Alone the cruise ships off the coast of Mauritius speak volumes: together with the Seychelles, the island is one of the most popular destinations in the Indian Ocean! However, we had completely different plans. We wanted to compare the underwater fauna of Mauritius with that of Madagascar and the Seychelles. How different is the coral growth? Do the water values differ? So we loaded up two boats in the morning and set out to different dive sites.
It’s not easy to evaluate the growth rate of corals. But when you know when a wreck sank you can use this to assess coral growth rate very accurately. We visited the two wrecks Emily and Waterlilly, which sank in 1981 and 1982 respectively and were lying on sand at a depth of about 25m.
Acropora stone corals were growing on the side walls, and had reached a size of about 40 cm in 37 years. Thus the growth rate was only one centimetre per year. In the aquarium and in other places stone corals can grow over 10 cm a year!
At a depth of 25 metres, only a part of the sunlight spectrum penetrates the water. From a depth of 8 m the red part is completely absorbed and so everything appears quite blue at this depth. The coral types on the wreck show this reduced solar radiation very well. There are more soft corals than hard corals. Soft corals usually have no endosymbiontic algae (zooxanthellae) which depend on sunlight. They feed completely on plankton.
Wreck diving in a large group is a bit of a challenge. Smaller wrecks are quickly overcrowded and more air bubbles than wreck parts can be seen when photographing. Ideally you should be the first or the last on the wreck. Then you’ll get beautiful photos without any divers or air bubbles to bother you.
Any creatures inhabiting the wreck will still be there at the beginning of the dive. Later they’ll hide. We found lionfish, boxfish, paperfish and even some stonefish.
Only the anemone fish (Amphiprion chrysogaster) are patient enough to tolerate all the divers and their photography. Don’t forget they are bound there by the anemone.
The water analyses showed the following values: magnesium content 1220 mg/l, pH 8.2, KH 8 ° dKH, calcium 460 mg/l, density 1.025. Thus only the magnesium content differed from Madagascar, which was 120 mg/l higher there.
The water temperature of 25 °C was about 4-5 °C below that of Madagascar. Overall, biodiversity (variety and variability of life) was visibly lower than in northern Madagascar, which was only 1200 km northwest.
The JBL importer Goolam Sufraz and his brother organized a very interesting excursion for our research team on the last day. All in all we were very grateful to Goolam and his team. He was so much like a mother to us that we now refer to him as Mother Goolam. I’d like to take this occasion once more to thank him for his great help on site!! We went by speedboat to two small islands (Flat Island), which lay 16 km north of Mauritius. One island was surrounded by high cliffs and had beautiful cliff overhangs which sheltered the marine life underneath from the sun. I wonder why this island is called Flat Island!
The water was extremely clear and the marine fauna was very different from that seen so far. We observed great numbers of large marine angelfish, rare butterflyfish and surgeonfish. We just had to be careful that the waves and the rocks didn’t process us into finely grated fish food. In this clear water free diving without scuba gear was ideal. The fish always show less shyness with snorkellers than with bubbling scuba divers.
But while we were in Mauritius, we didn’t want to miss its most beautiful pet shop! Besides his import work our importer operates this pet shop with aquarium tanks which are worth seeing. The minute he entered the shop our sales manager, Didier Lergenmuller, immediately started re-organising the space management on the shelves. In one of the aquariums we discovered the beautiful and endemic cichlid species Paratilapia polleni, which we unfortunately had not found in Madagascar.
Of course we were also interested in the rainforest and the freshwater biotopes of Mauritius. There was little or nothing about these in books or on the internet. A very experienced biologist accompanied us to a national park in the center of Mauritius. He very knowledgably answered our query about freshwater fish in the stream as we walked along: "There are almost no fish. Only one trout species lives here.“
But we could already see various fish species through the water surface. It was definitely an incentive to climb into what was unfortunately quite cold water. The goby species were difficult to identify, but we definitely saw a marbled eel and a Kuhlia species.
These encounters with freshwater fish happened completely unexpectedly. Countless species, unknown gobies and a marbled eel. We were glad to have our Bresser ActionCam with us.