The effect of flow and morphology on boundary layers in the scleractiniansDichocoenia stokesii (Milne-Edwards and Haime) and Stephanocoenia michilini (Milne-Edwards and Haime)
Dj. Gardella et Pj. Edmunds, The effect of flow and morphology on boundary layers in the scleractiniansDichocoenia stokesii (Milne-Edwards and Haime) and Stephanocoenia michilini (Milne-Edwards and Haime), J EXP MAR B, 256(2), 2001, pp. 279-289
Citations number
37
Categorie Soggetti
Aquatic Sciences
Journal title
JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY
Mass transfer characteristics of scleractinian corals are affected by their
skeletal morphology and the concentration gradients that develop as a cons
equence of the interactions of their morphology and biomass with the overly
ing seawater. These interactions can have a profound effect on coral metabo
lism. In this study, boundary layer characteristics were compared between d
ifferent size colonies of the corals Dichocoenia stukesii and Srephanocoeni
a michilini to determine the relative roles of colony size and corallite st
ructures (i.e. surface roughness) in mass transfer. Colonies of both specie
s were rounded in shape, but differed in small-scale roughness as measured
by the elevation of corallites. Additionally, D. srokesii had a greater asp
ect ratio than S. michilini, and their colonies were slightly taller fur a
given diameter. Boundary layers were characterized by placing dead coral sk
eletons in a flow tank and estimating shear velocities (u*) at different fl
ow speeds. The effects of Row speed, size, and roughness on shear velocitie
s were estimated for two juvenile size classes (10-20 and 30-40 mm diameter
) of each species that were exposed to unidirectional Row regimes (4 and 17
cm s(-1)). Shear velocities were significantly greater in high, compared t
o low flow, and there was a significant interaction between colony size and
surface roughness: the interaction was caused by a difference in magnitude
, rather than direction, of the effect of roughness and size on u*. Thus, t
here was a greater degree of turbulence at high flow compared to low flow,
regardless of roughness or size, and the greatest turbulence occurred over
large colonies of D. stokesii at high Row. Together, these results suggest
that boundary layers around small corals are heavily influenced by upstream
roughness elements, and more strongly affected by flow regimes than skelet
al features. The relationship between colony morphology (i.e. aspect ratio
and, possibly, surface roughness) and boundary layer characteristics may be
non-linear in small corals. (C) 2001 Elsevier Science B.V. All rights rese
rved.