Effects of season and latitude on the diet quality of the invasive Asian shore crab Hemigrapsus sanguineus

Abstract

Invasive species alter invaded ecosystems via direct impacts such as consumption. In turn, an invasive species’ ability to thrive in new habitats depends on its ability to exploit available resources, which may change over time and space. Diet quality and quantity are indicators of a consumer’s consumptive effects and can be strongly influenced by season and latitude. We examined the effects of season and latitude on the diet quality and quantity of the invasive Asian shore crab Hemigrapsus sanguineus throughout a non-winter sampling year at 5 different sites spanning 8° of latitude across its invaded United States range. We found that diet quality, averaged through time, largely follows an expected latitudinal cline, being higher in the center of its range and lower toward the southern and northern edges. We also found that while some sites show similar patterns of diet quality variation with season, no pattern is consistent across all latitudes. Finally, we found that crabs at sites with low diet quality during summer reproductive months did not compensate by increasing total consumption. Because the Asian shore crab is an important consumer in its invaded ecosystems, understanding how its diet quality and quantity vary with season and latitude can help us better understand how this species influences trophic interactions and community structure, how it has been able to establish across a wide ecological and environmental range, and where future range expansion is most likely to occur.

Using external morphology as a proxy for stomach size in Hemigrapsus sanguineus

“…( 2022 , 2023 ) and Reese et al. ( 2023 ); however, measurements of the carapace progastric region were collected specifically for use in this study.…”

“…For each of the analyses described below, we had to control for the effect of body size on cardiac stomach and progastric region width. Previous diet studies in this species based on cardiac stomach size have used either residual stomach size after accounting for CW, or standardized stomach width (stomach width divided by body width, a unitless ratio) (Griffen et al., 2020 ; Griffen & Mosblack, 2011 ; Reese et al., 2023 ). However, when the standardized approach was used for the progastric region (i.e., progastric width divided by CW), this standardized metric increased with CW.…”

“…Using these same crabs, Reese et al. ( 2023 ) demonstrated that standardized stomach size differed between sites throughout the invaded range. In our study, we tested whether residual stomach size and residual progastric region width show similar patterns between sites with two separate one‐way ANOVAs followed by Tukey's HSD tests, again using residuals to control for differences in crab size.…”

“…Brachyuran crabs are important consumers in many marine systems (Boudreau & Worm, 2012 ; Howard et al., 2017 ). As with other animals, stomach size in crabs is negatively correlated with diet quality (Griffen & Mosblack, 2011 ) and stomach width has therefore been used to successfully assess diet quality for a variety of species (Bas et al., 2014 ; Cannizzo et al., 2018 ; Carver et al., 2021 ; Gül & Griffen, 2020 ; Reese et al., 2023 ). However, internal stomach size can only be measured via animal sacrifice.…”

“…Griffen and Mosblack ( 2011 ) empirically demonstrated that individual of H. sanguineus that chose to consume animal material had smaller stomachs than individuals that selected an algal diet. Using this relationship, stomach size has been used to infer changes in diet quality in H. sanguineus across season and latitude (Griffen et al., 2012 ; Reese et al., 2023 ), as well as across sites that differ in prey availability (Griffen et al., 2020 ). Thus, it is clear that stomach size can be used to assess diet quality in H. sanguineus ; however, it is unclear whether size measurements of external morphological traits such as the progastric carapace region could be used to make similar diet predictions.…”