Impacts of Acidic Seawater on Early Developmental Stages of Fucus gardneri at Burrard Inlet, British Columbia

Abstract

Increases in stressors associated with climate change such as ocean acidification and warming temperatures pose a serious threat to intertidal ecosystems. Of crucial importance are the effects on foundational species, such as fucoid algae, a critical component of rocky intertidal shorelines around the world. The impact of climate change on adult fronds of fucoid algae has been documented but effects on early developmental stages are not as well understood. In particular, ocean acidification stands to impact these stages because zygotes and embryos are known to maintain internal pH and develop a cytosolic pH gradient during development. To assess the effects of seawater acidification on early development, zygotes of Fucus gardneri were exposed to artificial seawater (ASW) buffered to conditions that approximate current global averages and extend largely beyond future projections. Exposure to acidic seawater had significant effects on embryonic growth. Specifically, rhizoid elongation, which occurs by a process known as tip growth, was significantly reduced with each 0.5 unit drop in pH. When pH was decreased from 8.0 to 7.5, which is similar to levels that have been observed in Burrard Inlet, there was reduction in rhizoid growth rate of almost 20%. Under more extreme conditions, at pH 6, rhizoid growth rates were reduced by 64% in comparison to embryos exposed to seawater at pH 8.0. On the other hand, acidic seawater had no effect on earlier processes; zygotes became multicellular embryos with well-formed rhizoids on a similar time course within the first 24 h of development, even when exposed to pH 6, an extreme pH well below what is expected in the future. This suggests that zygotes can maintain an internal pH that allows germination and cell division to occur. Tip growth, however, depends on the extended maintenance of an internal pH gradient. It is therefore possible that disruptions to this gradient could account for the observed reductions in rhizoid elongation. Under acidic conditions proton influx into the cell becomes energetically more favorable than at pH 8, and expulsion would be more difficult. This could disrupt the cytosolic pH gradient and in turn affect rhizoid growth.

Examining the reproductive success of bull kelp (Nereocystis luetkeana, Phaeophyceae, Laminariales) in climate change conditions

“…Bull kelp exposure to warm temperatures has also been shown to reduce adult blade morphological plasticity to changes in hydrodynamic flow regimes (Supratya et al, 2020), but the physiological impacts of warm waters on bull kelp need to be further studied. Studies of bull kelp microscopic developmental stages in British Columbia and Alaska have observed that increased temperatures have resulted in reductions in settlement and reduced germination and growth (Lind & Konar, 2017; Muth et al, 2019; Schiltroth, 2021), but the impact of rising temperatures on microscopic bull kelp stages in the southern portion of their range in Northern California remains unclear. California bull kelp populations represent the range extreme of bull kelp, existing in low‐latitude areas that are the most exposed to El Niño–Southern Oscillation (ENSO) warm water events when compared with more northern populations.…”

Kelps on demand: Closed‐system protocols for culturing large bull kelp sporophytes for research and restoration

“…The bull kelp, Nereocystis luetkeana , is an ecologically important canopy forming species in the Northeast Pacific (Berry et al., 2021; Schiltroth, 2021). Extensive, climate‐driven declines of N. luetkeana have received widespread attention and prompted numerous research and conservation initiatives (Beas‐Luna et al., 2020; Berry et al., 2021; Carney et al., 2005; Oster et al., 2020; Pfister et al., 2018; Rogers‐Bennett & Catton, 2019; Schroeder et al., 2020; Springer et al., 2006).…”

Reproductive Ecology of the Rockweed Fucus distichus in an Urban Estuary

“…These stressors can be detrimental to the distribution, survival, and development of many coastal organisms, but responses to these changes vary across species and life cycle stages within a species (AghaKouchak et al, 2014;Bible et al, 2017;Chang et al, 2018b). For example, the timing of F. gardneri zygote germination was not affected by acidified conditions but in the following developmental stage its rhizoid growth decreased (Schiltroth et al, 2019). However, in the same study, zygote germination success was negatively affected by increased water temperature (Schiltroth et al, 2019).…”

“…For example, the timing of F. gardneri zygote germination was not affected by acidified conditions but in the following developmental stage its rhizoid growth decreased (Schiltroth et al, 2019). However, in the same study, zygote germination success was negatively affected by increased water temperature (Schiltroth et al, 2019). This highlights the complexity of responses that macroalgal species have to climate change and why studying unique responses for each species and life stage is important.…”

“…SFB, like most estuaries, is an example of a highly variable system and organisms in these systems must adapt and evolve to variable environmental conditions. However, responses to stressors and changing conditions vary not only amongst species but within life stages within a species (AghaKouchak et al, 2014;Bible et al, 2017;Chang et al, 2018b;Schiltroth et al, 2019). Under highly variable environmental conditions of salinity, pH, and air temperatures, this study examined the multiple stages of F. distichus: 1) oogonia release under different salinity and pH conditions, 2) juvenile density and the influence of salinity, pH, and air temperature on juvenile abundance, 3) adult density, 4) total density and cover, and 5) distribution in SFB.…”