Elevated aerial temperature modulates digestive enzyme activities in Mytilus californianus.

The marine intertidal mussel Mytilus californianus aggregates to form beds along the Pacific shores of North America. As a sessile organism it must cope with fluctuations in temperature during low-tide aerial exposure, which elevates maintenance costs and negatively affects its overall energy budget. The function of its digestive gland is to release enzymes that break apart ingested polymers for subsequent nutrient absorption. The effects of elevated aerial warming acclimation on the functioning of digestive gland enzymes are not well studied. In this study we asked whether digestive gland carbohydases and proteases could be overstimulated in warm condition to possibly mitigate the costs related to the heat-shock response. We compared mussels acclimated to a + 9 °C heat-shock during daily low-tide aerial exposure to mussels acclimated to isothermal tidal conditions in a simulated intertidal system. The results showed fairly consistent activities of cellulase, trypsin, and amino-peptidase across tidal variation and between thermal treatments; however, amylase activity was lower in warmed versus cool mussels across low and high-tide. We also observed the expression of heat-shock genes in gill tissue during warm tidal conditions, suggestive that moderate temperatures during aerial exposure can induce a stress response.

The observation of starch digestion in blue mussel Mytilus galloprovincialis exposed to microplastic particles under varied food conditions.

Microplastic continues to be an environmental concern, especially for filter feeding bivalves known to ingest these particles. It is important to understand the effects of microplastic particles on the physiological performance of these bivalves and many studies have investigated their impact on various physiological processes. This study investigated the effects of microplastic (10 µm) on digestive enzyme (amylase) activity of Mytilus galloprovincialis at 55,000 and 110,000 microplastic particles/L under laboratory conditions. Additionally, our study measured the expression of an isoform of Hsp70 in the gills to assess whether or not these particles may cause protein denaturation. Results revealed that this regime negatively affect the ability of M. galloprovincialis to digest starch under high food conditions but not low food conditions. Exposure to extreme levels of microplastic raised amylase activity. Furthermore, Hsp70 transcript abundance was not elevated in treatment mussels. These results show that mussels may be resilient to current microplastic pollution levels in nature.