Marine Biology

, Volume 158, Issue 1, pp 47–58 | Cite as

Problems of the gonad index and what can be done: analysis of the purple sea urchin Strongylocentrotus purpuratus

Original Paper


The gonad index, GI, is widely used as a measure of changes in reproductive state. There are, however, problems with its use because it is based on the implicit assumption of an isometric relationship between gonad size and some measure of total size. If, for example, gonad weight and total weight are used, the exponent for an allometric relationship usually is ignored and hence assumed to be 1.0. It is further assumed that this exponent is fixed for all states of the reproductive cycle and that gonads begin to develop at size = 0. Data for the purple sea urchin Strongylocentrotus purpuratus at Gregory Point, Oregon, USA, gathered over a period of 31 months showed that these assumptions cannot be supported. The relationship is better modeled with a function that (1) takes into account size of initial gonad production and (2) allows allometric exponents that vary with site or season. Thus, a better approach is to use a wide range of sizes to estimate size when gonads begin to develop and then, with this correction, ANCOVA to test for differences of gonad size among samples. Gonad changes at Gregory Point were estimated using fixed sizes of 5 cm diameter and 60 g total weight. Publishing means for X and Y, the standard error of the estimate, R 2, and slope for each regression are shown to be sufficient to compare our results with results across studies.


Logarithmic Transformation Gonad Development Gonad Index Gonad Weight Test Diameter 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



Dissections of sea urchins from Gregory Point were done by B. Miller. Those from Arena Cove, California, were done by M. Morris and N. Sandoval. Assistance with dissections from Yaquina Head, Oregon, was by C. Ebert. The manuscript benefited from comments made by 3 anonymous reviewers. Funding for this work was from the Ocean Sciences Division Biological Oceanography of the US National Science Foundation (grants OCE 84-01415 and OCE-0623934). We are grateful for all of this support.

Supplementary material

227_2010_1541_MOESM1_ESM.xls (20 kb)
Supplementary material 1 (XLS 19 kb)


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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • T. A. Ebert
    • 1
  • J. C. Hernandez
    • 2
    • 3
  • M. P. Russell
    • 2
  1. 1.Department of ZoologyOregon State UniversityCorvallisUSA
  2. 2.Department of BiologyVillanova UniversityVillanovaUSA
  3. 3.Departamento de Biología Animal (Ciencias Marinas) Universidad de La LagunaTenerifeIslas Canarias

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