Ecology of Botany Bay. I. Growth of Posidonia australis (Brown) Hook. f. in Botany Bay and other bays of the Sydney basin

Abstract

The distribution, biomass and density of various beds of P. australis have been determined for Botany Bay (N.S.W.). Comparisons have been made with sites at Broken Bay, Port Hacking and Jervis Bay and these include observations of other seagrass beds (Zostera capricorni, Heterozostera tasmanica, Halophila ovalis and Halophila decipiens).

The P. australis plants observed were all of the broad-leaved (1.0-1.2 cm) variety. The length of leaves appears to be correlated with depth and with degree of exposure to wave action.

The distribution of P. australis in Botany Bay is almost entirely restricted to the southern side and is limited to a maximum depth of - 3 m compared with -7 to -9 m at other sites. The growth of plants in well-established beds seems to be as vigorous in Botany Bay as elsewhere but flowering is poor and infrequent and the overgrowth of epiphytes is very great at certain seasons.

Clearing experiments in Botany Bay indicate that recolonization by surrounding plants or seedlings is extremely slow. Transplant experiments indicate that mature plants will survive transplanting to cleared sites on both the northern and southern sides of the Bay.

Evidence for a much more extensive distribution of P. australis in Botany Bay in times past and the possible effects of pollution are discussed.