This year’s students carried out a detailed survey in Idkroken bay, close to Stockholm University's Askö Laboratory . Idkroken is a sheltered shallow bay with a muddy seabed and a range of different alga and plant species forming an underwater forest  which is host to many invertebrates . The students first quantified the density of the main species of flora and fauna, using quadrats and vegetation surveys in the field (Picture 1), as well as identifying and quantifying smaller organisms in the laboratory. Seven plants, two algae and nearly 30 animal taxa were identified.

Picture 1. A snorkeller delivers a sample to the boat in Idkroken. The contents of the sample will later be picked through in the lab and all species identified and counted.
Picture 1. A snorkeller delivers a sample to the boat in Idkroken. The contents of the sample will later be picked through in the lab and all species identified and counted.

In order to calculate energy fluxes to and from the main species, they held individual species in sealed containers, measured changes in oxygen concentrations in the water over several hours and converted these oxygen measurements to calories (Picture 2). Oxygen (and energy) is consumed by plants, algae and animals respiring, while oxygen (and energy) is produced by photosynthesis. Multiplying up from individual species to the total area of the seabed in the bay produced some startling numbers: Idkroken consumes around 2.3 million calories every 24h – the equivalent of about 9300 Mars Bars, or 2200 Big Mac Meals!! However, the bay also produces 2.6 million calories every 24h (10300 Mars Bars or 2400 Big Mac Meals) through photosynthesis, so this ecosystem is a net producer of energy, at least on a sunny summer’s day.

Picture 2. Oxygen measurements being done back at the lab; each plastic beaker contains a sample of invertebrates collected at Idkroken.
Picture 2. Oxygen measurements being done back at the lab; each plastic beaker contains a sample of invertebrates collected at Idkroken.

Shallow bays like Idkroken are important nursery grounds for fish and nesting areas for birds, so this energy production will not go to waste, but will be used by other organisms in the food web. Luckily it comes in a healthier form than chocolate or burgers!

Are you interested in taking the course next year? For more information see here.

Stockholm University also has a Bachelor’s and Master’s programme in Marine Biology: see here and here.