University of Exeter

Marine bivalve populations are under threat globally due to the synergistic effects of climate change and human exploitation. Understanding the impacts of these pressures is critical for better managing bivalve populations, as well as for securing the many socio-economic benefits these key organisms provide for us. Bivalves often display multiple adaptations and broad phenotypic plasticity in the response to changing coastal environments, therefore a holistic multi-parameter approach to assessing physiology and behaviour is key for accurately determining the fate of these economically and ecologically important animals in a future ocean.

Set-up

At Exeter we have developed MeGaH an intermittent flow respirometry system that concurrently measures Metabolic rate, Gape behaviour, and Heart rate - enabling the simultaneous and prolonged recording of bivalve whole-phenotype response to changing water conditions in a controlled environment (FIG. 1). The system consists of a series of respirometry chambers fitted with a suite of sensors to record heart rate, oxygen consumption (Firesting-O2® meter connected to robust oxygen probes OXROB10), clearance rate, and shell gaping behaviour of an individual. These chambers are then periodically flushed, enabling metabolic rate and clearance rate measures to be taken repeatedly, without disturbance, during extended experimental periods for chronic exposures, whilst heart rate and gape are monitored continuously.

Results

Using the MeGaH system, we recently obtained the first set of combined whole-organism performance data, to assess the impact of algal concentration on the various performance measures in mussels – particularly relevant in a context of coastal eutrophication and algal blooms. These data show that an increase in algal concentration induces an increase in mussel clearance rate (FIG. 2A), with higher cell concentrations leading to elevated filtering activity. This increased feeding is reflected by the mussel’s heart rate, with significantly elevated heart rate at all algal concentrations above 2,500 cellls/mL, compared to non-feeding animals (FIG. 2B). Nonetheless, despite this link between clearance rate and heart rate, there was no measurable effect of increased cell concentration on either shell gaping activity or respiration rate, demonstrating the decoupling of these performance indices, and the need to measure multiple performance indicators to fully understand organism responses at a whole organism level (FIG. 2C and D).

Conclusion from data and application

Using the MeGaH system, we will generate key data on whole organism mussel performance, specifically nutrient remediation capacity, across a suite of environmental conditions, which is vital to inform policy and stakeholders about the potential use of bivalves for improving coastal water quality, and the viability of bivalve restoration under changing climatic conditions.

For further information, please contact:
Robert Ellis  r.p.ellis@exeter.ac.uk