Chaetopterus antarcticus in fishing grounds: from infaunal to epifaunal life habits.

L. SCHEJTER; . BREMEC C.,

Simposio; V Simposio Latinoamericano de Polychaeta. San José, Costa Rica. 17-19 Julio 2018.; 2018

Abstract The shelf-break frontal area in the Argentine Sea is characterized by extensive beds of the Patagonian scallop Zygochlamys patagonica (King, 1832), species exploited since 1996 (Lasta & Bremec 1998, J.Shelfish.Res. 17:103-111). Early research on composition of the invertebrate by-catch in the spatial and temporal scales showed high frequency and abundance of the parchment worm Chaetopterus antarcticus Kinberg, 1866 collected within its U tubes, typical of infaunal habit, associated to the scallop assemblage between 37-39 ºS (Bremec & Lasta 2002, Bull.Mar.Sci. 70:89-105), while only 4% of Z. patagonica collected to study richness of epibionts were encrusted by the parchment worm during 2001 (Schejter & Bremec 2007, J.Mar.Biol.Ass.U.K. 87:917-925). The objective of this contribution is to report variability of life habits of C. antarcticus in areas subjected to trawling disturbance between 38º-39ºS. During 2007 and 2008, 892 scallops were collected between 99 and 106 m depth to record the settlement of epibiotic tube worms on scallops. In total, 468 (> 50%) scallops were encrusted with epibionts; C. antarcticus was settled in 66% (311 specimens) of them, coexisting up to 7 worms on the same upper valve. The other conspicuous colonizers were the sponge Iophon proximum and the sabellariid worm Idanthyrsus macropaleus, which builds sandy tubes. Previous research on the faunal benthic assemblage where Chaetopterus is distributed did not register the massive settlement of the worm on hard living substrates or the huge amounts of tubes that remain empty and cover the bottom. The study area is an important management unit of the scallop fishery (16.186 km2, 38ºS-39º52?S, CFP Res. 15/2012) and the extractive activity between 1998 and 2009 was intensive (Escolar et al. 2015, INIDEP Res.Rep. 84:1-23). During 2015 environmental monitoring, after temporal closures during the last years, worms were registered inside U tubes in 25% of the sampling sites.