Size-Density Relationships: a Cross-Community Approach to Benthic Macroinvertebrates in Mediterranean and Black Sea Lagoons

Cross-community scaling relationships (CCSRs), which result from individual density scaling with average individual body size at guild and community levels, enable investigation of energy constraints at high levels of the ecological hierarchy. Here, we studied cross-community scaling relationships in benthic macroinvertebrate guilds in 15 Mediterranean and Black Sea lagoon ecosystems characterized by strong habitat heterogeneity and high energy density, using data already available in the LifeWatch-Italy data portal. The study sought to describe CCSR patterns in lagoon ecosystems, analyzing their variability across habitat and ecosystem types and evaluating the relative influence on individual body size, macroinvertebrate guild density, or both, of proxies of ecosystem properties, including physiographic characteristics and external disturbance, acting as potential drivers. Significant CCSRs were observed in benthic macroinvertebrate guilds in Mediterranean and Black Sea lagoons. They were characterized by high internal variability and slopes less negative than the metabolic scaling theory expectation (b = -0.75), ranging between b = -0.27 and b = -0.50. Lagoon ecosystem typology, inter-lagoon variation, and ecosystem properties explained part of the variation in internal CCSRs, while habitat variation and intra-ecosystem habitat heterogeneity did not show any influence. CCSR intercepts expressing macroinvertebrate-specific densities showed patterns of variation that were consistent with those of proxies of ecosystem energetics and parsimony, such as eutrophication, chemical and physical disturbances, and openness. These relationships highlight the relevance of CCSRs, which enable inferences on the properties, functioning, and ecological status of ecosystems from simple analyses of community structure.