The effects of the Patagonian shelf-break front on copepod abundance, biodiversity, and assemblages

SEVERO, AYELÉN; CEPEDA, GEORGINA DANIELA; ACHA, EDUARDO MARCELO

JOURNAL OF MARINE SYSTEMS

ELSEVIER SCIENCE BV

Año: 2024 vol. 241

0924-7963

Fronts play an important role in ecological processes, having multiple effects on the structure of planktoncommunities. The Argentine Sea is characterized by the presence of the large and very productive Patagonianshelf-break front (PSBF). This is a permanent front, with high thermohaline gradients defined between therelatively warmer and fresher shelf waters and those of the Malvinas Current. We studied the effects of the PSBFin the vertical and horizontal structure of the copepod community along two transects crossing the front. For allthe variables studied, the outer shelf plus the front behaves as a unity, different of the offshore oceanic region.The highest copepod abundances were recorded on the outer shelf and shelf-break front, while the highest diversitywas verified in the oceanic regime. Three copepod assemblages were identified associated to differentregions: outer shelf and front (OS-PSBF), upper (UMW) and deeper (DMW) Malvinas waters, each one characterizedby its own set of indicator species, having different reproductive and feeding strategies. Sac-spawners,ambush or cruise-feeders, and detritivore or omnivore species, occurred in DMW, while broadcasters, filterfeedersand mainly herbivores dominated at UMW and OS-PSBF. The PSBF acts as a leaky boundary betweenthe oceanic regime (UMW and DMW) and the outer shelf-front regime (OS-PSBF), the first one characterized byhigher copepod diversity and several functional groups, and the last one depicted by higher copepod abundanceand only one functional group. In addition to its high primary production, the PSBF and surroundings areimportant to provide diversity of pelagic habitats that promote the existence of different assemblages, which arecharacterized by species having similar functional traits and that could play a similar role in the ecosystem.