Predator!

Its been a while since my last update and quite a lot has happened.

The spiny starfish has basically decimated the molluscs, it has lived up to its reputation as a voracious predator and wiped out the cockles, clams, mussels and snails. A few limpets still hang on - but otherwise the display tank is a mollusc free zone.

This has had a dramatic effect on the plant life, however, at the same time a failure in the power packs to the lights has resulted in a progressive, but imperceptible decrease in illumination. Hair algae has multiplied, as has green microalgae. With no grazer these green algaes have smothered many surfaces. Higher algaes have suffered and coralline algaes have been inhibited.

The loss of bivalve filter feeders has allowed phytoplankton to bloom and water clarity has suffered as a consequence. However, water quality - as far as nitrogenous compounds is concerned - has remained high. Nitrogen remains in the food chain and doesnt seem to end up as nitrates in the water column. No water changes have been carried ou since the tank was created.

This weekend wil see the spiny starfish released and a couple of hundred snails introduced. A 50 gallon water change will be effected and another manual removal of algae will be carried out. The lights have been repaired - the difference is astonishing. It was only by looking at old photographs that I was able to detect that the lights had decreased in intensity, because the drop-off was so slow it simply wasnt noticed. I didnt expect a fall off, as I would with flourescents, so didnt look for it. My fault.

I allowed the strafish to carry on with its rampant feedimng to see what the effects of snail predation might be in an enclosed enviroment. The lights failing has rather spoiled the experiment - but I am still of the opinion that snails and other grazers have a vital role in determining the vegetation of rocky shores. However, I want my tank to look pretty again, so the starfish must go and ruthless grazing will be the regime again.