Ocean acidification alters anti-predator responses in a competitive dominant intertidal mussel

A global synthesis of predation on bivalves

Predation is a dominant structuring force in ecological communities. In aquatic environments, predation on bivalves has long been an important focal interaction for ecological study because bivalves have central roles as ecosystem engineers, basal components of food webs, and commercial commodities. Studies of bivalves are common, not only because of bivalves' central roles, but also due to the relative ease of studying predatory effects on this taxonomic group. To understand patterns in the interactions of bivalves and their predators we synthesised data from 52 years of peer-reviewed studies on bivalve predation. Using a systematic search, we compiled 1334 studies from 75 countries, comprising 61 bivalve families (N = 2259), dominated by Mytilidae (29% of bivalves), Veneridae (14%), Ostreidae (8%), Unionidae (7%), and Dreissenidae and Tellinidae (6% each). A total of 2036 predators were studied, with crustaceans the most studied predator group (34% of predators), followed by fishes (24%), molluscs (17%), echinoderms (10%) and birds (6%). The majority of studies (86%) were conducted in marine systems, in part driven by the high commercial value of marine bivalves. Studies in freshwater ecosystems were dominated by non-native bivalves and non-native predator species, which probably reflects the important role of biological invasions affecting freshwater biodiversity. In fact, while 81% of the studied marine bivalve species were native, only 50% of the freshwater species were native to the system. In terms of approach, most studies used predation trials, visual analysis of digested contents and exclusion experiments to assess the effects of predation. These studies reflect that many factors influence bivalve predation depending on the species studied, including (i) species traits (e.g. behaviour, morphology, defence mechanisms), (ii) other biotic interactions (e.g. presence of competitors, parasites or diseases), and (iii) environmental context (e.g. temperature, current velocity, beach exposure, habitat complexity). There is a lack of research on the effects of bivalve predation at the population and community and ecosystem levels (only 7% and 0.5% of studies respectively examined impacts at these levels). At the population level, the available studies demonstrate that predation can decrease bivalve density through consumption or the reduction of recruitment. At the community and ecosystem level, predation can trigger effects that cascade through trophic levels or effects that alter the ecological functions bivalves perform. Given the conservation and commercial importance of many bivalve species, studies of predation should be pursued in the context of global change, particularly climate change, acidification and biological invasions.

Effects of ocean acidification and polystyrene microplastics on the oysters Crassostrea gigas: An integrated biomarker and metabolomic approach

The adverse impacts of microplastics (MPs) or ocean acidification (OA) on mollusks have been widely reported, however, little is known about their combined effects on mollusks. The oysters Crassostrea gigas were exposed to two sizes of polystyrene MPs with 1 × 104 particles/L (small polystyrene MPs (SPS-MPs): 6 μm, large polystyrene MPs (LPS-MPs): 50-60 μm) at two pH levels (7.7 and 8.1) for 14 days. The antagonistic effects between MPs and OA on oysters were mainly observed. Single SPS-MPs exposure can induce CAT enzyme activity and LPO level in gills, while LPS-MPs exposure alone can increase PGK and PEPCK gene expression in digestive glands. Ocean acidification can increase clearance rate and inhibit antioxidant enzyme activity, whereas combined exposure of OA and SPS-MPs can affect the metabolomic profile of digestive glands. This study emphasized that the potential toxic effects of MPs under the scene of climate change should be concerned.

Effects of nano-TiO2 and pentachlorophenol on the bioenergetics of mussels under predatory stress

Organic and nanoparticle pollutants are the main environmental problems affecting marine species, which have received great attention. However, the combined effect of pollutants on marine life in the presence of predators needs to be clarified. In this study, the effects of pentachlorophenol (PCP) and titanium dioxide nanoparticles (nano-TiO2) on the energy metabolism of mussels (Mytilus coruscus) in the presence of predators were assessed through cellular energy allocation (CEA) approach. Mussels were exposed to PCP (0, 1, and 10 μg/L), nano-TiO2 (1 mg/L, 25 and 100 nm), and predators (Portunus trituberculatus presence/absence) for 14 days. Exposure to high concentrations of PCP (10 μg/L) with small particle size nano-TiO2 (25 nm) decreased cellular energy stores (carbohydrates, lipids, and proteins) and increased cellular energy demand (measured as the activity of the mitochondrial electron transport system, ETS). During the first 7 days, energy was supplied mainly through the consumption of carbohydrates, while lipids are mobilized to participate after 7 days. The presence of predators caused a further decrease in energy stores. These findings demonstrate that PCP, nano-TiO2 and predators have a negative impact on energy metabolism at the cellular level. Carbohydrates are not able to meet the metabolic demand, lipids need to be consumed, and energy metabolism was also mediated by the involvement of proteins. Overall, our results suggest that PCP, nano-TiO2 and predators disrupt the cellular energy metabolism of mussels through reduced cellular energy allocation, small particles and predators drive mussels to exert energetic metabolic adjustments for detoxification reactions when toxic contaminants are present.

Effects of ocean acidification and warming on physiological and behavioural responses of an herbivore snail to waterborne predator cues

Ocean Acidification (OA) and Ocean Warming (OW) represent major climate stressors that may disrupt species interactions. However, despite the knowledge about the impacts of OA and OW on the performance of individual species, it is still unclear how biological interactions can be modified by the combined effects of these stressors. Consequently, in this study, we assess the effects of changes in temperature (12 °C and 20 °C) and pCO2 (500 and 1600 μatm) levels in seawater, along with the presence/absence of waterborne cues from the predator crab Homalaspis plana on the physiological and behavioural performance of the snail Tegula atra. Snail consumption rate was positively affected by OW and negatively by predator cues whereas absorption efficiency (AE) was positively affected by OW without interactions among these stressors. Oxygen uptake of snails reared in OW conditions was greater than those in control conditions, but only at control pCO2 levels. When pCO2 level was also raised, the positive effect of warmer temperature on oxygen uptake was reduced. While biomass was negatively affected by OW, OA and predator cues, without interactions. In the presence of predator cues the self-righting times of snails were significantly slower in individuals reared at OW conditions. Additionally, OA and OW conditions do not affect the prey hunting, efficiency (consumption) and preference, and claw strength of the predatory crab. These results indicate that OA and OW affect physiological and behavioral traits of snails but no the predatory behavior of crab. This environmentally-induced decoupling of co-evolutionary predator-prey dynamics may have important consequences on the structure and stability of coastal communities and ecosystems under the influence of climate change.

Using meta-analysis to explore the roles of global upwelling exposure and experimental design in bivalve responses to low pH

Low pH conditions, associated with ocean acidification, represent threats to many commercially and ecologically important organisms, including bivalves. However, there are knowledge gaps regarding factors explaining observed differences in biological responses to low pH in laboratory experiments. Specific sources of local adaptation such as upwelling exposure and the role of experimental design, such as carbonate chemistry parameter changes, should be considered. Linking upwelling exposure, as an individual oceanographic phenomenon, to responses measured in laboratory experiments may further our understanding of local adaptation to global change. Here, meta-analysis is used to test the hypotheses that upwelling exposure and experimental design affect outcomes of individual, laboratory-based studies that assess bivalve metabolic (clearance and respiration rate) responses to low pH. Results show that while bivalves generally decrease metabolic activity in response to low pH, upwelling exposure and experimental design can significantly impact outcomes. Bivalves from downwelling or weak upwelling areas decrease metabolic activity in response to low pH, but bivalves from strong upwelling areas increase or do not change metabolic activity in response to low pH. Furthermore, experimental temperature, exposure time and magnitude of the change in carbonate chemistry parameters all significantly affect outcomes. These results suggest that bivalves from strong upwelling areas may be less sensitive to low pH. This furthers our understanding of local adaptation to global change by demonstrating that upwelling alone can explain up to 49 % of the variability associated with bivalve metabolic responses to low pH. Furthermore, when interpreting outcomes of individual, laboratory experiments, scientists should be aware that higher temperatures, shorter exposure times and larger changes in carbonate chemistry parameters may increase the chance of suppressed metabolic activity.

The influence of upwelling on key bivalves from the Humboldt and Iberian current systems

Eastern Boundary Upwelling Systems (EBUS) deliver cold, nutrient-rich waters, influencing coastal biota from the molecular to the ecosystem level. Although local upwelling (U) and downwelling (DU) conditions are often known, their influence on body attributes of relevant species has not been systematically compared within and between EBUS (i.e., below and above regional scales). Hence, we compared the physical-chemical characteristics of U and DU sites in the Humboldt Current system (Chile) and the Iberian Current system (Portugal). We then assessed the influence of U and DU upon eight body attributes in purple mussels (Perumytilus purpuratus) and Mediterranean mussels (Mytilus galloprovincialis), from the Humboldt and Iberian systems, respectively. We hypothesized that bivalves from U sites display better fitness, as measured by body attributes, regardless of their origin (EBUS). As expected, waters from U sites in both systems showed lower temperatures and pH, and higher nitrite concentrations. We also found that mussels from U sites showed better fitness than those in DU sites in 12 out of 16 direct U vs DU comparisons. Shell length, shell volume, organic content of soft-tissues, and mechanical properties of the shell averaged consistently higher in mussels from U sites in both Current systems. In addition, total weight, soft-tissue weight, shell weight and shell thickness were all higher in the U site at the Humboldt system but had less consistent differences at the Iberian system. Altogether, most results supported our working hypothesis and indicate that U conditions support better fitted mussels. The few attributes that did not exhibit the expected U vs DU differences in the Iberian system suggest that local and species-specific differences also play a role on the attributes of these species. These results may also serve as a reference point for further studies addressing the influence of upwelling in these productive, critically important systems.

Combined effects of climate change stressors and predators with contrasting feeding-digestion strategies on a mussel species

We investigated the combined effects of Ocean Warming (OW), Acidification (OA) and predator cues (Non-Consumptive Effects; NCEs) of two predators with contrasting feeding-digestion strategies on the mussel Perumytilus purpuratus. We considered starfish-NCEs (partially external digestion) and snail-NCEs (internal digestion). Mussels were exposed for 13 weeks to cross-factored OA (~500 and ~1400 μatm, pCO2) and OW (~15 and ~20 °C) conditions, in the presence/absence of NCEs from one or both predators. Mussels exposed to both NCEs exhibited smaller length and buoyant weight growth than those under control or snail-NCEs conditions. Mussels exposed to starfish-NCEs exhibited smaller wet mass than control mussels. OW and starfish-NCEs in isolation or combined with snail-NCEs increased mussel oxygen consumption. Byssal biogenesis was affected by the three-factors interaction. Clearance rates were affected by the OW × OA interaction. We suggest that mainly starfish-NCEs, in isolation or interacting with OA or/and OW, can threat mussel traits and the associated community.

Metabolic rate allometry in intertidal mussels across environmental gradients: The role of coastal carbonate system parameters in mediating the effects of latitude and temperature

We assess the role of direct and indirect effects of coastal environmental drivers (including the parameters of the carbonate system) on energy expenditure (MR) and body mass (M) of the intertidal mussel, Perumytilus purpuratus, across 10 populations distributed over 2800 km along the Southern Eastern Pacific (SEP) coast. We find biogeographic and local variation in carbonate system variables mediates the effects of latitude and temperature on metabolic rate allometry along the SEP coast. Also, the fitted Piecewise Structural Equation models (PSEM) have greater predictive ability (conditional R² = 0.95) relative to the allometric scaling model (R² = 0.35). The largest standardized coefficients for MR and M were determined by the influence of temperature and latitude, followed by pCO₂, pH, total alkalinity, and salinity. Thus, physiological diversity of P. purpuratus along the SEP coast emerges as the result of direct and indirect effects of biogeographic and local environmental variables.

Non-consumptive effects of a predatory snail (Acanthina monodon) on a dominant habitat-forming mussel species (Perumytilus purpuratus)

Predators can influence prey through direct consumption as well as through non-consumptive effects (NCEs). NCEs usually occur mediated by behavioral changes in the prey upon detection of predator cues. Such changes may involve reduction of feeding with a variety of physiological consequences. We evaluated NCEs from an intertidal predatory snail (Acanthina monodon) on a dominant habitat-forming mussel species (Perumytilus purpuratus) from the southeastern Pacific coast. We tested whether A. monodon exerts negative NCEs on clearance rate, oxygen consumption rate, biodeposit production, and between-valve gap size in P. purpuratus. We found that waterborne predator cues triggered a decrease in these variables except biodeposit production. However, the organic content of the biodeposits increased in the presence of predator cues. The snail's physical contact with the mussels strengthened the negative NCEs on between-valve gap size. Since P. purpuratus is a dominant filter-feeder and foundation species in rocky intertidal habitats, predator NCEs on this species might indirectly influence ecosystem-level processes and community structure.