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Feeding strategies provide essential information to help understand symbiotic relationships and resource competition as well as environmental integrity. This study examined the feeding ecology of the spider crab Libinia ferreirae, which is commonly associated with the jellyfish Lychnorhiza lucerna during part of its life cycle, especially the juvenile stage. In the adult phase, the crab is a host for many epibionts that live on its carapace. The crabs were collected in 1 year, and the stomach contents were analyzed by the percentage points and the frequency of occurrence of the food items. We identified ten food items (food in the advanced stage of digestion was unidentifiable) and microplastic particles in the gastric contents of the crabs. The food items with high abundances were sediment, crustaceans, and cnidarians. We found niche partitioning of the spider crab’s diet during the benthic (free-living) and planktonic (L. lucerna association) phases. The fact that microplastic is part of the diet of L. ferreirae is concerning and shows how environmental contamination with plastic material has been incorporated into the marine food chain as a whole.

Abstract Symbiotic relationships in marine environments are not fixed and can change throughout the animal’s life. This study investigated the ontogeny of symbiosis of the spider crab Libinia ferreirae with the host medusa Lychnorhiza lucerna. We described the type of relationship, the temporal correlation among species, and food habits. More than 50% of the sampled crabs were symbionts, most in early life stages. The highest number of crabs found in a single medusa was 11. Symbiosis was observed throughout most of the year but was more evident in warm periods. The crab has many benefits in this relationship with a medusa. One is the use of food resources captured by the medusa, primarily copepods. Because the crab steals the medusa’s food, it is a kleptoparasitic relationship. There is a niche partition between symbiont and the free-living crabs as they occupy different habitats and use nonoverlapping food resources. Previous research reported that symbiosis first developed during the crab’s last larval phase (megalopa) when crab and medusa are in the same habitat. Observation of the crab’s behavior shows that symbiosis occurs when the crab can grab to the medusa when the host touches the sea bottom. The crab also took advantage of water currents, releasing itself from the substrate and then drifting toward the medusa. The symbiotic relationship that crabs have with the medusa provides then with a nursery, food resources, shelter, dispersion, and decreased competition with free-living adult crabs, all essential for the crab’s survival.

We investigated the population dynamics of the spider crab Libinia ferreirae, focusing on the frequency distribution of individuals in size classes, sex ratio and the action of environmental variables (temperature, salinity, texture and organic matter content in the sediment) on reproduction and recruitment. Monthly collections were made in the Ubatuba region from January 1998 to December 2000. A total of 222 individuals were collected, including 123 juveniles (males and females), 43 adult males, 25 non-ovigerous adult females and 31 ovigerous females. Unlike most adult brachyurans, there was no significant size difference between sexes, and sexual dimorphism seems to be a varying characteristic for this crab genus. The reproductive period and recruitment were continuous with peaks that could be related to water mass dynamics and higher food availability in the Ubatuba region. In addition, our results increase knowledge about part of the life cycle of L. ferreirae, which could be useful for comparative studies.

We described the ecology of the spider crab Libinia ferreirae testing the habitat segregation during the ontogenetic shifts. Collections were performed monthly by trawling along the coastal area of Cananéia, São Paulo State (southeastern Brazil). Medusae were examined for the presence of any symbionts, and crabs were classified as juveniles (abdomen sealed to the sternite), adults (unsealed abdomen), and ovigerous females (embryos adhered to the pleopods). The environmental factors related to the water column were obtained using a multiparameter probe. In total, 564 adults and 357 juveniles were collected. However, all juveniles were obtained in association with Lychnorhiza lucerna medusae. An increase in the abundance of ovigerous females was observed as chlorophyll levels (phytoplanktonic production) increased, which is consistent with the patterns proposed for crustaceans with planktotrophic larval stages, i.e., the association of larval hatching with oceanic productivity could explain the success in juvenile recruitment approximately two months after the peak in the abundance of ovigerous females (cross-correlation: r  = 0.96). This spider crab shows an ecological strategy of habitat segregation among juvenile and adult individuals, thus avoiding competition for resources among different life cycle stages.