Differences in ecological indices between areas from eDNA
Differences in fish composition in the eDNA samples and their
association with specific functional traits drove distinct functional
composition and diversity indices across the two areas. A species
accumulation curve analysis showed that the two areas accumulated
different levels of functional diversity (Figure 2b). For the same level
of species richness all the functional indicators were higher in
Valentijnsbaii except the functional divergence
(FdivWillemstad = 0.79 ± 0.003;
FdivValentijnsbaai = 0.788 ± 0.002; Figure 2b). The
functional evenness (FeveValentijnsbaai = 0.58 ± 0.021;
FeveWillemstad = 0.55 ± 0.025; Figure 2b), the
functional richness (FRicValentijnsbaai = 0.00031 ±
3x10-5 ; FRicWillemstad = 0.00027 ±
4.2x10-5; Figure 2b) and the functional originality
(ForiValentijnsbaai = 0.040 ± 0.003;
ForiWillemstad = 0.037 ± 0.002; Figure 2b) were higher
in Valentijnsbaai. Functional differences were due to the detection of
specific species in Valentijnsbaai such as the Whitespotted eagle ray
(Aetobatus narinari ) and of Istiophoridae family which harbors a
singular combination of traits which have a large contribution to the
delimitation of the functional space.
In contrast, we found that phylogenetic diversity was systematically
higher in Willemstad compared with Valentijnsbaai for all the indices
computed, where phylogenetic accumulation curves showed different levels
of saturation (Figure 2c). This was not caused by a higher number of
taxa recovered by eDNA, which was similar across the two areas (64 taxa
for Willemstad and 66 taxa for Valentijnsbaai; Figure 2b), but was
mainly caused by the presence of evolutionary distinct taxa including
Albulidae, Elopidae (genus Elops ), Neoscopelidae
(Neoscopelus macrolepidotus ) or Engraulidae in the Willemstad
area. The mean length of the tree branches represented by the unique
taxa present in Willemstad was 73.68 ± 0.66 and was higher than the
length of the unique taxa present in Valentijnsbaai (45.38 ± 2.35;
Figure 2c). This difference in branch length led to a higher PD value in
Willemstad than in the Valentijnsbaai area (PDWillemstad= 5157.3 ± 22.32; PDValentijnsbaai = 4824.8 ± 34.6;).
The phylogenetic divergence facet characterized by the MPD or the MNTD
index was also higher in Willemstad than in the Valentijnsbaai area
(MPDWillemstad = 264.7 ± 0.08,
MPDValentijnsbaai = 255.5 ± 0.08; Figure 2c).
Consequently, the taxa identified in Willemstad were more dispersed and
presented a higher variability in distances in the phylogenetic tree
(VPD = 5089.9 ± 24.3) than the taxa identified in Valentijnsbaai
(VPDWillemstad = 5089.9 ± 24.3
VPDValentijnsbaai = 4657.2 ± 22.9; Figure 2c).