Horizontal distribution and dominant species of heteropods in the East China Sea

Abstract

This article discusses the horizontal distribution and dominant species of heteropods in the East China Sea. The ecological characteristics of heteropods and their adaptability to the environments were also considered. Oceanographic census was carried out in the East China Sea (23 � 30 0 � 33 � Na nd 118 � 30 0 � 128 � E) in four seasons from 1997 to 2000. It was found that the total abundance showed obvious seasonal variations. It peaked in autumn with a mean value of 21.03 ind. (100 m 3 ) –1 , followed by summer (4.89 ind. (100 m 3 ) –1 ). The lowest abundance occurred in winter and spring. As to the horizontal distribution, abundance in summer and autumn was higher in the nearshore than in the offshore of the East China Sea. In winter and spring, heteropods were barely found in the northern nearshore. Three dominant species were observed in four investigated seasons, in which only Atlanta rosea dominated in winter, spring and summer while Atlanta peroni and Atlanta lesueuri mainly dominated in autumn. These two dominant species observed in autumn exhibited a rather higher occurrence frequency than A. rosea. Temperature was found to be a major influencing factor whereas salinity was a minor one. Comparing their adaptability, A. rosea can survive in a wider temperature range (16� 28 � C), which enables it to dominate in four seasons, while A. peroni survives in a relatively narrow temperature range (19� 28 � CC) and the range for A. lesueuri was even more narrow (21� 28 � CC). Moreover, A. rosea was also adapted to a wider range of salinity. However, the abundance of A. rosea in autumn was lower than those of A. peroni and A. lesueuri. It can be thereby inferred that the multiplication speed of A. rosea was lower than the other two species within the same favorable temperature range. Due to their adaptability to high salinity, the distribution of heteropods was closely related to the domain of the Taiwan Warm Current and Kuroshio. Especially for A. peroni and A. lesueuri, their high abundance areas are always indicative of the lasting existence of strong warm currents. The negative values of aggregation indices indicated relatively even distribution of heteropods in the East China Sea. The high abundance area (31 � 00 0 N, 126 � 00 0 E) of heteropods in autumn is on the migration pathway of the mackerel (Scomber japonicus Houttuyn). Thus, there is also a fishing ground of the mackerel. This suggested that the high abundance area of heteropods in autumn is important to the fisheries in the East China Sea. Comparing with the historical records, the abundance of heteropods appeared to increase in the past 40 years. This may be a result of strengthened warm currents due to global warming.