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Comparative study of Condition factor, Stomach Analysis and Some Aspects of Reproductive Biology of Two Land Crabs: Cardiosoma armatum (Herklots, 1851) and Cardiosoma guanhumi (Latreille, 1825) from a Mangrove Swamp Ecosystem, Lagos - Nigeria

¹Environmental and Resource Management, Brandenburg University of Technology, Cottbus, Germany

²Department of Marine Sciences, University of Lagos, Lagos, Nigeria

*Corresponding Author:

Isa Olalekan
Environmental and Resource Management
Brandenburg University of Technology, Cottbus, Germany
Tel: +49 (0) 355 69-0
E-mail: isaelegbede@gmail.com

Received date: September 04, 2013; Accepted date: December 23, 2013; Published date: December 30, 2013

Citation: Olalekan EI, Lawal-Are AO (2013) Comparative study of Condition factor, Stomach Analysis and Some Aspects of Reproductive Biology of Two Land Crabs: Cardiosoma armatum (Herklots, 1851) and Cardiosoma guanhumi (Latreille, 1825) from a Mangrove Swamp Ecosystem, Lagos – Nigeria. J Marine Sci Res Dev 4:143. doi: 10.4172/2155-9910.1000143

Copyright: © 2013 Olalekan EI, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

A total samples of 858 of Cardisoma armatum and Cardisoma guanhumi) collected from the Lagos Lagoon mangrove area of the University of Lagos were studied for their frequency, distribution, growth and sex ratio and a comparative analysis was done on both crabs. Investigation into their length-weight relationships, growth pattern, condition factor, food and feeding habits were carried out. The calculated Chi-square ( 2ÙÂ?ا ) test showed that male crabs of Cardisoma armatum and Cardisoma guanhumi were significantly (p<0.05) more abundant than the female crabs. The Condition factor K values for the Cardiosoma armatum and Cardiosoma guanhumi ranged from 3.3 to 30.7 and 3.1 to 28.6, respectively. This research study indicates almost similar biological features for both species.

Keywords

Reproductive biology; Land crabs; Mangrove swamp ecosystem; Cardisoma armatum

Introduction

Crabs belong to the brachyuran infra order family comprising more than 6,793 species peculiarly known for their ten legged creature (decapod) Hosseini et al. [1]. Crabs have flourished to be a predominant icon in the invertebrate fauna because of its ubiquitoes existence in almost all part of the world oceans including freshwater, marine even on land [2]. Crabs are least exploited amongst other and crabs have been commonly found in West Africa. The Gecarcinidae currently consists of 20 species and has been recognized to include 4 [3] or 6 genera [4,5].

The eggs of crabs have to hatch in the sea, where the larvae undergo typical planktonic development [3]. The mass migration of reproductive individuals to the surf for larval release has been reported for many crab species [6]. The aims of this research was to provide baseline data on condition factor, feeding pattern and sex ratio and to make comparison of populational differences based on morphological analyses of the two crabs species: Cardiosoma armatum [7] and Cardiosoma guanhumi [7].

Materials and Methods

Description of study site

The study was carried out in the coast/Mangrove area of University of Lagos Lagoon front which is located opposite the Lagos Lagoon on the geographical platform of 6°26’N and 6°39’N and longitude 3°29’E and 3°50’E (Figure 1). The lagoon is the largest of the four lagoon systems of Gulf of Guinea and is located at South Western Nigeria. The mangrove swamp connects to the Lagos Lagoon by tidal creek.

Collection of specimens

Specimens were collected at the mangrove part of the Lagos Lagoon of the University of Lagos. They were caught with hand at the same time and place between 7 pm-11 pm to allow for precise readings and analysis of the samples. The collection was done randomly and was collected over a period of six months on weekly bases between February and July, 2012. The crabs were collected in 2 different stations within the mangrove swamp. A total of 300 crabs were collected from the site and were preserved immediately in a deep freezer in the laboratory prior to examination.

Laboratory procedure

The crabs were removed from the freezer and allowed to thaw. Excess water was removed from the specimens using filter paper.

Condition factor

This is the condition of general well-being of a crab. It was studied in relationship to size. The equation for condition factor as follows:

K=100W/L³

Where K=condition factor

W=weight of the crab (g)

L=length of the crab (cm)

It is defined as a condition representing how lean or fat the crab.

Food analysis

The crabs were dissected and the stomachs removed for food analysis. Each stomach was studied as a unit in order to provide information on individual variation. The stomach is greenish in color, located underneath the carapace and it is divided into four parts. The stomach contents were examined and scored with regards to whether they were empty, one-quarter full (¼), half full (½), three-quarter full (¾) or full stomach (4/4). The methods of food analysis used were the numerical method and frequency of occurrence method.

Numerical method: The number of individuals of each food items in each stomach was counted. They were summed up to give totals for each kind of item in the whole sample. Then a grand total of all food items were obtained and each food item was expressed as a percentage of the total number of food found in all crabs examined.

Frequency of occurrence method: In this method, stomach content was examined and individual food organisms sorted and identified. The number of stomachs in which each item occur was recorded and expressed as a percentage of the total number of stomach with food. The method gives information only on the organisms fed on. Its main disadvantage is that it does give information on quantities or numbers;

Reproductive biology

Sex ratio: The crabs were sorted out and sexed using gonopod (a thin abdominal segment) and the gonophores (a broad abdominal segment). These structures were used to identify the male and female respectively. In the male, the abdominal segment is present only on the first and second abdominal somites and is modified to form copulatory organs. The female differs by having all the somites freely moveable and there is one pair of appendages on each of the 2nd, 3rd, 4th and 5th somites, these form the swimmerets to which the eggs are attached in ovigenous crabs.

Fecundity: This is defined as the number of ripe eggs in the female prior to the next spawning [7]. The egg mass was carefully removed from the pleopods using tweezers and washed in running water. The eggs were placed in a 50 ml beaker and filled with seawater. Egg diameter was determined using an ocular micrometer before the eggs were separated.

Results

418 and 440 specimens of Cardiosoma armatum (Plate 1) and Cardiosoma guanhumi (Plate 2) were studied respectively making a total of 858 species of crabs collected and studied. The specimens were studied for the length and width frequency distributions between the months of February to July, 2012.

Condition factor of Cardiosoma Armatum and Cardiosoma Guahunmi

The condition factor (CF) or coefficient of condition is referred to as the K factor which indicates the state or overall wellbeing of the Cardiosoma armatum and Cardiosoma guanhumi was calculated for the 418 C. armatum (combined sex) and 440 C. guanhumi (combined sex) in relation to size. The K values for the Cardiosoma armatum ranged from 3.3 in size group 8.5-9.4 and 30.7 in size group 2.5-3.4. For the Cardiosoma guanhumi the K value ranged from 3.1 in size group 8.5-9.4 and 28.6 in size group 2.5-3.4. This is illustrated in the Tables 1 and 2.

Table 1: Stomach Food Content of Cardiosoma armatum from the Lagos Lagoon mangrove Swamps.

Table 2: Stomach analysis of Cardiosoma guanhumi from the Lagos Lagoon mangrove swamps (February- July, 2012).

Sex ratio of Cardiosoma Armatum and Cardiosoma Guahunmi

The Carapace length of the male Cardiosoma armatum showed significant value as against the Carapace length of the female Cardiosoma armatum from the null hypothesis (H₀) of the expected ratio of 1:1 in the Chi-square test shown in Table 3. The chi-square test carried out to test if there is any significant difference in the sex ratio of Cardiosoma armatum gave 1.38 for 1 df at 5% level of significance. This is less than the tabulated value of 3.84 for 1 df at 5% level of significance (Table 4).

0.6889 + 0.6889

=1.378

Calculate x² (1df.5%)=1.378 (Non-significant)

Tabulated x² (1df.5%)=3.84

Hence, Tab X² > Cal.X²

No significance

Therefore, there is no significance between the male and female of Cardiosoma amatum from the Lagos Lagoon mangrove swamps (February- July, 2012).

=2.045

Calculated x² (1df.5%)=2.045 (No significant)

Tabulated x² (1df.5%)=3.84

Hence Tab x²>Cal.x²

No significance

Therefore, there is no significance between the male and female of Cardiosoma guanhumi from Lagos Lagoon mangrove swamps between February and July, 2012 (Table 5).

Table 3: Chi square Test on Sex ratio of Cardiosoma armatum from the Lagos Lagoon mangrove swamps (February- July, 2012).

Table 4: Stomach Food Content of Cardiosoma guanhumi from the Lagos Lagoon mangrove swamps (February- July, 2012).

Table 5: Chi square Test on Sex ratio of Cardiosoma guanhumi from the Lagos Lagoon mangrove swamps (February- July, 2012).

Discussion and Conclusions

In studies of population dynamics, high condition factor values shows favorable environmental conditions such as habitat and prey availability Moradinasab et al. [8] this assertion shows relevance to this research work, the condition factor for the Cardiosoma armatum and Cardiosoma guanhumi has a higher k values of 28.60 and 30.75 for both crabs respectively, though Cardiosoma guanhumi had a higher condition factor k than Cardiosoma armatum, this is obviously related to the relative difference in habitat condition and adequate prey inclusion. This is also supported by the works of Lawal-Are and Nwankwo [9] with k-values of Sersema huzadii from a tropical estuarine lagoon.

The stomach content analysis carried out on Cardiosoma armatum and Cardiosoma guanhumi from the Lagos Lagoon, Unilag Water front, indicated that the percentage empty stomach of Cardiosoma armatum and Cardiosoma guanhumi were 66(5.79%) and 53(2.05%) respectively. The result was in conformity with Lawal-Are and Bilewu [10] for Portunis validus off Lagos‘s coast Nigeria, the percentage empty stomach content was lowest in March and April for both C. armatum and C. guanhumi, this is due to the low environmental condition at the period of collection.

Both crabs showed leaf preference because of the flora associated to their habitat, they showed high level of omnivorous feeding habit, as shown in the stomach content analysis indicated that they both feed on plant materials, crustaceans, fish fragments (bone and scales), sand grains and unidentified items, this support the work of Micheli et al. [11] for Cardiosoma carnifex and Sesarma mainerti. Fish fragments and crustacean found in their stomach content was attributed to the inter migration to shallow part of coastal water. The wide opportunistic feeding pattern of Cardiosoma armatum and Cardiosoma guanhumi was due to their accidental predatorship [12]. The large amount of sand grains discovered was attributed to the burrowing nature of the crabs and inherent soil habitat.

The cumulative sex ratio of both crabs Cardiosoma armatum and Cardiosoma guanhumi showed that males are higher than female; the large number of males in both crab species conforms with [9] for Sersema huzadii which is a mangrove crab (Table 6). According to De- Rivera et al. [13] in a population of the California fiddler crab, Uca crenulata. Mensurative studies revealed there were almost twice as many adult males as females, mating occurred across half of the days within the breeding season, and females had much longer individual reproductive cycles than males. Hence more males than females were available for mating on each day. Perhaps as a consequence, males spent a large proportion of their time fighting with neighbors and rapidly waving their large claws when females passed by. Statistically the chi-square for male female ratio of both crabs showed no significance for male of both crab species and the females, based on the research of Male crabs were more abundant than females [14].

Table 6: Sex Ratio of Cardiosoma armatum and Cardiosoma guanhumi from the Lagos Lagoon mangrove swamps (February- July, 2012).

Thus, the conclusion was that the male Cardiosoma armatum were significantly more numerous than the female in the total number of crab sampled from the Lagos lagoon Unilag water front. There was no ripe female in the sample that could be used for fecundity study.

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