Effect of Various Salinities of Water on Osmoregulation in Green Shore Crab, H. oregonensis
Daria Cubberley
Department of Biological Sciences
Saddleback College
Mission Viejo, California 92692
Osmoregulation in green shore crab (Hemigrapsus oregonensis) was studied at three different salinities of water (approximately 33‰, 20‰, and 10‰). It was predicted that hemolymph osmolalities of H. oregonensis would be hypertonic to the surrounding media and significantly different from each other. Hemolymph osmolality was measured with a Wescor vapor pressure osmometer after the crabs were exposed to approximately 33‰, 20‰, and 10‰ salinities of water for 24 hours. The results showed that the mean hemolymph osmolalties of H. oregonensis acclimated to approximately 20‰ and 10‰ salinities were hypertonic to the medium, and there was a significant difference between these mean hemolymph osmolalities (ANOVA, p = 4.2×10-4; PostHoc, p < 0.05). The mean hemolymph osmolality of H. oregonensis acclimated to approximately 33‰ salinity water was hypotonic to the medium and not significantly different from the mean hemolymph osmolality of the crabs acclimated to approximately 20‰ salinity water (ANOVA, p = 4.2×10-4; PostHoc, p > 0.05), but significantly different from the mean hemolymph osmolality of the crabs acclimated to approximately 10‰ salinity water (ANOVA, p = 4.2×10-4; PostHoc, p < 0.05).
Introduction
Osmoregulation is a physiological process by which animals maintain optimal balance between water and solute concentrations within their bodies. The process of osmoregulation is of a particular interest in aquatic animals inhabiting environments of fluctuating salinity, such as, for example, crustaceans. According to Pequeux (1995), brackish, estuarine, and intertidal environments are the most stressful aquatic habitats, and the establishment of crustaceans in such environments implies highly adapted physiological features.
Crustaceans, like other animals, are categorized as either osmoconformers or osmoregulators depending on a pattern of osmoregulation they follow. Osmoconformers maintain concentration of hemolymph isoosmotic to the concentration of the surrounding water, while in osmoregulators concentration of hemolymph is, in most cases, hyperosmotic to the concentration of the water (Pequex, 1995). Both types of patterns are encountered in crustaceans that inhabit aquatic environment of varying salinity, osmoregulation being more common.
There have been conducted a number of experimental studies which investigated the effect of changing environmental salinities on osmolality of hemolymph in crustaceans. Tan and Van Engel (1966) subjected blue crabs (Callinectes sapidus) to 10‰, 20‰, and 30‰ salinities at 20° C and showed that the hemolymph concentrations were hypertonic to the media in which the crabs were kept and significantly different from each other. Brown and Terwilliger (1992) carried out a similar study on Dungeness crabs (Cancer magister) and obtained the same results.
The present study examined osmoregulation in green shore crab (Hemigrapsus oregonensis) at three different salinities of water (approximately 33‰, 20‰, and 10‰). H. oregonensis inhabits intertidal zone and is most commonly found under rocks. It was hypothesized that hemolymph osmolalities of H. oregonensis would be hypertonic to the surrounding media and significantly different from each other.
Materials and Methods
H. oregonensis were collected at Doheny State Beach, Dana Point, CA. In the laboratory the crabs were divided between two glass containers with water about 6 cm deep; the containers were set into an aquarium with gravel. In the course of the experiment water in the containers was 20°C and was aerated. First, H. oregonensis were placed into 33‰ salinity water. Crabs were allowed to acclimate for 24 hours; after that samples of hemolymph were collected from each crab. The same procedure was repeated after transferring the crabs into water of approximately 20‰ salinity, followed by transferring the crabs into water of approximately 10‰ salinity. Thus 3 rounds of hemolymph samples at three different salinities of water were collected.
A 27 gauge syringe was used to collect hemolymph. The needle of a syringe was inserted through the membrane of the last walking leg, and 10 µL of hemolymph were drawn. Osmolality of hemolymph samples was measured with a Wescor vapor pressure osmometer. Desired salinities of water were achieved by diluting 33‰ salinity water with distilled water in the appropriate proportion. For each salinity, a sample of water was taken after 24-hour acclimation period, and osmolality of water was measured. Upon completion of the experiment the crabs were released.
Results
The mean osmolality of water of approximately 33‰ salinity was 1058 mmol/kg ± 13mmol/kg (±SEM, N=2); the mean osmolality of hemolymph of H. oregonensis acclimated to this salinity was 955 mmol/kg ± 14.3 mmol/kg (±SEM, N=8), which was hypotonic to the surrounding medium. The mean osmolalities of water of approximately 20‰ and 10‰ salinities were 645 mmol/kg ± 1 mmol/kg (±SEM, N=2) and 312 mmol/kg ± 8 mmol/kg (±SEM, N=2) respectively; the mean osmolalities of hemolymph of the crabs acclimated to these salinities were 882 mmol/kg ± 9.20 mmol/kg (±SEM,N=11) in 645 mmol/kg water osmolality and 724 mmol/kg ± 57.3mmol/kg (±SEM, N=10) in 312 mmol/kg water osmolality, both of which were hypertonic to the surrounding medium(Figure 1) .
Figure 1. The mean osmolalities of hemolymph of H. oregonensis acclimated to three different water osmoalities. Error bars indicate standard errors of the mean.
There was no significant difference between the mean hemolymph osmolalities of H. oregonensis acclimated to 1058 mmol/kg water osmolality and the crabs acclimated to 645 mmol/kg water osmolality; there was a significant difference between mean hemolymph osmolalities of the crabs acclimated to 645 mmol/kg water osmolality and the crabs acclimated to 312 mmol/kg water osmolality; the mean hemolymph osmolalities of H. oregonensis acclimated to 1058 mmol/kg and to 312 mmol/kg water osmolalities were also significantly different (ANOVA, p = 4.2×10-4; PostHoc).
There was a linear relationship between hemolymph osmolality of H. oregonensis and the osmolality of surrounding medium (Figure 2).
Figure 2. Mean hemolymph osmolality of H. oregonensis as a function of water osmolality. Error bars indicate standard errors of the mean.
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Discussion
The results of the study essentially verified the hypothesis; however, the results obtained in 33‰ salinity water contradicted the hypothesis. Thus, the mean hemolymph osmolality of H. oregonensis acclimated to 33‰ salinity water was hypotonic to the surrounding medium as opposed to being hypertonic, as it had been predicted, and consequently there was significant difference between the mean hemolymph osmolalities of H. oregonensis acclimated to 1058 mmol/kg water osmolality and the crabs acclimated to 645 mmol/kg water osmolality. These results differ from the data collected by Dehnel (1962), who performed a similar study on the same species of crab, collected from the coast of Vancouver, British Columbia. Dehnel’s experiment demonstrated that hemolymph concentration of H. oregonensis was always hypertonic to the medium. However, Dehnel stated in his paper that Gross (1960), who studied a transient populatiof H. oregonensis in southern California, showed that H. oregonensis was capable of hypoosmoregulation in water of salinity above normal salinity of seawater. This might be a possible explanation why the mean hemolymph osmolality of H. oregonensis acclimated to 33‰ salinity water was hypotonic to the medium in the present study.
Another possible reason for the mean hemolymph osmolality of H. oregonensis being hypotonic to normal seawater stems from the fact that H. oregonensis might belong to the group of crustaceans called “hyper-hyporegulators” which means that they hyperragulate in dilute media and hyporegulate in normal seawater and in concentrated brines (Pequeux, 1995).
To verify if the above mentioned assumptions are correct, it is necessary to conduct a comparative study on H. oregonensis inhabiting Vancouver, British Columbia and southern California and investigate patterns of osmoregultion of this crab in normal seawater and in water of higher salinities. It will be also beneficial to see if there is a linear relationship between the hemolymph osmolality and the osmolality of the medium, similar to the relationship observed in the current study.
The results obtained in water of approximately 20‰ and 10‰ salinities were consistent with the findings of other researches (Dehnel, 1962; Tan and Van Engel, 1966; Brown and Terwilliger, 1992).
To study patterns of osmoregulation in H. oregonensis further, it will be reasonable to investigate the effect of water temperature on hemolymph osmolality of H. oregonensis acclimated to various salinities of water.
Acknowledgements
The author would like to thank Professor Steve Teh and Dr. Tony Huntley for their valuable guidance and help with setting up the equipment. The author also greatly appreciates the help of Arshan Ferdowsian in conducting the experiment.
Literature Cited
Brown, A. C. and Terwilliger, N. B.1992. Developmental Changes in Ionic and Osmotic Regulation in the Dungeness Crab, Cancer magister. Biological Bulletin,182 ( 2): 270-277.
Dehnel, P. A. 1962. Aspects of Osmoregulation in Two Species of Intertidal Crabs. Biological Bulletin, 122 ( 2): 208-227.
Pequeux, A. 1995.Osmotic Regulation in Crustaceans. Journal of Crustacean Biology, 15 (1): 1-60.
Tan, Eng-Chow and Van Engel, W. A. 1966. Osmoregulation in the Adult Blue Crab, Callinectes sapidus Rathbun. Chesapeake Science,7 (1): 30-35.
Review Form
Department of Biological Sciences
Saddleback College, Mission Viejo, CA 92692
Author (s):_____Daria Cubberly______
Title:Effect of Various Salinities of Water on Osmoregulation in Green Shore Crab, H. oregonensis
Summary
Summarize the paper succinctly and dispassionately. Do not criticize here, just show that you understood the paper.
The paper studied the osmoregulation of local green shore crabs from Doheny Beach in Dana Point, CA. It measured the green shore crab’s ability to osmoregulate in varying salt water concentrations. The research wanted to show if the the crabs had the possibility of conforming to the medium at all and to what extent the crabs did this.
General Comments
Generally explain the paper’s strengths and weaknesses and whether they are serious, or important to our current state of knowledge.
Strengths
-The paper studied a species that is found locally around our beach areas. This would spark interest with local scientists.
-The design project was simple with little room for experimenter error. The project took place in a 24 hour period more or less.
Weaknesses
- The way the paper is written, it does not provide for any connection to today’s current events. The experimenter might want to include, osmoregulation is important to green shore crabs because with an increase in global warming…. The glaciers are melting… thus causing a desalinization of sea water…. These animals must osmoregulate or face extinction.
- The paper could have discuss a more in depth topic, because from the sources it seems the same exact project has already been done.
- The paper did not describe how many crabs were used. A number of at least 10 is necessary to have sufficient data to test.
Technical Criticism
Review technical issues, organization and clarity. Provide a table of typographical errors, grammatical errors, and minor textual problems. It's not the reviewer's job to copy Edit the paper, mark the manuscript.
-2 typing errors were some words were missing or incomplete
- the materials and methods needs to be more thorough, it was hard to follow the disscusion without knowing the number of test subjects
-experimenter should define osmoregulation more in depth, cannot just assume everything knows the lingo
This paper was a final version This paper was a rough draft
Recommendation
o This paper should be published as is
o This paper should be published with revision
o This paper should not be published
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