Activity 8 - Answers
Possible responses are below.
| Starfish A | Starfish B | Starfish C | |
|---|---|---|---|
| Light | The light level will be a little higher when the tide is out, because there is no water but the animal is still shaded by the rock | The light level will be quite a bit higher when the tide is out, because the animal is no longer covered by the water | The light level will be higher when the tide is out, because the water depth will be shallower |
| Temperature | Temperature will probably be a little higher when the tide is out as the animal will no longer be cooled by the seawater; temperature may also be more variable during the period when the tide is out | Temperature will probably be higher, perhaps considerably higher, when the tide is out as the animal is on a dark surface, exposed to full sun; temperature may also be more variable during the period when the tide is out | Temperature will probably be higher when the tide is out as the animal as the water in the rock pool will be warmed by the sun; as the pool is shallow the water may become very hot, possibly exceeding the air temperature, as it is heated by the dark rock; temperature may also be rather more variable during the period when the tide is out |
| Oxygen level | Oxygen level will probably be higher when the tide is out because oxygen diffuses more rapidly through air than water and the animal is initially in a position where water movement may be limited | Oxygen level will probably be a bit higher when the tide is out because the animal is exposed to the air but the animal is in a location where currents and waves would bring oxygenated water even when the tide is in | Oxygen level may drop when the tide is out if organisms in the pool use oxygen faster than it can diffuse from the water surface |
| Salinity | When the tide is in, the water will be at normal salinity for the region (except during the wet season when runoff may lower salinity) | When the tide is in, the water will be at normal salinity for the region (except during the wet season when runoff may lower salinity) | When the tide is out, salinity will probably increase as water evaporates from the pool (except during the wet season when runoff may lower salinity dramatically) |
| Other comments | The animal under the rock is largely sheltered from waves and currents but could suffer if storms disturb the rock | The animal will probably be exposed to lower physical forces when the tide is out; it is exposed to waves and currents where it is | The animal will probably be exposed to somewhat lower physical forces when the tide is out; it is somewhat exposed to waves and currents where it is |