Grazing in the dark: A behavioural adjustment in a population of the black sea urchin Arbacia lixula.

In Mediterranean rocky shores, the black sea urchin Arbacia lixula is often associated with communities dominated by encrusting corallines, devoid of fleshy algae. While it is commonly known as a diurnal herbivore, this species also migrates at night from hidden to more exposed habitats. Here, we provide the first experimental evidence of an adjustment to a predominant nocturnal behaviour in a population of A. lixula. Sea urchin densities changed from nearly zero during daytime to more than 16 urchins m-2 at night in treatment plots where the sea urchins were removed. We suggest that the observed behaviour was triggered by our experimental manipulations and was a response to the presence of dead conspecifics and small predatory fishes attracted by the urchin culling. Further research is needed to assess whether our findings can be generalised to the behaviour of A. lixula in areas where sea urchins are under strong pressure from diurnal predators. In these cases, it is important to perform sea urchin density counts at night to avoid misleading assessments about the herbivore pressure in a littoral area.

A further review of European Magelonidae (Annelida), including descriptions of Magelona equilamellae and Magelona filiformis.

Following on from the partial review of European Magelonidae by Fiege et al. (2000), a dichotomous identification key, a table of characters and images of all nine known European magelonid species are provided. Magelona equilamellae is redescribed highlighting several features not reported originally by Harmelin. Notably the thoracic neuropodial lamellae, which are initially prechaetal but become distinctly postchaetal by chaetiger 7, an additional character allowing separation from the morphologically similar Magelona alleni. Records suggest that M. equilamellae is a Mediterranean species, more commonly occurring in shallow, transitional waters. Several new characters for Magelona filiformis are additionally highlighted as well as a number of corrections to the existing description, including the number of prostomial ridges, presence of abdominal lateral pouches, morphology of chaetiger 9, and the presence of smaller abdominal hooded hooks adjacent to lateral lamellae. The first image of M. filiformis minuta is provided, and its synonymy with M. filiformis further supported.

Macrobenthic assemblages, sediment characteristics and heavy metal concentrations in soft-bottom Ebre Delta bays (NW Mediterranean).

The spatial distribution of soft-bottom macrofaunal assemblages and their relationship with sediment characteristics were examined in two semi-enclosed shallow-water bays (Alfacs Bay and Fangar Bay) in the Ebre Delta (Catalonia, NW Mediterranean) during 2006 and 2011. Three assemblages were identified: group 1, present in sediments that contain a high percentage of silt-clay, small median particle size and high organic matter content and located at the most external areas of both bays and in the central basin of Alfacs Bay; group 2, present in the shallow northern platform in Alfacs Bay and in both platforms in Fangar Bay, the locations which feature highly variable sediment characteristics; and group 3, present in the shallow areas of both bays, which are characterised by low silt-clay and organic matter content. In Alfacs Bay, the differentiation of these assemblages has persisted since 1987, independently of the increase in organic matter content and heavy metal concentrations and of the shift in macrofaunal composition that have occurred over the past 20 years, most likely the result of increased agricultural activity.