Actual status of the sea urchin Diadema aff. antillarum populations and macroalgal cover in marine protected areas compared to a highly fished area (Canary Islands - eastern Atlantic Ocean)

1. The aim was to determine the status of subtidal rocky benthic assemblages in three marine protected areas (MPAs) of the Canary Islands: (1) La Graciosa; (2) Mar de Las Calmas; (3) La Palma. Sea urchin (Diadema aff. antillarum) populations and non-crustose macroalgal cover were surveyed, and used as an indicator of conservation status in the three MPAs as well as in a highly fished area (HFA-Tenerife Island). 2. Comparing characteristics between each MPA and the HFA, and considering issues of management and design, it was concluded that the three MPAs each have a different conservation status. 'Mar de Las Calmas' marine reserve was found to have the most desirable conservation status, followed by 'La Palma' marine reserve based on sea urchin Populations and non-crustose macroalgae assemblages. 3. Conversely, 'La Graciosa' had the highest density of D. aff. antillarum and the lowest cover of non-crustose macroalgae out of the three MPAs. Values were comparable to those at the HFA, which shows 'La Graciosa' to have the undesired conservation status. 4. Different spatial distribution patterns of non-crustose macroalgal as well as different algal composition cover were observed between the three MPAs and the HFA. These differences were principally attributed to the intensity of grazing activity of the key herbivore D. aff. antillarum. It is suggested that the different study areas correspond to different phase shifts that imply differing resilience of systems that should be taken into a count in future conservation strategies. Copyright (c) 2007 John Wiley & Sons, Ltd.