A research has been conducted in the near shore waters off Karachi, which aims to study the near shore marine benthic fauna, documenting the diversity of the marine fauna. For this purpose the benthic faunas was collected every month for one year. A total of 76 species of invertebrates belonging to 38 families were collected.
MATERIAL AND METHODS
The material was collected by means of an otter trawl operated from a commercial trawler during the period of one year from December 1992 to November 1993. During the study period one trip per month was undertaken. During this period the trawler AL-AHMEDI along the near shore waters off Karachi made a total of 36 hauls. The trawling operations were generally a daylong and are locally known by the name of “Hella” fishery. Random sample from the total catch of the trawl was separated on every trip for subsequent study in laboratory. Identifications of invertebrates were made to species or generic level with the help of available literature. During the monthly observations temperature was measured by the thermometer and salinity by refractometer in the laboratory.
RESULT AND DISCUSSION
On the fishing grounds off Karachi invertebrate fauna was found abundant. A total of 76 species of invertebrates belonging to 38 families were collected. In (Table 1) the month-wise occurrence of three most abundant invertebrate species in the study area were shown among these Oratosquilla nepa, Charybdis callianassaand and Bulla ampulla were found to be more numerous then other species in the area, while (Table 2) Shows the dominant number of individuals of invertebrate species in near shore waters off Karachi. Monthly distribution of invertebrate species shown in (Fig.1)
The Shannon and Wiener diversity index was use for the evaluation of species diversity in each collection of the months (Table 3). Diversity index is a mathematical measure of species diversity in a community. Diversity indices provide more information about community composition than simply species richness (i.e., the number of species present). Diversity indices provide important information about rarity and commonness of species in a community. The ability to quantify diversity in this way is an important tool for biologists trying to understand community structure. Diversity commonly depends on the number of species and individuals in the community at a given time and has been mathematically well documented. According to (Fig. 2 & 3). In northeast monsoon season lowest density was observed and higher density in pre monsoon and southwest monsoon seasons (Fig. 4) while in post monsoon season again low density occurred. This pattern shows the diversity of invertebrates high in warmer seasons and low in colder seasons.
Diversity index was calculated by using the Shanon Weiner diversity Index (H) (Shannon Weiner 1963) and equitability or evenness (J) (Pielou 1964) was also calculated. The following formulas were used for the calculations:
H = -å (1-i) (Pi) (log10 Pi)
J= H / H max
Where Pi = Relative percentage of species.
S = Number of species.
H max = Maximum number of species and is equal to log10 S
The study provides valuable information about the occurrence and abundance of marine fauna. It should be continued furthers. The results of the present study provide baseline data for acquiring a better understanding of the macro-benthic life of the near shore waters off Karachi.
Table .1 The month-wise occurrence of three most abundant invertebrate species.
Table . 2 Dominant invertebrate species in near shore waters off Karachi from December, 1992 to November, 1993. N= Total number of individuals.
Figure 1. Monthly distributions of invertebrate species in near shore waters of Arabian Sea off Karachi.
Table 3. Diversity and equitability of invertebrate species from near shore waters of Karachi.
Figure 2. Monthly Diversity index (H) of Invertebrates from near shore waters of Karachi, (Northern Arabian Sea)
Figure 4. Mean Seasonal Diversity index (H') of invertebrates from near shore Karachi,(Northern Arabian Sea)
Figure 3. Monthly Equitability (J') of Invertebrates from near shore waters of Karachi, (Northern Arabian Sea)
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