The across-shelf larval, postlarval, and juvenile fish community associated with offshore oil and gas platforms and a coastal rock jetty west of the Mississipp River Delta

Abstract

The fisheries aggregation value of oil and gas platforms in the continental shelf waters of the northern Gulf of Mexico (GOM) is well recognized, but the assessment of early life stages associated with these structures has not been adequately addressed. Ichthyoplankton assemblages were sampled at three offshore platforms: Green Canyon 18 (GC 18; 230 m depth, shelf slope); Grand Isle 94 (GI 94; 60 m depth, mid-shelf); and South Timbalier 54 (ST 54; 20 m depth, inner shelf) with passive plankton nets and light-traps and at a coastal rock jetty (Belle Pass; 3-5 m depth) with a light-trap and a plankton pushnet. Family richness was highest at GC 18 (52), followed by GI 94 (43), ST 54 (42), and Belle Pass (41). At the genus level, richness was highest at Belle Pass jetty (127), followed by GI 94 (114), ST 54 (86), and GC 18 (82). At all sites, clupeiforms dominated samples, comprising 59-97% of the total catch. Gobiids and blenniids dominated the reefassociated fish assemblages at all sites. Other relatively common reef-associated fish were serranids and lutjanids (GC 18), pomacentrids and opisthognathids (GI 94), Rhomboplites aurorubens (ST54), and Lutjanus griseus and L. synagris (Belle Pass). The ichthyoplankton assemblages sampled at each site were relatively dissimilar, based on Schoener’s Index of Niche Overlap, with the highest index value for any two sites being 0.45 for GI 94 and ST 54 (0-1 scale; clupeiforms excluded). No significant difference was observed between mean Shannon-Weiner diversity indices calculated for plankton net samples at each site. For light-trap samples, diversity was lowest at GC 18, significantly higher at GI 94, and then decreased inshore. Canonical correlation analyses indicated that temperature and salinity explained most of the variation in larval abundance for some dominant taxa at the platforms, while at Belle Pass jetty, dissolved oxygen and turbidity were also important environmental variables.