Temporal and spatial patterns of lanternfish (family Myctophidae) communities associated with a warm-core eddy

Abstract

To help assess the biological impact of warm-core eddies off eastern Australia, lanternfish (family Myctophidae) were sampled during cruises in August, September and October, 1979 and February and May 1980 as part of a 14 mo time-series study of Eddy J. During the study, Eddy J drifted some 500 km southward along the east coast of Australia and coalesced with another eddy, Eddy I. Myctophids were collected at night by midwater trawling (n=150) in the upper 500 m of the water column. In all, 46 species of myctophids (6 913 specimens) were caught. Percentage similarity indices and cluster analyses of species assemblages showed that: (1) temporally, the myctophid fauna changed markedly both inside and outside the eddy between October and February, but, within a season, the myctophid fauna inside Eddy J changed little between consecutive cruises; (2) spatially, myctophid communities generally corresponded more closely with sample location with respect to the eddy than with depth and temperature per se. The 4 most common species (Diaphus meadi, Hygophum hygomii, Lampanyctus alatus and Benthosema suborbitale), on the other hand, had ubiquitous distributions with respect to eddy location but had peaks of abundance at particular temperatures (15°, 17°, 19° and 21°C, respectively). The 5th most common species, Diaphus danae, was limited to outside or edge samples. The results suggest that the biological contrasts between a warm-core eddy and surrounding water masses are largely a function of the degree of the eddies' physical isolation after separation from the East Australian Current and that natural seasonal variations in myctophid communities may overshadow more subtle successional changes inside an eddy as the eddy ages.