Age, Height, and Annual Growth

Average total length (fig. 2) of the samples significantly varied by intertidal zone
(p = .028). Average heights of A. nodosum from the middle and lower intertidal were both 56 cm, where samples from the upper zone averaged 81 cm tall. Tall algae in the upper intertidal are able to self-shade better, and thus maintain a most constant temperature than if they were fully exposed to the elements, allowing them to avoid desiccation and freezing.

The ages (fig. 3) of the algae sampled were determined to be statistically significant
(p = .009), with the oldest samples in the upper zone, at an average age of 5.33 years. Algae from the middle zone averaged 3.33 years old and those from the lower zone were 4.5 years old. Overall, the data set is relatively young, given that Ascophyllum can live for over fifteen years. Stengel, et al. (1997), received different results from a similar study, of the oldest zone being the lower shore with A. nodosum ranging to seventeen years old. They found the upper zone to be the youngest, algae no older than six years old and ages from the middle zone ranged between six and eleven years. At least part of this difference can be attributed to differences in data collection. Stengel, et al. (1997) only looked at unbroken fronds, of which there are few old ones on the upper shore, given the drastic living conditions. Since completeness of fronds were not taken into account in this study, it is difficult to compare the data sets.

Regardless of intertidal zone, total length and age (fig. 1) were statistically significant (p = .0006), indicating that height is a factor of age. Given that annual growth (fig. 4) was not found to be statistically significant, it can be deduced that total height of the algae is influenced more by accumulation of growth over multiple years than varying incremental annual contributions dependent on zone.

Pigment Concentrations

This component of the study initially started out looking at only the variations between pigment concentrations of algae from different intertidal zones, however, in the end, portion of algae (basal portion vs. apical tip) were also taken into account. Portion ended up being a significant factor in all four pigment analyses. For both the chlorophylls and total pigment (fig. 5), there were statistically more pigments in the apical tips than found in the bases, regardless of zone. For fucoxanthin (fig. 8), the concentration of pigment in the apical tips and bases were similar from both the middle and lower zones, but significantly different in the upper zone, with a higher concentration of fucoxanthin in the base compared to the tip. This resulted in a significant zone by portion interaction (p = .0265). This would indicate that at the base of the algae, the most important accessory pigment in light harvesting is fucoxanthin, especially important in the upper zone where algae can be draped over itself during low tide, and thus blocked from sunlight. Chlorophyll c is an important light harvesting pigment in the apical tips of the algae, regardless of zone. In a study of seasonal changes between pigment contents of A. nodosum from different zones, Stengel (1998) determined that concentrations of chlorophyll a are different in the month of October than any other time of year, due to autumn tides leading to reduced light availability in the lower zone. Since this study was conducted in October, that could explain, in part, the significant difference chlorophyll a (fig. 6) pigmentation between apical tips and basal portions.

Given the high concentrations of chlorophyll c (fig. 7) compared to the concentrations of the other pigments, chlorophyll c is the major contributing factor to total pigment (fig. 5) in the algae studied. This also indicates that regardless of zone, chlorophyll c is a crucial pigment in the light harvesting of Ascophyllum nodosum. The smallest pigment concentrations were chlorophyll a, indicating that for these algae, light harvesting complex requires far more pigments than the role of chlorophyll a. In all cases, save chlorophyll a, concentration of pigment in the total sample was statistically significant. This is similar to a trend reported by Stengel (1998), in which chlorophyll a did not vary statistically between intertidal zones. This indicates that there is an overall difference between light harvesting in varying zones of A. nodosum.

Differences in pigments would be expected, given that the algae from different zones encounter different microhabitats, including light irradiances, self-shading, and nutrient levels (Stengel, 1998). Algae from the lower zone are often covered by water and must account for absorption and water column scattering of pigments (Stengel, 1998). Algae from the upper zone undergo aerial exposure; in which they receive increased irradiance from direct sunlight. This study displays that there are significant differences in pigment concentrations of total samples with variation to intertidal zone. Also, it would be expected that there would be a difference in pigmentation depending on position in the algae, since different portions of the algae experience different irradiances. Portions at the basal part of the alga are covered by water in the lower intertidal most of the time, and thus would require more light harvesting pigments to conduct photosynthesis. Likewise, tips are exposed to more direct sunlight and would require different pigment arrangements.