The structure of demersal assemblages off Namibia in relation to abiotic factors

Abstract

were used to describe the demersal assemblages of the northern Benguela along the Namibian coast. Multivariate analyses indicated a clear separation between shelf and slope habitats, which were divided into three and two assemblages respectively. These divisions were distinct, with clear distributional boundaries separating them. Species determining the structure of these divisions and subdivisions and their relative abundances were identified. Depth, bottom temperature, bottom salinity and dissolved oxygen were all significantly correlated with the spatial distribution of the assemblages. Minor changes or shifts in the distribution of assemblages were observed over the study period, although patterns of species associations remained relatively constant.

El Niño and similar perturbation effects on the benthos of the Humboldt, California, and Benguela Current upwelling ecosystems

“…We have no indications that the zone below the OMZ is affected by EN or similar impacts in any of the three EBC reviewed in this study, although only Hamukuaya et al (2001) explicitly mention that the BC slope communities were not disrupted by the 1995 Benguela Niño. Boyer and Hampton (2001) suspect effects on monkfish (Lophius spp.)…”

“…Only areas south of 20 • S are normally affected by severe hypoxia in this EBC (Helly and Levin, 2004). Persistent hypoxia in this ecosystem is usually restricted to within the 100 m isobath over innershelf areas in the central region but low dissolved O 2 values <3 ml l −1 are common (Hamukuaya et al, 2001).…”

“…the warm and cold phases of the ENSO cycle. However, as the HC resembles the Benguela Current (BC) rather than the CC, the BC is included despite the fact that the existence of a "Benguela Niño" is not universally accepted (cf., for example, Shannon and Nelson (1996) vs. Hamukuaya et al (2001)). There are, however, other perturbations such as H 2 S outbreaks or intrusions of unusually warm equatorial water, which the BC has in common with the two other large upwelling systems.…”

“…1). Some of the Benguela Niño impacts such as faunal migrations and mortalities resemble very much those of EN in the eastern Pacific (Gammelsröd et al, 1998) but seem to be restricted to shallower depths (Hamukuaya et al, 2001).…”

Assemblage Structure of Eastern Pacific Groundfishes on the U.S. Continental Slope in Relation to Physical and Environmental Variables

“…Not surprisingly, groundfish assemblages are commonly related to depth (Haedrich and Krefft 1978;Pearcy et al 1982;Gage and Tyler 1991;Merrett 1994;Weinberg 1994;Jay 1996;Lee and Sampson 2000;Hamukuaya et al 2001;Biagi et al 2002), which serves as a proxy for important environmental variables such as temperature, dissolved oxygen, salinity, and light. Similarly, latitudinal gradients (decreasing richness from the tropics to the poles) and discontinuities in species diversity and assemblage structure are well known and common in aquatic, marine, and terrestrial systems (Fisher 1960;Rex et al 1993Rex et al , 2005Willig 2000;Lyons and Willig 2002).…”