Hydromedusae in Buenos Aires coast, Argentina: the small ones are also rising up?

MIANZAN H.; GENZANO G. N.

Lecce, Italia

Workshop; Seventh International Workshop of the Hydrozoan Society; 2010

Hydrozoan society

Hydromedusae in Buenos Aires coast, Argentina: the small ones are also rising up? Mianzan H. 1,2  and G. Genzano 1,3 1CONICET, 2INIDEP, Argentina, 3Estación Nágera, Universidad Nacional de Mar del Plata, Argentina There is a general impression that jellyfish and other gelatinous organisms are increasing in number in some ecosystems having a notorious effect on many human economic activities such as tourism, fisheries and various coastal industries.  Long - term monitoring and large - scale studies are a possible way to confirm (or refuse) if such changes are occurring but for most of the cases the information about "normal" abundances of species is very limited to support our perceptions and this fact is even worst when referred to small hydromedusae. During eleven surveys on the same area (Buenos Aires coast) and within the same period of the year (last week of October to the first week of November),  1174 plankton samples were collected and allowed us to analize the changes on hydromedusae abundances and frequencies from 1993 to 2008. A gradual increase in hydromedusae frequency and abundance values from 1993 to 1996 was observed.  These values were two orders of magnitude higher during the period 1999 – 2008, as compared to early 90s. The contribution of the species varied in the long term, while some hydromedusae undergoing cycles of rarity and commonness (e.g. Liriope tetraphylla, Eucheilota ventricularis), others by the other hand, have become more frequent and abundant since the early 90´s (e.g. Proboscidactyla mutabilis, Obelia sp.). The role of environmental drivers in such pattern is here discussed.