Cover and edge length to area ratio of seagrass (Thalassia testudinum) meadows in coral reef lagoons (Veracruz Reef System, Southwest Gulf of México)

Abstract

ABSTRACT1. Habitat loss and habitat fragmentation are usually correlated while habitat degradation may occur independently of them. Natural and anthropogenic disturbances increase the spatial fragmentation of seagrass meadows with unknown consequences on the vegetative development achieved by seagrass.2. Cover and spatial fragmentation of Thalassia testudinum meadows in three coral reef lagoons of the Veracruz Reef System,VRS (SW Gulf of Me´xico) were quantified by analysing low-altitude images acquired by photographic and digital video cameras from a helium-filled blimp. Spatial fragmentation was quantified as the ratio of the length of meadow edge to meadow area. The number of blowouts (erosive gaps in seagrass meadows) was also recorded.3. Meadow cover was negatively correlated with the length of meadow edge to meadow area ratio. The number of blowouts per ha of T. testudinum meadow was negatively correlated with meadow cover and positively with the length of meadow edge to meadow area ratio. Wave exposure is probably a main component of the processes determining the cover and spatial fragmentation of T. testudinum meadows in VRS.4. Low cover and high spatial fragmentation of T. testudinum meadows in VRS are associated with low vegetative development of this seagrass species.

Seasonal effects of clams (Panopea generosa) on eelgrass (Zostera marina) density but not recovery dynamics at an intertidal site

“…Competition for space from bivalves can reduce rhizome extension (Reusch and Williams, ) or density of seagrass (Booth and Heck, ) and disturbances are also associated with poor shoot‐level performance (Terrados and Ramírez‐García, ). Interestingly, eelgrass shoots may individually perform better at low density, for instance, by increasing growth or asexual reproduction (Yang, ; Ruesink et al ., ).…”

“…Yet, geoduck clams did have several effects within intact eelgrass meadows, which ranged from abiotic changes (increased porewater ammonium, Figure 1(C)) to modification of eelgrass density (decrease in summer density, Figure 2(A)), clonal branching (Figure 3(D)), and size (Figure 3(A)). Competition for space from bivalves can reduce rhizome extension (Reusch and Williams, 1998) or density of seagrass (Booth and Heck, 2009) and disturbances are also associated with poor shoot-level performance (Terrados and Ramírez-García, 2011). Interestingly, eelgrass shoots may individually perform better at low density, for instance, by increasing growth or asexual reproduction (Yang, 2011;Ruesink et al, 2012).…”

Shifts in biodiversity and physical structure of seagrass beds across 5 decades at Carriacou, Grenadines

“…Within seagrass beds “blowouts”—characterized by an erosional scarp, a seagrass-free blowout floor and a gently sloping seagrass-colonized leeward face—form during high wave energy events and their persistence is dependent on recurrent wave- or current-induced erosion at the scarp face ( S3 Fig ) [ 35 , 87 , 88 ]. Scarps and blowouts generally are absent in more protected, low wave-energy areas [ 35 , 87 , 89 ]. No scarps were observed at LWE sites in 1969 and 1994, but 1 or 2 scarps occurred at 3 of the 4 sites in 2016, suggesting that mean wave energy at those sites had increased sufficiently to maintain their erosion.…”

“…They concluded that these factors were less important than the degradation of adjacent healthy coral reefs in explaining localized erosion within the bay. In a comparison of seagrass beds in three coral reef lagoons of the Veracruz Reef System (SW Gulf of Mexico), Terrados and Ramírez‐García [ 89 ] observed that seagrass cover was lowest, and fragmentation and blowout number highest, by a reef that had been used as a source of building materials. They attribute this to increasing wave exposure in the lagoon through a direct anthropogenic reef-flattening effect.…”

Evidence for ‘critical slowing down’ in seagrass: a stress gradient experiment at the southern limit of its range

“… 79 , have introduced the term ‘recovery length’ as a connectivity distant indication for population recovery. The perturbation size, especially edge to area ratio, is known to affect seagrass recovery time 87 , 88 and its inclusion into critical slowing down assessments will further improve our understanding and prediction to the future of seagrasses.…”