title used in an account of west-coast marine invertebrates entitled A Snail's Odyssey
  Habitat & community ecology
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  Other hazards of intertidal life
  Considered in this section is the topic of other hazards of intertidal life, while topics of INTRASPECIFIC COMPETITION andINTERSPECIFIC COMPETITION are dealt with in other sections.
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Research study 1

graph showing body sizes of barnacles Balanus glandula at 2 sites differing in degree of wave exposuremap of study sites in San Juan Island, Washington for observation of log-battering damage to barnacles Balanus glandulaIntertidal acorn barnacles are susceptible to damage from floating objects that bump and slide their way along the shore.  Do barnacles at sites subjected to more impact from debris have morphological features that make them more resistant to crushing than barnacles from less impacted sites?  This question is addressed in a study in San Juan Island, Washington in which graph comparing opercular depths in barnacles Balanus glandula at sites differing in amount of wave actionsolitary barnacles Balanus glandula from 2 sites graph showing shell mass of 2 populations of barnacles Balanus glandula differing in degree of wave exposure8km apart and differing in degree of wave exposure and impact from floating debris are compared.

Detailed measurements of body dimensions at both sites show that individuals at the more wave-exposed site (Cattle Point) have lower shells (see graph above Right), more massive shells (see graph lower Right), and a more protected placement of their opercular valves (see graph above left) than barnacles at a more wave-protected site (False Bay).  Moreover, when subjected to a standardised impact, barnacles from the exposed site are more resistant to crushing both on first impact and, for those surviving, on a second impact 2wk later.  The author considers that the difference in shell morphology, plus “remodelling” following small non-lethal impacts, provides improved resistance to crushing in the exposed population.  Additionally, the author’s data indicate features of morphology that allow prediction of a barnacle’s ability to resist crushing by impact, independent of site of origin. Pentcheff 1991 Mar Biol 110: 399.

NOTE  impact differences are assessed by attaching aluminum “honeycomb” frames to intertidal rocks at each site and leaving them for periods ranging from 20-107d.  Impact intensity, measured as % area dented per day, is over 240 times greater at the wave-exposed site (Cattle Point) than at the wave-protected site (False Bay)

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Research study 2

graph showing effect of trampling on percentage cover of brown alga Fucus gardneriAnother source of abrasive damage to barnacles and other sessile intertidal organisms is foot traffic associated with casual beach walkers, students on field trips, and university and other researchers.  There are only a few published assessments of this cause of mortality, but a recent study in San Juan Island, Puget Sound by University of Washington researchers shows that such effects are measurable and vary among different taxa.  The area in question, a foreshore in San Juan County Park, is regularly frequented by visitors and so has a “control” degree of wear.  To assess the effect of “augmented trampling”, the researchers establish 6 experimental strips of about 5m length perpendicular to the shore in the upper Fucus/Balanus zone and 6 adjacent control strips, then walk a defined area along each experimental strip 3 times per week with 250 steps over a 6wk period in springtime.  Impact on 5 taxa of algae and invertebrates is assessed by percentage change in cover over the 6wk treatment period and for several months post-treatment.  Results are significant only for the photograph showing log or foot damage to barnacles Balanus glandulabrown alga Fucus gardneri (see graph; 70% decline in cover).  Other taxa, including 3 species of barnacles Balanus glandula, Chthamalus stellatus, and Semibalanus cariosus, several species of motile gastropods, and other species of algae show expected trends but no statistical significance.  In most cases, as can be seen in the graphed data for F. gardneri, effects may extend for some time beyond the treatment period.  The authors comment on management challenges in foreshore parks to protect the natural habitat yet still provide access for visitors. Jenkins et al. 2002 Natural Areas J 22 (4): 260. 

Foot- or log-caused damage to bed of barnacles Balanus glandula.
Note the new colonisers, already several months old 0.3X