An Integrated Traits Resilience Assessment of Mediterranean fisheries landings.

An increasing number of studies have been examining the functional configuration of biological communities or ecosystems using biological traits. Here, we investigated the temporal dynamics and resilience of the traits composition in Mediterranean fisheries landings over 31 years (1985-2015). We transcribed the FAO Mediterranean landings dataset for 101 marine species into a dataset of 23 traits related to the life cycle, distribution, ecology and behaviour. Mediterranean mean Sea Surface Temperature (SST) was evaluated as a potential driver of the traits composition. Trait dynamics were evaluated both individually and holistically by developing an Integrated Traits Resilience Assessment (ITRA). ITRA is a variation of the Integrated Resilience Assessment (IRA), a method to infer resilience dynamics and build stability landscapes of complex natural systems. Changes in landings trait dynamics were documented both for individual traits and for the entire traits 'system', and a relevant regime shift was detected in the second half of the 1990s. The traits system switched to higher optimal temperature, more summer spawning, shorter life span, smaller maximum size, shallower optimal depth and planktivorous diet. This shift was found to be a lagged discontinuous response to sea warming, which gradually eroded the resilience of the original state of the traits system, leading it into a new basin of attraction. The inclusion of ecological/response traits (related to environmental preferences) in our analyses indicates potential mechanisms that explain the observed shift, while changes in functional/effect traits indicate potential impacts on ecosystem functioning. Our findings suggest that changes in the Mediterranean ecosystems are evidently larger than previously thought, with profound implications for the management of this highly impacted sea. ​.

Trait-based life strategies, ecological niches, and niche overlap in the nekton of the data-poor Mediterranean Sea.

Biological traits can determine species ecological niches and define species responses to environmental variation. Species have a specific functional position in the biological community, resulting in interactions like interspecific competition. In this study, we used biological traits in order to define the life strategies of 205 nektonic species of the Mediterranean Sea. Furthermore, traits related to resource use were analyzed to determine the level of trait and niche overlap and their relationship to life strategies. Focusing on habitats of importance (Posidonia beds, coralligène formations, and lagoons), we investigated strategies and niches of the species present there. Finally, we examined the life strategy of Lessepsian species and investigated the niche overlap between them and indigenous species. Archetypal analysis indicated the existence of three life histories corresponding to strategies already documented for fish (equilibrium, periodic, and opportunistic), with some species also placed in intermediate positions. Niche overlap was evaluated by multiple correspondence analysis and the generation of a single distance metric between all species pairs. This identified species occupying relatively empty (underexploited) ecological niches, like the Lessepsian species Siganus luridus and S. rivulatus, a finding that can also be associated with their establishment in the Mediterranean. Most Lessepsian species were associated with the opportunistic life history strategy, again an important aspect related to their establishment. Also, we documented that most species occurring in important habitats have a relatively high overlap of niches. No significant differences were found in the life strategies across Mediterranean habitats; however, variation in niche overlap and traits related to habitat use was detected. The findings can be useful to determine theoretical competition between species and to identify empty ecological niches. Fisheries science can also benefit from comprehending the dynamics of competing stocks or predict the responses of data-poor stocks to anthropogenic stressors from known examples of species with shared life strategies.

Mediterranean nekton traits: distribution, relationships and significance for marine ecology monitoring and management.

Biological traits are increasingly used in order to study aspects of ecology as they are related to the organisms' fitness. Here we analyze a dataset of 23 traits regarding the life cycle, distribution, ecology and behavior of 235 nektonic species of the Mediterranean Sea in order to evaluate the distribution of traits, identify rare ones, detect relationships between trait pairs and identify species functional groups. Trait relationships were tested using correlation and non-linear regression for continuous traits, parametric and non-parametric inference tests for pairs of continuous-categorical traits and cooccurrence testing for categorical traits. The findings have significant implications concerning the potential effects of climate change (e.g., through the relationships of the trait of optimal temperature), fisheries or habitat loss (from the relationships of traits related to tolerance ranges). Furthermore, some unexpected relationships are documented, like the inversely proportional relationship between longevity and age at maturity as a percentage of life span. Associations between functional traits show affinities derived from phylogenetic constraints or life strategies; however, relationships among functional and ecological traits can indicate the potential environmental filtering that acts on functional traits. In total, 18 functional groups were identified by Hill-Smith ordination and hierarchical clustering and were characterized by their dominant traits. For the assessment of the results, we first evaluate the importance of each trait at the level of population, community, ecosystem and landscape and then propose the traits that should be monitored for the regulation and resilience of ecosystem functioning and the management of the marine ecosystems.