Understanding the density patterns of the polychaete Diopatra neapolitana and its relationship with environmental factors in the NW Spain

To understand the density patterns of the tube-forming polychaete Diopatra neapolitana and their relationship with environmental factors, an extensive sampling was conducted in an intertidal, commercially exploited population in the Ría de Vigo (NW Spain). Interpolation of the sampled densities was carried out by Inverse Distance Weighting (IDW). The results showed a heterogeneous, patchy distribution: the average density was 2.56 tubes/0.25 m 2, although some areas exhibited a density with more than 30 tubes/0.25 m 2 while in others the species was completely absent. Our data also showed that the presence of vegetation (either algae or Zostera ) increased the densities of D. neapolitana. To better understand this finding, a second sampling was conducted targeting the three main permanent habitats identified in the study area. This revealed that the spatial location within the intertidal was the most important factor affecting densities. The higher densities observed with increasing latitude and longitude are a consequence of the higher flooding time, that means less water stress and longer submergence time, and involves a reduced likelihood of being caught by shellfish harvesters. The second most important factor explaining D. neapolitana densities was the sediment organic matter content, which is consistent with the observation that the presence of vegetation increases the density of tubes. This work is the first comprehensive approach to understand the spatial structure of densities of D. neapolitana.