On-board Diary: White nights in the Gulf of Bothnia

Author: Christina Abel
Date: May 28, 2011



Fortunately the weather has improved, so it again is possible to work and walk (!) onboard. As we were moving north the nights were getting longer and longer, which impressed even a Scandinavian as me; at 1:30 AM there was still twilight in the Bothnian Bay. As expectedly the temperature drops when going north, which indeed could be felt when being outside. We spotted the last small pieces of ice on the sea; these are probably melted in a few days from now.

The northern part, the Bothnian Bay, has the lowest salinity in the whole Baltic Sea, due to several rivers are running into the bay. The salinity can be as low as 2 ‰, which limits the number of species living here. What characterizes the benthic life here are few species of amphipods, the predatory isopod crustacean (Saduria entomon), the Baltic clam (Macoma balthica) and viviparous blenny (Zoarces viviparous). Viviparous blenny is, as the name “viviparous” indicates, giving birth to living offspring. Up to 300 eggs are developed within the female’s body, and the 4 cm young fish are born in the winter time. This striking strategy is the reason for why the viviparous blenny has such a successful distribution in large parts of Europe today.

In both the Bothnian Bay and the Bothnian Sea we did offshore ROV recordings, including at the deepest spots. At 130 meters depth we saw natural life, including isopods, and therefore these places don’t seem to suffer from the lack of oxygen. This match with the fact that the Gulf of Bothnia is the region in the Baltic Sea which is least affected by eutrophication. Especially in the Bothnian Bay we could see this with our own eyes, as we did the ROVs, because the visibility was good.

Today we have been doing scuba diving and ROVs in Finland’s new biggest National Park, placed close to the towns Pori and Rauma. We have seen the same species as earlier, including isopod, brown shrimp (Crangon crangon) and viviparous blenny. We are only having one week left of the expedition, but there are still interesting places we will like to explore, such as the Aland Islands, where we will be going the coming days.