Structure and Function Features of Abundant and Rare Prokaryotic Communities Along Nearshore to Offshore Transitions

Abundant and rare taxa are crucial members of the marine microbial community. However, their biodiversity, assembly mechanisms, functional characteristics and ecological response strategies remain poorly understood. In this study, 16S rRNA and metagenomic sequencing were carried out to reveal the structural and functional features of abundant and rare taxa across the transition from nearshore to offshore. The results showed that the biodiversity of both abundant and rare taxa decreased with increasing distance from shore, with rare taxa exhibiting relatively higher diversity indices than abundant ones. Neutral model analysis revealed that the assembly process gradually changed from deterministic to stochastic from nearshore to offshore among abundant taxa. In contrast, among rare taxa, a stochastic process dominated nearshore, whereas a deterministic process was predominant in the offshore environment. Meanwhile, the proportion of variance that could be explained by environmental factors was relatively higher among abundant communities than among rare ones. A co-occurrence network analysis indicated that rare communities displayed greater complexity and a higher degree of modularity than abundant communities. Functionally, abundant communities tended to favour an r-strategy, whereas rare communities leaned towards a K-strategy. Our results strengthen the understanding of the ecological mechanisms controlling microbial community patterns along coastal-to-open water transitions.