So which kids come from which spawning?

Multiple spawning events per year can be viewed as a bet hedging reproductive strategy in marine species. Oysters (Crassostrea virginica) in the Mid Atlantic states exhibit this reproductive habit. In the Virginia Chesapeake Bay historical records demonstrate both multiple spawning and multiple recruitment (first records of metamorphosis to supplied substrates) events each year. We pose the question: which of these recruitment events is responsible for observed young of the year (YOY, spatfall) in the subsequent fall months? We examine records of temporal variation in spatfall in three river systems (the James, Piankatank and Great Wicomico Rivers) and demographics  (density and length frequency) of YOY in quantitative fall surveys over a 15+ year period. Figure 1A and C illustrate the temporal sequence of spatfall as number of spat per shell on shellstring deployments for the James River in 2007 and 2012 respectively. Note that both the timing and the duration of the annual period of major spatfall are variable during the study period. The associated demographics of the YOY in fall surveys is illustrated in Figure 1 B and D, as YOY per m² by 5mm length increments. Again, note that the demographic changes between years. Using estimates of post recruit growth rates we hindcast dates of recruitment from YOY demographics to provide direct comparisons with quantitative records of impact for each recruit event.