MARTONE, P.T.; Hopkins Marine Station, Stanford University: Adapting to wave forces: tissue strengthening in an intertidal, articulated coralline alga

The decalcified joints (genicula) in the articulated coralline alga Calliarthron cheilosporioides are composed of a tissue that is much stronger than tissues from fleshy macroalgae. This tissue strength may contribute to the ability of articulated fronds to survive the intense wave forces of the intertidal zone. Previous research has shown that genicula in large fronds are composed of a stronger material than genicula in small fronds; that is, genicular tissue strengthens as the fronds grow. Since larger fronds presumably experience greater drag forces in the field, this tissue strengthening may be a direct response to increasing drag force and, thus, may help articulated fronds avoid breakage as they grow. To explore this process, I explicitly tested the hypothesis that genicular tissue strengthens in response to an applied force. Individual fronds of Calliarthron cheilosporioides were hung upside-down in aquaria, and certain branches were weighted with lead fishing weights. After one month, genicular tissue from weighted branches was significantly stronger than tissue from unweighted branches. But, surprisingly, genicular tissue from control fronds was more similar to weighted tissue than to unweighted tissue. Instead of weighted genicular tissue getting stronger, the data suggest that unweighted genicular tissue got weaker. Possible mechanisms underlying this pattern will be discussed.