Methodological Bias in Quadrat-Based Monitoring of Posidonia oceanica: A Structured Narrative Review and Framework for Monitoring Standardization

Abstract

Posidonia oceanica meadows form one of the most important coastal habitats in the Mediterranean Sea, providing key ecosystem services including carbon sequestration, sediment stabilization, biodiversity support, and coastal protection. Despite their ecological importance, these meadows have declined in many parts of the Mediterranean over recent decades due to coastal development, pollution, anchoring activities, and climate-related pressures. Detecting such changes requires reliable and comparable monitoring data. Among the available approaches, quadrat-based field surveys remain one of the most widely used methods for describing meadow structure through indicators such as shoot density, percent cover, and leaf biometry. In practice, however, these methods are applied in different ways across monitoring programs. Variations in quadrat size, sampling design, replication strategies, and measurement protocols often make it difficult to compare results among studies or regions. This review examines the methodological foundations of quadrat-based monitoring of P. oceanica and discusses the main sources of bias that may influence monitoring outcomes. A structured literature search identified five recurrent sources of methodological bias across the studies reviewed: sampling design, quadrat size effects, observer variability, depth gradients, and seasonal variability. These factors can affect both the precision of measurements and the interpretation of ecological trends. The review also evaluates commonly used monitoring designs and ecological indices and considers recent technological developments such as photogrammetry, remote sensing, and machine-learning-based image analysis that may help reduce some methodological limitations. Drawing on this synthesis, a conceptual framework is proposed linking sources of methodological bias with their potential consequences for monitoring outcomes, and practical recommendations are outlined to improve methodological consistency and enhance the comparability of P. oceanica monitoring across the Mediterranean basin.

Plant phenotyping relevance

Posidonia oceanicaの構造形質を測定する方形区モニタリング手法のバイアスと標準化を中心に扱う方法論レビューであり、植物フェノタイピング手法が中心的です。

Code and data availability

This is a structured narrative review of quadrat-based Posidonia oceanica monitoring methods. The Data Availability Statement explicitly states no new data were created or analyzed, and no public phenotype datasets, images, code, models, or supplements containing paper-specific phenotyping assets are mentioned. Seagrss

No evidence-backed public reproduction asset is currently recorded.