Nissei Foundation grant to Dr Wyatt et al.

The Nissei Foundation has awarded Dr Wyatt and colleagues a Grant for Environmental Issues Research by Young Researchers, 環境問題研究助成 (若手研究):

Title: Elucidating jungle-to-reef connections using state-of-the-art chemical tracers: Towards harmony between human activities and the pristine environments of Iriomote-jima, Japan | 最先端化学トレーサーによる亜熱帯林とサンゴ礁生態系のつながりの 解明:西表島の貴重な自然の保全と人間活動の調和に向けて

Participants: Alex. S.J. Wyatt, Toshi Nagata, Yusuke Yokoyama, Toshihiro Miyajima, James Leichter (Scripps)

This grant will facilitate ongoing work examining ecological links between oceanic and terrestrial processes in the pristine coral reef ecosystems of the west coast of Iriomote-jima.  Preliminary isotope tracer work has demonstrated that corals may be strongly dependent  on ancient carbon exported from the forested catchment feeding into Funauki Bay, which suggests that reef habitats across the bay may depend on the preservation of the intact upstream sub-tropical forest.

More info: http://www.nihonseimei-zaidan.or.jp/kankyo/04_jisseki.html

Thank you to the Nissei Foundation for their support.

 

New paper on advances in amino acid nitrogen isotopic analysis (Ohkouchi et al., Organic Geochemsitry)

Advances in the application of amino acid nitrogen isotopic analysis in ecological and biogeochemical studies

Naohiko Ohkouchi1,*, Yoshito Chikaraishi1,13, Hilary G. Close2, Brian Fry3, Thomas Larsen4, Daniel J. Madigan5, Matthew D. McCarthy6, Kelton W. McMahon7, Toshi Nagata8, Yuichi I. Naito1,14, Nanako O. Ogawa1, Brian N. Popp9, Shawn Steffan10,11, Yoshinori Takano1, Ichiro Tayasu12, Alex S.J. Wyatt8, Yasuhiko T. Yamaguchi8,15, Yusuke Yokoyama8

1 Department of Biogeochemistry, Japan Agency for Marine-Earth Science and Technology, Japan; 2 Rosenstiel School of Marine and Atmospheric Science, University of Miami, USA3 Australian Rivers Institute, Griffith University, Australia; 4 Leibniz-Laboratory, University of Kiel, Germany; 5 Harvard University Center for the Environment, USA; 6 Department of Ocean Sciences, University of California, Santa Cruz, USA; 7 Graduate School of Oceanography, University of Rhode Island, USA; 8 Atmosphere and Ocean Research Institute, The University of Tokyo, Japan; 9 Department of Geology and Geophysics, University of Hawaii, USA; 10 US Department of Agriculture, Agricultural Research Service, USA; 11 Department of Entomology, University of Wisconsin-Madison, USA; 12 Research Institute of Humanity and Nature, Japan; 13 Present address: Institute of Low Temperature Science, Hokkaido University, Japan; 14 Present address: Nagoya University Museum, Japan; 15 Present address: Lake Biwa Environmental Research Institute, Japan

Compound-specific isotopic analysis of amino acids (CSIA-AA) has emerged in the last decade as a powerful approach for tracing the origins and fate of nitrogen in ecological and biogeochemical studies. This approach is based on the empirical observation that source amino acids (AAs) (i.e., phenylalanine), fractionate 15N very little (< 0.5‰) during trophic transfer, whereas trophic AAs (i.e., glutamic acid), are greatly (∼6–8‰) enriched in 15N during each trophic step. The differential fractionation of these two AA groups can provide a valuable estimate of consumer trophic position that is internally indexed to the baseline δ15N value of the integrated food web. In this paper, we critically review the analytical methods for determining the nitrogen isotopic composition of AAs by gas chromatography–isotope-ratio mass spectrometry. We also discuss methodological considerations for accurate trophic position assessment of organisms using CSIA-AA. We then discuss the advantages and challenges of the CSIA-AA approach using published case studies across a range of topics, including trophic position assessment in various ecosystems, reconstruction of ancient human diets, reconstruction of animal migration and environmental variability, and assessment of marine organic matter dynamics with new classification of microbial fractionation patterns. It is clear that the CSIA-AA approach can provide unique insight into the sources, cycling, and trophic modification of organic nitrogen as it flows through systems. However, this approach will be greatly improved through continued exploration into how biochemical, physiological, and ecological mechanisms affect isotopic fractionation of individual AAs. We end this review with a perspective on future work that will promote the evolution of the rapidly growing field of CSIA-AA.

Impacts of internal waves on the twilight zone @ ICRS 2016, Hawaii (Dr Wyatt)

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.

Adding to our isotope axes @ IsoEcol 2016 (Dr Wyatt)

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
*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 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. pacifica14C 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.

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.

Isotope discrimination in captive whale sharks @ IsoEcol 2014 (Dr Wyatt)

Isotope Discrimination in Planktivorous Elasmobranchs Focusing on the World’s Largest Fish, Captive Whale Sharks Rhincodon typus

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

Accurate diet-tissue discrimination factors (DTDF) are essential for quantifying diets and trophic positions (TP) using stable isotope analyses (SIA), with potential variation between diets, tissues, organisms and environments arguing against untested application of meta-analysis averages (e.g. 3.4 ‰ for bulk nitrogen (Δ15Nbulk), ~0.5 ‰ for bulk carbon (Δ13Cbulk), and 7.6 ‰ and 0.4 ‰ for nitrogen of glutamic acid (Δ15Nglu) and phenylalanine (Δ15Nphe), respectively). Experimental derivations of DTDF in elasmobranchs (sharks and rays) are scarce, with large-bodied organisms difficult to maintain in captivity and non-lethal multi-tissue sampling problematic for both captive and wild individuals. SIA of captive whale sharks Rhincodon typus, one male (8.5 m in length) and two females (7.1 and 7.2 m), fed a mixed diet composed mainly (~ 48 % each) of Antarctic krill Euphausia superba15N = 3.45 ‰, δ13C = -26.3 ‰) and North Pacific krill E. pacifica15N = 5.88 ‰, δ13C = -21.6 ‰), provide an opportunity to examine DTDF in the world’s largest fish and one of three planktivorous sharks. DTDFs estimated based on temporally averaged diets for easily sampled but slow turnover fin tissue were close to previous observations, but varied between individuals, perhaps reflecting differing growth rates with size or physiological differences between the sexes: Δ15Nbulk (2.6, 3.3, 3.1 ‰), Δ13Cbulk (3.9, 4.5, 5.9 ‰), Δ15Nglu (7.6, 6.5, n.d. ‰) and Δ15Nphe (0.3, 0.2, n.d. ‰). Short turnover tissues, such as liver or blood, may be difficult or impossible to obtain for these species, requiring non-lethal isotopic proxies to examine diet and TP at higher temporal resolution. For instance, SIA of faecal material was highly variable but reflected day-to-day variation in minor (<3 %) components of the sharks’ diets. DTDF will be discussed in the context of sampling constraints related to multi-tissue SIA and recent radioisotope approaches for understanding feeding and aggregations of planktivorous elasmobranchs, including recent application to a wild caught (4.4 m) specimen of the smallest planktivorous shark, the rare 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

Formation and maintenance of high-nitrate, low pH layers (Waite et al., Biogeosciences)

Formation and maintenance of high-nitrate, low pH layers in the eastern Indian Ocean and the role of nitrogen fixation

A. M. Waite, V. Rossi, M. Roughan, B. Tilbrook, P. A. Thompson, M. Feng, A. S. J. Wyatt, and E. J. Raes

We investigated the biogeochemistry of low dissolved oxygen high-nitrate (LDOHN) layers forming against the backdrop of several interleaving regional water masses in the eastern Indian Ocean, off northwest Australia adjacent to Ningaloo Reef. These water masses, including the forming Leeuwin Current, have been shown directly to impact the ecological function of Ningaloo Reef and other iconic coastal habitats downstream. Our results indicate that LDOHN layers are formed from multiple subduction events of the Eastern Gyral Current beneath the Leeuwin Current (LC); the LC originates from both the Indonesian Throughflow and tropical Indian Ocean. Density differences of up to 0.025 kg m−3 between the Eastern Gyral Current and the Leeuwin Current produce sharp gradients that can trap high concentrations of particles (measured as low transmission) along the density interfaces. The oxidation of the trapped particulate matter results in local depletion of dissolved oxygen and regeneration of dissolved nitrate (nitrification). We document an associated increase in total dissolved carbon dioxide, which lowers the seawater pH by 0.04 units. Based on isotopic measurements (δ15N and δ18O) of dissolved nitrate, we determine that ~ 40–100% of the nitrate found in LDOHN layers is likely to originate from nitrogen fixation, and that, regionally, the importance of N-fixation in contributing to LDOHN layers is likely to be highest at the surface and offshore.

DON isotopes over a coral reef (Thibodeau et al., Coral Reefs)

Heterogeneous dissolved organic nitrogen supply over a coral reef: first evidence from nitrogen stable isotope ratios

B. Thibodeau, T. Miyajima, I. Tayasu, A. S. J. Wyatt, A. Watanabe, N. Morimoto, C. Yoshimizu, T. Nagata

Dissolved organic nitrogen (DON) potentially plays a major role in sustaining the high productivity and biological diversity of coral reefs. However, data are scarce regarding sources and sinks of DON. This study, for the first time, determined the 15N isotopic composition of total dissolved nitrogen (δ15NTDN), reflecting the isotopic signature of DON, in the water column over a coral reef. The uniformity in δ15NTDN during high tide (3.2 ± 0.3 ‰) indicated that the DON was mainly derived from offshore waters. In contrast, higher spatial heterogeneity of δ15NTDN (3.1 ± 0.9 ‰) and DON concentrations during low tide indicated the existence of local DON sources patchily distributed over the reef. Low δ15NTDN values located mid-reef were indicative of DON release from organisms that obtained their N via N2 fixation, whereas high δ15NTDN appeared to reflect localized release of DON by organisms exposed to dissolved inorganic nitrogen with elevated 15N, such as from terrestrial and offshore inputs. Collectively, the results highlight the importance of spatial patterns in DON release from reef communities in the N cycling of coral reefs.

Coral reef POM dynamics (Wyatt et al., L&O)

Particulate nutrient fluxes over a fringing coral reef: Source-sink dynamics inferred from carbon to nitrogen ratios and stable isotopes

Alex S. J. Wyatt, Ryan J. Lowe, Stuart Humphries and Anya M. Waite

We examined spatial and temporal variations in particulate organic matter (POM) dynamics over a fringing coral reef (Ningaloo Reef) in Western Australia during the austral autumn and spring. Total POM concentrations generally did not differ between seasons or reef zones, but the composition of POM, in terms of carbon isotope ratios (δ13C-POM), carbon to nitrogen ratios (C : N), and fatty acids, changed consistently in water flowing across the reef. Both δ13C-POM and C : N increased from the fore reef to the reef flat and lagoon, −23.0‰ to −20.1‰ and 7.31 to 8.34, respectively. Average rates of net POM uptake by the reef community were highest over the reef crest (4 to 30 mmol N m−2 d−1 and 6 to 130 mmol C m−2 d−1), with a Bayesian isotope model confirming independent measurements of high uptake rates of allochthonous POM (oceanic phyto- and zooplankton). In contrast, over the reef flat, net release of POM was observed (−4 to −5 mmol N m−2 d−1 and −50 mmol C m−2 d−1), with gross release rates (estimated as −6 to −8 mmol N m−2 d−1 and −30 to −90 mmol C m−2 d−1) indicating that the release of autochthonous POM may be of similar magnitude to allochthonous uptake. Examining POM dynamics in terms of gross fluxes reinforces the dependence of coral reef systems on oceanographic processes for allochthonous POM supply, as well as highlighting the potential for autochthonous POM production to supply nutrients to benthic and pelagic communities downstream.