Biol. Bull. Sign up for etocs!
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (3)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Grady, S. P.
Right arrow Articles by Valiela, I.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Grady, S. P.
Right arrow Articles by Valiela, I.
Related Collections
Right arrow Ecology
Right arrow Molluscs
Right arrow Population Biology
Right arrow Chelicerates
Biol. Bull. 201: 296-297. (October 2001)
© 2001 Marine Biological Laboratory

Age Structure of the Pleasant Bay Population of Crepidula fornicata: A Possible Tool For Estimating Horseshoe Crab Age

Sara P. Grady, Deborah Rutecki, Ruth Carmichael and Ivan Valiela

Boston University Marine Program, Marine Biological Laboratory, Woods Hole, Massachusetts 02543

Crepidula fornicata, the common slipper shell, lives on rocks, horseshoe crabs (Limulus polyphemus), and other hard surfaces, often in stacks of one animal atop another. Unlike many other gastropods, they tend to remain sessile, and as they grow, their shells contour to the substrate (1). The association between horseshoe crabs and C. fornicata offers the possibility to use the slipper shell as a tool to determine the ages and average lifespan of horseshoe crabs (2). Knowing this information would be helpful for trying to understand horseshoe crab ecology for use in conservation efforts.

It is difficult to directly estimate horseshoe crab age because horseshoe crabs lack any hard parts that could be sectioned and analyzed for growth rings. Their chitinous exoskeleton is molted with decreasing frequency until a theoretical "terminal molt" (3). There are also a variety of sizes within visually estimated age classes because growth is very slow or stops in adults (3).

Other methods have been suggested for aging horseshoe crabs, including qualitative aging criteria and tagging studies. From the results of tagging studies it has been estimated that horseshoe crabs live 9 to 12 years before maturity and 5 to 7 years as adults, for a total lifespan of 14 to 19 years (4). These age spans are consistent with the prediction of Botton and Ropes (2) based on laboratory work using C. fornicata as a proxy for horseshoe crab age.

C. fornicata could indicate age of host horseshoe crabs if 1) horseshoe crabs have a terminal molt or do not molt often as adults, 2) C. fornicata remain on the same horseshoe crab, and 3) C. fornicata age can be determined with some degree of accuracy (5). It is also assumed that C. fornicata attach to a host horseshoe crab as soon as the new cuticle hardens.

Botton and Ropes (2) used a regression proposed by Walne (1) of C. fornicata length to age to quantitatively estimate the ages of horseshoe crabs. These C. fornicata were used to formulate this regression without comparison to a local population of horseshoe crabs, since the C. fornicata data was from England and horseshoe crabs were not measured at all.

In this study we measured shell length of C. fornicata and prosomal width of Limulus polyphemus in Pleasant Bay, Chatham, Massachusetts. We measured 496 crabs and their corresponding C. fornicata, with the number of C. fornicata per crab ranging widely from 1 to 30, with an average of 4 per crab. From these data we fitted cohorts of C. fornicata to a size-frequency distribution. We also related size of C. fornicata to prosomal width of L. polyphemus to see if C. fornicata could provide a proxy for L. polyphemus size and age.

The analysis of cohorts demonstrated that C. fornicata in Pleasant Bay can be divided into 5 size cohorts (Fig. 1A), with C. fornicata of approximately 4–6 mm in length appearing to represent the most recent spatfall. The cohorts differed in abundance, reflecting different magnitudes of recruitment from year to year. Growth rates in this study did not decrease with increased size and age (Fig. 1B). This may be due to low numbers of larger (50 mm +) and older C. fornicata. Published data of sizes and ages (1,2) match those found in this study, and thus confirm the conversion from size to age of the C. fornicata. The largest C. fornicata found resident on a horseshoe crab was 58 mm. This size C. fornicata could be from 8–11 years old (2).



View larger version (24K):
[in this window]
[in a new window]
  		Figure 1. (A) Cohorts of Pleasant Bay population of Crepidula fornicata: 8.9 mm (~1.5 y), 17.6 mm (~2.5 y), 27.0 mm (~3.5 y), 37.9 mm (~4.5 y), and 46.0 mm (~5.5 y). (B) C. fornicata length vs. age; extrapolation data from Botton and Ropes (2). (C) Length of largest C. fornicata on horseshoe crabs of different prosomal width. Filled circles (•) represent males,open circles ({circ}) represent females.

 
There was no evident relationship between maximum length and age of C. fornicata and size of the host horseshoe crabs (Fig. 1C). Male horseshoe crabs were consistently smaller than females, but in both sexes the length and presumed age of C. fornicata varied greatly, and was independent of the size of the crab.

It is not possible to establish a strong relationship between true horseshoe crab length and the length of the C. fornicata upon it. At most the data of Figure 1C support that a minimum age can be calculated by adding the maximum C. fornicata length on a given horseshoe crab to the minimum age of horseshoe crabs at maturity. Using 9 years as the age at maturity (4), the crabs in this study were from 12 to 17 years old.

This study was funded by the Woods Hole Marine Science Consortium and a grant from the Friends of Pleasant Bay.

Literature Cited

  1. Walne, P. R. 1956. Fish. Investig., 6:1–50.
  2. Botton, M. L., and J. W. Ropes. 1988. J. Shellfish Res., 7:407–412.
  3. Shuster, C. 1950. Third rept. investigations of methods of improving the shellfish resources of Massachusetts. WHOI Contr. No. 564: 18–23.
  4. Shuster, C. 1982. Pp. 1–52 in Physiology and Biology of Horseshoe Crabs. Alan R. Liss, New York.
  5. Ropes, J. 1961. Trans. Am. Fish. Soc., 90:79–80.



This article has been cited by other articles:


Home page
 Journal of PaleontologyHome page
E. L. Bamforth, G. M. Narbonne, and M. M. Anderson
Growth and Ecology of a Multi-branched Ediacaran Rangeomorph from the Mistaken Point Assemblage, Newfoundland
Journal of Paleontology, July 1, 2008; 82(4): 763 - 777.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (3)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Grady, S. P.
Right arrow Articles by Valiela, I.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Grady, S. P.
Right arrow Articles by Valiela, I.
Related Collections
Right arrow Ecology
Right arrow Molluscs
Right arrow Population Biology
Right arrow Chelicerates

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS