Download The Intertidal Ecosystem

The Intertidal Ecosystem:
A Field Study
Introduction:
The intertidal zone is the area on the seashore between the highest and lowest tides. While
this region represents only a very small portion of the earth’s surface, it is an important
place where two very different types of environments meet and in which a complex web of
interactions takes place.
The intertidal zone is one of the most physically harshest living environments on earth. As
the tides ebb and flow, this community is in a constant state of change, plunged back and
forth each day (twice!) between their own world and another that they are not built well
for. With the loss of their watery habitat, organisms are left ‘high and dry’ exposed to the
abiotic (environmental) pressures from above. Without water, they are not only at risk of
drying out, they are without their source of food and oxygen as well. While some intertidal
animals are able to move/relocate themselves during the low tide, others are sessile or
dependent on water for locomotion and are therefore ‘stuck’ until the tide comes back in.
Low tide is a time of high vulnerability, and many intertidal organisms die each day from
desiccation, temperature/salinity extremes, physical damage/dislodgement by waves, or
from overhead predators. You may ask, “So why live there?! “ Despite the risks and harsh
conditions, the seashore can also be a very beneficial place to live. First, it provides plants
and animals a ‘space’, a high commodity in the ocean with so many other species to compete
with. Also, by separating themselves from their predators below, it gives them another
enormous ecological advantage. Their largest battle is that with the environment above,
which they combat through adaptations: structural (how they are built) and behavioural
(what they do).
Activity:
1. In your small group (3-4) make a quick sketch (on back of handout) of the study site
showing the general landscape of your study area. Include i)the nature of the land
immediately inland off the beach, ii)the types of substrate on the beach (rock, sand, mud
etc) iii) any unique geological features (rock structures, tide pools etc), and iv) 2 lines to
separate the 3 subzones: upper, mid, and lower intertidal.
2. Carefully (and stealthily!) explore the beach in each of the subzones (begin with the
lower intertidal to take advantage of the rising tide!). Peer into crevices, turn rocks, lift
seaweeds… Using the table provided, identify and record all species (or use common
name) of plants and animals (P/A) you find. Note what subzone (U,M,L) and habitat it
was found, and keep a tally of the #organisms (if <20; otherwise record as “20+”).
Finally, study the plant or animal carefully, and note any structural and/or
behavioural adaptations you see. That is, is there anything about how it is built or what
it is doing that could protect it from life in the intertidal zone.
3. Consider the following questions and prepare to discuss:
Q1. What trends in structural or behavioural development do you notice, moving
vertically through the 3 intertidal subzones?
Q2. What parallels can you make between the dynamics in this ecosystem and the
ones we see in our own social system?
Table: Record your data for all species found in the 3 intertidal sub zones
Species
P/A Zone # Habitat
Adaptations
Type
(Structural/Behavioural)