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).