Search for: All records

Abstract Background and AimsThe increased likelihood and severity of storm events has brought into focus the role of coastal ecosystems in provision of shoreline protection by attenuating wave energy. Canopy-forming kelps, including giant kelp (Macrocystis pyrifera), are thought to provide this ecosystem service, but supporting data are extremely limited. Previous in situ examinations relied mostly on comparisons between nominally similar sites with and without kelp. Given that other factors (especially seafloor bathymetry and topographic features) often differ across sites, efforts to isolate the effects of kelp on wave energy propagation confront challenges. In particular, it can be difficult to distinguish wave energy dissipation attributable to kelp from frictional processes at the seabed that often covary with the presence of kelp. Here, we use an ecological transition from no kelp to a full forest, at a single site with static bathymetry, to resolve unambiguously the capacity of giant kelp to damp waves. MethodsWe measured waves within and outside rocky reef habitat, in both the absence and the presence of giant kelp, at Marguerite Reef, Palos Verdes, CA, USA. Nested within a broader kelp restoration project, this site transitioned from a bare state to one supporting a fully formed forest (density of 8 stipes m−2). We quantified, as a function of incident wave conditions, the decline in wave energy flux attributable to the presence of kelp, as waves propagated from outside and into reef habitat. Key ResultsThe kelp forest damped wave energy detectably, but to a modest extent. Interactions with the seabed alone reduced wave energy flux, on average, by 12 ± 1.4 % over 180 m of travel. The kelp forest induced an additional 7 ± 1.2 % decrease. Kelp-associated declines in wave energy flux were slightly greater for waves of longer periods and smaller wave heights. ConclusionsMacrocystis pyrifera forests have a limited, albeit measurable, capacity to enhance shoreline protection from nearshore waves. Expectations that giant kelp forests, whether extant or enhanced through restoration, have substantial impacts on wave-induced coastal erosion might require re-evaluation. 

Abstract Wave‐generated flows, associated hydrodynamic forces, and disturbances created by them play critical roles in determining the structure and health of near‐shore coastal ecosystems. Oscillatory motions produced by waves increase delivery of nutrients and food to benthic organisms, and can enhance vertical mixing to facilitate delivery of larvae and spores to the seafloor. At the same time, wave disturbances can remove individuals and biomass with far‐reaching effects on critical coastal ecosystems and the biodiversity within them. Commercial instruments designed to measure wave characteristics and the effects of wave energy can be expensive to purchase and deploy, limiting their use in large quantities or in areas where they may be lost. We have developed an inexpensive open‐source pressure transducer data logger based on an Arduino microcontroller that can be used to characterize wave conditions for deployments lasting multiple months. Our design criteria centered around simplicity, longevity, low cost, and ease of use for researchers. Housed in ubiquitous polyvinylchloride (PVC) plumbing and constructed primarily with readily available materials, the Open Wave Height Logger (OWHL) can be fabricated in a college setting with basic shop tools. The OWHL performs comparably to commercial pressure‐based wave height data loggers during tests in the field, creating the opportunity to expand the use of these sensors for applications where sufficient spatial replication or risk of instrument loss would otherwise be cost prohibitive.