Zonation of Rocky Shores
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what is zonation?
patterns of organisms on sea shore
what causes the vertical gradient of zonation?
• physical factors-> heat, stress, desiccation, wave shock • biological factors -> reduced feeding time, gas exchange, competition, predation
how does heat stress/desiccation affect zonation?
• varies on small spatial scales • reduction of SA/vol = reduces heat gain and water loss • evaporation cooling aids heat loss • well-sealed exoskeleton aid in retarding water loss • location affects which animals can survive
what are the adaptations to prevent desiccation?
• shape (spherical retains moisture) • aggregate (A. elegantissima) • cover surface in sand and shells • evaporative cooling
how does wave shock affect zonation?
• abrasion: from particles in suspension • pressure: breaking waves can crush structures • drag: can pull organisms off surface and carry organisms from burrows
what kind of organisms have less time to feed?
higher intertidal organisms
what forms grow more slowly than lower intertidal organisms?
sessile
what kind of organisms feed more effectively in lower intertidal regions?
mobile carnivores
when can sessile animals not feed?
unless submerged
what kind of animals cannot respire at low tide?
intertidal animals
what state to respiratory organs need to be in order to acquire oxygen?
moist
what do animals do at low tide?
reduce metabolic rate
what do high intertidal animals do?
some can respire from air even at low tide if air is not too dry (mussels)
what is the adaptation of Pacific sand bubbler crab?
• membrane on each leg for gas exchange
what is the adaptation of Leather limpet?
carries air bubble into tide pools
how is a vertical zonation physically formed?
physiological tolerance of diff species at diff levels of shore
how is a vertical zonation biologically formed?
• larval and adult preference -> larvae may settle at high tide at high levels, mobile juv/adults have series of behavioral responses that keep them at certain levels of shore • competition -> species may be capable of excluding others from certain levels of shore • predation -> mobile predators more effective usually lower shore (affects distributions of vulnerable prey species
what is the point of the Connell’s field experiment?
interspecific competition
describe the Connell’s field experiment
• barnacle Chthamalus highest on shore • barnacle semibalanus below that • below mean low water, barnacles are rare • mobile predators, gastropod snail Nucella are more common in lower regions
what happened when transplanted newly settled Chthamalus to all tidal levels?
• took rock with barnacles and moved them to lower intertidal • found another barnacle species (Semibalanus) grew over it or squeezed it off rocks
what happens when some transplants are caged in lower intertidal zone?
• to exclude Nucella • found Semibalanus grew fine in cages
what were the results of Semibalanus and Chthamalus?
• semi not tolerant of higher zones • chtha better recruiting to high intertidal zones • chtha competed out of lower zones • semi eaten by snails in lower zones
what conclusions were drawn from the Connell experiment?
• physical factors control upper limit of distribution • biological factors control lower limit of species occurrence -> predation important for lower intertidal
what allows for recruitment into a lower zone?
• disturbance • competition or predation will determine who survives