1. St. Francis College, Brooklyn, NY and Fordham College, New York, NY
EFFECTS OF CHANGING SALINITIES ON HORSESHOE CRAB LARVAE BODY CONTRACTIONS
Lauren Clark, Mamuna Faizi, Alina Zhyvotovska, James Foo, Kathleen Nolan, and Mark Botton
St. Francis College, Brooklyn, NY and Fordham College, New York, NY
Results
There was no consistent pattern of contractions for either small (<1 mm) vs. large (1-2mm) larvae. Two Chi-square values were calculated using the average number of contractions for the small and the large larvae at the various salinities for our expected values. The X2 for the small larvae was 7.9 and 9.78 for the large. Since the p value at 0.1 is 9.24 for five degrees of freedom, we do not reject the null hypothesis (there is no difference in number of contractions for small larvae among various salinities, but we do reject the null (there are significant differences in number of contractions of the larger larvae among various salinities.
ABSTRACT: The null hypothesis for this experiment was that there would be no changes in larval body contractions due to changing salinities that were a simulation of environmental change at a constant temperature (20oC). Larvae were placed in salinities ranging from 0-50ppt, (0 ppt, 10 ppt, 20 ppt, 30 ppt, 40 ppt and 50 ppt) which would mimic the extreme and average conditions that might be faced by horseshoe crabs in their natural environment. The number of body contractions per minute was recorded to show the effects of varying salinities. Initial sampling revealed decreased body contractions in horseshoe crab larvae at 0 ppt, 30ppt 40 ppt and 50 ppt, which caused us to reject our null hypothesis. However, subsequent sampling did not allow us to reject our hypothesis for smaller larvae.
MATERIALS & METHODS:
Hundreds of horseshoe crab eggs were collected along Connecticut beaches from Long Island Sound in June They were refrigerated in finger bowls, and many hatched into larvae. Their development was delayed, most likely due to a sub-optimal temperature. Several hundred crab larvae were then placed in an aquarium with a salinity of 20 ppt (Instant Ocean Salt). The water was changed weekly and larvae began emerging in August. During November through December, larval development was observed and recorded using a Motic camera and a dissection scope. Larvae were placed in salinities ranging from 0-50 ppt, (0 ppt, 10 ppt, 20 ppt, 30 ppt, 40 ppt and 50 ppt) which would mimic the extreme and average conditions that might be faced by horseshoe crabs in their natural environment. The number of body contractions per minute was recorded to show the effects of varying salinities. .
Photo by Gulf Specimen Marine Lab
Table 1. Number of Body Contractions of HSC Larvae at Various Salinities
0ppt
10ppt
20ppt
30ppt
40ppt
50ppt
2012 sm lg
1/26 56 15 27 17 23 9 32 30 44 45
2/1 20 52 18 28 22 31 34 29 46 51 59
2/3 42 21 35 40
2/25 63 68 54 64
3/5 78 77 50 66 69
3/8 19 24 36 25 26 12
averages
29.83
25.17
28.5
40.17
47.17
32.67
36.33
44.17
50.17
42.33
48.17
Photo credits: Lauren Clark
INTRODUCTION: Horseshoe crabs are marine arthropods with a domed horseshoe-shaped shell, a long tail spine, and ten legs. In the Northeast, they are found in the greatest numbers from May through August along Atlantic beaches. The females lay their eggs in the sand and the males fertilize them. The eggs serve as a food source to thousands of migrating birds. Horseshoe crabs have had the same body plan for over 350 million years. However, they are in danger because of overfishing for bait and medical purposes. The blood cells, or amoebocytes, of horseshoe crabs react with bacterial endotoxins and results in massive clotting. Endotoxins are waste products left behind by bacterial cells when they disintegrate and are known to cause infections and disease. Endotoxins often escape sterilization in medical facilities. Pharmaceutical companies use the amoebocytes from horseshoe crabs to test drugs for endotoxins.
Discussion
The results are important in lieu of increased harvesting pressure and possible ecological changes in salinity due to climate change. For example there may be a decrease in salinity over time due to increased rains that could result from climate change. It is necessary to increase the numbers of larvae that we have sampled, as well as age ranges. We plan to do this in the future. It is also important to try different variables and to try to understand if the contractions could be a result of physiological stress. These experiments could be coupled with LD50 studies at the various salinities. This research has provided a broader understanding of conditions that could possibly affect survival of these medically (and ecologically) important organisms.
Photo credits: Kathleen Nolan