A tank system for studying benthic aquatic organisms at predictable levels of turbidity and sedimentation: Case study examining coral growth

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 corresponding 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 ϭ ϳ1-16 mg L Ϫ1 ), whereas the growth rates of P. cylindrica were unaffected by particle load. The shading effects corresponding to 16 mg SPM L Ϫ1 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.

Comparative analysis of energy allocation to tissue and skeletal growth in corals

“…To assess the nature of deviations from these model assumptions, we analyzed data on tissue and skeletal growth for small colonies of G. retiformis (ϳ2.5 cm radius) and branches of P. cylindrica (4.5-6.5 cm length, ): filt 0.6-0.9, raw 1.8-2.9, low 3.6-4.4, high 14.4-17.2. 0.5-0.7 cm radius) from the study by Anthony and Fabricius (2000). Colony sizes of G. retiformis thus approximated r crit (see above), and branch dimensions for P. cylindrica satisfied r Ͻ r crit and Ͻ crit .…”

“…First, to compare effects of tissue mass, tissue quality, and skeletal density on energy investment patterns as a function of morphology and size, we developed a mathematical growth model based on coral geometry and the bioenergetics of tissue synthesis and calcification. Second, to assess variation in energy allocation patterns in response to environmental stress (and thus partially examine model assumptions and deviations from predictions), we examined patterns of energy allocation for colonies of a hemispherical and a branching coral species subjected to manipulated light and sediment levels in a tank experiment (see Anthony 1999b). Third, to investigate the trophic basis for patterns of energy allocation to tissue and skeleton under varying resource (light) and stress (sediment) conditions, we analyzed empirical growth data using the model of scope for growth (SfG) defined as the difference between energy acquisition and loss (Warren and Davis 1967;Maltby 1999; see also Sebens 1979;Kim and Lasker 1998).…”

“…Tissue parameters: Estimates of mass-specific energy content ( T ) were based on the enthalpy of the major tissue constituents: lipid (39.5 J mg Ϫ1 ), protein (23.9 J mg Ϫ1 ), and carbohydrates (17.5 J mg Ϫ1 , Gnaiger and Bitterlich 1984;Anthony and Fabricius 2000). Recent biochemical data for eight coral species (S. Leuzinger pers.…”

Ingestion and assimilation of nitrogen from benthic sediments by three species of coral

“…Several recent studies show that corals feed on, and benefit from, suspended and sedimenting particles (Anthony 1999a(Anthony , 1999b2000;Anthony and Fabricius 2000;Mills et al 2004). Likewise, corals can sort sediments on their surfaces and remove specific particles (Mills and Sebens 1997).…”

Phototropic growth in a reef flat acroporid branching coral species

“…Given the central role of photosynthesis in supplying the energetic needs of corals and their symbionts, light plays a key role in the biology and development of corals. Similar to plants, corals need sufficient external light intensities to have enough energy for survival, growth and reproduction Anthony, 1999) while minimizing the chances of photoinhibition and photodamage (Jones and Hoegh-Guldberg, 2001). It is common for terrestrial plants to use plant geometry and physiology to optimize their photosynthetic response (reviewed by Herbert, 1996).…”