The state of the Baltic Sea is worsening due to climate change and eutrophication. The blue mussel is a filter feeder that effectively improves water quality while filtering, removing phytoplankton, and therefore nutrients from the water. One way to maintain and increase high density mussel populations is to construct artificial reefs, but the substrate choice can affect settlement. To increase high density mussel beds on manmade structures it is important to thoroughly investigate the materials used as substrates. In this study, different materials were examined to evaluate M. edulis substrate preferences. A settling study was conducted, in the spring, in Kalmar harbour. The cables placed in the harbour gave no data, possibly due to the cold spring and late spring bloom of phytoplankton, postponing M. edulis spawning. In addition to this, survey videos of Kårehamn wind farm, established in 2013, were studied to estimate the degree of colonisation and what species were present. The substrates investigated here were wind turbine foundations, submerged cables, and macadam sacks. The video survey of Kårehamn wind farm showed that M. edulis attach to all investigated substrates but dominated on the macadam sacks and the cable. They also dominate at depths below 12 m on all three of the substrates. Moreover, a coastal inventory of F. vesiculosus and its substrates was done to determine if macroalgae aquaculture can also function as substrate for M. edulis. The inventory was done at two locations around Kalmar in the fall and spring. The inventory showed that M. edulis was only found in extremely low numbers on F. vesiculosus and on the same substrate as F. vesiculosus. One way to do this would be to increase the number of macadam sacks used to hold the cable down. Placing the substrates below 12 m would also increase the chance of M. edulis colonising the substrates without being outcompeted by other biota.