How coastal bluffs support shorelines: Guiding protection and recovery efforts

Jenn Hoskins
16th October, 2025

How coastal bluffs support shorelines: Guiding protection and recovery efforts

While built to protect the coast, this rock armor could actually degrade beach ecosystems, according to the study.

Image adapted from: Toft et al. / CC BY (Source)

Key Findings

  • This study, conducted in the Salish Sea, Washington, USA, found that natural, unarmored bluffs support significantly higher overall ecological health compared to armored bluffs
  • Removing shoreline armor does not fully restore beach health to levels seen in natural bluffs, suggesting that the presence of armor itself causes lasting damage
  • The amount of wrack, logs, and overhanging vegetation on the upper beach are the strongest indicators of overall beach ecological function
Coastal bluffs naturally erode, supplying sand to beaches – a process vital for maintaining shorelines. However, increasing development often leads to the construction of artificial structures like seawalls and bulkheads (collectively termed ‘armoring’) to protect property, disrupting this natural sediment flow. A recent study by researchers at the University of Washington and the U.S. Geological Survey[1] investigated the ecological consequences of shoreline armoring and assessed the potential benefits of restoration efforts in the Salish Sea, Washington, USA. The study focused on identifying beaches with the highest and lowest priority for management interventions, either restoring natural sediment supply (removing armor) or protecting existing natural sediment sources (preventing new construction). The goal was to determine if these prioritized beaches differed in their ecological health and physical characteristics. Recognizing that shoreline hardening reduces ecosystem services[2], the researchers aimed to quantify these differences and inform more effective coastal management strategies. To assess beach health, the team sampled 30 different metrics across the entire beach profile, from the top of the bluffs down to the low tide line. These measurements included the abundance and types of plants growing on the bluffs (riparian vegetation), the invertebrates living in the sand and water, the presence of large woody debris like logs, the amount of organic matter washed ashore (beach wrack), fish populations, and the characteristics of the sand itself, such as its size and how evenly sorted it was. The researchers then grouped the beaches into four categories based on their management priority and armoring status: “Protect High” (natural, high priority), “Protect Low” (natural, low priority), “Restore High” (armored, high priority), and “Restore Low” (armored, low priority). They calculated an average ‘beach function’ score for each group, allowing them to compare the ecological health of beaches under different management scenarios. The results showed a clear pattern: beaches with natural, unarmored bluffs – both “Protect High” and “Protect Low” – had significantly higher overall ecological function, scoring more than double the function of beaches with armoring (“Restore High” and “Restore Low”). Importantly, the “Restore High” group only showed a slight improvement over “Restore Low”, suggesting that simply having the potential for sediment supply isn’t enough; the presence of armoring itself causes consistent degradation. Statistical analysis revealed that the upper beach environment – specifically the amount of wrack, logs, and overhanging vegetation – were the strongest predictors of overall beach function. This is consistent with findings from other research demonstrating the importance of organic matter subsidies like wrack and carrion in supporting beach ecosystems[3]. The researchers noted that metrics related to the lower beach environment and bluff geomorphology were more variable, likely due to differences in location and distance from the eroding bluff. This study builds upon previous work highlighting the negative impacts of shoreline hardening on biodiversity and organism abundance[2]. While earlier research focused on broad comparisons between armored and natural shorelines, the study refined this understanding by incorporating a prioritization scheme based on potential sediment supply. This allowed the researchers to demonstrate that even beaches with limited sediment source potential benefit significantly from remaining unarmored. The findings emphasize that maintaining natural bluff erosion processes is crucial for supporting coastal ecosystems, and that restoration efforts focused on removing armoring can substantially improve beach health, potentially doubling ecological function.

EnvironmentSustainabilityEcology

References

Main Study

1) Functions of coastal feeder bluff systems: Implications for prioritizing protection and restoration

Published 15th October, 2025

https://doi.org/10.1371/journal.pone.0334742

Related Studies

2) Ecological Consequences of Shoreline Hardening: A Meta-Analysis.

https://doi.org/10.1093/biosci/biw091

3) The role of inputs of marine wrack and carrion in sandy-beach ecosystems: a global review.

https://doi.org/10.1111/brv.12886


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