Ocean acidification drives global reshuffling of ecological communities

First published: 29 September 2022The paradigm that climate change will alter global marine biodiversity is one of the most widely accepted. Yet, its predictions remain difficult to test because laboratory systems are inadequate at incorporating ecological complexity, and common biodiversity metrics have varying sensitivity to detect change. Here, we test for the prevalence of global responses in biodiversity and community-level change to future climate (acidification and warming) from studies at volcanic CO2 vents across four major global coastal ecosystems and studies in laboratory mesocosms. We detected globally replicable patterns of species replacements and community reshuffling under ocean acidification in major natural ecosystems, yet species diversity and other common biodiversity metrics were often insensitive to detect such community change, even under significant habitat loss. Where there was a lack of consistent patterns of biodiversity change, these were a function of similar numbers of studies observing negative versus positive species responses to climate stress. Laboratory studies showed weaker sensitivity to detect species replacements and community reshuffling in general. We conclude that common biodiversity metrics can be insensitive in revealing the anticipated effects of climate stress on biodiversity—even under significant biogenic habitat loss—and can mask widespread reshuffling of ecological communities in a future ocean. Although the influence of ocean acidification on community restructuring can be less evident than species loss, such changes can drive the dynamics of ecosystem stability or their functional change. Importantly, species identity matters, representing a substantial influence of future oceans.Ivan Nagelkerken, Sean D. Connel

Is Ocean Acidification Really a Threat to Marine Calcifiers? A Systematic Review and Meta-Analysis of 980+ Studies Spanning Two Decades

First published: 07 August 2022Ocean acidification is considered detrimental to marine calcifiers, but mounting contradictory evidence suggests a need to revisit this concept. This systematic review and meta-analysis aim to critically re-evaluate the prevailing paradigm of negative effects of ocean acidification on calcifiers. Based on 5153 observations from 985 studies, many calcifiers (e.g., echinoderms, crustaceans, and cephalopods) are found to be tolerant to near-future ocean acidification (pH ≈ 7.8 by the year 2100), but coccolithophores, calcifying algae, and corals appear to be sensitive. Calcifiers are generally more sensitive at the larval stage than adult stage. Over 70% of the observations in growth and calcification are non-negative, implying the acclimation capacity of many calcifiers to ocean acidification. This capacity can be mediated by phenotypic plasticity (e.g., physiological, mineralogical, structural, and molecular adjustments), transgenerational plasticity, increased food availability, or species interactions. The results suggest that the impacts of ocean acidification on calcifiers are less deleterious than initially thought as their adaptability has been underestimated. Therefore, in the forthcoming era of ocean acidification research, it is advocated that studying how marine organisms persist is as important as studying how they perish, and that future hypotheses and experimental designs are not constrained within the paradigm of negative effects.Jonathan Y. S. Leung, Sam Zhang, and Sean D. Connel

Fabrication and lubrication performance of sustainable Pickering‐like water‐in‐water emulsions using plant protein microgels

Aqueous multiphasic systems have attracted a great deal of interest recently owing to the growing demands of sustainability for the development of stable “oil-free” emulsions, often complicated by their limited stability against droplet coarsening. Although particles may provide ultrastability to water-in-water (W/W) emulsions formed in phase-separating polymer systems, the need for lubrication in such W/W emulsions presents an important challenge for their use in diverse applications. Herein, W/W Pickering emulsions were stabilized by sustainable plant protein (pea)-based microgels (PPM) using starch and xanthan gum as the biopolymers to generate the W/W phase separating droplet structures. The lubricity of these systems was compared with that of parallel systems stabilized by animal (whey) protein microgels (WPM). New results reveal that PPM are more soft and adhesive than WPM and outperform the latter in boundary lubrication performance, in striking contrast to the behavior of the non-microgelled pea or whey proteins. Furthermore, the PPM tend to stabilize a different, less spherical type of W/W droplet than the WPM that may explain the lower friction observed in PPM-stabilized systems. The novel approach of fabricating W/W emulsions stabilized by sustainable microgels opens up new solutions in designing aqueous lubricants for future nutritional and biomedical applications

Ocean acidification may slow the pace of tropicalization of temperate fish communities

Poleward range extensions by warm-adapted sea urchins are switching temperate marine ecosystems from kelp-dominated to barren-dominated systems that favour the establishment of range-extending tropical fishes. Yet, such tropicalization may be buffered by ocean acidification, which reduces urchin grazing performance and the urchin barrens that tropical range-extending fishes prefer. Using ecosystems experiencing natural warming and acidification, we show that ocean acidification could buffer warming-facilitated tropicalization by reducing urchin populations (by 87%) and inhibiting the formation of barrens. This buffering effect of CO₂ enrichment was observed at natural CO₂ vents that are associated with a shift from a barren-dominated to a turf-dominated state, which we found is less favourable to tropical fishes. Together, these observations suggest that ocean acidification may buffer the tropicalization effect of ocean warming against urchin barren formation via multiple processes (fewer urchins and barrens) and consequently slow the increasing rate of tropicalization of temperate fish communities.Ericka O.C. Coni, Ivan Nagelkerken, Camilo M. Ferreira, Sean D. Connell and David J. Boot

Phenotypic responses in fish behaviour narrow as climate ramps up

Natural selection alters the distribution of phenotypes as animals adjust their behaviour and physiology to environmental change. We have little understanding of the magnitude and direction of environmental filtering of phenotypes, and therefore how species might adapt to future climate, as trait selection under future conditions is challenging to study. Here, we test whether climate stressors drive shifts in the frequency distribution of behavioural and physiological phenotypic traits (17 fish species) at natural analogues of climate change ( CO2 vents and warming hotspots) and controlled laboratory analogues (mesocosms and aquaria). We discovered that fish from natural populations (4 out of 6 species) narrowed their phenotypic distribution towards behaviourally bolder individuals as oceans acidify, representing loss of shyer phenotypes. In contrast, ocean warming drove both a loss (2/11 species) and gain (2/11 species) of bolder phenotypes in natural and laboratory conditions. The phenotypic variance within populations was reduced at CO2 vents and warming hotspots compared to control conditions, but this pattern was absent from laboratory systems. Fishes that experienced bolder behaviour generally showed increased densities in the wild. Yet, phenotypic alterations did not affect body condition, as all 17 species generally maintained their physiological homeostasis (measured across 5 different traits). Boldness is a highly heritable trait that is related to both loss (increased mortality risk) and gain (increased growth, reproduction) of fitness. Hence, climate conditions that mediate the relative occurrence of shy and bold phenotypes may reshape the strength of species interactions and consequently alter fish population and community dynamics in a future ocean.Almendra Rodriguez, Dominguez, Sean D. Connell, Ericka O. C. Coni, Minami Sasaki, David J. Booth, Ivan Nagelkerke

Ocean acidification boosts reproduction in fish via indirect effects

Ocean acidification affects species populations and biodiversity through direct negative effects on physiology and behaviour. The indirect effects of elevated CO₂ are less well known and can sometimes be counterintuitive. Reproduction lies at the crux of species population replenishment, but we do not know how ocean acidification affects reproduction in the wild. Here, we use natural CO₂ vents at a temperate rocky reef and show that even though ocean acidification acts as a direct stressor, it can indirectly increase energy budgets of fish to stimulate reproduction at no cost to physiological homeostasis. Female fish maintained energy levels by compensation: They reduced activity (foraging and aggression) to increase reproduction. In male fish, increased reproductive investment was linked to increased energy intake as mediated by intensified foraging on more abundant prey. Greater biomass of prey at the vents was linked to greater biomass of algae, as mediated by a fertilisation effect of elevated CO₂ on primary production. Additionally, the abundance and aggression of paternal carers were elevated at the CO₂ vents, which may further boost reproductive success. These positive indirect effects of elevated CO₂ were only observed for the species of fish that was generalistic and competitively dominant, but not for 3 species of subordinate and more specialised fishes. Hence, species that capitalise on future resource enrichment can accelerate their reproduction and increase their populations, thereby altering species communities in a future ocean.Ivan Nagelkerken, Tiphaine Alemany, Julie M. Anquetin, Camilo M. Ferreira, Kim E. Ludwig, Minami Sasaki, Sean D. Connel

The Contrasting Behavior of Strongly and Weakly Interfacially Active Asphaltenes on the Rheology of Model Waxy Oils

Asphaltenes and waxes are two components of crude oil that cause flow assurance issues. Although the components coexist, few studies have considered the effect of asphaltenes on wax crystallization and gel-forming properties. Furthermore, the current understanding remains contradictory with both wax-alleviating and wax-aggravating behaviors observed. In this study, asphaltenes extracted from a heavy crude oil were fractionated into strongly and weakly interfacially active asphaltenes by partitioning at a water–oil interface. The two asphaltene fractions exhibited contrasting physicochemical properties, with the strongly interfacially active asphaltenes (IAA) being more polar due to their higher heteroatom content (particularly S and O) and forming larger aggregates in the solution compared to the weakly interfacially active asphaltenes (referred to as remaining asphaltenes, RA). The two asphaltene fractions lowered both the wax gelation temperature and wax appearance temperature; however, the effect was comparable. The unit cell lattice structure of the wax particle remained unchanged in the presence of asphaltenes, but the wax particles were found to be smaller with RA compared to IAA. However, the key finding of the study is how the two asphaltene fractions affected the yield strength of the gelled wax. For RA, the yield strength was lowered with an increasing asphaltene concentration, whereas for IAA, the overall effect was to increase the gel yield strength. Because the properties of the wax particles were largely unchanged by the two asphaltene fractions, the result suggests that the asphaltene–asphaltene interaction contributes to the overall yield strength. It was shown that the interaction between RA and RA is repulsive with negligible adhesion, whereas that between IAA and IAA is attractive with strong adhesion. These structure-breaker and structure-maker properties of the two asphaltenes confirm that the asphaltene–asphaltene interaction significantly contributes to modifying the yield strength of a waxy gel