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Darrell Welles


M.Sc.: 1997 - 2002

Present occupation: Policy analyst, Department of Environment and Local Government, Fredericton, Canada

Thesis: Seasonal and geographical variations in growth, reproduction and nutrient composition of Ascophyllum nodosum (L.) Le Jolis and its associated species Polysiphonia lanosa (L.) Tandy, Pilayella littoralis (L.) Kjellman and Elachista fucicola (Velley) Areschoug in the Bay of Fundy, Canada

darrell welles photoDarrell Welles working on rockweed samples at a site in the Bay of Fundy, Canada (photo: Thierry Chopin).

Abstract: The growth, reproduction, epiphyte biomass, and nutrient contents of Ascophyllum nodosum were studied over a 14 month period at a wave-exposed site (Maces Bay) and a wave-sheltered site (Limekiln Bay), in the Bay of Fundy, New Brunswick, Canada. Linear growth rates, reproductive biomass, associated species biomass, and nutrient contents [nitrogen (N), phosphorus (P), and carbon (C)] of A. nodosum and its associated species were measured for small (60-80 cm), medium (80-100 cm), and large (>100 cm) fronds from both sites. Seawater samples were also collected from both sites so tissue nutrient contents could be compared to ambient dissolved nitrogen and phosphorus.

The growth rate of large fronds from the sheltered site was higher than that of all other sized fronds from both sites with a maximal rate of 4.36 ± 0.60 cm/month. All other sizes fronds achieved mean maximal growth rates between 3.48 plusmn; 0.42 and 3.87 plusmn; 0.36 cm/month. Reproductive biomass, as a percentage of total frond dry weight, was significantly higher at the exposed site reaching 30.54 plusmn; 1.05 % DW as compared to a maximal value of 24.17 plusmn; 1.09 % DW at the sheltered site.

The associated species studied were Polysiphonia lanosa, Pilayella littoralis, and Elachista fucicola. Of these species, Polysiphonia lanosa was most abundant at the exposed site contributing up to 4.27 plusmn; 0.69 % DW of fronds of A. nodosum. At the sheltered site the biomass of P. lanosa did not exceed 0.59 ± 0.21 % DW of fronds of A. nodosum. In contrast, Pilayella littoralis and E. fucicola achieved greater abundance at the sheltered site. While P. littoralis displayed an affinity for the large fronds of A. nodosum, E. fucicola occurred in similar quantities on all sizes of fronds at each site.

With the exception of tissue total phosphorus content of the tips of A. nodosum which were as much as 0.26 mg P/g DW higher at the exposed site, nutrient contents and nutrient ratios (C:N, C:P and N:P) did not vary significantly between the two sites. However, the seawater concentrations of the dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) differed greatly between the two sites. The DIN concentration was always lower at the exposed site, ranging between 2.11 µM and 10.90 µM, as compared to minimal and maximal values of 7.53 µM and 14.55 µM at the sheltered site. The DIP concentration at the exposed site ranged between 0.34 µM and 1.06 µM, whereas DIP concentration at the sheltered site was 0.64 µM at its lowest, and peaked at 1.67 µM. The elevated nutrient levels at the sheltered site are assumed to be caused by increased inorganic and organic loading in the area, and not to an intrinsic feature of sheltered sites in general. Although there was no obvious correlation between tissue nutrient contents and ambient seawater nutrient concentration, it may have contributed to the increased growth rate observed at the sheltered site.

Nutrient contents and ratios exhibited significant seasonal variations, and variations among the four species analysed. Nutrient contents did not vary significantly between size classes of fronds of A. nodosum, nor did frond size impact the nutrient contents of the associated species.