Plastic responses of bryozoans to ocean acidification

Abstract

Phenotypic plasticity has the potential to allow organisms to respond rapidly to global environmental change, but the range and effectiveness of these responses are poorly understood across taxa and growth strategies. Colonial organisms might be particularly resilient to environmental stressors, as organizational modularity and successive asexual generations can allow for distinctively flexible responses in the aggregate form. We performed laboratory experiments to examine the effects of increasing dissolved carbon dioxide (CO) (i.e. ocean acidification) on the colonial bryozoan sampled from two source populations within a coastal upwelling region of the northern California coast. Bryozoan colonies were remarkably plastic under these CO treatments. Colonies raised under high CO grew more quickly, investing less in reproduction and producing lighter skeletons when compared with genetically identical clones raised under current surface atmosphere CO values. Bryozoans held under high CO conditions also changed the Mg/Ca ratio of skeletal calcite and increased the expression of organic coverings in new growth, which may serve as protection against acidified water. We also observed strong differences between source populations in reproductive investment and organic covering reaction norms, consistent with adaptive responses to persistent spatial variation in local oceanographic conditions. Our results demonstrate that phenotypic plasticity and energetic trade-offs can mediate biological responses to global environmental change, and highlight the broad range of strategies available to colonial organisms.

Abiotic and biotic interactions in the diffusive boundary layer of kelp blades create a potential refuge from ocean acidification

“…This trend was less pronounced at pH 7.7 in the dark whereby the DBL oxygen concentrations looked similar for epiphytized and bare blades. The pH decrease in the mainstream seawater did not affect the respiration rates of the epiphyte/blade complex at the blade surface likely because bryozoans present a great plasticity and different strategies which enable them to cope with pH decrease (Swezey, Bean, Hill, et al., ; Swezey, Bean, Ninokawa, et al., ). Moreover, the pH fluctuations occurring in the microenvironment of seaweeds can reach very low levels, from 8.1 down to 7.0 in the dark (De Beer and Larkum, ; Hurd et al., ), and bryozoans living upon the blades may be used to these daily drops in the surrounding pH.…”

Individual and population level effects of ocean acidification on a predator-prey system with inducible defenses: bryozoan-nudibranch interactions in the Salish Sea

“…In the bryozoan C. cornuta, increased growth was associated with costs including reduced investment in reproduction and lighter skeletons (Swezey et al 2017a). We did not find a cost associated with calcifi- Table 2).…”

“…At pH 7.0, the domain was not filled after 75 d due to slow colony growth rates, so costs of defense are not displayed conditions. The calcifying bryozoans Electra pilosa (Saderne & Wahl 2013), Celleporella cornuta (Swezey et al 2017a) and Jellyella tuberculata (Swe zey et al 2017b) exhibited increased growth in response to moderately high pCO 2 , corresponding with moderately low pH conditions, relative to ambient (E. pilosa, 1200 μatm; C. cornuta, 1150 μatm; J. tuberculata, 1050 μatm). E. pilosa displayed a parabolic growth response curve exhibiting maximum growth at 1200 μatm (Saderne & Wahl 2013), similar to our results, suggesting these types of response curves may not be unusual in bryozoans.…”

“…. In C. cornuta, OA also increased the expression of protective organic coverings in areas of new growth, which can prevent dissolution while allowing calcification to continue (Swezey et al 2017a). A combination of strong chemical control over a calcifying space and protective membranes might be responsible for Membranipora's robust calcification response to OA.…”

“…In the Salish Sea and San Juan Archipelago, WA, USA, naturally low seawater pH levels result from regular upwelling and river input (Murray et al 2015). While open ocean pH averages well above 8.0 (Doney 2010), the San Juan Archipelago experiences pH around 7.8 and can reach as low as 7.67 in San Juan Channel during seasonal up welling (Sullivan 2012, Murray et al 2015. Consequently, the Salish Sea is a natural laboratory to investigate OA effects where organisms already experience pH values that open ocean organisms will likely not experience until the end of the century.…”