diversity Article Trophic Ecology of Juvenile Southern King Crab Associated with Kelp Forest: Evidence of Cannibalism Luis Miguel Pardo 1,2,3, * , Claudia Andrade 4 , Lisette Zenteno-Devaud 5 , Bastián Garrido 1,2 and Cristóbal Rivera 4   Citation: Pardo, L.M.; Andrade, C.; Zenteno-Devaud, L.; Garrido, B.; Rivera, C. Trophic Ecology of Juvenile Southern King Crab Associated with Kelp Forest: Evidence of Cannibalism. Diversity 2021, 13, 556. https:// doi.org/10.3390/d13110556 Academic Editors: Michael Wink and Alexander Dvoretsky Received: 3 October 2021 Accepted: 21 October 2021 Published: 1 November 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Laboratorio Costero de Calfuco, Facultad de Ciencias, Instituto de Ciencias Marinas y Limnológicas, Universidad Austral de Chile, Valdivia 5090000, Chile; bastiangarridouach@gmail.com 2 Centro de Investigación de Dinámica de Ecosistemas Marinos de Altas Latitudes (IDEAL), Universidad Austral de Chile, Valdivia 5090000, Chile 3 Centro de Investigación en Ecosistemas de la Patagonia (CIEP), Coyhaique 5951601, Chile 4 Laboratorio de Ecología Funcional, Instituto de la Patagonia, Universidad de Magallanes, Punta Arenas 6210427, Chile; claudia.andrade@umag.cl (C.A.); cnre88@gmail.com (C.R.) 5 Departamento de Ecología, Facultad de Ciencias, Universidad Católica de la Santísima Concepción, Concepción 4030000, Chile; lisette.zenteno@gmail.com * Correspondence: luispardo@uach.cl Abstract: The southern king crab, Lithodes santolla, is a well-known predator/scavenger species during its adult phase but its feeding strategy in early stages is less studied. This information is important to understand their role in ecosystems and to improve fishery management (i.e., stock enhancement). Based on stomach contents and stable isotope analysis, we determined variation in the composition of diet and niche overlap in vagile and cryptic phase collected within and outside a kelp forest, Macrocystis pyrifera, of Aguila Bay at the Magellan Strait in Patagonia, Chile. Results of juvenile stomach content analysis showed 60% dissimilarity between cryptic and vagile juvenile phases. Algae dominated the volumetric contribution in cryptic juveniles while crustacean dominated the diet in vagile phase. Exoskeleton of other king crabs occurred in 43% of juveniles with crustaceans in their stomach. This fact confirms cannibalistic behavior in the wild in this species, which is consistent with findings in massive laboratory cultures. There was no evidence of isotopic niche shift between cryptic and vagile juvenile phases. Overlapping isotopic niches of different-sized juveniles suggest that they exploit similar food resources. However, vagile individuals occupy a higher trophic position than cryptic individuals, which could suggest a switch in dietary preference, from detritivorous/herbivory within kelp forests to omnivory outside of kelp forests, and an increase in the level of cannibalism in vagile juveniles. Keywords: Patagonia; Macrocystis; stable isotopes; stomach content; Decapoda; Lithodes santolla 1. Introduction King crabs around the world have been a target of intensive fishery activity [1,2] and represent one of the most ubiquitous species in benthic non-tropical communities [3]. They are generalist, opportunistic epibenthic predators and scavengers, feeding on multi- ple food items from different trophic levels including algae, mollusks, echinoderms and crustaceans [4]. However, their diet has been principally described for adults, with less attention on early juveniles [5–7]. Under laboratory conditions, species such as the red king crab, Paralithodes camtschatica (RKC), and the southern king crab, Lithodes santolla (SKC), have been successfully maintained on carnivorous diets and juveniles exhibit high levels of cannibalism when they are held in high densities [8–10]. Therefore, king crab juveniles are assumed to have a carnivorous diet like adults. In decapods, types of diet and relative importance of specific items can change during ontogeny, especially in cases when juveniles and adults use different habitats [7,11,12]. For Diversity 2021, 13, 556. https://doi.org/10.3390/d13110556 https://www.mdpi.com/journal/diversity