Invited by the Youth Parliament in Hilden, Germany, to a flee market for driving longer use of cloths and household items together with information about how to live more sustainably, Mundus maris participated with a range of information offers and participant explorations.

Besides the Ocean game loved particularly by the kids, Mundus maris engaged passers by with a lot of other information about what can be done to protect the ocean better as a means to secure continued services for stabilising the climate, produce the oxygen we breathe, provide us with food, jobs, recreation and more. In the light of threats to marine biodiversity, particularly from publicly subsidised industrial fishing, and wreckless expansion of plastic pollution, visitors to the booth were interested to figure out the extent of the threats and  what they could do individually and collectively to regenerate the ocean and its ecosystems.

Do it yourself info materials at the Mundus maris booth

In animated conversations, visitors figured out who eats whom in a marine foodweb. In the sea, most oxygen and organic matter is produced by microscopic algae – the phytoplankton. Phytoplankton and other marine algae are have in this respect the roles of plants like grasses and trees on land. They represent trophic level 1, the basis of the marine food web. The phytoplankton is eaten by small animals, collectively called zooplankton, trophic level 2. Few people knew that the energy intensive life of water breathing animals means that only ten percent of the biomass or energy from the basis level 1 of plant producers gets transferred to the next level. When zooplankton is eaten by small fish like sprat, herring and sardine like fish, or jelly fish these represent trophic level 3 and again represent only about ten percent of the biomass of the zooplankton. These small fish are still quite abundant and in turn are eaten by squid, bigger fish and marine mammals.  At what level animals feed in the food web influences the quantities that can exist. In other words, predators at the very top of the pyramid such as oceanic sharks, big tunas, and orcas, while important for the overall functioning  of the food web, will have more modest population sizes and longer lives. They are vulnerable to heavy fishing pressure. After decades of heavy industrial fishing it is estimated that many of the top predators have less than ten percent of their biomass a century ago so that the overall health and productivity of the ecosystems has suffered severely. Climate change induced warming of the ocean puts further pressure on the populations as warmer water contains less dissolved oxygen.

Enforcement of declared marine protected areas, reducing fishing pressure and CO2 emissions are among the priorities for regenerating ocean biodiversity and food webs so that we can continue benefiting from ocean products and services. Supporting the EU Green Deal, national measures and local action should therefore be high on the agenda. In addition, the FishBase Guide app providing information about minimum reproductive size of all commercial fish species can help ocean lovers also at individual level to protect juvenile fish and contribute to regeneration.

The event took place in the town center on 23 August 2025, from 11 to 16h. Indeed, exchanges were so engaging at the Mundus maris booth that we extended by another hour.