Life in an extreme environment: Characterizing wave-imposed forces in the rocky intertidal zone using high temporal resolution hydrodynamic measurements

Abstract

Hydrodynamic forces produced by breaking waves make the rocky intertidal zone one of the most physically stressful environments on the planet, and for many ecological studies, it is important to quantify intertidal flows. However, hydrodynamic measurements with a response time rapid enough to reliably identify “impingement events” – large, transient increases in force occurring at wave arrival – have not been made, although impingement events are hypothesized to be the largest hydrodynamic forces in the intertidal zone. We built a custom force transducer to measure short‐duration flows in the intertidal zone, and took measurements of force acting on both a drag sphere and a rigid limpet model. Based on our results, we estimate impingement events occur in 7–14% of waves, and when present, they are the dominant force in the wave. The mean ratio of maximum force to the second largest force within a wave was approximately 1.5 for impingement waves, in contrast to 1.2 for non‐impingement waves. However, contrary to previous hypotheses, impingement events are not necessarily the largest forces imposed on intertidal organisms. At our site, non‐impingement waves recorded on the drag sphere had a mean maximum force 61% greater than the mean maximum force of waves with impingement events. Our results thus suggest that impingement is not necessarily the greatest hydrodynamic danger to organisms. Future studies should use high temporal resolution measurements to identify the largest transient forces regardless of when they occur in a wave, and to assess how such brief forces might affect intertidal organisms.

Attachment strength differs amongst life‐history stages of an intertidal, isomorphic red alga

“…Breaking waves rapidly produce complex, highly‐energetic turbulence in which the primary force experienced by an alga is drag, with rapid changes in velocity associated with impingement of breaking waves (Gaylord et al . ; Jensen & Denny ; Jensen & Denny ). Such hydrodynamic forces place enormous stresses on intertidal algae.…”

“…Intertidal algae on wave-swept rocky shores frequently experience water velocities of 2 m s −1 (Denny 1988), sometimes reaching 25 m s −1 (Denny & Gaylord 2002). Breaking waves rapidly produce complex, highly-energetic turbulence in which the primary force experienced by an alga is drag, with rapid changes in velocity associated with impingement of breaking waves (Gaylord et al 2008;Jensen & Denny 2015;Jensen & Denny 2016). Such hydrodynamic forces place enormous stresses on intertidal algae.…”

Ocean change within shoreline communities: from biomechanics to behaviour and beyond

“…Thus, although attenuated heat and mass exchange to and from the interior of mussel beds may ameliorate thermal and desiccation stresses for resident organisms at low tide, and although analogous reductions in momentum flux at high tide may provide shelter from large hydrodynamic forces that characterize rocky intertidal habitats (e.g. Denny, 1995; Gaylord, 1999, 2000; Gaylord et al., 2008; Jensen and Denny, 2016), tradeoffs can arise. In particular, elevated chemical stresses can manifest within the interstices of dense aggregations of marine organisms during immersion.…”

Comparison of Evolutionary Selection Acting on the Mitochondrial Protein-Coding Genes Between Intertidal and Deep-Sea Gastropods

“…The intertidal zone is the region between the highest and lowest tides, depicting the transition from ocean to terrestrial conditions. Organisms inhabiting this zone are able to maintain mitochondrial homeostasis amidst regular oscillations of immersion and emersion, along with tremendous variations of abiotic factors such as light, temperature, salinity and oxygen concentrations [15]. Consequently, gastropods living in this area need to withstand the dynamic conditions of the intertidal zone.…”