Hentschel, B. T. Inst. Marine and Coastal Sci. Rutgers Univ., hentsche@ahab.rutgers.edu

 
GROWTH RATES OF INTERFACE-FEEDING BENTHOS: EFFECTS OF FLOW AND THE FLUX OF NUTRITIOUS COMPONENTS OF NATURAL SEDIMENT
 
Like many benthos that feed at the sediment-water interface, spionid polychaetes switch between deposit feeding and suspension feeding depending on flow velocities and particle fluxes. This facultative feeding behavior varies as juveniles of a species grow to adults; recently settled juveniles of Polydora cornuta tend to suspension feed almost exclusively -- even in still water -- while larger adults do not switch from deposit feeding to suspension feeding unless flow exceeds ~10 cm/s. Here, I present evidence that the growth rate of juvenile spionids depends strongly on boundary-layer flow. In a series of experiments in counter-rotating annular flumes containing natural sediment, I exposed Polydora cornuta juveniles of 2 size classes (2-4 and 6-9 mm length) to several velocities ranging from 0.2 to 18 cm/s (at 5 mm above the bottom) for 1 wk. As expected based on knowledge of flow's effects on feeding behavior and the flux of nutritious components of sediments (quantified as organic C, N, and enzymatically hydrolyzable amino acids), growth rates depended strongly on flow speed. In nearly still water (U = 0.2 cm/s, U* = 0.13 cm/s), the body volume of individual P. cornuta generally doubled during 7 days. At the fastest flow tested (U = 18 cm/s, U* = 0.82 cm/s), body volume increased by 10X. Under fast flows in which rates of sediment transport are high, recently settled juveniles can reach sexual maturity in 1 wk without any nutrient enrichment, suggesting that hydrodynamic conditions in the field have profound impacts on recruitment and population dynamics. Similar results for another spionid, Streblospio benedicti, also will be presented.
 
Day: Wednesday, Feb. 3
Time: 02:45 - 03:00pm
Location: Hilton of Santa Fe
 
Code: SS21WE0330H