Members of the family Spongillidae within the phylum Porifera, otherwise known as freshwater sponges, are systematically understudied worldwide despite their fascinatingly intricate microbiomes, intriguing holobiont system interactions, and their keystone roles in freshwater ecosystems. Remaining true to this international trend, New Zealand’s freshwater sponge fauna is largely uncharacterised, currently represented by a single formally named endemic species, Heterorotula kakahuensis (Traxler 1896). However, the phylogenomic analyses in this investigation challenge the notion of a single species. Using transcriptomics and morphological comparisons, we identify a novel species, likely belonging to the Ephydatia lineage. Our phylogenetic analyses show this novel species clusters with the globally distributed Ephydatia genus, yet displays unique gemmosclere morphology, suggesting New Zealand is home to cryptic freshwater sponge diversity.
There has been little exploration of the habitual range of freshwater sponges in a New Zealand context, which eDNA is ideally suited to determine. We employ commercially available eDNA kits and metabarcoding techniques to detect freshwater sponges in the Karori Reservoir, and to characterise the assemblage of microbiota and other organisms. Spatial and temporal fluctuations in community composition were observed, highlighting broader ecological interactions involving New Zealand’s freshwater sponge taxa. These sponges were also found co-occurring with pollution-sensitive macroinvertebrates, Plecoptera and molluscs.
A well-known and important aspect of sponge survival is their functionality as holobionts. The recruitment of symbiotic microorganisms has allowed sponges in both marine and freshwater contexts to adapt to climatic pressures and their respective ecosystems. Sponges rely on symbiotic microbes for essential functions like nutrient acquisition and defence. Despite their importance, the selective abilities and seasonal changes that sponge microbiomes show are not well studied, even though this information informs conservation strategies and reflects organism health. Our 16S rRNA amplicon sequencing reveals dynamic holobiont relationships that are responsive to seasonal transitions and show distinct communities across spatially separate collection sites. Furthermore, gemmule-forming sponges showed clear differences in microbial community composition, demonstrating the influence of life-stage transitions on freshwater sponge microbiomes.