Introduction
Intertidal zones are peculiar habitats. What makes them peculiar is the occurrence of dominant organisms in distinct bands whose respective upper and lower limits coincide with specific horizontal level relative to the tide level. 1 Both biotic limitations, such as competition and predation, and abiotic limitations, such as wave exposure and desiccation stress help determine where an organism will dwell, which in turn helps determine the zone bands. 2 One factor that is related to both wave exposure and desiccation stress is temperature. The relation is such that during low tide the temperature of the zones increases and the possibility of desiccation increases also. Temperature changes can also affect metabolic and biochemical processes, retard cellular activities, inhibit behavioral activities, and inhibit reproductive behavior among the organisms living in the various zones. 3
The aim of the present study was to investigate the temperature fluctuations for the four intertidal zones (white, black, gray, and yellow) in Graham’s Harbor on the island of San Salvador, Bahamas. There were two main questions that would be investigated: 1) is there a difference in temperature between the intertidal zones and 2) if there is a difference, which zone reaches the hottest temperature and which zone reaches the lowest temperature. The study group predicted that there would be temperature differences among the four zones with the black zone having the highest temperature and the yellow zone having the coolest temperature.
Methodology
Graham’s Harbor is the location selected for the study. The site is in a low energy bay and has areas that show good representation of the four zones. The transect chosen was one of excellent representation of the zone bands which made the temperature probe placement an easy task. Hobo Data Logger was the temperature probe program used to collect the data on a daily basis.
A transect of 35.1 meters was marked along the eastern side of Graham’s Harbor and each zone was identified and measured. (Table 1) The location for placement of the temperature data probes was determined by using the middle point of each zone. (Table 1) Once the middle point was located the area was evaluated for aesthetics such as crevices, holes, or any other physical handicap that would deter the probe from performing properly. The probes were attached so that they were in direct contact with the sun and fluorescent orange markings were attached to the probe for easy identification when returning to download data each day.
Table 1. Various zone measurements
ZONE ZONE LENGTH
(meters) MIDDLE POINT OF ZONE (meters)
White 35.1 – 25.75 29.1
Black 25.75 – 21.5 24.8
Gray 21.5 – 19.0 20.1
Yellow 19.0 – 10.0 15.8
The probes were set to record a temperature data point every five minutes. They were placed in their location on 17 June 2001 in the afternoon and were removed on 21 June 2001. Due to the time of placement and removal of the probes the only two full days of data were the 18th and 19th, so all evaluations will be made based upon those specific 48 hours of data. The data was downloaded every 24 hours on site. The downloading of the data did not affect the temperature recordings in any way due to the fact that the probes could remain in place and virtually untouched to retrieve the information. Over one thousand points of data were obtained over the 48 hours for each zone. The points were entered into an Excel spreadsheet for easy interpretation.
Results
The data showed normal distributions for all zones over the 48 hours. (Figure 1)
The patterns of temperature changes are the same for all four (i.e. peaking in the afternoon and dropping out in the middle of the night.
Figure 1. Temperature distributions for the four intertidal zones.
Even though the zones had similar distribution patterns, the temperatures varied for all four zones. The yellow zone showed the smallest range between minimum and maximum temperature, with a difference of 27.48 degrees. The white zone exhibited the largest temperature range with a difference of 45.53 degrees. (Table 2) The difference between the highest high temperature and the lowest high temperature among all four zones was 18.91 degrees. The difference between the highest low temperature and the lowest low temperature was 1.88 degrees. Over the 48 hours of data, the white zone had the hottest temperature reading at 120.59 degrees and the gray zone had the coolest reading at 73.67 degrees.
Table 2. Minimum and maximum temperature readings for the four zones.
ZONE MINIMUM TEMPERATURE (0F) MAXIMUM TEMPERATURE (0F)
White 75.06 120.59
Black 75.55 119.36
Gray 73.67 114.61
Yellow 74.2 101.68
Discussion
The evaluation of the data answered the study question and either proved or disproved the predictions set by the study group. There were temperature differences among all four zones, with no two zones exhibiting the exact same temperature readings. The distributions were the same, but this can be attributed to all four zones being subjected to normal sun and moon patterns. The yellow zone showed a slightly different pattern with the areas of sudden temperature change around midnight each day, This pattern can be explained because the yellow zone is closest to the water and is covered by high tide entirely as compared to the other three zones which are either only slightly submerged or not affected by the tide at all. One of the more interesting conclusions is the showing of the white zone reaching a higher temperature than the black zone. It was assumed in the predictions that the black zone would reach a higher temperature due to the fact of heat absorption differences between white and black surfaces. The study group could come up with no explanation for this phenomenon. One possible reason could be that the white zone is located on the uppermost elevation of the intertidal zone, but there is nothing to substantiate this assumption. The other unique conclusion is that the yellow zone did not reach the coolest temperature, rather the gray zone did. The assumption was that the yellow zone would reach the coldest temperature due to the cooler water blanketing the zone. The explanation for this finding could be that the water acts more as an insulator than as a cooling mechanism.
All of these findings have little significance by themselves, but when the organisms that are living in these zones are looked at, the temperature gradient is very significant. Intertidal animals experience extreme physiological stress during low tide periods and those species inhabiting the upper intertidal zone are often more tolerant of thermal and desiccation stress than those found lower down. 4 Using this study in conjunction with species habitat research could be very useful in understanding the habitat selection of various animals and behavior modifications that occur when species are adapting to a changing environment.
Selected Bibliographies
1. Cummins, H. Course Guide to Tropical Marine Ecology, Geology 499/599.
Summer 2001. pg 205.
2. Stillman, J.H. The Journal of Experimental Biology. Adaptation to Temperature
Stress and Aerial Exposure in Congeneric Species of Intertidal Porcelain Crabs (Genus Petrolisthes): Correlation of Physiology, Biochemistry and Morpholgy with Vertical Distribution. 1996. 199, pgs 1845 – 1855.
3. Cummins, H. Course Guide to Tropical Marine Ecology, Geology 499/599.
Summer 2001. pg 205.
4. Jones, K.M., Boulding, E. G. Journal of Experimental Marine Biology and Ecology.
State-dependent Habitat Selection by an Intertidal Snail: the Costs of Selecting a Physically Stressful Microhabitat. 1999. 242, pgs 149 – 177.
Next Article
Previous Article
Return to Topic Menu
It is 8:12:09 AM on Tuesday, May 13, 2008. Last Update: Saturday, May 4, 2002