Sponge diversity and richness
The inner bays of Curaçao and Aruba yielded a total of 22 sponge species at eight localities, which differed in number of colonies, species richness, percentage cover and composition of the community (Table 1).
Table 1. Total abundance of sponges as percentage cover of the total examined substrate and corresponding biodiversity measures. Abbreviations of study sites (PB I-AUA II) as presented in Figure 1.
Nineteen different species were found at Curaçao compared to eight at Aruba. Localities showing the higher diversity were Fuikbaai (11 species) and Spaanse Water (SWI - ten species; all localities of Spaanse Water combined yielded 13 species). Some species were regularly encountered (e.g., Tedania (Tedania) ignis (Duchassaing and Michelotti), Mycale (Carmia) microsigmatosa Arndt and Dysidea etheria De Laubenfels), whereas some species (e.g., Chelonaplysilla erecta Carter) were found only once during this inventory. No sponges were present in Jan Thiel Baai, St. Jorisbaai, Santa Cruzbaai and SWIV. Cluster analysis revealed variability in faunal composition among localities, whereas neighboring sites within the same bay did not cluster (Figure 2).
Fig. 2. Dendrogram of investigated localities based on Euclidian distance and Ward’s method. Locations within bays are encoded as presented in Figure 1. Analysis presents 3 separate clusters in which sites located near each other do not cluster, thereby revealing local heterogeneity.
Except for Fuikbaai, all sample sizes (28-40 roots) seemed adequate, as rarefaction curves revealed their asymptote (data not presented). Rarifying the data revealed differences in species density between most of the investigated sites and showed significant (p < 0.05) differences in species richness between several localities, including sites located within a single bay (Table 1).