# Effect of Food Mass in the Gut on the Metabolic Rate of Carcinus maenas in the Field

## TL;DR

This study shows that digestion costs affect the energy balance of European green crabs in the wild, even when other factors are not controlled.

## Contribution

The study demonstrates the detectable but minor role of digestion costs in the field metabolism of Carcinus maenas.

## Key findings

- Metabolic rate increased with body mass and gut food mass in European green crabs.
- Digestion costs (SDA) were detectable but played a minor role in overall energetic costs.
- Gravid crabs had lower metabolic rates compared to non-gravid individuals.

## Abstract

Numerous laboratory studies have shown that meal size can influence the metabolism of individual organisms. However, in nature, meal size can vary simultaneously with a host of other factors that are often controlled under experimental conditions (e.g., reproductive state, health or physiological condition, temperature, meal composition, etc.). This study examines the influence of the mass of food in the gut (i.e., a proxy for meal size) on the metabolic rate of the European green crab (
Carcinus maenas
) in the field when other factors are not controlled in order to examine the relative influence of meal size on postprandial metabolism (i.e., specific dynamic action or SDA) compared to other factors known to influence metabolism. We collected 383 crabs intertidally during low‐tide periods and measured their metabolic rates in situ, followed by dissection to assess the mass of food in the gut, as well as reproductive and body condition metrics. We found that metabolic rate increased with body mass and with the mass of food in the gut, and decreased with gravid individuals. Our results show that SDA has an effect that can be observed despite leaving other influential factors uncontrolled, demonstrating the importance of the costs of digestion to the everyday energy balance of these organisms.

We measured the metabolic costs of digestion of crabs in the field to determine its impact relative to the many other factors that can influence metabolic rates. We show that the costs of digestion are detectable, but play a relatively minor role in the overall energetic costs of the European green crab.