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Surf zones are highly dynamic marine ecosystems that are subject to
increasing anthropogenic and climatic pressures, posing multiple
challenges for biomonitoring. Traditional methods such as seines and hook
and line surveys are often labor intensive, taxonomically biased, and can
be physically hazardous. Emerging techniques, such as baited remote
underwater video (BRUV) and environmental DNA (eDNA) are promising
nondestructive tools for assessing marine biodiversity in surf zones of
sandy beaches. Here we compare the relative performance of beach seines,
BRUV, and eDNA in characterizing community composition of bony (teleost)
and cartilaginous (elasmobranch) fishes of surf zones at 18 open coast
sandy beaches in southern California. Seine and BRUV surveys captured
overlapping, but distinct fish communities with 50% (18/36) of detected
species shared. BRUV surveys more frequently detected larger species (e.g.
sharks and rays) while seines more frequently detected one of the most
abundant species, barred surfperch (Amphistichus argenteus). In contrast,
eDNA metabarcoding captured 88.9% (32/36) of all fishes observed in seine
and BRUV surveys plus 57 additional species, including 15 that frequent
surf zone habitats. On average, eDNA detected over 5 times more species
than BRUVs and 8 times more species than seine surveys at a given site.
eDNA approaches also showed significantly higher sensitivity than seine
and BRUV methods and more consistently detected 31 of the 32 (96.9%)
jointly observed species across beaches. The four species detected by
BRUV/seines, but not eDNA were only resolved at higher taxonomic ranks
(e.g. Embiotocidae surfperches and Sygnathidae pipefishes). In frequent
co-detection of species between methods limited comparisons of richness
and abundance estimates, highlighting the challenge of comparing
biomonitoring approaches. Despite potential for improvement, results
overall demonstrate that eDNA can provide a cost-effective tool for
long-term surf zone monitoring that complements data from seine and BRUV
surveys, allowing more comprehensive surveys of vertebrate diversity in
surf zone habitats.
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