CO2-Driven Ocean Acidification Alters and Weakens Integrity of the Calcareous Tubes Produced by the Serpulid Tubeworm, Hydroides elegans

Abstract

As a consequence of anthropogenic CO2-driven ocean acidification (OA), coastal waters are becoming increasingly challenging for calcifiers due to reductions in saturation states of calcium carbonate (CaCO3) minerals. The response of calcification rate is one of the most frequently investigated symptoms of OA. However, OA may also result in poor quality calcareous products through impaired calcification processes despite there being no observed change in calcification rate. The mineralogy and ultrastructure of the calcareous products under OA conditions may be altered, resulting in changes to the mechanical properties of calcified structures. Here, the warm water biofouling tubeworm, Hydroides elegans, was reared from larva to early juvenile stage at the aragonite saturation state (ΩA) for the current pCO2 level (ambient) and those predicted for the years 2050, 2100 and 2300. Composition, ultrastructure and mechanical strength of the calcareous tubes produced by those early juvenile tubeworms were examined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and nanoindentation. Juvenile tubes were composed primarily of the highly soluble CaCO3 mineral form, aragonite. Tubes produced in seawater with aragonite saturation states near or below one had significantly higher proportions of the crystalline precursor, amorphous calcium carbonate (ACC) and the calcite/aragonite ratio dramatically increased. These alterations in tube mineralogy resulted in a holistic deterioration of the tube hardness and elasticity. Thus, in conditions where ΩA is near or below one, the aragonite-producing juvenile tubeworms may no longer be able to maintain the integrity of their calcification products, and may result in reduced survivorship due to the weakened tube protection.

Effect of temperature rise and ocean acidification on growth of calcifying tubeworm shells (<i>Spirorbis spirorbis</i>): an in situ benthocosm approach

“…However, the tubes that are formed at lower CaCO 3 saturation may be more fragile. This is in line with results from cultured juvenile worm tubes of the tropical serpulid species Hydroides elegans, which showed reductions in shell hardness and wall thickness at lowered pH and CaCO 3 saturation states (Chan et al, 2012Li et al, 2014).…”

“…Most studies have focused on the tropical species Hydroides elegans (Lane et al, 2013;Chan et al, 2012Chan et al, , 2013Mukherjee et al, 2013;Li et al, 2014). The results indicated reduced growth, increased porosity and reduced mechanical strength of the worm tubes, as well as increased mortality of larvae at lowered pH (< 7.9).…”

Proteomic response of marine invertebrate larvae to ocean acidification and hypoxia during metamorphosis and calcification

“…Diverting their finite energy resources to cope with the climatic changes would disrupt these energy-expensive processes. The larval shells or tubes are made of the CaCO 3 mineral aragonite, which is highly soluble in low pH seawater (Chan et al, 2012). Even a slight decrease in pH (from control pH 8.1 to 7.7) delays or hinders the calcification processes in the larvae of metamorphosing tubeworms .…”

Effects of hypoxia and non-lethal shell damage on shell mechanical and geochemical properties of a calcifying polychaete

“…This process is highly associated with the fitness and survival of calcifying organisms because shell growth not only allows continuous somatic growth, but also strengthens protection against physical and chemical damages. The protective role of shells is particularly important under life-threatening conditions (e.g., following nonlethal shell damage), where many calcifying organisms are able to produce stronger shells at a higher rate to increase physical protection (Cheung et al, 2004;Brookes and Rochette, 2007;Hirsch et al, 2014). Indeed, such inducible defence response via enhanced calcification plays an important role in the survival of calcifying organisms (Harvell, 1990).…”