Analysis of agglutinated benthic foraminifera from surface samples collected in the San Pedro
and Santa Catalina Basins reveals a predictable relationship between the proportions of morphogroups
with decreasing bottom water oxygen levels and with the TOC content of the surficial sediment.
Living (Rose Bengal stained) foraminiferal faunas from dysaerobic environments display
low diversity and high dominance, suggesting stressed conditions. There is an inverse relationship
between oxygen and the relative abundance of deep infaunal morphogroups.
Samples collected from shallow stations above the oxygen minimum zone are comprised of
epifaunal and shallow infaunal morphotypes. At intermediate depths (~500 m), there is a peak in
the abundance of suspension-feeding and "climbing" forms (watchglass-shaped trochamminids
attached to Rhabdammina). Specimens from intermediate stations display the largest overall size.
Deeper in the San Pedro Basin the living fauna is dominated by a small, flattened, tapered,
species that is interpreted as having a deep infaunal microhabitat. In the dysaerobic environments
off California the greatest degree of faunal change occurs when bottom water dissolved oxygen
values drop from 0.5 ml/l to 0.2 ml/l.
The effect of TOC content on the benthic fauna is demonstrated at two stations from the same
depth in the San Pedro Basin. The station with the higher TOC content (4.2% vs. 2.9%) contains
greater proportions of the small, deep infaunal morphotype. These faunal changes may be
attributed to differences in the depth of the oxygenated zone within the sediment surface layer.
Agglutinated faunas from areas that experience seasonal anoxia are comprised of a large
proportion of opportunistic forms such as Reophax and Psammosphaera. These are the same taxa
that colonised abiotic sediment trays in a recolonisation experiment in the Panama Basin. This
study further demonstrates that agglutinated foraminiferal morphotypes respond in a similar
manner to calcareous benthic foraminifera in dysaerobic environments
