Distribution and abundance of hyperiid amphipods in relation to summer mesoscale features in the southern Gulf of Mexico

Seventy-one hyperiid species were identified from 97 zooplanktonsamples collected in the southern Gulf of Mexico during July1988. About 91% of the adult individuals belonged to five species:Lestrigonus bengalensis (86.56% of total hyperiid numbers),Anchylomera blossevillei (1.20%), Phronimopsis spinifera (1.05%),Hyperioides longipes (1.00%) and Hyperietta vosseleri (0.99%).Overall, up to 74% of the hyperiids were collected at night,although a reverse migration was observed in the anticyclones.The mean abundance was 5-fold higher at the neritic stationsthan in the oceanic areas. This tendency was even more markedat night. Night samples yielded about the same number of speciesas during the daytime (56 taxa versus 61). Four mesoscale features(two anticyclones, one cyclone and one upwelling) characterizedthe oceanic mesoscale circulation in the surveyed area. Theabundance of the oceanic hyperiid community showed significantdifferences related to some of the mesoscale features activein the area, i.e. the abundance in the Lazy Eddy anticyclonewas lower than that in the cyclone (day and night). Overall,the upwelling areas showed a tendency to have higher abundancesthan the downwelling features (anticyclones). Cluster analysisindicated neritic–oceanic differences rather than mesoscalefeature-related differences in the local hyperiid community.The neritic community showed differences that were attributedto the effect of upwelling. The summer and spring hyperiid communitieshad important differences in the same area, thus suggestinga seasonal succession of the gulf hyperiid community.