P1.47 Jan. 4 Skeletal modification in response to flow during growth in colonies of the sea whip, Junceella fragilis CHANG, W-L*; CHI, K-J; FAN, T-Y; DAI, C-F; NTU; NCHU; NMMBA; NTU email@example.com
Marine sessile organisms depend on water motion for important physiological functions yet face dislodgement or breakage caused by hydrodynamic forces. During growth, these organisms may be subjected to disproportionately greater bending moments from ambient flows. To survive, they must modify their mechanical supports over the period of growth. To test this hypothesis, we used a sea whip Junceella fragilis as a model species because of its simple geometry for empirical measurements and theoretical calculations. We examined the mass and morphometrics of the axial skeleton, sclerites, and fleshy tissue of 81 J. fragilis colonies (5 - 156 cm in length) from two populations in southern Taiwan. Regional variations were examined by measurements taken from the bottom, middle, and top of colonies. The typological distribution of sclerites was examined in another 31 colonies. Our results revealed that the relative amount of axial skeleton increases while that of sclerites decreases with colony length, which suggests that during growth, the colony switches from using sclerites to the stronger gorgonin axial skeleton as the main support system. The axial skeleton at the colony base thickens possibly to maintain or even slightly decrease its bending stress. A greater density of sclerites, mostly double-heads at the colony base also complements the resistance to bending. Club sclerites, dominating the upper colony, are believed to support the feeding polyps and maintain the integrity of local cortex. Our data also revealed that colonies living in environments with greater flows incorporate more skeletal materials. This study demonstrates how marine sessile organisms cope with increasing hydrodynamic forces during its life history by modifying the constitution and construction of their support system.