The effect of the 1997-1998 ENSO on the benthic macrofaunal biomass in the southwestern Gulf of Mexico

Abstract

Long term macrofaunal biomass measurements made since 1987 were used to evaluate the effect of episodic inputs of biogenic carbon during ENSO on the shelf and slope benthos in the southwestern Gulf of Mexico. This study was based on the hypothesis that wind-induced mixing over long periods on the sea surface of the Gulf of Mexico increases primary productivity exported to depth, that trophically sustains the benthic community by enhancing the macrofaunal biomass. The content of organic nitrogen in sediment was used to estimate sediment organic enrichment. Geographical and seasonal changes recorded previously in the region showed that macrofaunal biomass maxima occur during mixing in the water column and decrease with the onset of stratification. Macrofaunal biomass recorded during 1998 was larger than in previous years: shelf 0.93±0.22 gC.m^-2, slope 0.55±0.23 gC.m^-2, as compared to shelf 0.57±0.11 gC.m^-2, slope 0.18±0.09 gC.m^-2. The shelf macrofaunal biomass showed a large variability in contrast to the values recorded on the slope. Seasonal inputs of phytodetritus produce sediment enrichment and correlate with macrofaunal biomass changes (shelf r= 0.77; slope r= 0.85). ENSO promotes stochastic pulses of phytodetrital material induced by wind forcing that enrich the sediment and lead to a significant increase in the macrofaunal biomass.