Comparative study of predatory responses in blue mussels (Mytilus edulis L.) produced in suspended long line cultures or collected from natural bottom mussel beds

Abstract

Blue mussels (Mytilus edulis L.) are a valuable resource for commercial shellfish production and may also have uses as a tool in habitat improvement, because mussel beds can increase habitat diversity and complexity. A prerequisite for both commercial mussel production and habitat improvement is the availability of seed mussels collected with minimum impact on the benthic ecosystem. To examine whether mussels collected in suspended cultures can be used for bottom culture production and as tool in habitat improvement, the differences in predatory defence responses between suspended and bottom mussels exposed to the predatory shore crab (Carcinus maenas L.) were tested in laboratory experiments and in the field. Predatory defence responses (byssal attachment and aggregation) and morphological traits were tested in laboratory, while growth and mortality were examined in field experiments. Suspended mussels had an active response in relation to the predator by developing a significantly firmer attachment to the substrate and a closer aggregated structure. Bottom mussels had a passive strategy by having a thicker shell and larger relative size of the adductor muscle. In a field experiment mussels originated from suspended cultures had a higher length increment and lower mortality when compared to bottom mussels. It is concluded that suspended mussels potentially are an alternative resource to bottom culture and can be used in habitat improvement of mussel beds, but that the use of suspended mussels has to be tested further in large-scale field experiments.

Area-intensive bottom culture of blue mussels Mytilus edulis in a micro-tidal estuary

“…The results from the commercial and the experimental bottom cultures indicated that these densities of mussels did not adversely affect shell growth. The estimated shell growth rates in bottom cultures are in the same range as those in natural mussel beds in Limfjorden (Kristensen & Lassen 1997, Dolmer 1998, Christensen et al 2012 and other eutrophic Danish estuaries (Petersen et al 1997). It appears that the present procedure for transplanting blue mussels in tracks or long beds provides sufficient heterogeneity to avoid a decline in growth across the culture bed.…”

“…Interactions with predators (e.g. Carsinus maenas) reduce growth of blue mussels due to disturbance of filtration activity or due to increased aggregation of the mussels (Christensen et al 2012), which may increase food competition in the mussel bed and reduce CI.…”

“…This calculation assumed that the seed transplanted to Sites A and B was fished from a biomass density of 5 kg m −2 . Moreover, the areas affected by the production of blue mussels in bottom culture can be reduced further by using seed produced on suspended col lectors , 2009, Christensen et al 2012, although the suspended cultures may also affect both pelagic and benthic habitats (McKindsey et al 2011). …”

“…In 2009, the macrostructure of the culture bed was similar to the original transplantation tracks established the previous year. Blue mussels can be assumed to aggregate within the tracks (van de Koppel et al 2005, 2008, Christensen et al 2012, but not at a scale that changes the macrostructure of the tracks. Using a model, van de Koppel et al (2005van de Koppel et al ( , 2008 demonstrated that self-organised spatial heterogeneity of blue mussels improves productivity compared to a completely homogeneous bed of blue mussels at the same density.…”

Aggregation and attachment responses of blue mussels, Mytilus edulis—impact of substrate composition, time scale and source of mussel seed

“…A number of studies document that the bed formation in relation to aggregation and attachment strength is enhanced if blue mussels are exposed to predators (e.g. Christensen et al 2012;Schneider et al 2005;Reimer and Tedengren 1997). Young (1985), demonstrated that byssal threads are produced by the individual mussel in response to a number of contributing factors, of which agitation was the most powerful effect observed.…”