A critical approach to the use of published data for baseline characterisation of marine fish assemblages: An exercise on Portuguese coastal waters

Policy-makers are becoming increasingly aware of the importance of coastal fish communities for the integrity of marine habitats. However, initial assessments are often done prior to any major funding and available published data is sometimes seen as a low-cost approach to this problem. The present work constituted an exercise on marine fish assemblage characterisation, by relying only on published data from mainland Portugal, covering soft substrate areas and near-shore rocky reefs. Regardless of the characterisation itself, this exercise aimed to critically approach these procedures, by pinpointing problems and highlighting achievements. Criteria were defined for the inclusion of published studies and included datasets were standardised in terms of species proportions, spatial and temporal scales. Species were assigned to ecological guilds and all analyses were performed separately for species and guild data. The influence of season, depth and latitude were analysed through multivariate analysis of variance using permutations and distance-based linear models and assemblages were characterised based on multivariate ordination and hierarchical classification methods. Significant differences were found between studies employing different methods in rocky reefs and outliers were not used in assemblage characterisation. Due to limitations in spatial and temporal detail in published data, only a rough, large scale characterisation of assemblage types was accomplished, with datasets divided in rocky reefs, shallow soft-substrate (0–20 m), intermediate soft-substrate (20–100 m) and deep soft substrate (100–200 m). No seasonal differences were detected, but a non-linear relationship with latitude was found in deep soft-substrate assemblages. During the exercise, spatial and temporal scales were forced by the quality of the data and some analyses failed to detect known patterns. Differences between methods, designs and types of data required assumptions to be made regarding data comparability. Overall, the exercise provided a hands-on insight into the use of published data for planning in a coastal management context, pinpointing data comparability, scale and information gaps as severe limitations of these approaches. In order to improve planning and design, some proposed measures were highlighted, such as the establishment of national databases and the use of pilot studies.