Modern polychaete reefs in Western Mediterranean lagoons: Ficopomatus enigmaticus (Fauvel) in the Albufera of Menorca, Balearic Islands

The calcareous serpulid worm Ficopomatus enigmaticus (Fauvel) is prominent in the coastal lagoon of the Albufera of Menorca, where it encrusts “hard substrates”. Its bioconstructions differ in shape depending on location, substratum and water level. This worm occurs along the entire littoral area, forming a continuous layer up to 3 m thick. On the bottom of the lagoon, they develop as micro-atolls (in the shallowest areas) and patch reefs (over 2 m height and 4 m in diameter) encrusting molluscan shells, boulders and small rock outcroppings. Although the worm needs a hard substratum for fixation, growth over molluscan shells can result in a spread-out worm reef overlying a muddy substrate. Fluctuations in water level causes death of the emergent parts of the reef, although these are easily recolonized when the environmental conditions change. The best physico-chemical conditions for the development of Ficopomatus on these islands seem to be in the Albufera of Menorca, where it attains an annual production in dry weight of 21.269 kg m−2 yr−1. The environmental conditions present are 9.6–27.2°C temperature, 9.5–30.0‰ salinity, 1.75–3.75 meq 1−1 alkalinity and 36–202% oxygen saturation, of annual oscillation. The rapid and spectacular growth of these bioconstructions that occurs in the coastal lagoon can cause change in the ecological dynamics. The lagoon can be progressively filled up by reefs and skeletal debris of serpulids and associated benthic organisms.