Daily cycles of suspended sand at coral reefs: A biological control

Abstract

Sediment resuspension has a major ecological role in many coastal habitats, lakes, and marine environments. Waves and currents are generally thought to be the major control on sediment resuspension. In this study, the temporal and spatial distributions of suspended sand concentrations (SSAC) were measured at five coral reefs in the northern Gulf of Aqaba, Red Sea, by directly filtering seawater through 100-m mesh nets. Levels of nearbottom SSAC were twice as high during the day (4.8-9.7 mg m Ϫ3 ) than at night (2.3-5.2 mg m Ϫ3). Vertical profiles showed a sharp increase of SSAC (2-6-fold) toward the bottom during the daytime but not at night. The contributions of wind, waves, and currents to variations in SSAC were nonsignificant except during rare southern storms. Temporal and spatial changes in the level of SSAC during the day corresponded with the abundance of benthivorous fish and their activity pattern. Resuspension activities by fish numbered Ͼ1.5 resuspension events m Ϫ2 h Ϫ1 and were confined to daytime. An in situ experiment in which fish were excluded from a large section (250 m 2 ) of the reef resulted in elimination of the day-night differences and a significant decrease in daytime SSAC over the treated reef section in comparison to the open, control sites. This study is the first report of a daily pattern of suspended sediment at coral reefs with fish activity as its causative agent. AcknowledgmentsWe are indebted to I. Ayalon, M. Ohavia, Y. Shiff, D. Weil, E. Booton, M. Pery, A. Pery, A. Brandes, R. and C. Wyeth, A. and A. Bookai, S. Rickel, R. Motro, S. Eckstein, R. Holzman, T. Zalogin, A. Rivlin, R. Shem-Tov, and Lt. Cdr. Amr Attia for their professional and most dedicated help with the field and laboratory work. S. Fridman and K. Madmoni greatly assisted with the English writing. A. Almogi-Labin helped with the sediment analysis. Special thanks to M. Reidenbach, M. Brennan, and the journal reviewers P. Larcombe and an anonymous reviewer, who greatly improved the manuscript.

In situ feeding and element removal in the symbiont‐bearing sponge Theonella swinhoei: Bulk DOC is the major source for carbon

“…For a description of the study site, see Yahel et al (1998Yahel et al ( , 2002. Two sampling sessions were conducted: the first in 1998 at the height of the summer stratification (10 specimens) and the second in 2000 soon after the termination of spring bloom (20 specimens).…”

Intense Benthic Grazing on Phytoplankton in Coral Reefs Revealed Using the Control Volume Approach

“…At both reef sites, coral cover was approximately 14%, with a typical topographic relief of the order of 0.5 m . The local reef community was described by Fishelson (1971), Benayahu and Loya (1977), and Yahel et al (2002). Briefly, the reef was dominated by stony corals and a diverse guild of phytoplanktivores, including sponges, bivalves, ascidians, actinians and polychaetes (see Results).…”

Resuspension by fish facilitates the transport and redistribution of coastal sediments

“…6B). Previous work already associated groundfish activity with the formation of BNLs (Yahel et al 2002(Yahel et al , 2008. When such resuspension occurs along a slope, fine resuspended particles can be transported from the slope bottom by offshore currents to form INLs.…”

“…Lateral transport and dispersion of marine sediments require the initial resuspension of surface sediments, which is not necessarily caused by physical forces. Instead, in many marine habitats, the activity of organisms such as fish (Yahel et al 2002(Yahel et al , 2008, marine mammals (Nelson et al 1987), and benthic invertebrates (Colin et al 1986) controls sediment resuspension. Recently, we showed that the activity of groundfish (i.e., fish that live near or at the seafloor) controls sediment resuspension in Saanich Inlet (Yahel et al 2008), a deep fjord with anoxic bottom water in Vancouver Island, British Columbia, Canada (Fig.…”