Tide Pools

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Tide Pools

Lab report by Ben White

Introduction:
Tide pools are found between the high and low tidemarks. They are formed when the tide recedes. At high tide, the pools are susceptible to high wave action. At low tide, the pools are susceptible to abitoic changes including desiccation, high salinity, and low dissolved oxygen. Tide pools have hard substrate bottoms and walls. Because of the high energy of crashing waves, a survival strategy organism’s use is attaching to the hard rock surface, which eventually results in space competition.

In a tide pool, the abiotic conditions are always fluctuating. When the tide recedes, the pool is exposed to the sun, and it begins to desiccate. As the water in the pool begins this evaporation process, the salt concentration increases with the loss of water. Because the tide pool has no water flowing in or out, the temperature in a pool will begin to rise, which in turn lowers the dissolved oxygen in the tide pool. Organisms that live in the tide pools are highly adapted to living in these conditions.

Tide pools obviously have a wide range in size. For a steno- organism, a bigger pool is better than a smaller one because it heats slower, looses less dissolved oxygen, and retains it’s salinity better than a smaller pool. For a eury- organism, smaller is better, because it has less competition in its niche for space and food. With this same concept in mind deeper pools hold more volume of water, and are better for living than a shallow pool for the same reasons listed above. The location is also important to animals making a living in tide pools. The closer a tide pool is to the water the less time it spends exposed to the sun, and the more time it spends submerged in the sea. Consequently, the farther a pool is from the water, the more time it spends exposed to the sun.

Most organisms living in the tide pools are either stenohalne meaning they are sensitive to high concentrations of salt. The opposite of stenohalne is euryhalic, meaning organisms are highly tolerable to salt concentrations. Organisms can also be stenothermic, meaning they are sensitive to large temperature fluctuations. The opposite of stenothermic is of course eurythermic, meaning they can survive a wide range of temperatures.

The purpose of this experiment was to view and identify organisms in tide pools of three different sizes that were relatively the same distance from the shore. The experiment was designed to compare organisms from one pool to the next and determine how abiotic factors such as depth, size and temperature affected the species abundance and diversity if any.

The other purpose of the experiment was to sample 10 different tide pools found various distance from shore with various different abiotic factors. The experiment was to observe one stenohalic organism and one eurythermic organism and to describe their niche based on 3 abiotic parameters.

Methods:
On May 22, 2002 the group used vans to travel to the south side of Acadia Island in Maine, a place where many tide pools are found. The area was first scouted to find tide pools that were in relative distance from the water. Three pools were chosen; one small pool, one medium sized pool, and one large pool, respectively. Two to three people were assigned to a pool. Species data was collected from each pool. The species data included, common name, scientific name, and abundance, measured as: rare, common, or abundant. Field guide Martinez, 1999 was used to identify species.

While tide pool data was collected, another group of students measured the three pools. Measurements included depth, distance from shore, length and width (if the pool was shaped like a square) or diameter (if the pool was circular). These measurements were calculated to determine the average volume of the pool. Depth was measured with a ruler in meters. Distance from shore was measured with a tape measure. Length/width or diameter was measured with the tape measure as well.

Another group of students were assigned to survey and measure 10 other tide pools in the area. Along with the measurements, students had to observe whether the pool contained Halicondria panicea also known as Breadcrumb sponge (which is a stenohalic organism) and or Mytilus edulis also known as Blue mussel (Which is a euryhalic organism). Measurements that were taken were size, depth, distance from shore, and above named species’ abundance. Criteria for depth was as follows: Shallow = <15cm, Medium = 15-30cm, Deep = >30cm. Criteria for size was as follows: Small = 1-2m, Medium = 2-5m, Large = >5m. Criteria for species abundance was as follows: Absent = 0, Few = <5, Many = 5-25, “Boat Load” >25. Distance from shore was measured with a tape measure in meters.

Results:
The abiotic data that was involved for this experiment included depth, temperature, size, and distance from the shore. When comparing species found in each of the three tide pools, species were recorded as rare, common or abundant. The small tide pool, which was 9.5cm in depth, 26.7m from the shore, and 5.3m in area yielded the discovery of the fewest organisms. The medium tide pool, which was 26cm in depth, 29.3m from the shore, and an area of 8.8m yielded the second fewest organisms. While the large tide pool with a depth of 46.25cm, 22.4m from the shore, and an area of 90.9m yielded the discovery of the most organisms. The small tide pool had ten species in total, such as Littorina littorea, and Ulva lactuaca. Three species were rare, three were common, and five were abundant. The medium sized pool had thirteen species including Fucus spiralis, Nucello lapillus and Mytilus edulis. Five species were rare, five species were common, and four species were abundant. The large pool had fifteen species such as Halichondria panicea, Carcinus maenas, and Desmarestia acuelata. Two of the species were rare, nine were common, and three were abundant (fig1).

The second part of the experiment dealt with a stenohalic and a euryhalic organism and their respective niches. Of the ten pools tested, the depth ranged from shallow to deep, the distance to shore was from 50.4m to 3m, and the area from small to large (table 1). As the results show, Halichondria did not grow in pools that were any more than 11m from shore. M. edulis was found as far as 50.4m away from the shore. Distance from shore was plotted against area for both blue mussel and with sponge (fig. 2). Distance from shore was also plotted against pool depth for both sponge and blue mussel (fig.3).

Discussion:
When observing the data collected on the three tide pools, it can be concluded that factors like desiccation, salinity and dissolved oxygen play a role in determining the organisms and what size tide pool they live in. Distance from the sea is another factor that is important to organisms, however this factor was eliminated from the experiment because the three tide pools that were chosen were relatively the same distance from the shore. For example, Carcinus maenas, the green rock crab was only found in the large tide pool. This is because the large pool was cooler, deeper, and less influenced by desiccation. The green crab also had a lot more surface to search for food and to hide from predators. If the crab was caught in the small tide pool, it would not have places to hide, it would have less food to eat, or it would probably die from one of the abiotic factors, such as lack of oxygen, or overheating.

It can also be concluded that the abiotic factors determined species richness found in a tide pool. The smallest tide pool had the fewest species in it, while the largest had the most. There was not a great difference in species richness perhaps because of the season. For example, the data was collected in May when it was quite cold; therefore, the water in the tide pool did not warm up as much as it might in say July or August.

Lognormal distribution is a way of calculating species diversity. In a lognormal situation, there will be a low number of species that are rare in an environment; there will be a higher number of species that are common in the environment, and smaller number of species that are abundant. Not enough species were identified in the small and medium sized pools during the experiment; this perhaps lead to abnormal graphs of a and b on fig. 1. As the species numbers increased in the larger pool c, results started to look more accurate for lognormal species distribution.

The other part of the lab dealt with niche. Niche is the range of conditions that an organism can withstand. It includes how an organism makes a living, for example, what it eats, what eats it, and how is reproduces. When looking at two lognormal graphs for two competing organisms super imposed on each other, the place where they overlap is where they compete for a niche.

The two organisms that were looked at in the experiment were competing for space on rock substrate in the tide pools. Halicondria panicea and Mytilus edulis are two dominating organisms that compete for space. One major difference between the two is that Halicondria panicea is stenohalic, and Mytilus edulis is euryhalic. The difference was a major factor in determining where the organisms were found in the tide pools or not.

Halicondria panicea was mainly found near the edge of the sea. Pools closer to the shore are lower in salinity than the ones found farther because they are covered by the tide most of the time and exposed to the sun for a shorter amount of time, meaning they desiccate less, which leads to less of a salinity loss. Farther from the shore Mytilus edulis was found in high numbers absent of Halicondria panicea. This is because Mytilus edulis can tolerate the high levels of salinity produced by desiccation and water evaporation.

For the same lowered salinity reasons as above, it could be predicted that Halicondria panicea would be found in large and deep pools as well, however the data that was collected did not prove this hypothesis. It was probably because not enough pools were sampled in the experiment. Another anomalous result that was later discovered in the experiment was miscalculated in distance from the shore. The distance from shore was a large factor in understanding species abundance. Because of the various contours of the rocky shore, some measurements from tide pool to the shore would be measured on a gradual slope, meaning the distance from the pool to the sea was longer. Some measurements would be at a steeper slope to the water, resulting in a shorter distance. Using altitude from tide pool to the shore would have been more accurate.

Literature cited:
Martinez, Andrew J. Marine Life of the North Atlantic. Down East Books: Camden, Maine. 1999.