Effects of ocean acidification on macroalgal communities

Abstract

There are high levels of uncertainty about how coastal ecosystems will be affected by rapid ocean acidification caused by anthropogenic CO 2 , due to a lack of data. The few experiments to date have been short-term (b 1 year) and reveal mixed responses depending on the species examined and the culture conditions used. It is difficult to carry out long-term manipulations of CO 2 levels, therefore areas with naturally high CO 2 levels are being used to help understand which species, habitats and processes are resilient to the effects of ocean acidification, and which are adversely affected. Here we describe the effects of increasing CO 2 levels on macroalgal communities along a pH gradient caused by volcanic vents. Macroalgal habitat differed at taxonomic and morphological group levels along a pH gradient. The vast majority of the 101 macroalgal species studied were able to grow with only a 5% decrease in species richness as the mean pH fell from 8.1 to 7.8. However, this small fall in species richness was associated with shifts in community structure as the cover of turf algae decreased disproportionately. Calcitic species were significantly reduced in cover and species richness whereas a few non-calcified species became dominant. At mean pH 6.7, where carbonate saturation levels were b 1, calcareous species were absent and there was a 72% fall in species richness. Under these extremely high CO 2 conditions a few species dominated the simplified macroalgal assemblage and a very few exhibited enhanced reproduction, although high CO 2 levels seemed to inhibit reproduction in others. Our data show that many macroalgal species are tolerant of long-term elevations in CO 2 levels but that macroalgal habitats are altered significantly as pH drops, contributing to a scant but growing body of evidence concerning the long-term effects of CO 2 emissions in vegetated marine systems. Further study is now needed to investigate whether the observed response of macroalgal communities can be replicated in different seasons and from a range of geographical regions for incorporation into global modelling studies to predict effects of CO 2 emissions on Earth's ecosystems.

Persistent natural acidification drives major distribution shifts in marine benthic ecosystems

“…Only the aragonite-calcifying Peyssonnelia rosa-marina was able to survive in the acidified waters, as previously noted in very shallow waters too [35]. Our results lend support to the idea rspb.royalsocietypublishing.org Proc.…”

“…R. Soc. B 282: 20150587 that high-magnesium-calcifying organisms are more sensitive to OA than aragonite-calcifying ones [35,36]. They also challenge the widespread concern over the global fate of calcified algae in the near future, as there are species such as P. rosa-marina showing a moderate resilience to OA [36].…”

Adaptation and acclimatization to ocean acidification in marine ectotherms: anin situtransplant experiment with polychaetes at a shallow CO2vent system

“…In our study, we did not carry out a systematic collection of polychaetes living around the CO 2 vents, our data requiring further validation; nonetheless, our sampling is the outcome of the haphazard selection of the larger adult individuals we could find. Thus, our measure represents an estimate for the 'mean maximum body size' that individuals of P. dumerilii and A. mediterranea reach when chronically exposed to conditions found inside or outside the CO 2 vents, including different pCO 2 levels, altered algal composition and habitat complexity among others [45,117]. Nevertheless, differences in body size patterns observed between A. mediterranea and P. dumerilii could be explained by the fact that the strain of P. dumerilii from the CO 2 vents shows overall a higher mean metabolic rate when compared with those of the non-acidified strain.…”

Calcareous green alga H alimeda tolerates ocean acidification conditions at tropical carbon dioxide seeps

“…Volcanic CO 2 seeps and areas of CO 2 upwelling have been described worldwide in temperate (Calosi et al 2013;Cigliano et al 2010;Hall-Spencer et al 2008;Inoue et al 2013;Johnson et al 2012;Porzio et al 2011) and tropical (Fabricius et al 2011(Fabricius et al , 2014Johnson et al 2012;Noonan et al 2013;Russell et al 2013;Uthicke and Fabricius 2012;Uthicke et al 2013) regions. So far, studies suggest reduced pH at CO 2 seeps in PNG lead to a decline in coral diversity with structurally complex species being particularly affected, and reduced taxonomic richness and density of coral juveniles, and low cover of crustose coralline algae (Fabricius et al 2011(Fabricius et al , 2014.…”