Effects of sediment influx on the settlement and survival of canopy-forming macrophytes

Abstract

Kelp forests on coastal rocky shores are negatively impacted by sudden sediment loads that can occur with storms and floods. Using laboratory experiments, we studied the effects of sediment deposition on the survival of the large brown alga Eisenia bicyclis juveniles (zoospores and gametophytes) to quantify the potential impacts of particulate matter on kelp forests. The zoospore adhesion rate and the gametophyte survival and growth rates all declined markedly with increasing sediment load, particularly with smaller particle diameter. Using experimental results, we derived an equation to calculate the rate of initial kelp depletion with sediment load based on the quantity and size distribution of sediment particles. The equation enabled the estimation of E. bicyclis depletion rates in the field by measurement of particle quantity and diameter distribution of sediments on the reef substrate.

Figure 1. Relationship between sediment quantity and zoospore attachment rate for each sediment particle size.

Figure 2. Relationship between sediment quantity and the gametophyte survival rate for each sediment particle size.

Figure 3

Relationship between the reciprocal of particle diameter and the involution coefficient of (a) the adhesion rate as determined by equations 1, 2, 3, 4, and (b) the survival rate as determined by equations 5, 6, 7, 8.

Figure 4. Size distribution of sediment particles.