Balearic seabed litter study

A study of seabed litter reveals the negative impacts of tourism and maritime activity in the Balearic Sea

Environmental foundations Mallorca Preservation, Menorca Preservation and IbizaPreservation join forces for the first time to quantify the presence of litter on the seabed of the archipelago.

A new pilot study of the Balearic seabed highlights the widespread and persistent presence of litter, particularly items linked to tourism and maritime activity. This has been revealed by the foundations Mallorca Preservation, IbizaPreservation and Menorca Preservation, which presented their conclusions as part of the joint project “Weaving the Future: An Alliance for the Preservation of the Balearic Islands.”

The study, carried out throughout 2025, was based on two sampling campaigns conducted in spring and autumn at 21 locations across the four Balearic Islands, where 136 underwater transects between 25 and 40 metres in length were studied. Using self-contained underwater breathing apparatus (SCUBA), a total seabed area of 16,120 m² was surveyed. The methodology followed the protocol established by the European Commission’s Technical Group on Marine Litter, enabling the data to be integrated in a standardised way into public databases such as those of the Spanish Institute of Oceanography (IEO), contributing to larger-scale studies.

Main results

Across the two campaigns, 355 objects were identified, with a clear predominance of plastic materials on all islands and in both seasons. The average litter density was higher in spring (2.59 objects per 100 m²) than in autumn (1.79 objects per 100 m²), and notable spatial variability was observed between islands and sampling sites.

In terms of density and concentration (objects/100 m²), Mallorca recorded the highest values and Menorca the lowest, while the Pityusic Islands were in an intermediate position. Regarding the types of litter, plastics clearly predominated across all four islands, especially fibreglass items, fragments and hard plastic objects. Among the most striking items found were plastic brushes or combs, sunglasses, plastic cups and items of clothing.

The analysis of the possible origin of the litter, carried out using an adaptation of the Matrix Scoring Technique (MST), suggests that activities linked to tourism, commerce, hospitality and navigation represent the main potential source of litter on the seabed. Fishing activities ranked second, with greater relative weight in the autumn campaign. The presence of wastewater-related litter was low and mainly located in areas close to outfalls.

“It should be noted that the study focused exclusively on litter deposited on the seabed, that is, items that have sedimented. This means that litter floating or suspended in the water column — which has greater mobility in the water mass — has not been considered,” explains Carla Alfonso, one of the project coordinators. She also notes that “the determination of the possible origin of the objects identified is based on a probabilistic methodology, so this study provides a first approach. The sources indicated should therefore be interpreted as estimates based on the typology of the litter and its distance from the study site.”

The study also detected a variable relationship between litter accumulation and proximity to certain anthropogenic pressures resulting from human activity. In spring, a greater tendency for accumulation was observed in areas close to urban centres, while in autumn the relationship was more evident with proximity to outfalls.

“This pilot study offers an initial characterisation of the litter present in submerged areas closest to the coast — key areas for the islands’ ecology for which there is still little information regarding the impact of plastic pollution,” explained Patricia Martin Cabrera, one of the authors of the study. She also emphasised the importance of the report as “a solid scientific basis to guide future management actions, prevention measures and long-term monitoring programmes in the Balearic Islands.”

Results for Menorca

In Menorca, 42 transects were carried out across a total area of 6,720 m², identifying 95 objects. Of these, 63 items were recorded during half of the spring surveys, corresponding to a density of 1.88 objects per 100 m². In autumn, 32 objects were identified, resulting in a density of 0.95 objects per 100 m² — almost half the spring value.

Of the 20 most frequently identified objects, 73.6% were plastic waste. Nearly half of these (35.79%) were identifiable hard plastic items such as rigid packaging, fragments of plastic utensils, lids or pieces of equipment.

“These first data from Menorca allow us to better understand what is happening with plastic waste in the marine environment. Although the densities detected in Menorca are lower than on the other islands, the fact that nearly three out of four items identified are plastic shows that this material remains a significant problem for our ecosystems, and that we must urgently continue advancing solutions to reduce its use,” says Rebecca Morris, Director of Menorca Preservation.

In Menorca, the collaborating dive centres were Binibeca Diving (Es Grau and Punta Prima), Blue Islands Diving (Macarella and Cala Galdana) and Diving Menorca (Cavalleria, Arenal d’en Castell and Algaiarens).

Results for Mallorca

In Mallorca, thanks to the commitment and support of 24 volunteer divers, 39 transects were conducted across a total area of 3,900 m² at various locations on the island — Cala Anguila, Cala Figuera, Cala Ratjada, Cala en Gossalba, Port d’Andratx, Port de Sóller and Santanyí — where 126 objects were identified on the seabed.

The densities recorded were very similar in both campaigns — 3.29 objects per 100 m² in spring and 3.17 in autumn — reflecting a persistent presence of litter throughout the year. Plastic materials clearly predominated, alongside a significant presence of glass and metal elements. The most common items included fibreglass objects, glass bottles, fragments of non-foamed plastic and fishing-related waste such as nylon lines and lead weights.

“This study allows us to obtain a first approximation of the presence and typology of litter on Mallorca’s seabed. The data point to a clear predominance of plastic materials, along with glass and elements linked to navigation and fishing, consistent with the main activities taking place along our coastline. This information helps us better guide management priorities and continue working with greater knowledge to protect the sea,” highlights Ana Riera, Director of Mallorca Preservation.

In Mallorca, the collaborating dive centres were Mar Balear (Calvià), Mallorca Diving Adventure (Andratx), Soller Divers (Sóller), Skualo Porto Cristo (Porto Cristo), Mero Diving (Cala Ratjada), Cala Santanyí Diving Center (Santanyí) and Tramuntana Diving (Pollença).

Results for Ibiza and Formentera

In Ibiza and Formentera, 55 transects were carried out at seven sites: the Bay of Portinatx, S’Estanyol in the Bay of Portmany, Cala Martina in Santa Eulària and Sa Xanga in Sant Josep in Ibiza, as well as Migjorn, Punta Prima and s’Espalmador in Formentera. The action involved the collaboration of 45 volunteers from various dive centres, including SubFari, Aquadiving, Anfibios, Arenal Diving and Formentera Divers.

Across a total surveyed area of 5,500 m², 134 objects were identified. Regarding object density, the study shows a marked seasonal difference: 2.93 objects per 100 m² in spring, compared with 1.93 per 100 m² in autumn. According to Elisa Langley, who coordinated the initiative for IbizaPreservation, the difference may be because:

“In spring we collected objects that had accumulated over several years in those locations. In autumn, however, we found objects that had accumulated in the six months between the two phases of the study, although variations in local hydrodynamics must also be considered.”

Among the most common items found in the Pityusic Islands were plastic fragments between 2.5 cm and 50 cm, other identifiable hard plastic objects such as bottles of different types, shopping bags, ropes and plastic filaments exclusively associated with fishing.

According to Inma Saranova, Director of IbizaPreservation:

“The data from Ibiza and Formentera confirm a worrying reality: waste associated with tourism and maritime activity accumulates and remains on our seabed. This study finally provides us with a scientific basis to prioritise concrete measures, from prevention to management in ports and regular anchoring areas, including reducing plastics, scheduling underwater clean-ups in temporary buoy fields and ports, and controlling gear losses. The goal is to move towards stable monitoring that protects the coastal habitats supporting our biodiversity and our economy.”

A joint project

The project “Weaving the Future: An Alliance for the Preservation of the Balearic Islands” is led by Mallorca Preservation, IbizaPreservation and Menorca Preservation to address plastic pollution in the archipelago through three complementary lines of action: scientific research, the promotion of a circular economy and public awareness.

The one-year initiative is funded by the musical group Depeche Mode and the Swiss watch brand Hublot, channelled through Conservation Collective, the global network of environmental foundations of which the three organisations are members.

Throughout 2025, the three foundations committed to tackling plastic pollution through three pillars: scientific research, through the present study; circular economy, by promoting a collaborative network in the Balearic Islands aimed at transforming plastic waste into raw material, which brought together more than 30 artisans and artists from across the islands at a gathering in Menorca; and public awareness, through the show “The Magic of Recycling”, which has raised awareness among more than 900 children from the four islands about the importance of the “7Rs”: recycle, reduce, reuse, repair, rethink, refuse and collect.