SUMMARY This paper synthesizes previous research on the Bot River estuary, including that on its past and present geology, sedimentology, hydrology, history, plant life, invertebrates, birds and fish. The estuary is periodically breached to form a deep mouth and this restores estuarine conditions and allows recruitment of fish; but it also disrupts the system and results in massive losses of aquatic weeds and invertebrates, and a twentyfold reduction in bird-life. A key feature in the ecology is that the Bot is connected to the adjacent Kleinmond estuary by overflow channels which act as a spillway when water-levels in the Bot are high. Because of this the Bot will slowly become diluted by river-water and change into a fresh-water lake if it is not breached. Six proposed plans for the management of the Bot River estuary are discussed. Only two are viable: either the estuary should never be breached (and thus be managed as fresh-water lake) or breaching should be controlled and undertaken about every three...

Synopsis of the impact of artificially opening the mouth of the bot river estuary: implications for management

The typical habitat of the rare, endemic South African mudsnail Hydrobia knysnaensis is the leaves of upper-shore Zostera capensis within high-salinity salt-marsh pools and channels. In the Knysna estuarine system, it is the numerically dominant member of a guild of six small microphytophagous gastropods; it is absent from lower level and more exposed Zostera meadows, where its place is taken by Rissoa pinna. H. knysnaensis is also here recorded from the nearby Swartvlei Estuary, in the same habitat type. This unusual habitat for a Hydrobia may in part account for the failure of earlier surveys to detect its presence, notwithstanding that it may well locally be the most numerous gastropod in each of these systems. Generally, however, it (and probably other small gastropods) seem to have been confused in estuarine fauna lists with Assiminea. Experiments show that the rate of feeding in H. knysnaensis is curtailed at population densities exceeding 2000–4000m−2 and in salinities below some 10psu. The proport...

The distribution and habitat in the knysna estuary of the endemic south african mudsnail hydrobia knysnaensis and the influence of intraspecific competition and ambient salinity on its abundance

SUMMARY The effect of temperature and salinity variations on the suspended bacterial population of the Bot River estuary, a closed estuary, was examined. The population was found to be salt tolerant, and saline water was required for maximal growth rates. Temperatures below 15°C inhibited growth. Bacterial isolates fell into two groups as regards temperature optima, the one having an optimum of 23°C and the other 30°C. The bacterial population in the Bot River estuary is clearly adapted to estuarine conditions.

The effect of salinity and temperature variations on the bacterial population in the bot river estuary

SUMMARY The Bot River estuary is normally closed to the sea and its bacterial population fluctuates seasonally, peaking in late summer. Parameters such as temperature, salinity, organic nutrients and turbidity may directly or indirectly cause these fluctuations. The spatial distribution of this bacterial population differs from that of open estuaries studied elsewhere. However, artificial opening of the estuary results in a distribution pattern similar to that of open estuaries.

G. M. Branch

Papers

The effect of salinity and temperature variations on the bacterial population in the bot river estuary

The annual cycle of free-floating bacteria in the bot river estuary