Sumitomo Foundation grant to Dr Wyatt et al.

The Sumitomo Foundation has awarded an Environmenal Research Grant (環境研究助成) to Dr Wyatt and colleagues for their pioneering work on the environmental drivers of the structure and function of ‘twilight reefs’ (deep-water mesophotic coral ecosystems).

Title: A refuge for coral reef biodiversity: trophic function and reproduction in the twilight zone | 危機に瀕したサンゴ礁生物の避難場所:薄明帯の学際的解明による保全・再生の支援

Participants: Alex S.J. Wyatt, Toshihiro Miyajima, Toshi Nagata, James Leichter (Scripps), Satoshi Mitarai (OIST), Kazuhiko Sakai (U Ryukyu), Rob Toonen (U Hawaii).

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Thank you to the Sumitomo Foundation for their support.


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.

Bio-physical interactions on a coral reef island (Leichter et al., Oceanography)

Biological and Physical Interactions on a Tropical Island Coral Reef: Transport and Retention Processes on Moorea, French Polynesia

Leichter, J.J., Alldredge, A.L., Bernadi, G., Brooks, A.J., Carlson, C.A., Carpenter, R.C., Edmunds, P.J., Fewings, M.R., Hanson, K.M., Holbrook, S.J., Hench, J.L., Nelson, C.E., Schmitt, R.J., Toonen, R.J., Washburn, L. and Wyatt, A.S.J.

The Moorea Coral Reef Long Term Ecological Research project funded by the US National Science Foundation includes multidisciplinary studies of physical processes driving ecological dynamics across the fringing reef, back reef, and fore reef habitats of Moorea, French Polynesia. A network of oceanographic moorings and a variety of other approaches have been used to investigate the biological and biogeochemical aspects of water transport and retention processes in this system. There is evidence to support the hypothesis that a low-frequency counterclockwise flow around the island is superimposed on the relatively strong alongshore currents on each side of the island. Despite the rapid flow and flushing of the back reef, waters over the reef display chemical and biological characteristics distinct from those offshore. The patterns include higher nutrient and lower dissolved organic carbon concentrations, distinct microbial community compositions among habitats, and reef assemblages of zooplankton that exhibit migration behavior, suggesting multigenerational residence on the reef. Zooplankton consumption by planktivorous fish on the reef reflects both retention of reef-associated taxa and capture by the reef community of resources originating offshore. Coral recruitment and population genetics of reef fishes point to retention of larvae within the system and high recruitment levels from local adult populations. The combined results suggest that a broad suite of physical and biological processes contribute to high retention of externally derived and locally produced organic materials within this island coral reef system.

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.

Organic Matter Release by Benthic Primary Producers (Haas et al., PLoS One)

Effects of Coral Reef Benthic Primary Producers on Dissolved Organic Carbon and Microbial Activity

Andreas F. Haas, Craig E. Nelson, Linda Wegley Kelly, Craig A. Carlson, Forest Rohwer, James J. Leichter, Alex Wyatt, Jennifer E. Smith

Benthic primary producers in marine ecosystems may significantly alter biogeochemical cycling and microbial processes in their surrounding environment. To examine these interactions, we studied dissolved organic matter release by dominant benthic taxa and subsequent microbial remineralization in the lagoonal reefs of Moorea, French Polynesia. Rates of photosynthesis, respiration, and dissolved organic carbon (DOC) release were assessed for several common benthic reef organisms from the backreef habitat. We assessed microbial community response to dissolved exudates of each benthic producer by measuring bacterioplankton growth, respiration, and DOC drawdown in two-day dark dilution culture incubations. Experiments were conducted for six benthic producers: three species of macroalgae (each representing a different algal phylum: Turbinaria ornata – Ochrophyta; Amansia rhodantha – Rhodophyta; Halimeda opuntia – Chlorophyta), a mixed assemblage of turf algae, a species of crustose coralline algae (Hydrolithon reinboldii) and a dominant hermatypic coral (Porites lobata). Our results show that all five types of algae, but not the coral, exuded significant amounts of labile DOC into their surrounding environment. In general, primary producers with the highest rates of photosynthesis released the most DOC and yielded the greatest bacterioplankton growth; turf algae produced nearly twice as much DOC per unit surface area than the other benthic producers (14.0±2.8 µmol h−1 dm−2), stimulating rapid bacterioplankton growth (0.044±0.002 log10 cells h−1) and concomitant oxygen drawdown (0.16±0.05 µmol L−1 h−1 dm−2). Our results demonstrate that benthic reef algae can release a significant fraction of their photosynthetically-fixed carbon as DOC, these release rates vary by species, and this DOC is available to and consumed by reef associated microbes. These data provide compelling evidence that benthic primary producers differentially influence reef microbial dynamics and biogeochemical parameters (i.e., DOC and oxygen availability, bacterial abundance and metabolism) in coral reef communities.