# Latitudinal variations in morphometric traits and bioenergetic status of adult red squat lobsters Grimothea monodon (H. Milne Edwards, 1837) in the Southeast Pacific Ocean

## TL;DR

This study examines how environmental changes along a latitude gradient affect the physical and biochemical traits of red squat lobsters in the Southeast Pacific Ocean.

## Contribution

The study reveals latitudinal variations in the bioenergetic condition of two morphotypes of G. monodon linked to environmental factors.

## Key findings

- Temperature and dissolved oxygen show abrupt changes between 15°S–17°S, affecting lobster traits.
- Biochemical constituents like glucose, proteins, and lipids vary significantly along the latitudinal gradient.
- Fatty acid composition differs between morphotypes and localities, indicating environmental influence on nutritional status.

## Abstract

Adults of the red squat lobster (Grimothea monodon) present two morphotypes (small-pelagic (SP) and large-benthic (LB)) in their wide geographic distribution range in the Southeastern Pacific Ocean (SEPO). In this marine ecosystem, they are exposed to conspicuous latitudinal variations in oceanographic and physicochemical parameters that affect their nutritional and fitness status. The objective of this study was to determine variations in the bioenergetic condition at the level of morphometric, sexual and biochemical traits of G. monodon, considering a wide spatial scale of their populations’ distribution along a latitudinal gradient (from 9°S to 36°S) in the SEPO. According to the environmental parameters, temperature and dissolved oxygen presented abrupt changes between 15°S–17°S, while chlorophyll and salinity showed a constant reduction along the latitudinal gradient. When environmental parameters were related to the size of the two morphotypes (SP, LB) of G. monodon, some trends of change were observed, while the relative condition factor showed significant differences along the latitudinal gradient. The biochemical condition of SP individuals showed an increasing trend in glucose from Chimbote to Chala, proteins showed abrupt changes in three zones (between Huacho-Lima, Lomitas, and Chala), and lipids showed a notable change between Lima-Cañete. In turn, in LB individual’s increases were recorded in all their biochemical constituents towards high latitudes. A slight variability in fatty acids was observed between SP individuals from the north (Chimbote, Huarmey, Huacho) and SP individuals from the south (Marcona, Chala, Planchada, Mollendo). In addition, significant latitudinal differences were observed in the fatty acids of the two morphotypes (SP, LP). The nutritional condition index (docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA) ratio) showed significant differences for the locality factor. Our findings revealed conspicuous differences in the bioenergetic condition of G. monodon adults at the latitudinal level. These variations were strongly linked to the predominant environmental conditions in the SEPO. It is consequently recommended that future sustainable exploitation models consider a physiological and ecosystemic approach that includes key aspects of the nutritional condition and its habitat, thus establishing, in real time, the health status of the natural populations of this resource.