Identifying suitable proxies for climate change impacts in shallow Mediterranean habitats: sponge filtration not a ready-to-use tool yet

The identi#cation of reliable proxies is crucial to undertake experimental manipulation and test hypotheses on climate change impacts. We evaluated the potential use of sponge #ltering activity as a proxy for the e$ect of temperature (T) increase in shallow marine habitats since: i) Porifera are ubiquitous, sessile and long-lived aquatic organisms; ii) Porifera are active #lter feeders and play a key-role in benthic-pelagic coupling; iii) #ltering activity already proved reliable to detect T e$ects on bivalves. The systematic screening of current literature to gather data and test the assumption “T increase -> increase in sponge #ltering activity” led to a #rst list of 840 sources (title relevance level). After abstract screening, 85 documents related to Porifera #ltration or feeding activities were retained. Yet, information and results are highly heterogeneous in terms of purpose of study, species, habitat, methods and measured units. A high fraction of studies do not report #ltration data and less than 10% include relevant information about T. Given such dispersion of data, formal meta-analysis may not be performed and the assumption could not quantitatively be tested, thus evidencing a knowledge gap that needs further research e$orts. At the state of the art, sponge #ltering activity is not a ready-to-use proxy for climate change.