Temporal and spatial dynamics of ephemeral drift-algae in eelgrass, Zostera marina, beds

TY - JOUR

T1 - Temporal and spatial dynamics of ephemeral drift-algae in eelgrass, Zostera marina, beds

AU - Rasmussen, Jonas Ribergaard

AU - Pedersen, Morten Foldager

AU - Olesen, Birgit

AU - Nielsen, Søren Laurentius

AU - Pedersen, Troels Møller

PY - 2013

Y1 - 2013

N2 - Aggregations of unattached, filamentous macroalgae showed high temporal and spatial dynamics in two shallow and relatively sheltered eelgrass (Zostera marina) beds in Aarhus Bay and the Isefjord, Denmark. The changes in algal abundance were followed in permanent plots at 1–3 days intervals during three different periods of the growth season (May–September). Drift-algal assemblages were present within the 3000 m2 study areas in relatively high and constant abundance (>47% cover) throughout the study period. However, significant changes in average site cover did occur on short timescales (days) suggesting that variability in algal cover may be undetected in monthly assessments. The changes in cover were caused either by algal growth or by physical forces moving large aggregations of algae into or out of the study area. Within plots (1 m2) variability was even higher and algal cover changed regularly between observations (days). Hence, the algae were continuously rearranged within the eelgrass beds; also during periods with no change in average algal cover. The variability in cover of individual plots was negatively correlated to eelgrass cover, suggesting that algae were retained by the eelgrass leaves. This highly dynamic nature of filamentous macroalgal aggregations in eelgrass beds should be considered when evaluating implications of macroalgal blooms for seagrass growth and survival. A frequent relocation of drift-algae at small spatial scale may moderate the formation of poor oxygen conditions within mats and shorten the duration of exposure experienced by individual shoots.

AB - Aggregations of unattached, filamentous macroalgae showed high temporal and spatial dynamics in two shallow and relatively sheltered eelgrass (Zostera marina) beds in Aarhus Bay and the Isefjord, Denmark. The changes in algal abundance were followed in permanent plots at 1–3 days intervals during three different periods of the growth season (May–September). Drift-algal assemblages were present within the 3000 m2 study areas in relatively high and constant abundance (>47% cover) throughout the study period. However, significant changes in average site cover did occur on short timescales (days) suggesting that variability in algal cover may be undetected in monthly assessments. The changes in cover were caused either by algal growth or by physical forces moving large aggregations of algae into or out of the study area. Within plots (1 m2) variability was even higher and algal cover changed regularly between observations (days). Hence, the algae were continuously rearranged within the eelgrass beds; also during periods with no change in average algal cover. The variability in cover of individual plots was negatively correlated to eelgrass cover, suggesting that algae were retained by the eelgrass leaves. This highly dynamic nature of filamentous macroalgal aggregations in eelgrass beds should be considered when evaluating implications of macroalgal blooms for seagrass growth and survival. A frequent relocation of drift-algae at small spatial scale may moderate the formation of poor oxygen conditions within mats and shorten the duration of exposure experienced by individual shoots.

KW - algal mats

KW - seagrass

KW - drift

KW - transport

KW - algal blooms

U2 - 10.1016/j.ecss.2013.01.006

DO - 10.1016/j.ecss.2013.01.006

M3 - Journal article

VL - 119

SP - 167

EP - 175

JO - Estuarine, Coastal and Shelf Science

JF - Estuarine, Coastal and Shelf Science

SN - 0272-7714

ER -