Partitioning of food resources at the intertidal zones between the marble rocky crab, Pachygrapsus maromratus (Grapsidae) and warty crab, Eriphia verrucosa (Eriphiidae) along the Mediterranean Sea coasts, Alexandria, Egypt

Document Type : Original Article

Authors

1 Egyptian Environmental Affairs Agency, Nature Conversation Sector, Egypt.

2 Faculty of Science, Al-Azhar University, Naser City, Cairo, Egypt

3 Egyptian Environmental Affairs Agency, Nature Conversation Sector, Egypt

Abstract

The food habits of the warty crab, Eriphia verrucosa and the marbled rocky crab Pachygrapsus marmoratus are examined during this study using the frequency occurrence (% F) and point assessment (% P) methods. The overall annual stomach contents exhibited that E. verrucosa tends to be carnivore; whereas P. marmoratus is herbivorous. The two species consume a wide variety of benthic organisms comprised benthic animals as well as macro and micro algae. The stomach contents of E. verrucosa contained 57.40 % of animal origins, 23.26 % from algae and 19.34% of bottom sediments. In P. marmoratus, the stomach contents comprised 53.85 %, 27.30 % and 18.85 % of the benthic animals, benthic algae and bottom sediments, respectively. The benthic animals in the stomachs of the two species belong to different phyla, dominated by Mollusca representing 24.95 % in E. verrucosa and 21.68 % in P. marmoratus, followed by Crustacea, which have 14.04 % and 11.68 % in the two species, respectively. Results have also shown remarkable seasonal fluctuations in the diet composition and stomach fullness (feeding intensity) of the two species. The highest ratios of algae was 32.58 % and 27.32 % recorded during winter in P. marmoratus and E. verrucosa, respectively, declined sharply to the minimum values (21.49% and 19.12 %) during autumn, associated with the lowest values of sediments during winter. Animal ratios reached the maximum (60.11 % and 63.42%) in autumn and winter, but declined to the minimum (46.36% and 53.26 %) during summer in P. marmoratus and E. verrucosa, respectively. These results indicated that, both of E. verrucosa and P. marmoratus had succeeded in sharing their food resources and escape or decrease competition between them by changing types of food items either temporally or spatially according available foods.

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