Food Habits and Ultrastructure of Gastric Mill of the Grapsid Crab, Metopograpsus Messor (Forskal, 1775) From the Red Sea, Egypt.

Abstract

D uring the present study, the stomach contents of a medium-sized grapsid crab, Metopograpsus messor (Grapsidae, Brachyura) inhabiting different habitats (rocky, sandy-rock, and mangrove swamps) of the Red Sea (southern Aqaba Gulf) were examined by both frequency occurrence and percentage points. The results show that this species is opportunistic omnivore, with general food items consisting of algae (brown, red, green and blue green), benthic animals dominated by crustacean copepods, isopods, amphipods and other crustaceans,. in addition to foraminiferans, polychaetes and animal eggs, with few fragments of hydroids, bryzoans as well as organic debris and unidentified items. Higher plants including leaves and adventious roots of mangroves and seagrass leaves were also reported among stomach contents. Moreover, sediments were represented by considerable amounts at both different habitats and seasons. The types of foods were significantly different through various habitats and seasons.The gastric mill of the crab, which deals mainly with mechanical digestion was investigated by both light and scanning electron microscopes. It appeared as a very complex structure, composed of 6 240

The fishing behaviour of Metopograpsus messor (Decapoda: Grapsidae) and the use of pneumatophore-borne vibrations for prey-localizing in an arid mangrove setting

“…The trophic relationship observed in this study identified a unique trait associated with M. messor as the crab is generally considered an opportunist detritivore, herbivore and omnivore but not an active predator (El-Sayed et al ., 2000). Indeed, the results highlight that the prey-localizing and predatory fishing behaviour are not just opportunistic traits for a few specimens but are an established pattern for the entire population (Figure 5D).…”

“…This characteristic has not been recorded in other Grapsid crabs (Fratini et al ., 2000; Linton & Greenaway, 2007; Poon et al ., 2010; Lee, 2015). Metopograpsus messor was observed predating not only A. d. dispar but also the shrimp P. khori and smaller M. messor demonstrating that the crab is more of a generalist predator rather than a specialist (El-Sayed et al ., 2000; Walton et al ., 2014). It is possible that a genetic trait has dominated this specific population of M. messor to evolve from opportunistic foragers to generalist hunters/fishers.…”

“…Similar behaviour has been reported in other grapsid species (Nara et al ., 2006) but not for M. messor . The observed cannibalism of smaller M. messor by the larger alphas highlights the voracity of this hierarchical social standing (El-Sayed et al ., 2000; Walton et al ., 2014). It should be noted that the most dominant alphas displayed the red chelae (Holthuis, 1977; Naderloo, 2011), an indicator which could be related to the individual's hierarchical position.…”

“…A Grapsidae crab, it belongs to a group of terrestrial tree climbers described as occupying herbivorous, detritivorous and omnivorous niches within the trophic chain. It is considered a habitat-generalist and is common in a variety of coastal environments including muddy substrates, rocky shores and mangroves (El-Sayed et al ., 2000; Linton & Greenaway, 2007; Poon et al ., 2010; Naderloo, 2011; Lee, 2015). The species is easily identifiable by its dark coloured dashes and in some specimens by red chelae (Holthuis, 1977; Naderloo, 2011).…”