Humberto Diaz

Orientation of blue crab, Callinectes sapidus (Rathbun), megalopae : Responses to visual and chemical cues

Post-larvae (megalopae) of the blue crab Callinectes sapidus are transported from offshore areas into estuaries where they settle and metamorphose in specific areas, such as seagrass beds. The present study tested the hypothesis that intermolt and premolt megalopae had different behavioral responses to visual and chemical cues that are associated with predator avoidance and settlement. Visually directed movements to solid and striped rectangular targets subtending different visual angles (5–350°) were tested in an arena in the presence of either Offshore Water, Seagrass (Zostera marina) Odor Water or Predator (Fundulus heteroclitus) Odor Water. Intermolt megalopae generally swam away from 10° to 180° targets in all water types which was interpreted as a predator avoidance response. Premolt megalopae had similar behavior in Offshore and Seagrass Odor Water. However in Predator Odor water, they displayed different predator avoidance behavior. When presented with a solid target, premolt megalopae either remained motionless or swam directly away from the target. If presented with targets resembling stalks of seagrass (vertical stripes), they swam in all directions which was interpreted as a startle response. In a chemical choice chamber, both molt stages were not attracted to Seagrass Odor Water but avoided Predator Odor Water. There was no evidence that megalopae used chemical cues for orientation toward settlement sites. Thus, the hypothesis was supported and the results suggest that behavioral responses to the test chemical and visual cues are involved in predator avoidance.

Orientation of the Fiddler Crab, Uca cumulanta: Responses to Chemical and Visual Cues

Behavioral responses of the fiddler crab Uca cumulanta to flat geometric shapes mimicking natural objects were measured in a circular arena by using zonal recovery as a behavioral measurement. Crabs were tested either in presence or absence of odors from two common predator species, the blue crab Callinectes sapidus, and the pufferfish Sphoeroides testudineus. The study tested the hypothesis that U. cumulanta have different behavioral responses to visual cues in the presence of chemical cues associated with predators. Escape direction tests demonstrated that U. cumulanta is able to show zonal recovery behavior based upon astronomical references. When tested in water lacking predator odor, crabs failed to exhibit a consistent orientation if a single silhouette target was interposed in the landward direction. However, when animals were tested in different predator odor concentrations, an orientation response was obtained at 10 and 20 g/liter/hr blue crab odor and 10 g/liter/hr pufferfish odor, demonstrating U. cumulanta ability to detect the potential presence of its natural predators by this odor. Thus, the hypothesis was supported, and the results suggest that behavioral responses to chemical and visual cues are involved in predator avoidance.

Visual Orientation of Postlarval and Juvenile Mangrove Crabs

ABSTRACT Visually directed movements of juveniles of the mangrove crabs Aratus pisonii and Chlorodiella longimana and postlarvae (megalopae) of A. pisonii to black horizontal rectangles subtending visual angles from 5-350° were measured in a circular arena. The study tested the hypothesis that early stage crabs use visual cues for attraction to potential refuge sites represented by silhouettes of mangrove roots and for avoidance of large dark areas that represent predators. The habitats of the 2 species differ in that A. pisonii lives in the supralittoral/littoral area among the roots and branches of mangrove forests, while C. longimana lives sublittorally in this area and is rarely exposed to air. Megalopae and juveniles of A. pisonii were significantly attracted by relatively narrow rectangles subtending angles up to 30°. In contrast, juvenile C. longimana exhibited attraction to all dark sectors, except a 5° dark rectangle. Orientation away from large dark rectangles subtending angles of 90-350° was exhibited only by A. pisonii. These different responses are interpreted to reflect the demands for shelter and predator avoidance in the habitat of each species. Chlorodiella longimana responded to all dark objects as if they were refuge sites, while A. pisonii differentiated between refuge and predators on the basis of horizontal extent.

Chemically stimulated visual orientation and shape discrimination by the hermit crab Clibanarius vittatus (Bosc)

ABSTRACT Orientation of the hermit crab Clibanarius vittatus (Bosc) to black geometric shapes of equal surface area was measured in a circular arena. This study tested the hypotheses that crabs can visually discriminate between different shapes and that attraction is related to the potential habitability of gastropod shells represented by the shapes. Test crabs were untrained and exhibited chemically induced shell-seeking behavior. This behavior indicated that they inhabit suboptimal gastropod shells (small relative to their body size). When presented with single silhouettes, crabs were significantly attracted to a horizontal rectangle, horizontal diamond, square, semicircle, and triangle, but not to a vertical rectangle or a vertical diamond. When exposed to pairs, the most and least attractive shapes were the horizontal rectangle and vertical diamond, respectively. Since responses were a complex function of the dimensional characteristics of the shapes, it was concluded that attraction was based on shape recognition. The hypotheses were further supported because crabs oriented poorly to the shape of the suboptimal shell which they inhabited (triangle), but oriented very well to shapes (horizontal rectangle, horizontal diamond, square, and semicircle) that represented more optimal gastropod shells.

Orientation of the hermit crab Clibanarius vittatus (Bosc) to visual cues: effects of mollusc chemical cues

Abstract Orientation of the striped legged hermit crab Clibanarius vittatus (Bosc) to black horizontal areas of different sizes was studied in a circular arena. Crabs were tested either in the presence or absence of chemicals that signal the potential availability of a gastropod shell. The chemical cue was generated by freezing and thawing muscle tissue from the gastropod Busycon carica Gmelin. Upon pre-experimental exposure to the chemical cue, crabs could be differentiated into two categories: those showing investigative interest in gastropod shells (Investigating), and those with no evident interest (Non-Investigating). The chemicals stimulated increased activity in the Investigating groups but not in the Non-Investigating groups. Clibanarius vittatus exhibited a uniform circular distribution when exposed to an all white horizon, independently of the presence of the chemical cue. Both crab categories showed little interest in black sectors subtending angles of 5, 10, 20 and 30° when the chemical cue was not present in the experimental arena. However, Investigating crabs were attracted to these sectors in the presence of the chemical cue. This response ceased once the dark sector exceeded ≈40° in size and both groups showed an avoidance response, with increasing number of crabs moving towards the white section of the arena as the dark sector increased in size. The attraction towards the small black sectors was interpreted as a shell investigating response, for which the visual cue seems to be activated by the chemical cue. The avoidance of increasingly larger black sectors was interpreted as predator avoidance reaction, which was not affected by the chemical cue. These interpretations were verified as Investigating crabs were attracted to a gastropod shell and both groups generally avoided a large blue crab.

Effects of chemical cues on visual orientation of juvenile blue crabs, Callinectes sapidus (Rathbun)

Abstract Stage I crabs of Callinectes sapidus occur in beds of submerged vegetation in estuarine nursery areas. After reaching the IV–V instars, juveniles leave nursery habitats and disperse throughout estuaries. This study tested the hypothesis that I and IV–V stage crabs have different behavioral responses to visual targets in the presence of chemical cues. Orientation to solid (black) and vertically striped (black and white) rectangular targets subtending different visual angles (20° to 350°) as viewed by the crabs was tested in a circular arena in the presence of chemical cues from Offshore water (control), and odor from estuarine aquatic vegetation, and predators (estuarine chemical cues). In the presence of Offshore water Stage I crabs oriented away from almost all solid targets, which was interpreted as an escape response for predator avoidance. Exposure to all estuarine chemicals cues dramatically changed their behavior, as they displayed an alarm response, in which they did not orient to visual cues and their predominant behavior was to remain immobile. Stages IV–V crabs were very responsive to solid targets, as they generally swam away from the 30° and 90° targets and toward the 270° solid targets in all water types. Responses of all stage crabs tested to striped targets were more diverse. Stage I crabs generally did not orient to striped targets in any odor environment. In contrast, Stages IV–V crab responses to striped targets varied with the odor type. Thus, the hypothesis was supported because there was an ontogenetic change in orientation to visual cues. Subtle changes in orientation upon exposure to chemical cues (e.g. aquatic vegetation versus predator odor) were not evident. Crabs appeared to have two sets of behavioral responses. They showed an escape response in Offshore water and a combination of escape and alarm responses in the presence of chemical cues from estuarine nursery areas.

Mass mortality in a mangrove roots fouling community in a hypersaline tropical lagoon

Massive mortality of the fouling community associated with red mangrove (Rhizophora mangle L.) roots was observed in February 1989 throughout most of La Restinga, a hypersaline coastal lagoon located in the central part of Margarita Island, Venezuela. The presence of species in the community was monitored on 6 field trips through 21 consecutive months, revealing a trend towards the restoration of the initial (May 1988) species composition. Although the factor or factors responsible for the community changes were not identified, physical disturbances associated with the passage of hurricanes Gilbert and Joan seem to be connected with the observed massive mortality. Apparently, the same factors and those preventing larval transport and settlement, i.e., slow water currents and siltation, are responsible for the slow community recovery.

The tidal rhythm in activity of the mole crab Emerita talpoida

The mole crab Emerita talpoida occurs in the swash zone of sandy beaches. Although crabs move with the tide, field studies found that the smaller crabs are distributed higher intertidally than the larger crabs. The present study tested the hypothesis that the rhythm, timing of activity, and activity amplitude with respect to tides would be different among megalopae, juveniles, small females, small males, mature males and large ovigerous females and underlie the observed field distributions. Activity of individuals in columns was observed under constant conditions with a video system and quantified as the number of ascents from the sand each 0·5 h. All life history stages had a circatidal rhythm in vertical swimming with median free running period lengths near 12·4 h and activity peaks after the time of high tide. Period length and time of activity peaks did not differ significantly among the life history stages. Activity amplitude was related to tidal amplitude of consecutive high tides at the collection site. Larger crabs had greatest activity after the lower amplitude high tides whereas small crabs had equal activity amplitude on consecutive tides. The test hypothesis was partially supported because the difference in activity amplitude predicts an oscillation between overlapping distributions of small and large crabs after low amplitude high tides, with the smaller crabs distributed higher on the beach after high amplitude high tides. The rhythm was not affected by a light:dark cycle and could be entrained by mechanical agitation.

A novel running wheel apparatus to monitor locomotor rhythms in land crabs

This article was downloaded by: [Duke University]On: 23 August 2009Access details: Access Details: [subscription number 906453949]Publisher Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

A Laboratory study on the visual and chemical orientation of the gastropod Nerita Fulgurans Gmelin, 1791

Behavioural responses of the gastropod Nerita fulgurans Gmelin, 1791 to flat black rectangles and intraspecific mucus trails were measured in a circular arena. Snails were tested in water either in the presence or absence of chemicals generated from a predator gastropod, Chicoreus brevifrons (Lamarck, 1822). The test hypothesis was that this snail has different behavioural responses as result of visual and chemical cue integration. Nerita fulgurans has the capacity to orient to solid targets subtending angles larger than 10° and follow its own mucus trails. In water conditioned by the predator C . brevifrons, snails exhibited an avoidance response when 10°, 20° and 45° sectors were presented, demonstrating an integration of chemical and visual information. The simultaneous presentation of two orienting cues (black sectors and mucus trails) was tested to determine the nature of the interaction. When the two cues were oriented in the same direction there was no effect. When the two cues were presented from directions 180° apart a preference for visual cues over mucus trail cues was evident when the visual angle of the visual cue subtended angles greater than 90°. This result demonstrates a hierarchical usage of the orienting references.