<p><em style=\"mso-bidi-font-style: normal;\"><span style=\"line-height: 115%; font-family: \'Times New Roman\',\'serif\'; font-size: 10pt;\">Crustaceans that filter plankton or bacteria from the water are common and diversified in estuarine environments. Other crustaceans are active predators or scavenge nutrients from detritus. A few are adapted to high salinity and are parasitic or sessile, hatching young that resemble miniature adults; others go through larval stages.<span style=\"mso-spacerun: yes;\">&nbsp; </span>This study examined the diversity, abundance, and distribution of macrobenthic crustaceans in the Cochin estuary on the southwest coast of India. Samples from nine stations in the estuary were collected between June 2009 and May 2011. The major crustaceans were amphipods, tanaids, isopods, insects, decapods, and acarina. Corophium volutator and Cirolana fluviatilis were the dominant amphipod and isopod species, respectively. Tanais philetaerus Stebbing was the dominant tanaid species. The crab species Halicarcinus messor was the dominant decapod and Neumania spp. (water mite) were the major Acaridae. Chironomid larvae were the most abundant insects.<span style=\"mso-spacerun: yes;\">&nbsp; </span>The temperature and pH of the sediments and benthic waters varied seasonally, and the dissolved oxygen content of the latter greatly influenced the diversity and abundance.<span style=\"mso-spacerun: yes;\">&nbsp; </span>The spatial abundance of the crustaceans varied between the stations, with a low at Station 8 (80 no/m<sup>2</sup>) and a high at Station 5 (9733 no/m<sup>2</sup>). The seasonal abundance was least (182 no/m<sup>2</sup>) during the pre-monsoon season of 2011, and maximum (7935 no/m<sup>2</sup>) in the post-monsoon season in 2009&ndash;10. The numerical abundance varied between the three zones of the estuary, with the maximum mean abundance found in the central region (4452 no/m<sup>2</sup>), followed by the southern (2582 no/m<sup>2</sup>) and northern (1157 no/m<sup>2</sup>) regions. The crustacean abundance fell remarkably between the first (3705 no/m<sup>2</sup>) and second (1674 no/m<sup>2</sup>) years. The numerical abundance was highest in the region of the estuary with high salinity, a moderate pH, and a high percentage of silt and clay. </span></em></p>
<p><span style=\"line-height: 115%; font-family: \'Times New Roman\',\'serif\'; font-size: 10pt;\">Keywords: Crustaceans, macrobenthos, amphipod, decapods, Cochin estuary.</span></p>
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