The ichthyofauna of the Chacahua Lagoon in the western Oaxaca State of Mexico was sampled every 2 months, using a trawl net over seven sampling cycles. The estuary mouth closed in late January, generating hypersaline conditions in the system. A total of 33 species belonging to 20 families were recorded; most of them marine species, showing tropical and subtropical affinities. The most abundant species were Diapterus peruvianus, Centropomus robalito, Anchovia macrolepidota, Lile stolifera, and Lutjanus novemfasciatus. Total fish abundance and species richness were not significantly affected by the mouth closing, and this was related to the presence of a permanently open entrance channel with an adjacent lagoon, which allowed easy exchange of fish between these two systems. Canonical correspondence analysis (CCA) revealed that salinity and dissolved oxygen were the most important environmental variables in determining the observed variability in fish community composition. Two fish groups were evident: the fish assemblage of the lowsalinity period (open-mouth phase), in which Eucinostomus currani, Sciades guatemalensis, Centropomus armatus, Citharichthys stigmaeus, and Caranx caninus constituted the majority of the catch; and the fish assemblage of the high-salinity period (closed-mouth phase), with A. macrolepidota, L. stolifera, and Harengula thrissina as the most abundant species. Multivariate analyses showed differences in the composition of the fish community between both periods. Other species, such as the permanent residents D. peruvianus and C. robalito, which showed the widest range in tolerance of ambient salinity, were caught during both periods. Seasonal succession of fish populations may be related to differences in life cycle and tolerance of the environment among those species adapting to ecological conditions.

Low-crested detached breakwaters (LCDBs) have been widely employed as a mitigation measure against beach erosion. However, only a few studies have assessed their performance in sea-breeze-dominated environments. This work investigates the beach morphodynamics behind LCDBs deployed on a micro-tidal sea-breeze-dominated beach. The study area, located in the northern Yucatán peninsula, is characterized by low-energy, high-angle waves, which drive a persistent (westward) alongshore sediment transport (O(104) m3/year). High-resolution real-time kinematics global positioning system (GPS) beach surveys were conducted over a one-year period (2017–2018) to investigate the performance of LCDBs at three sites. Moreover, unmanned aerial vehicle flights were employed to evaluate far-field shoreline stability. Field observations revealed a distinct behavior in the three study sites, dependent on the breakwaters’ transmission characteristics, geometry, stability, and shoreline orientation. Impermeable LCDBs, made of sand-filled geosystems, induced significant beach accretion (erosion) in up-(down-)drift areas. On the other hand, permeable LCDBs, made of Reef Ball™ modules, induced moderate beach changes and small erosion in down-drift areas owing to higher transmission coefficients. Measurements of LCDBs’ freeboard height show that sand-filled geosystems’ breakwaters presented a significant loss of sand during the study period, which explains the unexpected beach morphodynamic response on the lee side of the structure. Observations suggest that the study area is highly sensitive to the presence of LCDBs with low transmissivity.

The Yucatan coastline has been experiencing beach erosion during the past few decades, reaching critical levels at some locations such as in Chelem beach located near the Progreso Pier. Despite this problem, only few studies have been devoted to investigate the role of coastal structures on explaining the high erosion rates. Therefore, the aim of this work is to evaluate the effects of the 6-km long Progreso Pier on the nearshore wave transformation and alongshore sediment transport in the study area. Field surveys were conducted in a monthly basis to measure the changes in the beach profiles. Furthermore, wave conditions were determined with an ADCP installed at 8 m water depth. Observations confirmed the high erosion trends(1m/year) that have produced coastal infrastructure damage and property loss along 10 km of coast. The wave measurements were employed as forcing on a third generation wave transformation model (MIKE 21 SW). Firstly, the numerical model is implemented in the study area for two different scenarios, with and without the Progreso Pier structure, in order to estimate the nearshore wave conditions. Subsequently, wave conditions predicted at 5 m water depth were employed for the estimation of longshore sediment transport in the study area. The modeling results showed that the pier acts as a large scale wave-sheltering structure that induces important longshore sediment transport gradients during mean wave conditions coming from the NE. On the other hand, during winter storms, when the dominant direction of the waves is from the NNW, the structure does not seem to play an important role on wave transformation into the study area. As a result, the Progreso Pier enhances beach erosion in the Chelem area by inducing longshore sediment transport gradients during mean wave climate and decreasing the capacity of waves to recover the summer beach profile.

Beach width, dune height, and vegetation coverage are key parameters to assess beach resistance and resilience to storms. However, coastal development often causes beach ecosystem degradation due to poor coastal management. We propose a Coastal Resilience Index from Remote Sensors (CRIfRS) for urbanized coasts based on aerial photogrammetry. The study area, located along a 7.8 km stretch of coast on a barrier island, is characterized by persistent alongshore sediment transport and the presence of coastal structures and beach-front houses. Contrary to previous studies, we focus on anthropogenic perturbations (coastal urbanization and coastal structures), instead of hydrodynamic conditions (storms), since erosion in this region is mainly associated with alongshore sediment transport gradients induced by coastal structures. Thus, the CRIfRS is based on the relation of three indicators that affect the beach functionality for coastal protection: beach width, coastal structure influence area, and vegetation coverage. The CRIfRS was divided into five categories: Very Low resilience (VL), Low resilience (L), Medium resilience (M), High resilience (H), and Very High resilience (VH). The CRIfRS presented an important spatial and temporal variability due to changing environmental conditions and the deployment of new coastal structures. For the study period, the percentage of the coast within the VL and L resilience classification increased, whereas the percentage of the coast classified as M, H, and VH resilience decreased. During the winter storm season, the resilience increased mainly due to the cross-shore transport whilst during mean wave conditions (i.e., sea-breeze conditions) the long-shore transport becomes more persistent and thus the coastal structures play an important role interrupting the sediment flux. Additionally, the CRIfRS trajectory shows an overall increase of the L resilience and an overall decrease of the H resilience values. This study highlights the important role of anthropogenic perturbations on the assessment of coastal resilience for highly urbanized coasts. The CRIfRS can help to improve the coastal management by assessing the coastal protection capability of beaches considering both natural and anthropogenic factors.