BLOOFINZ-INDITUN: EVIDENCE FOR A HABITAT QUALITY SHIFT FOR LARVAE OF SOUTHERN BLUEFIN TUNA IN THEIR EASTERN INDIAN OCEAN SPAWNING REGION

Southern bluefin tuna (Thunnus maccoyii, SBT) range broadly in high latitudes of the southern hemisphere but spawn only in a small tropical area off northwestern Australia. Their larvae, restricted to the upper 30 m, feed and grow under oligotrophic conditions and unavoidably experience the surface-ocean warming, stratification and acidification associated with climate change. BLOOFINZ and INDITUN Programs are a collaborative effort to understand the determinants of larval tuna habitat quality and climate recruitment vulnerabilities in the SBT spawning region. In Jan-Feb 2022 (peak spawning season), four multi-day Lagrangian experiments and transect sampling were conducted to assess controls of primary production, nitrogen budgets, plankton structure, grazing pathways and food web fluxes that support larval feeding, growth and survival in the spawning habitat. This presentation highlights one element from the study that compares 2022 results to those from the same region in 1987. Surface waters were warmer, many variables were similar, but larval feeding incidence, prey number per stomach and growth rates were significantly higher in 2022. The main change was a larval dietary shift from copepods in 1987 to appendicularians in 2022, which improves transfer efficiency from the microbially dominated food web. While not necessarily indicative of a positive long-term outcome for SBT, this result illustrates that climate-change impacts can involve complex trophic interactions that are difficult to predict from general warming and stratification trends in oligotrophic systems.

Presentation Preference: Oral

Primary Presenter: Michael Landry, University of California, San Diego (mlandry@ucsd.edu)

Authors:

Raúl Laiz-Carrión, Centro Oceanográfico de Málaga, Instituto Español de Oceanografía (IEO-CSIC), Spain  (raul.laiz@ieo.csic.es)

Estrella Malca, Southeast Fisheries Science Center, NOAA National Marine Fisheries Service  (Estrella.Malca@noaa.gov)

Rasmus Swalethorp, Scripps Institution of Oceanography, Univ. California San Diego, La Jolla, CA, USA  (rswalethorp@ucsd.edu)

Moira Décima, Scripps Institution of Oceanography, Univ. California San Diego, La Jolla, CA, USA  (mdecima@ucsd.edu)

José María Quintanilla, Centro Oceanográfico de Málaga, Instituto Español de Oceanografía (IEO-CSIC), Spain  (jose.quintanilla@ieo.csic.es)

Ricardo Borrego-Santos, Centro Oceanográfico de Málaga, Instituto Español de Oceanografía (IEO-CSIC), Spain  (ricardo.borrego@ieo.csic.es)

Claire Davies, CSIRO Environment, Castray Esplanade, Hobart, Tasmania, Australia  (Claire.Davies@csiro.au)

Sven Kranz, Dept. BioSciences, Rice Univ., Houston, TX, USA  (sk235@rice.edu)

Karen Selph, Dept. Oceanography, Univ. Hawai’i at Manoa, Honolulu, HI, USA  (selph@hawaii.edu)

Michael Stukel, Earth, Ocean, and Atmospheric Science Dept., Florida State Univ., Tallahassee, FL, USA  (mstukel@ucsd.edu)

David Die, Cooperative Institute for Marine and Atmospheric Studies, Univ. Miami, USA  (david.die@noaa.gov)

Akihiro Shiroza, Unaffiliated  (a.shiroza@me.com)

Natalia Yingling, Earth, Ocean, and Atmospheric Science Dept., Florida State Univ., Tallahassee, FL, USA  (nyingling@fsu.edu)

Lynnath Beckley, Environmental and Conservation Sciences, Murdoch Univ., Murdoch, Western Australia  (L.Beckley@murdoch.edu.au)

Barbara Muhling, Institute of Marine Sciences, Univ. California Santa Cruz, CA, USA  (barbara.muhling@noaa.gov)