Along the eastern side of Grahams Harbor, San Salvador Bahamas lay an intertidal zone. It has 4 distinctive zones: yellow, gray, black, and white, described on the colors each zone reflects. Each zone is divided based on the species found in within them, and how often it is submerged due to tidal cycles. The yellow zone is closest to the water, and is submerged part of the time when the tides rise. The gray zone is the next up the shore and is exposed to the water when the tides are high. The black zone follows the gray and is only exposed to water during spring high tides and storms. Finally, the white zone, with the black zone on one side, and the vegetation line against it is only exposed to the ocean during heavy storms.
By definition the intertidal zone is described as the area on the shoreline that is regularly covered and uncovered by the movement of the tides (Hofmann, Gretchen E., 1999). The emersion and immersion of organisms, because of tidal cycles exposes them to series of abiotic stresses, such as temperature. Each organism has a distribution pattern from low to high on the shore. Graham's Harbor intertidal zone shows this distribution of organisms. As you progress from yellow zone to the white zone the species change from ocean dependant species to terrestrial species. Studies of abiotic stresses, such as temperature, have show that species that live higher in the intertidal zone have a greater resistance to the abiotic factors, than do species lower in the intertidal zone (Stillman and Somero, 1996).
The purpose of this project is to examine one of the abiotic stresses, temperature. It does effect the distribution of organisms, but why? Is there is a difference in temperature between the intertidal zones (white, black, gray, and yellow) along Grahams Harbor, that could cause stress on the organisms. Between the four zones is there a difference?
A 35.1 meter transect, from the lower platform to the vegetation line, was identified along the eastern side of Grahams Harbor, San Salvador Bahamas in the intertidal zone. This transect was chosen because the individual zones were distinctive, and easily identifiable. The four intertidal zones were identified along this transect. The yellow zone began at 10.0 meters to 19.0 meters. The gray zone falls from 19.0 meters to 21.5 meters. The black zone was identified at 21.5 meters to 25.7 meters. The white zone goes from 25.7 meters to 35.1 meters.
To measure the temperatures within each of these zones Hobo data loggers were placed approximately in the middle of each zone. The probe in the yellow zone was placed at 15.8 meters. The temperature probe in the gray zone was placed at 20.1 meters, and in the black zone at 24.8 meters. The final probe was placed in the white zone at 29.1 meters. The probes were set to record the temperature every 5 minutes. The temperature in each of the four zones was recorded from 17 June 2001 to 21 June 2001. The data was downloaded from the probes on 19 June 2001 and on 21 June 2001. Once the data was collected and downloaded from the probes to the computer all the data was graphed in excel. In Statview an ANOVA was used to examine two full days of temperature data collected on 18 June 2001 and 19 June 2001. It was used to determine if there was a difference in overall temperature between each zone. The Scheffe test was used to determine if any significance occurred between the four zones.
All the data collected during the four days illustrates the highs and lows of the temperature for each of the zones. The yellow zone has the smallest range in temperatures, which extend from approximately 75 degrees Fahrenheit to 102 degrees Fahrenheit (Figure 1). A distinctive pattern is evident when looking at the graphs. As temperatures decrease, and increase from there lowest temperature they stabilize for a short period of time. On 18 June 2001 the temperature mean was approximately 85 degrees Fahrenheit and 86 degrees Fahrenheit on 19 June 2001 (Figure 2).
In the gray zone the temperatures extend from approximately 75 degrees Fahrenheit to 115 degrees Fahrenheit (Figure 1). The mean temperature on 18 June 2001 was approximately 86 degrees Fahrenheit, and on 19 June 2001 was 88 degrees Fahrenheit. In the black zone the temperature ranged from approximately 75 degrees Fahrenheit to 120 degrees Fahrenheit (Figure 1). For 18 June 2001 the mean temperature was approximately 91 degrees Fahrenheit, and approximately 92.5 degrees Fahrenheit on the following day (Figure 2). The white zone also had temperature ranges of 75 to 120 degrees Fahrenheit (Figure 1). In the white zone the mean average temperature on 18 June 2001 was 92 degrees Fahrenheit, and 91.5 on 19 June 2001.
According to the Scheffe test the yellow and gray zones are more closely related and not significantly different from each other, on both days (Table 1 and Table 2). There is also no significant difference between the black and gray zones. The rest of the combinations of zones show a significant difference.
According to the analysis there are important differences between the four zones, yellow, gray, black, and white, with respect to temperature. As distance increases from the ocean the temperature highs increases (Figure 1). All the zones reached low temperatures of approximately 75 degrees Fahrenheit , but reached varying highs throughout the day. The black and gray zones reach the highest temperatures, while the yellow and gray zones stayed cooler, below 115 degrees Fahrenheit, in particular the yellow zone.
There are significant differences between these zones not only in temperature (Table 1 and Table 2), but in organism distribution and behavior. As the temperature between the zones differs so do the organisms that inhabit them. Organisms in the intertidal zone along Grahams Harbor, are affected by the temperature gradient between the zones, there is more diversity in the yellow zone, than the white. In other cases temperatures in intertidal zones have been shown to affect the cardiac activity. The grapsidae crab (Pachygrapsus mamoratus) exhibits an increasing linear relationship with temperature. As the temperature increased so did the crabs heart rate (De Pirro, Cannicci, and Santini, 1999). In other cases temperatures can effect microhabitat choices and foraging periods. The gastropod Littorina sitkana on warm days on shore the snail would forage for food for shorter periods of time. They would also choose habitats that were cooler, such as barnacles and macro algae, rather than less complex microhabitats, crevices and bare rock surfaces (4).
Research has been done on the effects temperature has on organism in the intertidal zone, but more is needed. As more can be done in examining just temperature I the intertidal zone. Does the temperature gradient change with seasons, or reverse during extreme lows? How do the tides effect the temperatures in each zone. There many questions that can be asked and answered in this area. It is clear that there are differences between the zones, but do those difference change and what effect does it have on the organisms living there.
De Pirro, M., S. Cannicci, and G. Santini. 1999. A multi-factorial experiment on heart rate variations in the intertidal crab Pachygrapsus marmoratus. Marine Biology. Vol. 135. PP 341-345.
Hofmann, Gretchen E. 1999. Ecologocally relevant variation in induction and function of heat shock proteins in marine organisms. American Zoology. Vol. 29. PP 889-900.
Jones, K. Martha M., Elizabeth G. Boulding. 1999. State-dependant habitat selection by an intertidal snail: the cost of selecting a physically stressful microhabitat. Journal of Experimental Marine Biology and Ecology. Vol. 242. PP 149-177.
Stillman, Jonathon H., Gearge N. Somero. 1996. Adaptation to temperature stress and aerial exposure in congeneric species of intertidal porcelain crabs (Genus Petrolisthes): correlation of physiology, biochemistry and morphology with vertical distribution. The Journal of Experimental Biology. Vol. 199. PP 1845-1855.
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