Would you think of the ocean when you think of Hilden, near Düsseldorf, Germany? Probably not, yet the North Sea occasionally reached into what is now the lower Rhine area during the Trias period, approximately 251.9 million to 201.3 million years ago, as witnessed by calcareous strata of bivalve shells.

What remains over the last about 8000 years are the lowlands of the ‚Cologne Bights‘ with its mild climate benefiting from the Gulf Stream. So, the ocean makes itself felt even a few hundred kilometers inland now. One more reason to use the volunteering action day in town to promote more interest in a healthy ocean.

With a team of four, Mundus maris staffed its information booth, offering playful approaches through the ocean game with little tokens for a successful course. A biology student also supported do-it-yourself constructions of marine foodwebs.

Quite a few young adults were attracted to test their knowledge about who eats whom in the ocean and learning what the concrete results are of the fact that only about 10% of the energy or biomass from a lower trophic level in the food web get transferred to the next level.

That explains why Orcas (Orcinus orca) or other big, long-lived predators can only exist in relatively small numbers. There is simply not enough biomass available to sustain huge populations.

Conversely, huge animals like big baleen whales, such as a humpback whale (Megaptera novaeangliae), which can reach a size of 18m length and a weight of 35 tons, or a whale shark (Rhincodon typus – of 20 tons), need to feed low in the food web to find enough food organisms to reach such sizes.

Marine food web for construction

At the bottom of the pile are the smallest organisms – but in enormous numbers. Beautiful phytoplankton, some with bizarre shapes, microscopic balls or large filaments, and other plants are the only producers turning the energy of sunlight through photosynthesis into organic matter.

Primarily in the upper 60 meters of the ocean, as far as the sunlight penetrates, they produce about half the oxygen in the atmosphere and sustain all other life in the food web. We all depend on their metabolism working well.

Many passers-by took our flyers, bookmarks and visiting cards for the FishBase Guide app. At the end of the day, our stock had shrunk considerably – so much the better.

We also used the occasion to draw people’s attention to the forthcoming World Ocean Day and the planned clean-up of the surroundings of a local creek, a repeat activity that helps to collect all kinds of garbage, typically cigarette butts as the numerically most frequent.

During the four hours of the event, with the pedestrian zone packed with people enjoying the sunshine and learning about the wide range of voluntary initiatives, we were not idle for a minute. Mission accomplished – many good conversations and an agreement with the youth parliament to develop cooperation.