# Settlement and Growth of Mytilus galloprovincialis Pediveliger Larvae in Response to Biofilm-Based Microalgae and Chemical Neuroactive Compounds

## TL;DR

This study shows that biofilm and chemical treatments can improve mussel larval settlement and growth, helping to make mussel farming more sustainable and efficient.

## Contribution

The study introduces a large-scale operational trial combining biofilm and chemical inducers to optimize mussel spat production and growth.

## Key findings

- Biofilm treatment achieved the highest larval settlement rate (65%) and spat production (46.4 spat/cm²).
- GABA and KCl treatments increased post-larval growth rates compared to biofilm and control groups.
- Short exposure times (6 h) to low GABA concentrations improved settlement rates among chemical treatments.

## Abstract

Technical procedures and breeding systems need to be optimized to ensure the economic viability and sustainability of farm-raised mussel production. The blue mussel Mytilus galloprovincialis plays a crucial economic and environmental role, necessitating improvements in breeding due to the scarcity of natural seed sources. The present study aimed to evaluate the efficiency of biofilm in conjunction with chemical inducers (GABA and KCl) on larval settlement, post-larval growth, and spat production in a large-scale operational trial. This research offers a standardized approach to accelerate the production cycle and maximize its results, while maintaining optimal seed quality.

The sustainability of mollusc aquaculture relies, in part, on overcoming the challenges of spat production in captivity, particularly during the metamorphosis and settlement stages. The optimization of rearing technologies at these stages would ensure possible solutions for sustainably producing mollusc spat while simultaneously improving stock performance. The current work represents a large-scale trial examining the effect of biological and chemical inducers on larval settlement in Mytilus galloprovincialis. For this purpose, one batch of pediveliger larvae was directly transferred to settlement on microalgae-based biofilm (mature cylinders), while another batch was pretreated with gamma-aminobutyric acid GABA (10−4 M, 10−5 M and 10−6 M) and potassium chloride KCl (20 mM and 30 mM) according to two different exposure times (6 h and 24 h), before being transferred for settlement (immature cylinders). The impact of different treatments on larval performance was evaluated in terms of larval settlement rate (Sr), post-larval growth rate (Gr), and spat production rate (Pr). The biofilm treatment had the highest settlement rate and spat production (Sr = 65% and Pr = 46.4 spat/cm2) compared to chemical treatments. The highest settlement rate among chemical treatments occurred under short exposure times (6 h) to low GABA concentrations, i.e., Sr 40% and 45% at GABA 10−5 M and 10−6 M, respectively). GABA and KCl treatments ensured a faster post-larval growth rate than the biofilm, i.e., 15.54 ± 7.67 µm/day, 18.26 ± 9.39 µm/day, and 11.35 ± 6.73 µm/day, respectively, while control trials showed the lowest growth rate (6.80 ± 4.39 µm/day). These findings reveal a key trade-off: biofilm is the most effective measure for promoting spat production, while a targeted use of GABA and KCl at short exposure times (6 h) appears to significantly enhance post-larvae growth.