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The decapod fauna in the intertidal zone of the rocky shores of Chile is highly diverse, especially along the northern and central mainland coasts, where the influence of the cold Humboldt Current results in high productivity. One of the most abundant species in these ecosystems is the decapod Cyclograpsus cinereus Dana, 1851. The aim of the present study, carried out in the spring and summer seasons between 2018 and 2020, was to determine the spatial distribution patterns of the decapod C. cinereus in different sites along the rocky shores of Antofagasta bay, northern Chile, in order to establish probabilistic models that explain its distribution at each site. Individuals were counted in random quadrants in the intertidal zone. The data thus obtained were processed by application of the variance/mean ratio to determine whether the distribution of individuals was random, aggregated or uniform, associated with Poisson, negative binomial or positive binomial distributions, respectively. The data revealed aggregated (negative binomial) distribution in 15 sampling events, and uniform (positive binomial) distribution in 4 events. The sampling sites were located on rocky shores in four sectors of an urban zone, and two in a protected zone; no significant differences were found between the densities of the sites in the two zones. The results of the interpretative probabilistic models indicated aggregated distribution patterns, agreeing with previously reported interpretative probabilistic models for the distribution of decapods on the rocky shores of central and southern Chile. [ABSTRACT FROM AUTHOR]

The decapod fauna in the intertidal zone of the rocky shores of Chile is highly diverse, especially along the northern and central mainland coasts, where the influence of the cold Humboldt Current results in high productivity. One of the most abundant species in these ecosystems is the decapod Cyclograpsus cinereus Dana, 1851. The aim of the present study, carried out in the spring and summer seasons between 2018 and 2020, was to determine the spatial distribution patterns of the decapod C. cinereus in different sites along the rocky shores of Antofagasta bay, northern Chile, in order to establish probabilistic models that explain its distribution at each site. Individuals were counted in random quadrants in the intertidal zone. The data thus obtained were processed by application of the variance/mean ratio to determine whether the distribution of individuals was random, aggregated or uniform, associated with Poisson, negative binomial or positive binomial distributions, respectively. The data revealed aggregated (negative binomial) distribution in 15 sampling events, and uniform (positive binomial) distribution in 4 events. The sampling sites were located on rocky shores in four sectors of an urban zone, and two in a protected zone; no significant differences were found between the densities of the sites in the two zones. The results of the interpretative probabilistic models indicated aggregated distribution patterns, agreeing with previously reported interpretative probabilistic models for the distribution of decapods on the rocky shores of central and southern Chile.

Decapods have successfully colonized changing coastal habitats throughout the world by adapting their behavior, physiology, and biochemistry. Biochemical reserves, such as lipids and fatty acids (FAs), play fundamental roles in this adaptation process. These energy reserves are key for the development of decapods and their composition mainly depends on the type and quality of food available in their habitats. This study evaluated the lipid content and FA composition of three tissues (hepatopancreas, gills, and muscle) in two widely distributed, semi-terrestrial coastal crab species in Chile, Cyclograpsus cinereus from the upper intertidal and Hemigrapsus crenulatus from estuaries. This evaluation aimed to assess the physiological role of the bioenergetic reserves of these crabs, which tolerate fluctuating environmental conditions. Our results showed that both species had a higher lipid content in the hepatopancreas and a lower lipid content in its gills and muscle. All three of the evaluated tissues in C. cinereus showed high contents of saturated fatty acids (SFAs), and its hepatopancreas displayed the highest contents of monounsaturated (MUFAs) and polyunsaturated fatty acids (PUFAs). In turn, H. crenulatus had the highest contents of MUFAs and PUFAs in its gills and muscle tissues, including an important amount of eicosapentaenoic acid (EPA). The FA content of C. cinereus may indicate an adaptive physiological response aimed at maintaining its cellular fluid balance during periods of desiccation in the upper intertidal zone. In contrast, the FAs found in H. crenulatus may be linked to the high activity of the sodium‑potassium pump in its gills, in order to maintain osmoregulation in estuaries. [Display omitted] • Lipids and fatty acids are important to tolerate fluctuating coastal environments. • The habitat type determine the availability of lipid and fatty acid. • Cyclograpsus cinereus from the upper intertidal showed a high content of SFA. • Hemigrapsus crenulatus from the estuary showed a high content of PUFAs in its gills. [ABSTRACT FROM AUTHOR]