Effects of intertidal exposure in mussel lysosomes

Tide is a relevant source of variability for intertidal organisms in terms of general physiological and metabolic responses, as it includes intermittent environmental changes in several stress sources such as desiccation, temperature and wave action, as well as in food and oxygen availability. In this study we investigated the variations of lysosomal structures/functions and the condition index in mussels, Mytilus galloprovincialis, from various tidemark levels in two different coastal environments in the Northern Adriatic Sea — transitional (Lagoon of Venice) and open-sea (8 miles off-shore) areas. In each sampling site organisms were collected in May 2008, at different depths within the vertical zonation of the native population, either in the intertidal zone — i.e. both at the highest and the lowest zonation limits, and subtidally. In general, lysosomal parameters and condition index concurred to highlight the better health status in subtidal mussels. In addition, the Neutral Red Retention assay, used to evaluate membrane stability in haemocyte lysosomes, and the condition index, helpful in assessing the whole physiological status, indicated a clear continuous gradient among the three different tidemark levels. Intriguingly, levels of lipofuscins and neutral lipids, as well as values of lysosomal enlargement — evaluated in the digestive cells, highlighted more stressful conditions in the lower intertidal zone.