The impact of beach grooming on coastal habitat

A new study from Southern California affirms that the long-standing management practice of beach grooming is contributing to the loss of coastal strand habitat. Coastal strand plant communities grow along the edge of the high tide line and are comprised largely of endemic species adapted to grow in the dynamic environment of loose, shifting sand. Large stretches of coastal strand and dune habitat have been lost in Southern California and other regions due to a combination of factors including development and human use.

Jenifer Dugan and David Hubbard from UC Santa Barbara's Marine Science Institute published results showing that beach grooming directly and indirectly affects native coastal strand vegetation resulting in bare sand zone expansion. In southern California, a large portion of the coast is mechanically groomed or raked (>170 km) with heavy equipment. This seemingly beneficial practice removes macrophyte wrack - primarily kelp - and trash pollution.

The researchers surveyed 24 difference beaches (12 groomed and 17 ungroomed) between Santa Barbara and San Diego County. The surveys documented unvegetated, dry sand as well as cover and composition of dune vegetation and wrack.  They also conducted field experiments in which they seeded and raked plots at San Buenaventura State Beach to further support any findings.

Both the surveys and experiments exhibited detrimental effects from beach grooming. On average, unvegetated zones were four times wider on groomed beaches (108 m) than ungroomed beaches (27 m). The average cover of coastal strand vegetation was higher on ungroomed beaches (1.86 m), while groomed beaches contained no measurable cover. Species richness was also significantly higher on ungroomed beaches (4.3 species/ km) compared to groomed beaches (1.2 species/ km).

Plant performance was also consistently poorer on groomed beaches. Seed bank presence and recruitment suffered in the experimental plots - two native species were recruited in the unseeded plots of the ungroomed section (A. leucophylla and A. chamissonis), while no native plants were recruited on the groomed plots. The plants that were recruited in the groomed plots tended to grow slowly and rarely survived the summer seasons. Plants in the groomed plots did not produce flowers or seeds.

In the face of rising sea level, sediment accretion has become a main concern for coastal ecosystem survival. Reduced vegetation in these new, bare sand habitats inhibits sand capture and thus decreases sand accumulation. Although these effects seem severe, the authors state that beaches are able to self- restore once grooming has ceased. They also suggest that if coastal mangers devised “ a scheme of grooming in which designated longshore stretches or ‘islands’ of beach are left ungroomed year-round, [that] could represent a far more ecologically effective approach than seasonal grooming of the entire stretch of beach.”  

--Reviewed by Evyan Borgnis

Dugan, J., & Hubbard, D. (2009). Loss of Coastal Strand Habitat in Southern California: The Role of Beach Grooming Estuaries and Coasts DOI: 10.1007/s12237-009-9239-8