Intratentacular budding and zooid-dynamics in two coral genera

Zooids are the basic modules of colonial organisms. Despite the fact that they are the building blocks of coral colonies and by extension, of coral reefs, the role that zooids play in determining coral colony structure and growth has remained severely overlooked in ecological research. The patterns of addition of zooids (budding mechanics) determine much of the colony's shape and function. Yet because zooids are small in size and large in numbers, ecological studies often focus on coral colonies as unitary organisms and little is known about how zooids vary within and between colonies and species. Nevertheless, advances in computer vision and deep learning create an opportunity to count and classify zooids on the reef scale and to infer their role in colony growth and structure. Here we present the first quantitative analysis of zooid morphogenesis in two coral genera captured in situ. These genera, Lobophyllia and Dipsastraea, represent two evolutionarily distinct forms of corals. We classified over 6000 zooids according to their developmental phase to study their basic attributes including size, association with structural complexity, and intra-colony neighbor relations. Our findings suggest that the morphogenetic cycle of zooids is conserved and size-dependent, that budding mechanics are associated with structural complexity, and that zooids form coalitions by developmental phase implying concentrated growth and stagnation. The zooid-centric approach is transferable and scalable and can be implemented to track corals in different applications from nurseries to wide scale monitoring programs. It can improve our understanding of coral colony formation, and how coral colonies and individual zooids react to disturbances such as physical damage from storms, coral bleaching, and pollution. This work bridges the gap between theory and in situ observations, making it a valuable resource for informing other research on coral colony formation and growth modeling, self-organization in modular systems, and coral reef restoration strategies. Moreover, our dataset has broad interdisciplinary value, with potential applications ranging from computer graphics and geometric modeling to studies of natural tiling patterns and spatial organization in biological systems.