Unit 5 Living Things in the Intertidal Zone – An Exploration

Author: YU-Shun Yang(楊宜訓)  Translator: Nikki Wang(王月玲)

Ⅰ. The Tide

    Newton, the great scientist who was hit on the head by an apple, put forward a great theory: Gravitation. The theory, in short, says that any two objects will attract each other; the greater the quality is, the greater the gravitation will be; the longer the distance is, the smaller the gravitation will be. Aren’t they just like two magnets?

The sun and the moon are with bigger quality because they are closest to the earth, so the sea water on the earth is influenced by the gravitation of the sun and the moon. This is especially true in the case of the month. It is very close to the earth, the gravitation produced is relatively great, too, and this gravitational pull is the main force of tides. In addition, the centrifugal force produced by the earth’s rotation and the landforms undersea are also factors that will influence the changes of tides.

The following picture with a number of triangles is the tide table in Penghu. Do you know how to use it? In fact, it is very easy. The taller, blue triangles indicate the tide is rising, and the shorter triangles indicate the tide is ebbing, in other words, the top of the triangle represents full tide while the lowest triangles represent low tides. Therefore, before we go to the seashore, we can easily check the lunar date in the monthly or daily calendar to get the information about the tides.  Of course knowing the tides does not mean it is safe to go to the seaside; there are still many factors that will affect our safety, such as the currents. Therefore, even if we know it is ebb tide, we should still not go to an area along the shore that we are unfamiliar with without first taking the proper precautions.

Ⅱ. The Intertidal zone

    Penghu is surrounded by sea and the topography of the sea floor is even. When the tide is full, we can see a vast expanse of water when we stand on the bank to look at the sea; when the sea water retreats gradually, we can enter an area with abundant lives – the intertidal zone – the district flooded in the full tide while exposed in the universe tide.

    Since the intertidal zone will go through high and low tides twice in one day, it is flooded in water for a moment and then shine in the sun for another moment. The environment changes so quickly that there is no place where the living things can find shelter, and they can easily be found by their natural enemies. Therefore, the living things of this area mostly have unique ways of adapting to the environments. Take barnacles for example, it sticks firmly on the rock and reef and always makes a return journey along the tides, so nothing influences it; other things such as the swimmer crab, it moves fast and its body color and the environment are very similar; the zebra periwinkle gets its food in high tide, and hides under the stone or gets together to keep out of the sun during low tide...

Because the intertidal zone is rich in resources, a lot of people are attracted to the seashore for fun. However, be sure to check the tide tables before going out for water activities.  It is important for you to pay attention to your own safety. 　

Ⅲ. Living Things Commonly Seen in the Intertidal Zone

1.      Tidal up area: wharf roach

2.      Reef and gravel area: barnacles, chiton, rock oyster, turban shells, snail and basket stars

3.      Tides gathering area: hermit crab, cowrie ,blue crab and sea cucumber

4.      Silt mixed area: sea grass, frog’s bit, clam worm, sand shifting star(starfish), blue swimmer crab and geoduck

5.      Coast and wetland area: teddy bear crab, branching acropora and brain coral

Ⅳ. Intertidal Zone Activity Precautions:

1. Safe maintenance:

(1)   Tide and ocean current: The tide ranges of many places (Difference in height of sea at the rising tide and the ebbing tide) are more than one or two meters; there are ocean currents in some places, it will produce strong pulling force to the flows of the sea water, but this can not be detected on the sea surface. Therefore, when going into the sea in an area that we are not familiar with, we must be sure of the time of rise and ebb tide first before setting out, and do not go to the deeper places.

(2)    Personal safety: A sun hat and a long-sleeved jacket can prevent sunburn; a pair of slip resistant shoes or track shoes can reduce the possibility of slipping and injury; it is also useful to carry a light first-aid kit.

(3)    Identification of the poisonous creatures: poisonous creatures usually have warning coloration, so when we see living things that are bright and colorful on the seashore, we should avoid touching them with our hands.

 2. Observation activities

(1)   Methods of observing: The small lives of the intertidal zone will hide between the stones or among the marine alga clump in ebbing tide, so the simplest way of observation is to pick up. The skill lies in searching and searching, and we should pay more attention to those things in between the stones or alga. We also have to return the rocks we have stirred to their original positions so that the lives protected by the stones will not be injured.

(2)   Tools for observation:

l          Hydroscope or peep mirror: It enables us to see the things under the water clearly without being affected by the movements of the waves.

l          Gloves: They can prevent us from being scratched when moving the stones.

l          Nets: We can use nets to catch the living things with vigorous actions, and let them go after the observation is finished.

l          Equipment for photography and notebooks: They are for recording the observation results.

l          Other tools: A magnifying glass is useful when observing micro living things