Zandvlei Trust

 

Tubeworm Update.  (Extract article from the volume 2005/2 Newsletter)

The tubeworms beneath Park Island Road Bridge are being monitored at present. In February about 80 % of the population was removed ILLEGALLY.

Tubeworms contribute immensely to water quality and together with sandprawns (Callianassa kraussi) and pondweed (Pontamageton pectinatus) form an integral part of this last remaining functioning estuary on the False Bay coastline. They breed in April and May and require salinities measuring between 9.5 to 30 ppt and need to be submerged in water because they are marine filter feeders. Studies done in the late 1980s and early 1990s reflect far more a real coverage of tubeworms in the Zandvlei system (Harding, 2001). This decline is likely to be a result of the sustained low levels of salinity in the system (< 9 ppt) (Harding, 2001).

Surveys

As indicated by Dr. Harding in his recommendations future surveys should be conducted in mid-autumn of each year, vertical and horizontal wall coverage surveys should be repeated annually, future surveys of a real cover should include colony thickness, and the recolonization and growth rate trails should be conducted on an annual basis. The recommendations published in 2001 were however not sustained, due to lack of Naure Reserve staff. A need has arisen from public outcry, ecological importance and the future expansion of the Zandvlei Nature Reserve to monitor the tubeworms on an annual basis.
The growth was removed at an unfortunate time i.e. just before breeding season and because so much of the dead growth was removed, little spawning has taken place. Dead tubes will be inhabited by the larval stages and will then start building new tubes. The growth has been monitored in May and July of 2005. In May the population remaining was 32.63 %, the method used is not invasive and little damage is incurred. In July the population measured 22.63 %, a decrease of 10 %. Tubeworms are fragile because the adult form has limited locomotion capabilities and their only mode of protection is their tubes.

Recreational users

 For the benefit of recreational and ecological purposes 6 poles will be erected demarcating areas where recreational users will be able to navigate through by the end of July 2005. The area cordoned off will continue as a sight to be monitored and hopefully in the future more monitoring of tubeworms within Zandvlei and Marina da Gama channels should be done, this is however labour intensive. If tubeworm growth continues to decline, the management strategy of this specie will change. Tubeworms do limit locomotion through channels and under bridges, all of these factors will have to be considered when compiling a management strategy.

Farrah Feldman (Student Conservation Officer Zandvlei Estuary Nature Reserve)

                                                                                                                          

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