The Free-Living Hormosira banksii (Turner) Decaisne Associated with Mangroves in Temperate Eastern Australia

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Abstract
In the mangrove swamps of Botany Bay, there is an extensive development of free-floating H. banksii. Hormosira is restricted to the lower portion of the mangrove zone, which in this region fringes a well-developed salt marsh. The unattached plants lie on the open mud surface and appear to be trapped among the pneumatophores. At this level the population is subjected to tidal influence and can be considered as occurring in the lower eulittoral. In a habitat sense this Hormosira is comparable to some of the unattached fucoids of the northern hemisphere. In comparison to attached plants of Hormosira on adjacent rocky coasts, the free-living form exhibits the following characteristics: absence of sexual reproduction; absence of a holdfast; generally smaller thallus; and compact form with a close-set branching pattern. The biomass shows marked fluctuations, with a summer maximum followed by a marked depletion in autumn. On the basis of such changes alone, a conservative measure of productivity is estimated as 0.4 kg m-2 yr-1.