Gelatinous zooplankton assemblages associated with water masses in the Humboldt Current System, and potential predatory impact by Bassia bassensis (Siphonophora: Calycophorae)

Abstract

Large numbers of gelatinous zooplankton were collected off Mejillones Peninsula, Chile (Humboldt Current System) in January 1997 during an oceanographic cruise. The area was characterized by the mixing of 3 water masses and the development of coastal upwelling. Siphonophores were the predominant group at most of the stations and the calycophoran Bassia bassensis was overwhelmingly the most abundant species. Five group associations were distinguishable in relation to the water masses identified. Siphonophores were associated with Subtropical Surface Water, the ctenophore Pleurobrachia sp. with Subantarctic Water, the pelagic tunicate Salpa fusiformis with Equatorial Subsurface Water, an assemblage of all gelatinous groups with mixed waters, and a low occurrence of gelatinous groups with upwelled Equatorial Subsurface Water. Molluscs were the group least associated with any water mass. The potential percentage of small copepods removed by B. bassensis ranged between 2.9 and 69.3%. Our results indicate that B. bassensis was the most important secondary predator in the top 50 m of the water column, and could therefore have had a significant trophic impact on the population of small copepods off the Mejillones Peninsula during the sampling period, where small copepods constituted 80.6% of the total mesozooplankton community. This siphonophore potentially ingested an average of 17.3% of the total copepod biomass.

Seasonal and vertical distribution of medusae in Aysen region, southern Chile

“…Its presence in this area confirms its wide distribution in the northern ecosystem of interior waters (Palma et al, 2007a(Palma et al, , 2007bVillenas et al, 2009a). This is a common species in tropical and subtropical waters in all oceans (Segura-Puertas, 1984), and has a wide distribution in the northern area of the Humboldt Current System (HCS) (Pagès et al, 2001;Palma & Apablaza, 2004;Apablaza & Palma, 2006). It may be pointed out that except the other dominant species collected in both winter and spring, the presence of Bougainvillia muscus, Cunina peregrina, Hydractinia borealis, Rhopalonema velatum, Clytia simplex, Proboscidactyla ornata and P. stellata confirms the results previously obtained for this geographical area (Palma et al, 2007a(Palma et al, , 2007b, as well as those obtained for the northern sector (Reloncavi Fjord to Boca del Guafo) (Villenas et al, 2009a;Palma et al, 2011).…”

Species of Lensia (Cnidaria: Hydrozoa: Siphonophorae) from southeastern Brazilian waters

“…In South America, it occurs in the Pacific Ocean, in Chile, at 23°S off Antofagasta (Pagès et al 2001, PalMa & aPaBlaza 2004; and in the Atlantic Ocean, off French Guiana (lelouP 1934), and from Brazil to Argentina, from 0° to 38°S (alvariño 1968, 1971, cordeiro & MonTú 1991, nogueira & oliveira 1991, PugH 1999, MigoTTo et al 2002, silveira & Morandini 2011.…”

“…In view of their abundance, these organisms have great ecological importance (PugH 1999), and may affect, by predation, the supply of copepods, which also feeds economically important fish species (Pagès et al 2001).…”

Fauna of the Mediterranean Hydrozoa.

“…References : Totton (1965);Palma (1973);Daniel (1974); Kirkpatrick and Pugh (1984); Gili (1986); ; ; Lakkis and Zeidane (1995); Pagès et al (2001).…”