FY2015 Annual Report

Marine Biophysics Unit
Assistant Professor Satoshi Mitarai


Marine Biophysics Unit will develop forecasting system for the coastal ocean circulation processes around Okinawa and implement a validated connectivity assessment tool, coupling available modeling and observation techniques. This modeling tool will

  • Help marine biologists and genetics estimate rates of geneticists estimate rates of gene flow among sites,
  • Enable public agencies to build and evaluate marine protected areas based on population connectivity, and
  • provide marine ecologists with a modeling system for predicting the global and long-term dynamics of the marine ecosystem

Marine Biophysics Unit was established on Sep. 1, 2009 when Satoshi Mitarai joined OIST.

1. Staff

  • Satoshi Mitarai, Assistant Professor (September 2009 –)
  • Yuichi Nakajima, Postdoctoral Scholar (August 2013 –)
  • Mary Matilda Grossmann, Postdoctoral Scholar (October 2013 –)
  • Atsushi Fujimura, Postdoctoral Scholar (July 2015 – September 2016)
  • Yukiko Murabayashi, Technician (July 2011 –)
  • Shohei Nakada, Technician (August 2011 –)
  • Yuta Nunome, Technician (May 2014 –)
  • Kazumi Inoha, Technician (April 2015 –)
  • Takashi Ihara, Technician (April 2015 – March 2016)
  • Yuka Osawa, Technician (July 2015 – January 2016)
  • Ayumu Migita, Technician (August 2015 – January 2016)
  • Patricia Wepfer, Graduate Student (January 2015 –)
  • Maki Thomas, Graduate Student (September 2015–)
  • Margaret Mars Brisbin, Graduate Student (September 2015 –)
  • Chihiro Arasaki, Research Administrator (July 2012 – August 2016)

Past Members

  • Emile Trimoreau, Short-term Student (September 2010 – February 2011)
  • Flora Vincent, Short-term Student (July 2011 – December 2011)
  • Hirohito Yamazaki, Short-term Student (August 2011 – September 2011)
  • Fiona Francis, Internship Student (May 2012 – August 2012)
  • MiHye Seo, Internship Student (October 2012 – January 2013, July 2013 – August 2013)
  • Yuki Kamidaira, Internship Student (August 2013 – September 2013)
  • Shizuka Kuda, Research Administrator (February 2010 – July 2012)
  • Taichiro Sakagami, Technician (February 2010 – August 2013)
  • Daisuke Hasegawa, Postdoctoral Scholar (October 2011 – March 2014)
  • Masako Nakamura, Staff Scientist (March 2010 – March 2015)

2. Collaborations

2.1 Larval dispersal of coral reef species

  • Type of collaboration: Joint research
  • Researchers:
    • Prof. K. Sakai, University of the Ryukyus
    • Prof. M. Nakamura, Tokai University

2.2 Larval dispersal of hydrothermal vent species

  • Type of collaboration: Joint research
  • Researchers:
    • Dr. T. Maruyama, Japan Agency for Marine-Earth Science and Technology
    • Dr. Y. Fujiwara, Japan Agency for Marine-Earth Science and Technology
    • Dr. Y. Furushima, Japan Agency for Marine-Earth Science and Technology
    • Dr. H. Watanabe, Japan Agency for Marine-Earth Science and Technology

2.3 Regional ocean circulation modeling

  • Type of collaboration: Joint research
  • Researchers:
    • Prof. J. McWilliams, University of California, Los Angels
    • Dr. A. Shchepetkin, University of California, Los Angels
    • Prof. Y. Uchiyama, Kobe University
    • Dr. E. Gross, Stanford University

2.4 Okinawa coastal ocean observing system

  • Type of collaboration: Joint research
  • Researchers:
    • Mr. K. Hirate, Okinawa Prefectural Fisheries and Ocean Research Center
    • 11th Japan Regional Coast Guard
    • Dr. S. Gallager, Woods Hole Oceanographic Institution
    • Dr. M. Toda, Okinawa Churaumi Aquarium

2.5 Coral health and connectivity in South East Asia

  • Type of collaboration: Joint research
  • Researchers:
    • Dr. T. Yeemin, Ramkhamhaeng University
    • Dr. M. Sutthacheep, Ramkhamhaeng University

3. Activities and Findings

3.1Quantifying dispersal from hydrothermal vent fields in the western Pacific Ocean

Hydrothermal vent fields in the western Pacific Ocean are mostly distributed along spreading centers in submarine basins behind convergent plate boundaries. Larval dispersal resulting from deep ocean circulations is one of the major factors influencing gene flow, diversity, and distributions of vent animals. By combining a biophysical model and deep-profiling float experiments, we quantify potential larval dispersal of vent species via ocean circulation in the western Pacific Ocean. We demonstrate that vent fields within backarc basins could be well connected without particular directionality, whereas basin-to-basin dispersal is expected to occur infrequently, once in tens to hundreds of thousands of years, with clear dispersal barriers and directionality associated with ocean currents. The southwest Pacific vent complex, spanning more than 4,000 km, may be connected by the South Equatorial Current for species with a longer-than-average larval development time. Depending on larval dispersal depth, a strong western boundary current, the Kuroshio Current, could bridge vent fields from the Okinawa Trough to the Izu-Bonin Arc, which are 1,200 km apart. Outcomes of this study should help marine ecologists estimate gene flow among vent populations and design optimal marine conservation plans to protect one of the most unusual exosystems on Earth.

Figure 1: Dispersal processes in the deep sea show complex eddy motions, changing monthly or more often. (A) Trajectories of deep-sea profiling floats released from Hatoma Knoll (indicated with white arrows) in the Okinawa Trough, illustrating dispersal originating at a vent field within a back-arc basin. Floats were deployed semimonthly in 2013 and 2014 on dates indicated at the bottom right corner of the figure. Float tracks until March 2015 are shown here. These passively transported floats maintain their depth 1,000 m below the sea surface and return to the surface every 30 d (circles). Positions of each float at the sea surface are connected with cubic splines. The numbers show the cumulative sum of surfacing events, which indicate approximate drift times in months. (B) Close-up view of the same trajectories for the first three surfacing events.

Figure 2: The ocean circulation model effectively quantifies potential larval dispersal from Hatoma Knoll. (A) Distributions of deep-profiling floats (cross markers) from Hatoma Knoll (white arrow) after 90 d of drifting 1,000 m below the sea surface show good agreement with predictions by the ocean circulation model (color contour). Colors indicate probability densities of float displacement per unit area (square kilometers). (B) Transport from Hatoma Knoll to other vent fields at a dispersal depth of 1,000 m (lines and numbers) deduced from the model. Five representative vent fields are shown. Numbers in brackets indicate the depth of each vent field. Drift time was set to the population mean for the mean temperature at a depth of 1,000 m (83 d). Numbers indicate the number of expected connections out of 100 million independent events. The number beside Hatoma Knoll represents likelihood of self-recruitment.

Figure 3: Vent fields within back-arc basins could be well connected, whereas basin-to-basin transport shows dispersal barriers and directionality. (A) Potential larval dispersal from western Pacific vent fields quantified from the biophysical model (lines and numbers). Dispersal depth is assumed to be 1,000 m. PLD is set to 83 d. White ovals show 11 geographically separated regions defined in this study. Line colors show the direction of connections (see the circular diagram in the figure). For an explanation of the numbers, refer to the Fig. 2 legend. Close-up views of the (B) Okinawa Trough, (C) Manus Basin, and (D) Lau Basin suggest that back-arc basins should form well-mixed pools without directionality. (E) The gap between North Fiji and Woodlark could be bridged with above-average PLD (∼twice the mean). When there were multiple vent fields within a 30-km radius, only one of them was randomly selected so as to avoid graphical complications. See Movie S1 for dispersal patterns from all selected vent fields.

Figure 4: Larval transport among vent fields may be similar regardless of dispersal depth, except for regions affected by the Kuroshio Current. (A) Potential larval dispersal of the western Pacific vent fields for a dispersal depth of 500 m (lines and numbers), where PLD is set to the population mean of 43 d. See the legends of Figs. 2 and 3 for details. Close-up views showing unidirectional transport (B) from Okinawa to Izu-Bonin and (C) from Lau to North Fiji, following the Kuroshio Current and the South Equatorial Current, respectively. The overall pattern does not change much from the 1,000-m case (Fig. 3), with the exception of regions affected by the Kuroshio Current. (D) The southwest Pacific vent complex could be completely interconnected with above-average PLD (∼twice the mean), based on mostly westward transport.

3.2 Genetic differentiation and connectivity of morphological types of the broadcast-spawning coral Galaxea fascicularis in the Nansei Islands, Japan

Population connectivity resulting from larval dispersal is essential for the maintenance or recovery of populations in marine ecosystems, including coral reefs. Studies of species diversity and genetic connectivity within species are essential for the conservation of corals and coral reef ecosystems. We analyzed mitochondrial DNA sequence types and microsatellite genotypes of the broadcast-spawning coral, Galaxea fascicularis, from four regions in the subtropical Nansei Islands in the northwestern Pacific Ocean. Two types (soft and hard types) of nematocyst morphology are known in G. fascicularis and are significantly correlated with the length of a mitochondrial DNA noncoding sequence (soft type: mt-L; hard type: mt-S type). Using microsatellites, significant genetic differentiation was detected between the mitochondrial DNA sequence types in all regions. We also found a third genetic cluster (mt-L+), and this unexpected type may be a cryptic species of Galaxea. High clonal diversity was detected in both mt-L and mt-S types. Significant genetic differentiation, which was found among regions within a given type (FST = 0.009–0.024, all Ps ≤ 0.005 in mt-L; 0.009–0.032, all Ps ≤ 0.01 in mt-S), may result from the shorter larval development than in other broadcast-spawning corals, such as the genus Acropora. Nevertheless, intraspecific genetic diversity and connectivity have been maintained, and with both sexual and asexual reproduction, this species appears to have a potential for the recovery of populations after disturbance.

Figure 1: Collection sites for Galaxea fascicularis in the Nansei Islands in southwestern Japan

Figure 2: Mitochondrial DNA sequence types are genetically well differentiated. (A) Most multilocus lineages (MLLs) were correctly assigned by Bayesian clustering analysis when the number of clusters was set to 5. These clusters corresponded closely to the three G. fascicularis types. The X-axis shows the probability of MLL membership in each cluster. Using STRUCTURE with the number of groups set to five (K = 5), three MLLs in mt-L and two MLLs in mt-S showed a reversed genetic cluster (see black triangles). (B) Finer genetic differentiation was detected in each type among regions using InStruct instead of STRUCTURE, which is sensitive to high inbreeding coefficients. Using microsatellite markers, STRUCTURE classified five MLLs differently than their mitochondrial DNA sequence types. These MLLs were excluded from analyses with InStruct.

4. Publications

4.1 Journals

  1. Nakajima, Y., Shinzato, C., Satoh, N. & Mitarai, S.  Novel Polymorphic Microsatellite Markers Reveal Genetic Differentiation between Two Sympatric Types of Galaxea fascicularis. PLoS One 10, e0130176, doi:10.1371/journal.pone.0130176 (2015).
  2. Nakamura, M., Kumagai, N. H., Sakai, K., Okaji, K., Ogasawara, K. & Mitarai, S.  Spatial variability in recruitment of acroporid corals and predatory starfish along the Onna coast, Okinawa, Japan. Marine Ecology Progress Series 540, 1-12, doi:10.3354/meps11525 (2015).
  3. Nakajima, Y., Zayasu, Y., Shinzato, C., Satoh, N. & Mitarai, S.  Genetic differentiation and connectivity of morphological types of the broadcast-spawning coral Galaxea fascicularis in the Nansei Islands, Japan. Ecology and Evolution 6, 1457-1469, doi:10.1002/ece3.1981 (2015).
  4. Mitarai, S., Watanabe, H., Nakajima, Y., Shchepetkin, A. F. & McWilliams, J. C.  Quantifying dispersal from hydrothermal vent fields in the western Pacific Ocean. PNAS 113, 2976-2981, doi:10.1073/pnas.1518395113 (2016).

4.2 Books and other one-time publications

Nothing to report

4.3 Oral and Poster Presentations

  1. Grossmann, M. M., Nishikawa, J., J., L. D. & Mitarai, S.  Diversity and community structure of pelagic cnidarians in the Celebes and Sulu Seas, in The 14th Deep-Sea Biology Symposium, Aveiro, Portugal (2015).
  2. Mitarai, S., Nakajima, Y., Watanabe, H., Shchepetkin, A. & McWilliams, J. C.  Quantifying hydrothermal vent connectivity in the western Pacific, in The 14th Deep-Sea Biology Symposium, Aveiro, Portugal (2015).
  3. Fujimura, A., Reniers, A., Paris, C. B., Shanks, A., MacMahan, J. & Morgan, S.  Biophysical Modeling of Cross-Shore Plankton Transport, in 2016 Ocean Sciences Meeting, New Orleans, Louisiana, USA (2016).

5. Intellectual Property Rights and Other Specific Achievements

Nothing to report

6. Meetings and Events

6.1 Workshop: The influence of metapopulation structure and connectivity on the response of coral reefs to climate change and ocean acidification

  • Date: March 16–20, 2016
  • Venue: OIST Seaside House
  • Participants:
    • Prof. M. Adjeroud, Institut de Recherche pour le Dévelopment
    • Prof. PO. Jr. Ang, The Chinese University of Hong Kong
    • Ms. J. Bergman, California State University, Northridge
    • Prof. R. Carpenter, California State University, Northridge
    • Prof. M. A. Coffroth, State University of New York at Buffalo
    • Prof. P. Edmunds, California State University, Northridge
    • Prof. J. Hench, Duke University
    • Prof. S. Holbrook, University of California, Santa Barbara
    • Prof. J. Leichter, Scripps Institution of Oceanography
    • Dr. S. McIlroy, The University of Hong Kong
    • Dr. S. Muko, Tokyo Institute of Technology
    • Dr. M. Nakamura, Tokai University
    • Prof. C. Paris, University of Miami
    • Prof. K. Sakai, University of the Ryukyus
    • Prof. R. Schmitt, University of California, Santa Barbara
    • Dr. M. Sutthacheep, Ramkhamhaeng University
    • Dr. G. Suzuki, Seikai National Fisheries Research Institute
    • Prof. R. J. Toonen, University of Hawaii
    • Prof. L. Washburn, University of California, Santa Barbara
    • Dr. A. S. J. Wyatt, Atmosphere and Ocean Research Institute, The University of Tokyo

7. Other

Nothing to report.