The role of competitor, stress-tolerant and opportunist species in the development of indexes based on rocky shore assemblages for the assessment of ecological status

Pinedo, Susana Ballesteros, Enric. Ecological Indicators 107 : 105556 (2019)  DIGITAL CSIC

The existence of three different ecological strategies (competitor, stress-tolerant, opportunist) has been widely recognized in the scientific literature and in the development of several biotic indexes using marine macroinvertebrates. However, its use has been totally neglected in the creation of indexes dealing with macroalgal assemblages and developed to fulfill the requirements of the European Water Framework Directive. In this study we apply a new method considering these different ecological strategies to assess the Ecological Status (ES) in rocky shores, which are mostly macroalgal-dominated. We use a large data set consisting of 653 samples collected between 1999 and 2017 in Catalonia (northwestern Mediterranean). In this approach we distinguish four basic strategies (competitor, indifferent, stress-tolerant and opportunist). Our results emphasize the importance in the distinction between competitor and stress-tolerant species when calculating the ES and highlight the importance of good natural history knowledge prior to appropriately assign every species to the proper ecological strategy. On the other hand, the comparison of ES obtained with the application of the new method based on the four strategies and the Ecological Evaluation Index (EEI-c) and R/P ratio Index (R/P rt. I) shows that the combination of eco-physiological traits, morphology and life-history strategies involved in EEI-c and R/P rt. I indices does not work in detecting differences in ES. Finally, if we take into account not only the algae but also the invertebrates that sometimes are dominant organisms in rocky shore assemblages (e.g. mussels), results become more accurate.