|The impact of abiotic and biotic factors on the formation of mussel beds|
Ter Veld, J. (2019). The impact of abiotic and biotic factors on the formation of mussel beds. BSc Thesis. NIOZ Royal Netherlands Institute for Sea Research: Yerseke. 33 pp.
Mussels are a highly sustainable (ecological & economical) aquaculture ‘crop’. To improve the sustainability of mussel farming, the analysis, and the potential improvement of the current seeding techniques is needed. The current seeding techniques are highly inefficient (initial losses of up to 75% while seeding). This experiment was set up to test the hypothesizes that (1) an initial seeding density of 1.0 kg/m2 would do best in terms of the condition, persistence and growth of the mussels. The other hypothesis (2) states that the mussels would take on more optimal patterns (more striped or labyrinth-like patterns for optimal biomixing of the food above the mussel bed) with a reduced water flow, which in turn reduces the food availability whereas with an ambient water flow they would form more uniform pattern (no need to form patterns to facilitate food).To study this a field experiment was set up. This was on an intertidal culture plot (400m by 100m) near Bruinisse, where 12 bands of mussels were laid out in different densities (0.5, 1.0 and 1.5 kg/m2) and different depths (see Appendix II). Round metal cages were laid out on these bands (eight per band, total of 96) with different types of mesh covering them (small holes (Ø = 0.5cm) or large holes (Ø = 1.5cm), four of each type per band) where the small mesh reduced the water flow. Over the experiment core samples were taken from randomized cages for the condition index, size of the mussels and the amount of mussels per cm2 (3D patterning). The cover and perimenter:area ratio (2D patterning) was measured with pictures taken by gopros on the side of the cages (see figure 5A for the placement). With this data models were set up in R to test the hypotheses. These models were used for an AVOVA and if there was a significant interaction a Tukey’s post-hoc test was used to see where this interaction was in the data. The analysis of the data showed that the intermediate density (1.0 kg/m2) decreased the least of all densities in terms of the condition of the mussels, making it the more optimal seeding density then the high (1.5 kg/m2) or low (0.5 kg/m2) treatment. The data also showed that inside of the cages with the reduced water flow the mussels took on a more 3D pattern (amount of mussels per cm2) then inside the cages with an ambient water flow.For further research I would recommend galvanizing the metal of the cages to reduce the corroding effect of the salt water so that the cages can last longer without breaking. Also using weighted anchors to prevent the cages from moving. Also doing the experiment in spring/summer might provide more of an insight in the growth of the mussels.