MEPS 333:161-171 (2007)  -  doi:10.3354/meps333161

Effects of spatangoid heart urchins on O2 supply into coastal sediment

Kay Vopel1,*, Angelika Vopel2, David Thistle3, Nicole Hancock1

1National Institute of Water and Atmospheric Research, PO Box 11115, Hamilton, New Zealand
2202 Mandeno Street, Te Awamutu 3800, New Zealand
3Department of Oceanography, Florida State University, Tallahassee, Florida 32306–4320, USA

ABSTRACT: Spatangoid heart urchins are key bioturbators in the marine environment. They pump seawater from the sediment surface around their tests and, at the same time, constantly displace the surrounding sediment. To improve our understanding of the effects of this activity on the oxygenation of coastal sediment, we studied for the first time in situ [O2] around Echinocardium cordatum at sub-millimeter resolution under different hydraulic conditions. In the laboratory, we investigated the effects of E. cordatum on pore-water pH and sediment apparent diffusivity. Individuals advancing 1 to 3 cm h–1 through the upper 4 cm of the sediment displaced a greater volume of seawater than sediment per unit time. The O2 uptake of the sediment surrounding E. cordatum was at least twice the respiration of the echinoids. Besides creating additional sediment contact with oxygenated seawater, E. cordatum affected the supply of O2 to the sediment by altering photosynthetic O2 production at the sediment surface, and increasing the exchange area of the sediment–seawater interface and apparent diffusivity of the uppermost sediment layer. After the passage of an individual, pore-water [O2] profiles indicative of benthic photosynthesis recovered rapidly from the disturbance, but the pH of deeper pore water was altered. In situ, time series measurements of [O2] and hydrostatic pressure indicated that wind waves can increase the transport of O2 across both the sediment–seawater interface and the interface between the seawater surrounding E. cordatum and the adjacent sediment.

KEY WORDS: Bioturbation · Bioirrigation · Microphytobenthos · Benthic photosynthesis · Diffusion · Advection · Waves · Dissolved oxygen · Apparent diffusivity

Full text in pdf format