A tank system for studying benthic aquatic organisms at predictable levels of turbidity and sedimentation: Case study examining coral growth
Limnol. Oceanogr., 44(6), 1999, 1415-1422 | DOI: 10.4319/lo.19188.8.131.525
ABSTRACT: A tank system is described for long-term exposure of sessile organisms to well-defined ranges of particle loads on a background of natural flowing seawater. Using low technology and a simple mathematical model, the concentration of suspended particulate matter (SPM) and the rate of sedimentation could be predicted and sustained with high precision. The system and operational procedures were tested in an 8-week experiment investigating the effect of SPM concentrations on the growth rates of two species of symbiotic scleractinian coral (Goniastrea retiformis and Porites cylindrica). To also evaluate the effect of shading by SPM on coral growth, two light levels corre-sponding to 3-4-m depth at the low and high particle concentrations were included in the design. The growth rates of corals in control tanks were not significantly different from those of conspecifics in situ. However, the patterns of growth rates vs. SPM and shading treatments differed between species. The growth rates of G. retiformis generally increased as a function of SPM concentration (range =~ 1-16 mg L-1), whereas the growth rates of P. cylindrica were unaffected by particle load. The shading effects corresponding to 16 mg SPM L-1 at 3-4-m depth resulted in significantly reduced growth rates in both species. I hypothesize that the different growth patterns displayed by the two species are the results of different abilities to utilize SPM as a food source or different susceptibilities to SPM as a mechanical stress factor. The high level of environmental control and the constancy of SPM treatment levels were reflected in the absence of tank effects on growth rates and provided sufficient statistical power to detect relatively small differences in growth rates between corals from different treatments.