Sediment Particle Selection During Feeding by Four Species of UCA (Brachyura, Ocypodidae)

Abstract

Differences in sorting of sediment grain-size during the feeding activity of fiddler crabs were investigated experimentally in four Uca species that have different numbers of spoon-tipped setae on the second maxillipeds. Uca leptodactylus had the highest number of spoon-tipped setae, followed by Uca rapax and Uca thayeri; whereas Uca vocator had no setae of this type. The crabs were allowed to feed for 48 h, in containers filled with three types of sediments with different particle-size composition. The feeding pellets formed in each type of sediment were collected, and the proportion of each granulometric fraction was compared with the substrate in the container. The diameters of the sediment particles found in the crab stomachs were measured and compared among the species and the types of sediments. The granulometry of the feeding pellets in each substrate was similar among the species. The size of particles ingested by fiddler crabs reflected the granulometric composition of the experimental substrate. Only U. leptodactylus ingested the smallest grains in coarser sediments. Therefore, the variation in the number of spoon-tipped setae on the second maxilliped seems not to affect the ability of fiddler crabs to manipulate and sort different particle sizes during feeding. RESUMODiferenças na seleção de partículas de sedimento com distintos tamanhos, durante a atividade alimentar de caranguejos chama-maré foi avaliada experimentalmente, em quatro espécies de Uca que apresentam diferentes quantidades de cerdas em forma de colher nos segundos maxilípedes. Uca leptodactylus apresentou o maior número destas cerdas, seguida, por Uca rapax e Uca thayeri; no entanto, Uca vocator não possui tal tipo de cerda. Os caranguejos foram mantidos alimentando-se, por 48 h em containeres preenchidos com três tipos de sedimentos com diferentes composições granulométricas. Os pellets alimentares produzidos em cada sedimento foram coletados e a proporção de cada fração granulométrica foi comparada com a do sedimento do container. Os diâmetros das partículas de sedimento encontradas em seus estômagos foram medidos e comparados entre as espécies e os tipos de sedimentos. A granulometria dos pellets alimentares em cada 3 )

Sediment Bioturbation Potential of Uca rapax and Uca uruguayensis as a Result of Their Feeding Activity

“…However, the grain-size composition of the feeding pellets did not differ between U. uruguayensis and U. rapax. Similar results were reported by Robertson and Newell (1982a, b), Thurman (1987), and Colpo andNegreiros-Fransozo (2011). Mchenga (2007) observed bioturbation of mangrove sediments by increases of the particle diameter in areas post-processed by crabs, compared with areas without these crustaceans.…”

“…Therefore, the differences in the number of spoontipped setae between U. rapax and U. uruguayensis suggest that their niches do not overlap. In subtropical mangroves of Brazil, U. rapax is found in areas with approximately 14.8% silt and clay, whereas U. uruguayensis occurs in sediments with 8.1% (Colpo et al, 2011). However, U. uruguayensis occurs in temperate mudflats (Spivak et al, 1997a, b;Daleo et al, 2003;Ribeiro et al, 2005) and Thurman et al (2010) showed that U. rapax occupies habitats with a wide range of substrates and osmolalities.…”

“…After it is brought to the mouth by the claw, the sediment is processed by the buccal appendages (Miller, 1961;Colpo and Negreiros-Fransozo, 2011) to remove organic matter, algae, small organisms, and bacteria, which are ingested as food, together with small inorganic particles (Miller, 1961;Maitland, 1990;Silva et al, 1994;Takeda and Murai, 2003). During the mouthparts sorting, the larger sediment particles are discarded around the entrance of the burrow as small pellets (Miller, 1961;Crane, 1975).…”

“…Species of Uca show differences in the mouthparts, especially in the numbers of spoon-tipped setae on the second maxilliped (Crane, 1975;Icely and Jones, 1978;Robertson and Newell, 1982b;Thurman, 1987;Costa and Negreiros-Fransozo, 2001;Lim, 2004;Colpo, 2005;Bezerra et al, 2006). Miller (1961) suggested that the spoon-tipped setae function to prevent the ingestion of coarser inorganic particles and to scrape the sediment grains, releasing the organic matter adhered on them.…”

“…Uca uruguayensis (Nobili, 1901) and Uca rapax (Smith, 1870), which have different numbers of spoon-tipped setae on their second maxillipeds (Colpo, 2005), were chosen to evaluate variations in the bioturbation potential during their feeding activity. We evaluated the mangrove substrate bioturbation by comparing the grain-size spectrum and the organic content, between the sediment around the burrow and the feeding pellets.…”