Pen shell mass mortality recorded in the Mediterranean

Pen shell (Pinna nobilis) populations are rapidly decreasing in the Mediterranean due to a parasitic disease caused by a protozoan of the genus Haplosporidium. First cases have been recorded among the populations in the south-east of the Iberian Peninsula and Balearic Islands in late 2016 causing the mortality of around 99% of individuals. For the last year and a half the disease has infected most of the populations in the Western Mediterranean and is spreading along the Central Mediterranean.

One of the visible symptoms of the infection is absence of the reaction to stimuli like the inability to close their shells. Bivalves are filter-feeders which means they collect organic particles and planktonic organisms and digest them with the secretion from the digestive gland. The death of pen shells infected by the parasite is attributed to direct blockage of the digestive gland where the parasites breed.

Based on the currently available information the International Union for Conservation of Nature (IUCN) is proposing a series of measures in order to slow down this epidemic:

  1. Identification of the hotspots with high density of pen shell populations.
  2. Increased monitoring of the Pinna nobilis and Pinna rudis population status by visual means, observing the changes on the shells, as well as carrying out periodical tissue biopsies to determine the presence of the parasite.
  3. Establishment of a protection programme for the healthy populations inside the affected zones. The programme should include reduction of anthropogenic impacts, declaration of temporary protected areas and exclusion cages around specific individuals to decrease predation.
  4. Captivity breeding programme establishment with the aim of repopulation.

You can read more about pen shell mass mortality on this link.