LOW TROPHIC AQUACULTURE AS NATURE BASED SOLUTION: INNOVATIVE APPROACHES FOR ASSESSING MARINE BIODIVERSITY BOOST

Background

Nature-based solutions (NbS) can be classified according to how much humans intervene and alter ecosystems. These classifications are useful for terrestrial, coastal, and marine environments and aim to balance biodiversity protection, climate change mitigation, and social-ecological advantages. Low trophic aquaculture, such as bivalve aquaculture, is considered a sustainable aquaculture practice that helps maintain biodiversity and supports ecosystem services like food security, may fall under Type-3 NbS (Ghaedi et al., 2026). However, the extent to which systems like bivalve aquaculture boost or sustain biodiversity is not well understood or quantified, and the trade-offs between risks and benefits are still uncertain.

Methodology and aims

The primary objective of this research conducted in EU-funded TRANSEATION project is to evaluate the beneficial impacts of low trophic bivalve aquaculture as NbS on biodiversity in mussel production operations utilizing longline and raft infrastructures, while also considering possible adverse effects on ecosystems. Forty ropes measuring six meters each, seeded with mussels of 4-5 cm shell length (at a density of 400-600 individuals per rope linear meter), were deployed within longline and raft setups located in offshore and port environments, respectively. The study investigates biodiversity changes linked to longline and raft aquaculture by incorporating multi-method observations at multiple stages: before, during, and after production cycles. This methodology integrates both water column and benthic habitat assessments through diverse and complementary techniques. Acoustic data were obtained via an innovative triple-frequency acoustic buoy installed on both the longline system and mussel raft, permitting ongoing monitoring of the water column throughout 1-year cultivation period. These acoustic findings are augmented by detailed image analysis and direct sampling of the benthic habitat, furnishing a holistic understanding of biodiversity dynamics within ecosystem compartments. A comprehensive rating system integrating these datasets was developed to appraise the ecological effectiveness of these infrastructures as NbS, taking into account the temporal and spatial dimensions of mussel production.

This analysis aims to identify opportunities for expanding bivalve aquaculture by leveraging its environmental benefits—such as supporting biodiversity conservation—as NbS, while considering both the challenges and advantages involved in promoting sustainable aquaculture practices.

Results and conclusions

Preliminary findings indicate marked seasonal fluctuations in acoustic fish abundance at both aquaculture sites, with consistently greater values observed at the raft compared to the longline system (Figure 1). At the longline location, fish abundance reached its highest levels during autumn and spring and showed reductions in winter and summer. The shorter time series at the raft site similarly demonstrated seasonal variation, notably a distinct decline during the onset of cultivation and peak abundance in summer. Initiation of farming corresponded with significant alterations in vertical distribution: at the longline, maximum abundances transitioned from deeper strata prior to cultivation to surface layers during both daytime and nighttime post-cultivation; at the shallower raft site, changes were primarily apparent during daylight hours, with substantial decreases in bottom-layer abundances following the commencement of farming activities (Figure 1). Benthic surveys were undertaken within the culture areas, and benthos samples together with ROV imagery are currently being processed for taxonomic assessment of the benthic communities. Final results from this study are anticipated to be available in July 2026.

Figure 1. Fish abundance temporal and depth variations associated to mussel longline and raft culture areas.

The study demonstrates a scalable methodology for assessing ecological impacts and benefits of aquaculture practices, supporting more sustainable management and improved evaluation of NbS performance in marine systems.

References

Ghaedi, Z., Santos, C., & Monteiro, C. (2026). Nature-Based Solutions, Climate Change, and Biodiversity: A systematic review of opportunities and risks. Nature-Based Solutions (9), 100302. https://doi.org/10.1016/j.NbSj.2026.100302