Objective of the study
The main objective of the study was to note down the various behavior patterns of crabs in a span of 1 hour time i.e. from 15:30 to 16:30[afternoon was mainly chosen because during these period, crabs come out for many activities like foraging and sometimes in rare cases, mating.
Observations
During the span of an hour, these were the following behavioral patterns observed:-
Hunting
High speed swift movement for escaping predation.
Rarely but interesting observation i.e. Mate selection.
Shifting of colony during afternoon.
Their foraging behavior is based on the similar pattern observed by dumper trucks for dumping sand and construction material.
They usually try to stay in their own dwells.
Competition between 2 niches and even killing each other for survival.
They are using their short appendages to burrow and long appendages to get out.
Shell color changes behavior wise.
Their burrows are interconnected for communication between two colonies.
Discussion about crab behavior
The observations of the different crab behavior instances were noted down. These are further supported by pictures following them.
1 Crab though delicate crustaceans
show an immense and diverse pattern of behavior. One of the important
observations included that they are very sensitive to movement of
higher animals and quickly dodge underneath their burrows.
GHOST AND FIDDLER CRABS IN THE BEACH ENGAGED IN MOVENTS
2 Crabs have specialized weaponry [ i.e. their anatomical features] for hunting and so they can also be seen hunting other smaller insects and even other crabs.
CRABS MOVING TOWARDS SHORELINE
3 Rarely observed but during some instances we also noticed that few crabs are being surrounded by each other and it looks like they are exhibiting a mate selection pattern which is typical for their reproductive fitness and survival.
TYPICAL MATE SELECTION OBSERVATION BY CRAB
4 Another important observations were that they shift colony in the afternoon i.e. ghost crabs and fiddler crabs both shift each other’s colony especially during afternoon in search of food, exchange of various information, signal of predators, escape routes etc.
COLONY SHIFT OBSERVATION IN CRAB COLONIES
5 Due to predation risks and many other drastic situations, a fewer crabs try to stay in their own dwells.
THIS CRAB SEEM TO STAY IN ITS OWN BURROW
6 Crab interaction
During colony shift, another observations exclusively important for ecological study i.e. there exists a competition between 2 niches of same\different colony and sometimes there are fights so that there are killings\killing each other for survival.
6.1 Interactions- agonistic and non-agonistic
Generally non-agonistic interactions appear minimal, whereas defensive or agonistic interactions are typical of communal decapods. Many wandering crabs actively compete with residents for burrows and digging space, e.g. in O. ceratophthalma,O. gaudichaudii), O. laevis, , O. saratan, O. jousseamei, O. rotundata and O. platyarus,. Interactions are generally ritualised, like many in the genus Uca,. Lighterfound that as crabs developed, not only did their sand disposal behaviour get more complex, but so did their defensive behaviours, with added behavioural repertoires, ‘pushing’ and ‘grappling’ with chelae in O. ceratophthalma and ‘pushaside’, in O. laevis, being added to ‘chase’ and ‘threat’ behavior observed in juveniles.
6.2 Aggregative behavior
Wandering crabs often aggregate at the water’s edge before seeking a burrow.This is possibly to forage an unidentified food source, but parallels the seemingly aimless wandering stage exhibited by soldier crabs.This behaviour has clear social implications, and despite aggregating, individuals maintain individual distances between conspecifics, similar to that seen during foraging behaviour,. Such behavioural spacing appears, however, to be overridden when food sources are concentrated.
Burrows appear to be maintained if they are not naturally damaged often.For example O. ceratophthalma individuals subject to tidal action and burrow collapse tend to have temporary burrows, whereas supratidal individuals maintain burrows for at least 10 days.It is not known whether temporary residency has an effect on social interactions, but from studies on other crabs, reduced agonistic interactions seem likely and is supported by the observation that few competitive interactions are apparent in O. quadrata,. These have temporary burrows and prefer to takeover abandoned burrow. In fiddler crabs, long lived burrows can lead to complex social interactions, for example neighbour recognitionand territorial coalition.
6.3 Female centered competition
Some behavioural studies focus their attention on sexually mature males, which show strong burrow defence behaviour. Male Ocypode individuals encounter receptive females unpredictably in time and space due to their highly mobile nature and infrequent matings. Females also do not appear to require a suitable incubation burrow that they cannot provide easily for themselves, unlike most Uca females.Therefore Ocypode males have evolved ‘female centred competition’, a mating strategy where males attract and defend females. This is rare in decapods and found only in the family Ocypodidae.
TWO CRABS COMPITING WITH EACH OTHER