Selection of metrics based on the seagrass Cymodocea nodosa and development of a biotic index (CYMOX) for assessing ecological status of coastal and transitional waters

Trends of the seagrass <em>Cymodocea nodosa</em> (Magnoliophyta) in the Canary Islands: population changes in the last two decades

“…As a result, at local scales, the most representative structural attribute of C. nodosa to describe seagrass meadow integrity, at least from the perspective of temporal variation, is seagrass shoot density. This result apparently contrasts with those obtained by Oliva et al (2012), who selected alternative structural descriptors of C. nodosa to assess the quality of coastal waters. However, the scale of both studies is different.…”

“…The dimension of this study, including a large data set of records (684), different sources (49), and the temporal scale (over two decades), support the reliability of our interpretations. The overall decline experienced by C. nodosa meadows represents a further warning and an incentive to encourage research on C. nodosa conservation, particularly as a result of the importance of this species as a 'habitat engineer' and its sensitivity to deteriorating environmental conditions, which may be indicative of the state of the marine environment (Oliva et al 2012).…”

“…Seagrass coverage corresponds to the percentage of the bottom covered by C. nodosa, normally taken along 25-m transects, so it does not take into account the density of seagrass shoots and, most importantly, the overall area occupied by the seagrass. In other words, this descriptor measures the percentage of surface covered by the seagrass, but not the state of the meadow, a condition that, at least in the particular case of C. nodosa, is better explained by shoot density (Oliva et al 2012, Tuya et al 2014a. Consequently, even if a meadow has undergone regression by reducing its overall area and shoot density and then its integrity, this may not be revealed by the analysis of the coverage.…”

“…However, the scale of both studies is different. On the one hand, Oliva et al (2012) aimed at selecting seagrass structural attributes across spatial gradients in coastal water quality. The effect of pollution was better predicted by structural attributes that reflect the consequences of pollution, e.g.…”

“…Cymodocea nodosa (Ucria) Ascherson is a seagrass distributed across the Mediterranean Sea and along the nearby eastern Atlantic coasts, including the Macaronesian oceanic archipelagos of Madeira and the Canary Islands (Mascaró et al 2009, Oliva et al 2012). This marine spermatophyte plays a fundamental role as a result of its function as 'habitat engineer', particularly in the Canary Islands (Reyes et al 1995, Tuya et al 2014a.…”