01-05 December 2025
INCOIS, Hyderabad, India.
| Abstract Submission No. | ABS-06-0040 |
| Title of Abstract | ADCP-derived backscatter as a zooplankton proxy |
| Authors | Ranjan Kumar Sahu*, D. Shankar, P. Amol, S.G. Aparna, D.V.Desai |
| Organisation | CSIR-National Institute of Oceanography |
| Address | Dona Paula Panjim, Goa, India Pincode: 403004 E-mail: ranzan.ocean@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | We demonstrate the potential of acoustic Doppler current profiler (ADCP) backscatter measurements for generating continuous, high-resolution time series of zooplankton biomass. Data were acquired from ADCP moorings deployed at seven continental slope locations in the eastern Arabian Sea (EAS), compiling a robust data set spanning October 2017 to December 2023. The methodology involves the conversion of raw ADCP backscatter signals into zooplankton biomass in two major steps. First, we obtain the backscatter from echo intensity. Second, we convert the backscatter to biomass using a regression relationship between ADCP-derived backscatter and volumetric zooplankton samples collected via net hauls near the mooring sites. This sampling was conducted at all mooring locations over several years during each ADCP servicing cruise. Analysis of data across depths ranging from 24 to 140 m consistently indicated a decline in both backscatter intensity and zooplankton biomass with increasing depth, but the rate of decrease varies along the slope. A key finding from these ADCP data is the pronounced intraseasonal variability (periods of 30⿿90 days) in zooplankton biomass; the variability in this period band is particularly evident during August- November though only for a few years. The range of this high-frequency variability is comparable to and often exceeds that of the seasonal cycle of the zooplankton biomass and standing stock. Interannual variations (periods > 400 days) are observed with higher intensity in the southern EAS. Neither the rapid shifts, nor the longer year-to-year variations can be effectively determined by traditional, intermittent sampling methods over a large domain. This methodology marks a significant advance for environmental monitoring and assessment, offering insights into the marine ecosystem. Just as satellite chl-a measurements have changed the way we study phytoplankton dynamics, acoustics can change the way we study zooplankton dynamics. |
| Are you part of IIOE-2 endorsed project | no |
| Keywords | ADCP backscatter, moorings, zooplankton sampling, multiple plankton net, intraseasonal variability |
| For Awards | yes |
| Date Of Birth | 18-03-1998 |
| ECSN Registration Number | IIOE2-ECSN-0153 |