Seasonal variation in the effects of food availability on gametogenesis in the purple urchin (Strongylocentrotus purpuratus)

The amount of food and when it is available affect both the timing of reproduction and the number of gametes produced by purple sea urchins, Strongylocentrotus purpuratus. To investigate this further, the effects of food availability on feeding rates, gonad growth, and gamete development were examined in S. purpuratus collected from the Point Loma kelp forest near San Diego, California, USA (32.69 N, 117.26 W) in September (Fall) 2007, and February (Spring) and July (Summer) 2008, using laboratory mesocosms. Each seasonal laboratory feeding experiment lasted 3 months, and different levels of food availability were established with different feeding frequencies (from 1 to 7 days week). Gonad tissues of male and female urchins were staged at the end of each experiment using histological analyses. Reduced food availability resulted in increased daily consumption rates, especially in the Fall when gamete development began. Food limitation at this time resulted in failure to produce viable gametes, suggesting there is a critical period early in gonad development when food limitation affects reproductive competency. Food limitation later in gonad development did not stop viable gamete production, although it did reduce gamete output. Introduction Reproduction in marine invertebrates is a multistage process that begins with either storing nutritional resources or directly allocating them to reproduction in order to initiate gametogenesis, and ends with the spawning of mature gametes. When individuals become food limited, they may cease allocating nutritional energy to gamete production and redirect energy to growth and survival (Wade and Jones 2004). While organisms in these situations may still reproduce, the number and size of their offspring are often diminished, resulting in lowered fecundity (Moehrlin and Juliano 1998). However, in some cases, organisms will spawn even when it results in their immediate mortality, especially when the chances of surviving to the next reproductive period are low (Siems and Sikes 1998; Stoeckmann and Garton 2001), but if a critical amount of resources is acquired and stored early in gametogenesis, reproduction proceeds although possibly augmented by future changes in the parent’s nutritional condition (as in the green urchin Strongylocentrotus droebachiensis, e.g., Garrido and Barber 2001). In species with ‘‘fixed’’ development, the buildup and storage of nutritional resources early in gametogenesis determines whether and when individuals spawn, but the quantity of gametes they produce is influenced more by nutritional changes occurring later in gametogenesis (Moehrlin and Juliano 1998). In contrast, in species with ‘‘flexible’’ development, changes in nutritional condition following the early buildup of nutritional resources determine the quantity of gametes produced as well as whether and when the individuals spawn, or gametes can be reabsorbed and used for growth and maintenance. In both strategies, it is essential that individuals buildup and store a minimum amount of energy during early gametogenesis, because without this they Communicated by J. P. Grassle. Electronic supplementary material The online version of this article (doi:10.1007/s00227-011-1820-6) contains supplementary material, which is available to authorized users. C. A. Dodge (&) M. S. Edwards Department of Biology and Coastal and Marine Institute, San Diego State University, San Diego, CA 92182, USA e-mail: [email protected] C. A. Dodge Pacific Ridge High School, Carlsbad, CA 92009, USA 123 Mar Biol (2012) 159:427–433 DOI 10.1007/s00227-011-1820-6