Date of Award

Spring 1997

Document Type

Restricted Thesis

Terms of Use

© 1997 Molly W. Jacobs. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts


Biology Department

First Advisor

Rachel Merz


The dynamic viscosity of water varies inversely with temperature. From 5 to 15°C, a range experienced by many intertidal organisms, viscosity decreases from 1.623*10⁻³ to 1.221*10⁻³ Pascal-seconds (Pa s). Organisms operating in low Reynolds number regimes may be particularly vulnerable to changes in viscosity. Those regularly exposed to fluctuating temperatures must deal with the mechanical constraints of changing viscosity as well as the physiological effects of changing temperature. Ophiopholis aculeata, a suspension feeding brittle star, was used to test the relative effects of increasing viscosity and decreasing temperature. O. aculeata was allowed to feed while subjected to flowing seawater at both 1.623*10⁻³ and 1.221*10⁻³ Pa s, with and without the accompanying changes in temperature. Analysis of particles captured shows O. aculeata capture a high percentage of large particles compared to the range of particles obtained in water samples. Decreases in temperature were accompanied by substantial decreases in feeding rate and diminishments in the average size of particle captured. Increases in viscosity did not affect feeding rate, but caused a slight decrease in the average size of particle captured. Less effective mucus secretion at lower temperatures or increased drag on large particles may be partly responsible for these observed decreases. Temperature appears to be a dominant factor in brittle star particle capture, but viscosity also plays a substantial role.