Echinoderidae

Anguas-Escalante, Abril, Jesús-Navarrete, Alberto De, Landers, Stephen C. & Sørensen, Martin V., 2024, Kinorhynch assemblages on the southern Gulf of Mexico continental shelf, Zoologischer Anzeiger 313, pp. 228-240 : 231-232

3.1. Echinoderidae assemblage

A total of 568 specimens were found among the 29 sites studied, of which 57 could not be identified to species level, and 34 were juveniles. The total richness was represented by 28 species that belonged to two genera from the remaining 477 specimens ( Table 2). The species with the highest abundance were Echinoderes spinifurca and E. juliae Sørensen et al., 2018 with 91 and 70 specimens, respectively ( Table 2). A single specimen, Echinoderes sp. 1 , represented the lowest abundance, which was found at station 25 ( Table 2).

Observed richness by depth groups was similar in shallow and deep sites with 15 species respectively, but abundance was highest in shallow sites with 217 specimens ( Table 3), coverage was higher in shallow sites with 99 % versus 93 % on the deep sites ( Table 3). Regarding medium depth sites, richness was 25 species with a total abundance of 177 individuals and estimated coverage of 98 % ( Table 3). The most abundant species in shallow sites was E. spinifurca (84 individuals), in medium depth sites was E. juliae (57 individuals), and in deep sites was E. unispinosus (21 individuals). At each depth group, the lowest abundance recorded (a single individual) was consist of different set of species: in shallow stations, to E. juliae , Echinoderes sp. 8 , and Echinoderes sp. 21; in medium depth stations, E. augustae , Echinoderes sp. 4 , Echinoderes sp. 10, and Echinoderes sp. 21; and in deep sites Echinoderes sp. 1 , Echinoderes sp. 7 , Echinoderes sp. 8 , Echinoderes sp. 13 Echinoderes sp. 20.

The general diversity pattern according to bathymetry at 90 % sample coverage showed an increase from shallow sites (16–200 m depth) to medium depth sites (391–725 m), and a decrease when reaching deep sites (953–3214 m). However, differences were found only between shallow sites (lowest values) and medium depth sites (highest values) to richness and Hill–Shannon which intervals were not overlapped ( Table 3, Fig. 2 ).

Among the 28 species, seven were common for all depth groups ( E. unispinosus , Echinoderes sp. 5 , Echinoderes sp. 8 , E. joyceae , E. romanoi , E. juliae , E. spinifurca ), and 12 were shared between two depth groups, either shallow and medium ( E. augustae , E. bookhouti , E. charlotteae , Echinoderes sp. 3 , Echinoderes sp. 17, Echinoderes sp. 21) or medium and deep ( Echinoderes sp. 4 , Echinoderes sp. 7 , Echinoderes sp. 9 , Echinoderes sp. 10, Echinoderes sp. 13, Echinoderes sp. 20). No species were found exclusively sharing shallow sites and deep sites. Regarding species restricted to a single depth group, two species were exclusively found in shallow sites ( E. zacharyi and Echinoderes sp. 2 ), five species at medium depth ( Fissuroderes sp. 1 , Echinoderes sp. 6 , Echinoderes sp. 14, Echinoderes sp. 16, Echinoderes sp. 19), and two species in deep sites ( Echinoderes sp. 1 , Echinoderes sp. 18).

The SIMPER results show higher average dissimilarity in the comparison of the shallow stations and deep stations with 94 % ( Table 4), in which E. spinifurca and E. bookhouti obtained the major contribution with 19 % and 15 % respectively. Both species were abundant at shallow sites and scarce ( E. spinifurca ) or absent ( E. bookhouti ) at the deep stations. These same species also made the greatest contribution to the dissimilarity between shallow sites and medium depth sites, but in this comparison the average dissimilarity was lower (86 %), as well as the individual contribution of E. spinifurca (14 %) and E. bookhouti (11 %). The two species were present at medium depth sites but with very few specimens, compared to their abundance in shallow sites. Regarding to comparison between medium depth sites and deep sites average dissimilarity was 85 %, the greater contribution was of E. juliae (13 %) and E. joyceae (10 %). In the medium deep sites these species were the most abundant while in the deep sites were scarce ( Table 4).

The PERMANOVA outcome showed significant differences between composition of species by depth group (P <0.05, Supplementary Material Table 8) and pair-wise test output showed differences between all groups (P <0.05).

The nMDS analysis of community structure by each site was ordered mostly according to the vector of depth and temperature. This ordination placed shallow sites with higher temperatures and higher species abundance at the top of the graph and deep sites with lower temperatures at the bottom ( Fig. 4 ). Also, the global correlation between the matrix of species and environmental data showed a significant correlation (ρ = 0.49, p <0.001). According to BIOENV the principal environmental variables correlated with species matrix were depth and temperature (ρ = 0.61, p <0.001).

Figures

Fig. 2. Diversity estimated to same sample coverage by depth groups. SC, sample coverage.

Fig. 4. nMDS analysis of Echinoderidae community structure by sampling stations. Numbers indicate sampling station; size of the circles indicates the total abundance at the sites. Green, shallow stations; Red, medium depth stations; Black, deep stations.