Where and how can you find starfish

Question:

Why can't we find any more starfish on the beach in front of Warnemünde?

This is not impossible, although the starfish live here in the Mecklenburg Bay mainly in deeper areas far from the beach. The Baltic Sea, with its changing salt content, which is generally lower than that of the North Sea, causes major problems for most marine organisms and the further away you are from the access points to the North Sea, the more difficult the living conditions become. The Mecklenburg Bay has a salt content that is barely tolerable for many organisms.

The common starfish (Asterias rubens), for example, is one of the few echinoderms that can penetrate this far. However, even in the Mecklenburg Bay, it only looks for habitats that have more salty water: If the species is still found in the shallow water in the Kiel Bay, it is further east dependent on the deeper areas, since there is the denser (heavier), salty water is located. The amount of salty North Sea water that flows from the Kattegat over the Belte into the Baltic Sea determines how far the starfish can spread in the Mecklenburg Bay and ascend into flatter regions.

There are years and decades when this species is one of the rather rare inhabitants of the Baltic Sea floor. However, for about 3-5 years we have been able to observe a considerable increase in the number and distribution of Asterias rubens in the Mecklenburg Bay. Investigations in 1999 show a settlement of the water depths of 7 to 28 m with densities of 2 to 10 individuals per m². A few nautical miles from the beach in Warnemünde, it occurs regularly from about 10 m water depth. During stronger storms it is quite possible that the starfish will be thrown onto the beach. Artificial widening of the beach (flushing) can also cause species of deeper water (including starfish) to get onto the beach.


Map: Schematic distribution of the starfish (Asterias rubens) after investigations in 1999


Photo: Asterias rubens from the Bay of Lübeck, photo taken at a depth of 16 m, April 1999

The question was answered by Dr. Michael L. Zettler, IOW, Biological Oceanography Section.