Ramet dynamics for the clonal seaweed Pterocladiella capillacea (Rhodophyta): A comparison with Chondrus crispus and with Mazzaella cornucopiae (Gigartinales)

Little is known about the dynamics and the ecological interactions among ra mets: (fronds) from populations of clonal red seaweeds. Small ramets are ve ry difficult to tag, so their growth cannot be monitored directly, The temp oral variation of the relationship between stand biomass and ramet density offers information on ramet performance. We calculated this relationship fo r an intertidal population of Pterocladiella capillacea (Gmelin) Santelices et Hommersand (Gelidiales) from Baja California, Mexico. Biomass and densi ty were positively correlated on an annual basis, indicating that biomass a ccumulated without involving self-thinning among ramets, This contrasts wit h nonclonal seaweeds, for which self-thinning among individuals occurs duri ng growth, but agrees with other clonal red seaweeds, such as Chondrus cris pus Stackhouse and Mazzaella cornucopiae (Postels ef Ruprecht) Hommersand ( both Gigartinales), The growth pattern for these members of the Gelidiales and of the Gigartinales holds despite differences in holdfast morphology an d ramet branching degree and despite differences in the capacity of coalesc ence during early stages, known only for the Gigartinales, The positive slo pe for the dynamic biomass-density relationship, on a bilogarithmic scale, was statistically steeper for M, cornucopiae than For P. capillacea and for C, crispus. This suggests that the addition of new ramets during the growt h season may be relatively more beneficial for biomass accumulation rates f or M, cornucopiae, This would be expected for high-intertidal species subje cted to strong abiotic stress, for which ramet crowding constitutes a key p rotection, Pterocladiella capillacea occurs at the mid-intertidal zone and C, crispus at the subtidal zone, so ramets would be relatively less importa nt in that respect.