Distribution pattern of cetaceans in the South China Sea based on visual
surveys and environmental DNA metabarcoding
Abstract
The South China Sea is a crucial habitat and potential nursery for
cetaceans. This study involved five ship-based visual surveys in three
summers and two springs from 2020 to 2023, combined with environmental
DNA (eDNA) metabarcoding, an emerging tool, to understand the relative
abundance and spatial and temporal distribution of cetaceans in offshore
and abyssal areas of the South China Sea. The combination of visual
observations and eDNA metabarcoding enabled the detection of a total of
18 cetacean species, and 12 species were identified by both methods.
Cetaceans showed temporal variation; 7 species in the springs, and 17
species in the summers. Expedition route design, meteorological
conditions, and sea conditions between the two seasons can partly
explain the seasonal differences. The Hyperoodontidae and Physeteridae
species tend to occupy regions with high bathymetric drop gradients,
particularly those situated on continental slopes and seamounts. The
Delphinidae species are more widely distributed and relatively abundant.
Of the cetaceans successfully amplified by eDNA metabarcoding, species
with larger group sizes and closer distances tend to be more easily
detected. Although the complex and turbulent hydrographic environment of
the oceans reduces the duration of eDNA and increases the uncertainty in
capturing eDNA signals, our findings indicate that eDNA techniques can
provide additional information and hold promise as a potential
complementary tool for cetacean monitoring.