen fixing organisms (i.e. depleted in 15N), may promote nutrient recycling and supply to downstream communities. Linking SIA and local hydrodynamics offers a promising path towards elucidating the relative functional importance of oceanic and reef-level processes for reef communities.

Key words: dissolved organic matter, fluxes, particulate organic matter, recycling, stable isotope analyses

Dr Wyatt awarded Early Career Travel Award by JCRS

Dr Wyatt has been awarded an Early Career Travel Award  by the Japanese Coral Reef Society (JCRS) to support attendance at the 3rd Asia Pacific Coral Reef Symposium (APCRS) in Pingtung, Taiwan.

At the 3rd APCRS Dr Wyatt presented under “Mini-Symposium 2: Functional Approaches in Coral Reefs Ecosystems”on the “Functional understanding of ecosystem-scale inputs and recycling over coral reef communities from stable isotope analyses of organic matter”.  Complementary to the conference, Dr Wyatt was invited to visit Dongsha Atoll which provided the opportunity to tour the newly opened marine research facilities on the atoll and discuss the potential for collaborative research projects.

Dr Wyatt would like to sincerely thank the JCRS for the financial support that allowed him to attend the conference.

Dr Wyatt presenting at the 3rd APCRS in June 2014

Dr Wyatt presenting at the 3rd APCRS in June 2014

Early Career members of the Japan Coral Reef Society who participated in the 3rd APCRS.

Early Career members of the Japan Coral Reef Society participating in the 3rd APCRS