Valeria Montalto

Parameterisation of bivalve functional traits for mechanistic eco-physiological dynamic energy budget (DEB) models

Mechanistic models such as those based on dynamic energy budget (DEB) theory are emergent ecomechanics tools to investigate the extent of fitness in organisms through changes in life history traits as explained by bioenergetic principles. The rapid growth in interest around this approach originates from the mechanistic characteristics of DEB, which are based on a number of rules dictating the use of mass and energy flow through organisms. One apparent bottleneck in DEB applications comes from the estimations of DEB parameters which are based on mathematical and statistical methods (covariation method). The parameterisation process begins with the knowledge of some functional traits of a target organism (e. g. embryo, sexual maturity and ultimate body size, feeding and assimilation rates, maintenance costs), identified from the literature or laboratory experiments. However, considering the prominent role of the mechanistic approach in ecology, the reduction of possible uncertainties is an important objective. We propose a revaluation of the laboratory procedures commonly used in ecological studies to estimate DEB parameters in marine bivalves. Our experimental organism was Brachidontes pharaonis. We supported our proposal with a validation exercise which compared life history traits as obtained by DEBs (implemented with parameters obtained using classical laboratory methods) with the actual set of species traits obtained in the field. Correspondence between the 2 approaches was very high (>95%) with respect to estimating both size and fitness. Our results demonstrate a good agreement between field data and model output for the effect of temperature and food density on age-size curve, maximum body size and total gamete production per life span. The mechanistic approach is a promising method of providing accurate predictions in a world that is under in creasing anthropogenic pressure.

An energy budget for the subtidal bivalve Modiolus barbatus (Mollusca) at different temperatures

Clearance rates, respiration rates and food absorption efficiencies of the commercially interesting subtidal bivalve Modiolus barbatus were measured at different temperatures under laboratory conditions and scope for growth calculated. Clearance rates were highest at temperatures from 20 °C to 28 °C, whereas respiration rate was maximal at 9 °C and minimal at 26 °C. Highest mean values of absorbed energy occurred at 20 °C and 26 °C. Scope for growth trend had negative values at 9 °C, 15 °C and 28 °C and positive values at temperatures 20 °C and 26 °C. The profitable thermal window for M. barbatus to have energy sufficient for growth and reproduction corresponded to <5 months per year. Seawater temperature increases will potentially impact the eco-physiological responses of subtidal M. barbatus causing life history traits to change with important repercussions for subtidal biodiversity in the Mediterranean.

A Bioenergetics Framework for Integrating the Effects of Multiple Stressors: Opening a ‘Black Box’ in Climate Change Research *

Abstract Climate change is already impacting marine ecosystems across a range of scales, from individual physiology, to changes in species interactions and community structure, and ultimately to patterns in geographic distribution. Predicting how marine ecosystems will respond to environmental change is a significant challenge because vulnerability to climatic and non-climatic stressors is highly variable, and depends on an organisms functional traits, tolerance to stressors, and the environment in which it lives. We present a mechanistic approach based on biophysical and dynamic energy budget models that integrates the cumulative effects of multiple environmental stressors (temperature and food) and stress associated with the presence of predators (the “fear of being eaten”), with the functional traits of an organism. We describe how multiple factors such as feeding time, food availability, and weather can be combined into a few simple metrics and explore how the physiological and behavioral impacts of predation risk can be included in this framework by altering prey feeding time and performance. Importantly, we highlight several critical gaps in our basic understanding of the fundamental mechanisms that drive responses to multiple stressors in natural systems. The framework presented here is, thus, intended to serve as a guide for the formulation of explicit, testable hypotheses and further controlled experimentation.

Eco-physiological response of two marine bivalves to acute exposition to commercial Bt-based pesticide

Microbial products based on the entomopathogenic bacterium Bacillus thuringiensis (Bt) are among the most common biopesticides used worldwide to suppress insect pests in forests, horticulture and agricultural crops. Some of the effects of commercial Bt have been recorded for terrestrial and freshwater non-target organisms but little research is available on marine fauna. Nevertheless, due to the contiguity of agro-ecosystems and coastal habitats, marine fauna may be highly influenced by this control method. We studied the effect of a commercial Bt product on the physiological and ecological responses and the energy budget of two of the most frequent marine intertidal bivalves in the Mediterranean, the native Mytilaster minimus and the invasive Brachidontes pharaonis. To test the effects experimentally, we simulated the worst scenarios possible using the average dose applied to fields and a hypothetical accumulation dose. The results showed the feeding rates of both species were affected detrimentally by the different experimental conditions; higher concentrations led to higher respiration rates, however neither species showed any significant difference in excretion rates. The biopesticide had a significant effect on the energy budget, the values decreasing with doses. In addition, it led to high mortality for the worst treatments and, in both species, induced significantly higher cardiac activity than in the controls. These results indicate a measurable effect of Bt commercial products on marine organisms, and great attention should be paid to biopesticides composed by entomopathogenic bacteria and addictive compounds. In addition, the results highlight the urgent need to study not only the effects of anthropogenic pressures on target organisms but also to extend our view to other ecosystems not expected to be influenced. Gaining data at the organismal level should help increase the sustainability of pest control and reduce the consequences of side-effects.

A mechanistic approach reveals non linear effects of climate warming on mussels throughout the Mediterranean sea

There is a dire need to forecast the ecological impacts of global climate change at scales relevant to policy and management. We used three interconnected models (climatic, biophysical and energetics) to estimate changes in growth, reproduction and mortality risk by 2050, for three commercially and ecologically important bivalves at 51 sites in the Mediterranean Sea. These results predict highly variable responses (both positive and negative) in the time to reproductive maturity and in the risk of lethality among species and sites that do not conform to simple latitudinal gradients, and which would be undetectable by methods focused only on lethal limits and/or range boundaries.

Bioaccumulation of heavy metals in fish, crustaceans, molluscs and echinoderms from the Tuscany coast

The concentration of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn were analyzed in the edible part of several species of fish, crustaceans, molluscs and echinoderms collected in sensitive areas of the Tuscany coast (northern Italy). The concentration of As (0.39-78.1 μg g-1) and Hg (0.01-1.56 μg g-1) resulted in most cases higher than reference thresholds. Target hazard quotient (THQ) and lifetime cancer risk (TR) indexes were calculated to assess cancer and non-cancer risk due to oral exposure; the highest THQ values referred to As and Hg, with values ≥ 1 in 39% and 48% of cases, respectively. Total target hazard quotients (TTHQ) values suggested that the local population could experience adverse health effects due to consumption of local seafood, mainly of demersal and benthic species. Cancer risk was mainly associated with As exposure, and with Cd intake, especially through molluscs consumption. The NMDS model highlighted species specific bioaccumulation processes and specific sensitivity of species to different bioavailable heavy metals. Specifically, Mullus spp. and Scorpaena porcus preferentially accumulate Hg and Cr, Octopus vulgaris specimens were discriminated by the presence of Pb and Zn, while an evident preference for Cd and Cu was recorded in Squilla mantis. In addition, the distribution of heavy metals in organisms revealed sound differences between Follonica and Livorno sampling sites, demonstrating a highly heterogeneous anthropogenic impact in terms of heavy metals input from the industrial activity resting on land.