[IIOE2-EP46] Bluefin Larvae in Oligotrophic Ocean Foodwebs: Investigation of Nutrients to Zooplankton - Indian Ocean

Lead Investigator :

  1. Michael Landry,Scripps Institution of Oceanography, University of California, San Diego,USA

Other Key participants (s):

  1. Sven Kranz,Dept. of Earth, Ocean and Atmospheric Science, Florida State Univ.,USA
  2. Michael Stukel,Dept. of Earth, Ocean and Atmospheric Science, Florida State Univ.,USA
  3. Karen Selph,Dept. of Oceanography, University of Hawai'i at Manoa,USA
  4. David Die,RSMAS, University of Miami,USA
  5. Peter Morton,Dept. of Earth, Ocean and Atmospheric Science, Florida State Univ

Period of Project: 09/2019 - cruise dates Jan-Feb 2022 - 08/2024 (anticipated)

Brief description of the Project:

The BLOOFINZ cruise off of NW Australia will investigate how mesoscale variability in new production,food-web structure and trophic fluxes affects feeding and growth conditions for larvae of southern bluefin tuna (SBT). The timing (Jan-Feb, 2022) corresponds to the peak period of SBT spawning during the NW Monsoon, when wind influences on nutrient distributions and variability are highest. Sampling across mesoscale features will be done to test hypothesized relationships linking variability in SBT larval feeding and prey preferences (gut contents), growth rates (otolith analyses) and trophic positions (TP) to the environmental conditions of waters selected by adult spawners. Trophic Positions of larvae and their prey will be determined using Compound-Specific Isotope Analyses of Amino Acids (CSIA-AA). Lagrangian experiments will investigate underlying process rates and relationships through measurements of watercolumn 14C productivity, N2 fixation, 15NO3 - uptake and nitrification; community biomass and composition (flow cytometry, pigments, microscopy, in situ imaging, genetic analyses); and trophic fluxes through microand mesozooplankton grazing, remineralization and export. Biogeochemical and food web elements of the study will be linked by CSIA-AA (N source, TP), 15N-constrained budgets and modeling. The study will advance understanding of biogeochemical and ecological dynamics in the poorly studied eastern IO and provide vital information on the food webs and processes supporting SBT larvae, a critically endangered top marine predator, in its only global spawning ground. The core science will address issues of broad oceanographic relevance (diazotrophy, shallow nitrification, new production, food-web structure and function, and export) using an integrated biogeochemical-ecological approach and state-of-the-art techniques that allow multiple avenues for exploring mass and isotopic balances to constrain fluxes and flows. The project elements will comprise an end-to-end coupled biogeochemistry-trophic study.

Region of study:

Argo Basin region off of NW Australia in ITF-influenced tropical waters (12-20°S, 110-122°E). There is no formal cruise track. We will respond to real-time mesoscale variability and locations of larval tuna patches,which will be marked by satellite-tracked drifters for process study..