bio 207 chapter 11: between the tides

intertidal zone

the area between the mean low and high tide marks that borders the subtidal zone and is exposed during low tide

subtidal zone

the area that is always submerged

emersion

being out of the water and exposed to air, occurs during low tide

immersion

being submerged, occurs at high tide

substrate

the type of “bottom” that is present in a community

soft bottoms

vary from sand to silt or a mixture (mud)

rock bottom

vary as to the type of rock present and degree of slope

rocky shore intertidal communities

a type of intertidal community that occur on steep coasts without large amount of sediment and result from uplifting due to geologic activity on active margins or from glaciation events, West coast of the Americas

rocky shore glaciation events

weight of the ice forces coastline to sink into the mantle leaving a coastline of exposed rock when the ice melts, coastlines of eastern Canada and New England

epifauna

organisms that live on the surface of the substrate, mud snails on soft bottoms or barnacles on hard substrates

infauna

organisms that live in the substrate, clams burrowed in soft bottoms

meiofauna

organisms that are so small that they move between the grains of soft substrate

desiccation

potential water loss experienced when an organism is exposed, more pronounced on hot, dry, or windy days, organisms can hide or “clam up”

hiding

moving to a tide pool or area with more moisture, some organisms only live in areas where moisture will remain when the tide is out

“clamming up"

closing shells or walling off from the environment in an attempt to conserve moisture, no gas exchange or feeding will occur

temperature fluctuations

some organisms have mechanisms (body ridges or light colors) to allow heat to pass out of the shell or reflect heat

euryhaline

can tolerate a wide variety of salinities

stenohaline

tolerate a very low range of salinities

interrupted feeding

occurs when an organism “clams up”, snails can still feed at low tide by scraping algae, organisms can spend half their day emersed and not feeding

wave action

can directly expose organisms or dislodge them from their habitat, more prominent on rocky shorelines

adaptations to wave shock

seaweeds use holdfasts or encrust on rocks, barnacles glue themselves to substrate, mussels use byssal treads, limpets/chitons use muscular foot like a sucker, intertidal fish lack swim bladder

CO2

builds up to toxic levels when organisms cannot exchange gases with the environment

crabs

can exchange gases in air and water

oyster reefs

prominent in soft bottomed communities, prefer hard substrates because they cannot wash away

rocky shore food web

producers: seaweeds, diatoms, seagrasses
carnivores: sea stars, snails, crabs, flatworms, birds

zonation of the intertidal zone

upper, middle, and lower intertidal zones

upper intertidal zone

the most exposed

lower intertidal zone

the least exposed, greater in competition and more species rich because degree of exposure is less

little gray vs. rock barnacles

both settle out of plankton over wide intertidal range. young ones dry out and die at the upper edge, but little grays are more resistant to desiccation. rocks outcompete little grays in lower intertidal

competitive exclusion

some organisms are better competitors than others and will exclude others if the community is left undisturbed

succession

a predictable pattern that occurs when a habitat is disturbed and organisms move in and are later excluded

climax community

the end result, forms when the community is undisturbed for a long period of time

keystone predators

predators that reduce competition between other organisms (sea stars)

soft-bottom intertidal communities

any bottom that is composed of sediment that occurs when sediments accumulate, east coast of North America south of Cape Cod and the Gulf coast

grain size (big to small)

gravel, sand, silt, clay. the smaller the particle size, the less oxygen that can fit in those spaces

mud

mixture of silt and clay

anoxic zone

below the first few inches from the top, many anaerobic bacteria exist and break down organics

detritus

broken down organics particles

soft bottoms food web

producers: plankton and bottom diatoms
carnivores: fish, birds, moon snails