Clonally transmissible cancers are tumour lineages that are transmitted between individuals via the transfer of living cancer cells. In marine bivalves, leukaemia-like transmissible cancers, called hemic neoplasia (HN), have demonstrated the ability to infect individuals from different species. We performed whole-genome sequencing in eight warty venus clams that were diagnosed with HN, from two sampling points located more than 1000 nautical miles away in the Atlantic Ocean and the Mediterranean Sea Coasts of Spain. Mitochondrial genome sequencing analysis from neoplastic animals revealed the coexistence of haplotypes from two different clam species. Phylogenies estimated from mitochondrial and nuclear markers confirmed this leukaemia originated in striped venus clams and later transmitted to clams of the species warty venus, in which it survives as a contagious cancer. The analysis of mitochondrial and nuclear gene sequences supports all studied tumours belong to a single neoplastic lineage that spreads in the Seas of Southern Europe.

The fan mussel Pinna nobilis is a long lived species endemic to the Mediterranean Sea and is considered one of the biggest bivalve molluscs of the Mediterranean. A multitude of threats has provoked a great reduction in P. nobilis populations. To increase the knowledge about the recruitment period and number of Pinna nobilis recruits, two types of recruitment devices were deployed in July 2007 on a Marine Protected Area of Palma Bay, Mallorca (western Mediterranean). A total of 614 juveniles of P. nobilis, with a mean length and width of 2.76±0.04 and 1.10±0.01 cm respectively, were collected inside the artificial microhabitat generated by the knots of ‘device Type I’. Similarly, 691 P. nobilis were recruited with a mean length and width of 5.38±0.08 and 2.10±0.04 cm respectively from ‘device Type II’. Moreover, in the year 2007, the present study determined that P. nobilis recruitment takes place between the last week of August and the first week of September. This study produces some crucial information for effective protection and conservation of the fan mussel. Moreover, a Pinna nobilis artificial recruitment with seed collectors would permit an alternative tool for field studies without compromising the concentration of the vulnerable populations of this mollusc.

A devastating mass mortality event (MME) very likely caused by the protozoan Haplosporidium pinnae first detected in 2016 in the Western Mediterranean Sea, is pushing the endemic bivalve Pinna nobilis to near extinction. Populations recovery, if possible, will rely on larval dispersal from unaffected sites and potential recolonization through recruitment of resistant juveniles. To assess the impact of the MME on the species’ larval recruitment, an unprecedented network of larval collector stations was implemented over several thousands of kilometers along the Western Mediterranean coasts during the 3 years after the onset of the MME. The findings of this network showed a generalized disruption in recruitment with dramatic consequences for the recovery of the species. However, there were exceptions to this pattern and recruits were recorded in a few sites where the resident population had been decimated. This hints to the importance of unaffected populations as larval exporting sources and the role of oceanographic currents in larval transport in the area, representing a beacon of hope in the current extremely worrying scenario for this emblematic species.