Trophic Ecology of Juvenile Southern King Crab Associated with Kelp Forest: Evidence of Cannibalism

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.

Prey Selectivity in Juvenile Red King Crabs from the Coastal Barents Sea

“…Gastropods and echinoderms were favorable prey organisms of P. camtschaticus collected on mixed sediments and hard bottoms; barnacles were also favored by red king crabs in hard-bottom habitats. This trend, when the diversity of dietary components decreased from the mouth (open sea) to the apex of the bay, apparently reflected a decrease in the benthic diversity and biomass of preferable prey organisms in the environment [65]. Indeed, on soft substrata, we registered dramatic changes in the structure of local benthic communities (Figure 2, Table 2).…”

“…This fact confirms species-specific and site-specific prey selectivity in red king crabs and their high potential for adaptation to various food habits. A wide dietary composition has also been recorded in other lithodid crabs [65,[88][89][90].…”

“…In this type of aggregation, small red king crabs are so densely packed that it would be difficult for predators to distinguish individuals or remove them [64]. In lithodid crabs, segregation by size is a well-known pattern served to avoid inter-cohort cannibalism [65].…”

Patterns and drivers of benthic macroinvertebrate assemblages in the kelp forests of southern Patagonia

“…Examples include the Patagonian long-fin squid Loligo gahi, which selectively lay their egg clutches on Macrocystis pyrifera or Lessonia spp. near the forest edge, and both juvenile king crab Lithodes santolla and false king crab Paralomis granulosa, which have been observed seasonally in large aggregations within southern Chile's Macrocystis forests [25][26][27][28][29][30]. Commercial fisheries for these species throughout Patagonia and the South Atlantic provide economic opportunities for regional coastal communities.…”