Introduction
Suspended mussel aquaculture systems represent a dominant feature of productive coastal areas in NW Iberian Peninsula, substantially modifying benthic environments through shell deposition, organic enrichment, and the addition of secondary hard substrate. While these modifications can increase habitat heterogeneity and attract mobile benthic fauna, their potential for restocking species of commercial interest remains poorly quantified (Carbonell-Garzon et al., 2026). The objectives of this study were to evaluate the capacity of artificial reef (AR) structures deployed beneath mussel rafts and on adjacent sandy substrates to enhance invertebrates species of ecological and commercial importance; to determine whether habitats associated with suspended mussel aquaculture can retain deliberately released individuals of European lobster Homarus gammarus as a potential stock enhancement strategy; to assess whether the origin of released lobsters (aquaculture-reared versus wild-translocated) influences their post-release spatial behaviour and site fidelity.
Material and Methods
Study site and AR deployment: The study was conducted from October 2023 to September 2024 in the central mussel raft polygon of the outer R��a de Vigo (NW Spain; 42°14���49��� N, 008°49���15��� W; ~0.36 km2; 35 mussel raft). In May 2023, twelve concrete AR modules were installed at 14–16 m depth across four sites: two beneath mussel rafts (AR-M) and two on adjacent sandy substrates (AR-S), each comprising three blocks with removable sampling plates for non-destructive monitoring. An open sandy habitat (Sand) served as an unstructured control. Monthly diver-based visual censuses were carried out, estimating relevant invertebrates abundance, over the full 24-month period. Occurrence frequencies of commercially important taxa were recorded at AR-M and AR-S sites. Moreover, we used acoustic telemetry tools to study the post-release spatial behaviour and site fidelity of of a 46 H. gammarus (24 aquaculture-reared, 22 wild-translocated) released across three habitat configurations (AR-M, AR-S, and mussel-raft mooring without reef, MR). All individuals were tagged with Thelma Biotel LP-6 transmitters in two release periods (October 2023 and April 2024) and released. An array of 20 Thelma Biotel receivers (TBR-700L/800) monitored the central and peripheral polygons of mussel rafts in the study area, including the artificial reefs. Data were obtained in September 2024.
Results
Artificial reefs under mussel rafts (AR-M) generated significantly higher occurrence frequencies of commercially important species: Paracentrotus lividus (72.2% vs. 11.1%), Octopus vulgaris (25.9% vs. 16.7%), and Necora puber (20.4% vs. 0.93%) compare to AR-S. Differences were only significant during spring and summer months. During the first 72h after release, 27.9% of the 43 released lobsters remained close to the release site, 48.8% redistributed within the acoustic array, and 23.3% emigrated out site of the monitored area. This behavior differed significantly between origin groups (Fisher's exact test, p = 0.037), with 55.6% of aquaculture-reared individuals remained at the release receiver during hours de first 72h, compared with only 13.3% of wild-translocated individuals. Long-term residency and space-use metrics (Kernel density) differed by origin; wild individuals tended towards larger space use and earlier departure from the central array.
Discussion
The results confirm that AR deployment beneath suspended mussel rafts creates structurally and functionally complex microhabitats capable of supporting diverse benthic communities and retaining species of ecological and commercial value. The pronounced enhancement of species abundance at AR-M compared with AR-S suggests that the combined effect of hard substrate and aquaculture-derived organic enrichment — including shell accumulation and particulate organic matter fallout — acts synergistically to increase habitat suitability. The elevated occurrence of P. lividus, N. puber, and O. vulgaris, at mussel-raft-influenced AR sites is consistent with previous observations of aquaculture infrastructure functioning as de facto artificial habitat for mobile fauna. The behavioural divergence between aquaculture-reared and wild-translocated lobsters has direct implications for restoration program design. Higher site fidelity among hatchery-reared individuals during the critical post-release window may reflect reduced exploratory behaviour associated with captive rearing, rather than active habitat preference; longer monitoring is required to determine whether this translates into sustained retention or eventual dispersal. Wild-translocated individuals, despite showing broader initial movement across the array, may draw on prior experience of natural environments to locate and establish shelter in unfamiliar release areas. Together, these findings support a differentiated release strategy tailored to individual origin and habitat configuration. This work demonstrates the feasibility of integrating ecological restoration objectives into working aquaculture seascapes through targeted artificial reef deployment under mussel farms. The results provide a replicable model for ecological mitigation in aquaculture-modified coastal environments, directly relevant to EU Nature Restoration Law implementation in areas where productive use and biodiversity recovery must be reconciled.
Acknowledgment
This study was funded by the EU Horizon Europe project CLIMAREST: Coastal Climate Resilience and Marine Restoration Tools for the Arctic Atlantic basin (grant agreement 101093865).
References
Carbonell-Garzon, E., Mateo, A., Leyva, L., Daban, P., Troncoso, J., & Sanchez-Jerez, P. (2026). Positive Influence of Mussel Aquaculture on Epibenthic Macrofauna: An Example of Restorative Aquaculture in Coastal Ecosystems. Coasts, 6(1), 12. https://doi.org/10.3390/coasts6010012