Marine sponges, among the earliest diverging metazoans, play pivotal roles within their ecosystems, particularly coral reefs. Research conducted by E. Bautista-Guerrero and colleagues presents groundbreaking insights on how the coral boring sponge Thoosa mismalolli manages its microbiome during development and dispersal.
Dispersal is fundamental for species persistence and evolution; herein lies the significance of this sponge's microbiome dynamics. The study employs advanced techniques such as DNA sequencing and transmission electron microscopy, which reveal how Thoosa mismalolli acquires bacteria from both parental sponges and the surrounding environment. This unique characteristic enables the sponge to adapt to varying ecological conditions, especially important as coral reefs face unprecedented challenges.
The researchers discovered both vertical (VT) transmission, where bacteria are passed from parent to offspring, and horizontal (HT) transmission, where microorganisms are acquired from the environment. This dual approach helps sustain a diverse microbial community necessary for the sponge's health and functionality. Notably, adults, brooding larvae, and early free-swimming larvae initially share similar high-diversity microbial communities, primarily dominated by Proteobacteria and Chloroflexi.
Significant shifts occur during the larval dispersal phase; larvae collected offshore show drastic changes, including reduced inherited microbes and increased presence of environmentally sourced taxa like Bacteroidetes, Tenericutes, and Firmicutes. "The microbiome of the free-swimming pelagic larvae collected 1 km offshore had an 85% similarity to the bacterioplankton in the surrounding seawater," the authors note, emphasizing this sponge's adaptability.
Using 16S rRNA gene amplicon sequencing, the study cataloged over 700 distinct operational taxonomic units (OTUs), underscoring the sponge's microbiome complexity. The bacterial community composition varied significantly across life stages. For adults and brooding larvae, Chloroflexi was chief among the symbionts. Conversely, offshore pelagic larvae, collecting data at varying distances from the coast, exhibited separate microbial signatures.
Particularly intriguing was the dominance shift observed as dispersal distances increased. Sponges collecting 3 km offshore experienced substantial alterations, with Bacteroidetes becoming increasingly prevalent, signaling potential metamorphosis and enhanced larval settlement success. The study suggests, "The abrupt increase in the proportion of Bacteroidetes may be indicative of the onset of their metamorphosis or increase the settlement success of competent larvae."
This research highlights the sponge's remarkable ability to modify its microbial constituents as it encounters different environments, showcasing the interdependence between marine organisms and their microbiomes. Understanding these dynamics is fundamental not only for sponge ecology but also for the conservation of coral reefs facing ecological imbalances due to climate change and human activity.
Future investigations are warranted to explore the metabolic pathways utilized through maternal inheritance and indigenous bacterioplankton. Such studies may elucidate the role of symbionts not only as environmental filters but also as active participants shaping the sponge's capabilities for adaptation and resilience.