Interaction between stocking density and settlement on population dynamics in suspended mussel culture

• The settlement of conspecifics can alter the dynamics of adult mussel populations.
• We analyze the interaction between adult and recruits on mussel culture ropes.
• Settlement abundance is lower at high stocking densities.
• We observe a trade-off between competition for resources and seed settlement risks.
• Intra- and intercohort competition reduces survival and growth in adults and recruits.

Population dynamics on mussels growing on suspended culture depend mainly on the balance of several processes: mortality and/or dislodgements from the ropes, recruitment and growth. The negative effect of overcrowding on mussel growth and survival has been widely studied. Other works have addressed the effect of population size on recruitment on bottom beds. This study aims to provide insight into the processes underlying population dynamics. To this purpose, we analyzed the effect of stocking density on mussel growth, survival and seed settlement, and the post-settlement interaction between adults and recruits in suspended culture. The temporal pattern of the variables involved in population dynamics was fitted by GAM models, which in contrast with parametric models does not assume any prior relationships between variables. Our results show that mussel growth and survival depend on a trade-off between competition for resources at high densities and the risk of great settlements in less crowded adult mussel populations. Intracohort competition increased with stocking density, while seed settlement, which increases the risk of mussel dislodgements and leads to intercohort competition, was higher at moderate stocking densities. Post-settlement competitive pressures were driven by total population density and size composition. Both intracohort competition in adults and asymmetric competition between adults and recruits increase with higher adult–recruit ratios. All these density-dependent processes should be considered in future management strategies and research experimental designs.