Ascophyllum nodosum and its symbionts: XI. The epiphyte Vertebrata lanosa performs better photosynthetically when attached to Ascophyllum than when alone

Garbary, David J.,Miller, Anthony G.,Scrosati, Ricardo A. The Korean Society of Phycology 2014 ALGAE Vol.29 No.4

Vertebrata lanosa is an abundant and obligate red algal epiphyte of Ascophyllum nodosum that forms part of a complex and highly integrated symbiotic system that includes the ascomycete, Mycophycias ascophylli. As part of ongoing studies to resolve interactions among species in the symbiosis, we used pulse amplitude modulation fluorimetry of chlorophyll a fluorescence, from photosystem II (PSII), to measure the maximum quantum yield ($F_v/F_m$) of PSII [$QY(II)_{max}$] and relative photosynthetic electron transport rates (rETR), as a function of light intensity, in order to evaluate the photosynthetic capacity of the two algal symbionts in the field and in the laboratory under different treatments. Our primary question was 'Is the ecological integration of these species reflected in a corresponding physiological integration involving photosynthetic process?' In the laboratory we measured changes in $QY(II)_{max}$ in thalli of V. lanosa and A. nodosum over one week periods when maintained together in either attached or detached treatments or when maintained separated from each other. While the $QY(II)_{max}$ of PSII of A. nodosum remained high and showed no significant variation among treatments, V. lanosa showed decreasing performance in the following conditions: V. lanosa attached to A. nodosum, V. lanosa in the same culture, but not attached to A. nodosum, and V. lanosa alone. These results are consistent with observations in which rETR was reduced in V. lanosa maintained alone versus attached to A. nodosum. Values for $QY(II)_{max}$ in V. lanosa measured in the field in fully submerged thalli were similar to those measured in the laboratory when V. lanosa was attached to it obligate host A. nodosum. Our results provide evidence of a physiological association of the epiphyte and its host that reflects the known ecology.

Ascophyllum nodosum and its symbionts: XI. The epiphyte Vertebrata lanosa performs better photosynthetically when attached to Ascophyllum than when alone

David J. Garbary,Anthony G. Miller,Ricardo A. Scrosati 한국조류학회I 2014 ALGAE Vol.29 No.4

Vertebrata lanosa is an abundant and obligate red algal epiphyte of Ascophyllum nodosum that forms part of a complex and highly integrated symbiotic system that includes the ascomycete, Mycophycias ascophylli. As part of ongoing studies to resolve interactions among species in the symbiosis, we used pulse amplitude modulation fluorimetry of chlorophyll a fluorescence, from photosystem II (PSII), to measure the maximum quantum yield (Fv / Fm) of PSII [QY(II)max] and relative photosynthetic electron transport rates (rETR), as a function of light intensity, in order to evaluate the photosynthetic capacity of the two algal symbionts in the field and in the laboratory under different treatments. Our primary question was ‘Is the ecological integration of these species reflected in a corresponding physiological integration involving photosynthetic process?’ In the laboratory we measured changes in QY(II)max in thalli of V. lanosa and A. nodosum over one week periods when maintained together in either attached or detached treatments or when maintained separated from each other. While the QY(II)max of PSII of A. nodosum remained high and showed no significant variation among treatments, V. lanosa showed decreasing performance in the following conditions: V. lanosa attached to A. nodosum, V. lanosa in the same culture, but not attached to A. nodosum, and V. lanosa alone. These results are consistent with observations in which rETR was reduced in V. lanosa maintained alone versus attached to A. nodosum. Values for QY(II)max in V. lanosa measured in the field in fully submerged thalli were similar to those measured in the laboratory when V. lanosa was attached to it obligate host A. nodosum. Our results provide evidence of a physiological association of the epiphyte and its host that reflects the known ecology.

The clonal seaweed Chondrus crispus as a foundation species

Ricardo A. Scrosati 한국조류학회I 2016 ALGAE Vol.31 No.1

The clonal seaweed Chondrus crispus (Rhodophyta, Gigartinales) forms extensive stands at low intertidal elevations on wave-sheltered rocky shores of the North Atlantic. This study investigates if this bushy alga acts as a foundation species in such habitats. The abundance (percent cover) of C. crispus, all other algae, and invertebrates was measured in 390 quadrats spanning 350 km of coast in Nova Scotia, Canada. In these low-intertidal habitats, fucoid algae are the largest organisms and can form extensive canopies, but their cover was unrelated to benthic species richness and to C. crispus cover. Species richness, however, increased with C. crispus cover from low to intermediate cover values, showing little change towards full C. crispus cover. Species composition (a combined measure of species identity and their relative abundance) differed between quadrats with low (0–1%) and high (60–100%) cover of C. crispus. High C. crispus cover was associated to more invertebrate species but fewer algal species than low C. crispus cover. However, the average abundance of algal and invertebrate species occurring in both cover groups was often higher under high C. crispus cover, contributing to a higher average richness at the quadrat scale. Overall, only 16% of the observed variation in species richness was explained by C. crispus cover. Therefore, this study suggests that C. crispus acts as a foundation species but with a moderate influence.

The clonal seaweed Chondrus crispus as a foundation species

Scrosati, Ricardo A. The Korean Society of Phycology 2016 ALGAE Vol.31 No.1

The clonal seaweed Chondrus crispus (Rhodophyta, Gigartinales) forms extensive stands at low intertidal elevations on wave-sheltered rocky shores of the North Atlantic. This study investigates if this bushy alga acts as a foundation species in such habitats. The abundance (percent cover) of C. crispus, all other algae, and invertebrates was measured in 390 quadrats spanning 350 km of coast in Nova Scotia, Canada. In these low-intertidal habitats, fucoid algae are the largest organisms and can form extensive canopies, but their cover was unrelated to benthic species richness and to C. crispus cover. Species richness, however, increased with C. crispus cover from low to intermediate cover values, showing little change towards full C. crispus cover. Species composition (a combined measure of species identity and their relative abundance) differed between quadrats with low (0-1%) and high (60-100%) cover of C. crispus. High C. crispus cover was associated to more invertebrate species but fewer algal species than low C. crispus cover. However, the average abundance of algal and invertebrate species occurring in both cover groups was often higher under high C. crispus cover, contributing to a higher average richness at the quadrat scale. Overall, only 16% of the observed variation in species richness was explained by C. crispus cover. Therefore, this study suggests that C. crispus acts as a foundation species but with a moderate influence.

Community-level facilitation by macroalgal foundation species peaks at an intermediate level of environmental stress

Ricardo A. Scrosati 한국조류학회I 2017 ALGAE Vol.32 No.1

In rocky intertidal habitats, abiotic stress due to desiccation and thermal extremes increases with elevation because of tides. A study in Atlantic Canada showed that, at low elevations where conditions are benign due to the brief low tides, fucoid algal canopies (Ascophyllum nodosum and Fucus spp.) do not affect the structure of benthic communities. However, at middle and high elevations, where low tides last longer, fucoid canopies limit abiotic extremes and increase the richness (number of invertebrate and algal species, except fucoids) of benthic communities. Using the data from that study, this paper compares the intensity of facilitation and its importance (relative to all other sources of variation in richness) between middle and high elevations, which represent intermediate and high stress, respectively. Facilitation intensity was calculated as the percent increase in benthic richness between quadrats with low and high canopy cover, while the importance of facilitation was calculated as the percentage of variation in richness explained by canopy cover. Data for 689 quadrats spanning 350 km of coastline were used. Both the intensity and importance of facilitation were greater at middle elevations than at high elevations. As canopies do not affect benthic communities at low elevations, this study suggests that the facilitation-stress relationship at the community level is unimodal for this marine system. Such a pattern was found for some terrestrial systems dominated by canopy-forming plants. Thus, it might be ubiquitous in nature and, as further studies refine it, it might help to predict community-level facilitation depending on environmental stress.

Community-level facilitation by macroalgal foundation species peaks at an intermediate level of environmental stress

Scrosati, Ricardo A. The Korean Society of Phycology 2017 ALGAE Vol.32 No.1

In rocky intertidal habitats, abiotic stress due to desiccation and thermal extremes increases with elevation because of tides. A study in Atlantic Canada showed that, at low elevations where conditions are benign due to the brief low tides, fucoid algal canopies (Ascophyllum nodosum and Fucus spp.) do not affect the structure of benthic communities. However, at middle and high elevations, where low tides last longer, fucoid canopies limit abiotic extremes and increase the richness (number of invertebrate and algal species, except fucoids) of benthic communities. Using the data from that study, this paper compares the intensity of facilitation and its importance (relative to all other sources of variation in richness) between middle and high elevations, which represent intermediate and high stress, respectively. Facilitation intensity was calculated as the percent increase in benthic richness between quadrats with low and high canopy cover, while the importance of facilitation was calculated as the percentage of variation in richness explained by canopy cover. Data for 689 quadrats spanning 350 km of coastline were used. Both the intensity and importance of facilitation were greater at middle elevations than at high elevations. As canopies do not affect benthic communities at low elevations, this study suggests that the facilitation-stress relationship at the community level is unimodal for this marine system. Such a pattern was found for some terrestrial systems dominated by canopy-forming plants. Thus, it might be ubiquitous in nature and, as further studies refine it, it might help to predict community-level facilitation depending on environmental stress.