15.1 What communities exist along rocky shores?

epifauna = permanently attached to bottom or move over the bottom

Intertidal Zonation

most shorelines have intertidal zonation, which describes natural organization of ecosystems relative to sea level caused by varying environemtnal conditions:

• spray zone = above spring high tide line, only covered by water during storms

• intertidal zone = between high and low tidal extremes

intertidal zone can be separated into following subzones:

• high tide zone = relatively dry, only covered during the highest high tides

• middle tide zone = alternately covered by all high tides and exposed during all low tides

• low tide zone = usually wet but exposed during the lowest low tides

organisms living w/in intertidal zones have diff environmental conditions they must be adapted to:

• physical stress is worse in higher tide zones

• wave energy and predation by other marine organisms = worse in lower tide zones

• competition for space is biggest stress in middle tide zone

RESULT —> intertidal organisms have evolved specific adaptations to cope w/ environmental conditions they face

intertidal zone can have remarkably diff characteristics from place to place. it’s a difficult place to live

The Spray (Supratidal) Zone: Organisms and Their Adaptations

supratidal zone = above even highest tides —> continually exposed above sea level —> drying out = significant challenge to organisms that live w/in spray zone

• rock louse / sea roach: lives on exposed rocks or found among cobbles and boulders typically on floors of sea caves

• limpet: feeds on algae

  • flattened conical shell and muscular foot which helps it cling to rocks

The High Tide Zone: Organisms and Their Adaptations

most have protective coverings to prevent them from drying out

Ex. striped shore crab and periwinkle crabs - protective shell and can move between spray zone and high tide zone

Ex. rock weeds: algae w. thick cell walls to reduce water loss during periods of low tide

The Middle Tide Zone: Organisms and Their Adaptations

seawater constantly bathes middle tide zone —> more types of marine algae and soft-bodied animals can live there. total biomass >> high tide zone —> greater competition for rock space among sessile forms

Ex. mussels, gooseneck barnacles, acorn barnacles

• mussels often grouped together into a distinctive mussel bed that appears as a pronounced band or layer and can often be one of the most recognizable features of middle tidal zones along rocky coasts

• the mussel bed thickens toward the bottom until it reaches an abrupt bototm limit, where physical conditions restrict mussel growth

Ex. carnivorous snails and sea stars eat mussels

where the rock surface flattens out w/in middle tidal zone, tide pools trap water as the tide goes out —> supports many organisms. most conspicuous member is sea anemone

Ex. sea anemone has a flat foot disk that provides a suction attachment to rock surface, tentacles sting victims

Ex. hermit crabs inhabit tide pools

The Low Tide Zone: Organisms and Their Adaptations

low tide zone is almost always submerged —> abundance of algae

diverse community community of animals live here too but hidden by great variety of marine algae and surf grass

Ex. crabs, algae

RECAP

rocky shores divided into spray zone and high, middle, and low tide zones. many shelled organisms inhabit upper zones while more soft-bodied organisms and algae inhabit the lower zones.

CONCEPT CHECK 15.1

(1) What are some adverse conditions of rocky intertidal zones? What are some organisms’ adaptations for those adverse conditions? Which conditions seem to be most important in controlling the distribution of life?

(2) One of the most noticeable features of the middle tide zone along rocky coasts is a mussel bed. Describe general characteristics of mussels and include a discussion of other organisms that are associated with mussels.

(3) In which intertidal zone of a rocky shore would you typically find each of the following organisms: sea anemones, sea lettuce, rock lice, abalones, brittle stars, and buckshot barnacles?