Science Serving Maryland's Coasts

Andrew Ostrowski, University of North Carolina at Wilmington

Class Year: 

Project Title: 

Effects of Food Availability on the RNA: DNA ratio in the Habitats of Juvenile Atlantic Menhaden, Brevoortia tryannus, in the Patuxent River System


Estuaries are important nursery grounds for many economically and ecologically important species including Atlantic menhaden, Brevoortia tryannus (Clupeidae). The Chesapeake Bay serves as one of the most important nursery grounds for this species, with nearly 80% of the annual recruitment of this species thought to be derived from the Chesapeake Bay. Recently, recruitments of menhaden in Chesapeake Bay have declined. One potential cause is reduced production associated with declines in habitat quality. There are multiple ways to measure habitat quality, but due to the rapid response of cellular RNA concentrations to variation in resource availability to menhaden, RNA:DNA ratios represent an ideal metric to measure habitat quality. Our objectives were to quantify the relationship between food ration, RNA:DNA ratio, and growth of menhaden in the laboratory and then use these data to infer habitat quality from RNA:DNA ratios measured from menhaden collected in the Patuxent River. Laboratory RNA:DNA ratios were measured by spectroflourometric techniques on fish from a 14 day experiment with three varying food rations based on body weight. We detected a significant change in RNA:DNA ratio among treatments (F2,2 = 21.54,p = 0.0444), days (F1,26 = 54.05, p= 0.0001), and treatment-day interactions (F1,26 = 39.52, p = 0.0001). A change in weight and length was also observed with significance for day (F1,29 = 200.44, p = 0.0001; F 1,29 = 91.73, p = 0.0001), and treatment-day interaction (F 2,29 = 156.8, p = 0.0001; F2,29 = 31.96, p = 0.0001). These laboratory results represent the first measurements of RNA:DNA ratios for menhaden and will aid in future studies. Field work took place by seining in the Patuxent River on a weekly basis at multiple sites. Field results observed for CBL Pier were a decline in RNA:DNA ratio over the course of the summer months and based on laboratory results, show a RNA:DNA ratio equivalent to low treatment fish.