eDNA and UVC field sampling
In February 2020, we collected a total of 20 water samples, from 10
stations, with two filtration replicates per station, in the two
investigated coastal areas. Each station consisted of a transect of 2km
at an overall constant distance from the coast. We recorded the GPS
coordinates at the start and end of the transect, which we used to map
the transect positions (Figure 1). We conducted eDNA sampling by using a
filtration device composed of an Athena® peristaltic pump (Proactive
Environmental Products LLC, Bradenton, Florida, USA; nominal flow of
1.0 L.min−1), a VigiDNA® 0.20µM cross flow filtration capsule (SPYGEN,
le Bourget du Lac, France) and disposable sterile tubing for each
filtration capsule. We performed two filtration replicates in parallel
on each side of a boat, at each station, for 30 minutes corresponding to
a water volume of ~ 30 L of water filtered by each
capsule. At the end of each filtration, the water inside the capsules
was emptied, and we filled the capsules with 80 mL of CL1 Conservation
buffer (SPYGEN, le Bourget du Lac, France) and stored at room
temperature. We followed a strict contamination control protocol in both
field and laboratory stages (Goldberg et al. 2016, Valentini et al.
2016). Each water sample processing included the use of disposable
gloves and single-use filtration equipment.
Fish composition data from UVC were collected in 2015 by the Carmabi
institute. UVC sampling sites were approximately 700 meters apart along
the entire island’s southern protected coast. Researchers surveyed fish
composition by scuba diving at each of the sites. At each site,
researchers conducted a total of five transects that were 30 meters in
length. For each transect, divers quantified the number, size and
identity of all fishes. All transect lines followed a constant water
depth of 8 to 12 m. Survey times per transect were limited to
approximately 6 minutes per transect for a total of 30 minutes of
surveys, a sampling duration equivalent to the eDNA surveys. The data
from the five transects were pooled to provide the final assemblage of
all fish species at each site. We selected the sites occurring in the
coastal areas of focus, Willemstad and Valentijnsbaai.