Publication Abstract

Macrofaunal recolonization on intertidal mudflats: effect of sediment organic and sand content

S.G. Bolam, P. Whomersley and M. Schratzberger

A field manipulation experiment was conducted to investigate the effects of increased sediment organic content (from 0.9% to 2.8/2.9%) and sand content (from 12.0% to 47.0/49.0%) on macrofaunal recolonization and sediment physical (shear strength) and physico-chemical (redox potential) properties on an intertidal mudflat, Crouch Estuary, Essex, UK.

The results suggested that while increased sand content had no discernible effect on sediment property changes, increased organic content resulted in marked reductions in redox potential at 1, 2 and 4 cm sediment depths and increased shear strengths. These sediments exhibited a distinct ‘cracking’ appearance on their surfaces. Similarly, while macrofaunal recovery was not affected by increased sand content, total numbers of individuals, number of species and diversity took longer to recover in sediments with increased organic contents. Recolonization proceeded via a gradual increase in the abundance of those taxa present in ambient sediments rather than via a distinct successional sequence. Recovery was species-specific with organic content-tolerant species (Hediste diversicolor (Müller) and Hydrobia ulvae (Pennant)) recovering to ambient levels within the first week of the experiment. Multivariate analyses indicated that the community assemblages of the low-organic content treatments had recovered after 12 months while those of the high-organic content treatments were still significantly different to those of the controls at the end of the experiment.

We propose that the relatively rapid recovery and lack of successional sequence observed in this study can be explained by the opportunistic nature of the ambient assemblage and by the dispersive nature of the dominant species. Reduced sediments and/or increased shear strengths led to a slow recovery in high organic content treatments. Our experiment was necessarily limited in both spatial and temporal scale, the implications of this when scaling up to larger-scale generalisations are discussed.

Reference:

S.G. Bolam, P. Whomersley and M. Schratzberger (2004) Macrofaunal recolonization on intertidal mudflats: effect of sediment organic and sand content. Journal of Experimental Marine Biology and Ecology, 306(2): 157-180