The influence of species, density, and diversity of macroalgal aggregations on microphytobenthic settlement

Abstract

Intertidal macroalgae can modulate their biophysical environment by ameliorating physical conditions and creating habitats. Exploring how seaweed aggregations made up of different species at different densities modify the local environment may help explain how associated organisms respond to the attenuation of extreme physical conditions. Using Silvetia compressa, Chondracanthus canaliculatus, and Pyropia perforata, we constructed monocultures representing the leathery, corticated and foliose functional forms as well as a mixed tri-culture assemblage including the former three, at four densities. Treatment quadrats were installed in the intertidal where we measured irradiance, temperature, particle retention, and water motion underneath the canopies. Additionally, we examined the abundance and richness of the understory microphytobenthos with settlement slides. We found that the density and species composition of the assemblages modulated the amelioration of extreme physical conditions, with macroalgal aggregations of greater structural complexity due to their form and density showing greater physical factor attenuation. However, increasing the number of species within a patch did not directly result in increased complexity and therefore, did not necessarily cause greater amelioration of the environment. Microphytobenthic composition was also affected by species composition and density, with higher abundances under S. compressa and C. canaliculatus canopies at high and mid densities. These results support the idea that the environmental modifications driven by these macroalgae have a significant effect on the dynamics of the intertidal environment by promoting distinct temporal and spatial patchiness in the microphytobenthos, with potentially significant effects on the overall productivity of these ecosystems.

Photoacclimation and Photoprotection of Juvenile Sporophytes of Macrocystis pyrifera (Laminariales, Phaeophyceae) Under High‐light Conditions During Short‐term Shallow‐water Cultivation1

“…Before deployment at sea, 192 sporophytes were spliced into 48 braided polystrong ropes (6.35 mm in diameter, 36 cm in length) that were subsequently attached to plastic grids (36 × 30 cm) following the methods described in Umanzor et al. (). Each of the grids held four ropes and 16 sporophytes (i.e., four sporophytes per rope).…”

Intertidal Seaweeds Modulate a Contrasting Response in Understory Seaweed and Microphytobenthic Early Recruitment

“…This effect, however, is not always consistent, as the strength of adhesion depends on the species of seaweeds tested, their stage of development and the physicochemical properties of the substrate (Mieszkin et al, 2013). Although this study was repeated a year later, similarly to Umanzor et al (2017), we found that diatoms of the genus Cocconeis almost solely colonized all understories. This result provides further evidence of the relevance of particle retention for the settlement of benthic organisms, as particle transport and deposition significantly influence their establishment, survival, and development (Eckman and Duggins, 1991;Morrow and Carpenter, 2008).…”

“…Abiotic factors can affect both the distribution and abundance of organisms, thus modulating community structure (Crain and Bertness, 2006). In a recent contribution, Umanzor et al (2017) explored how different seaweed aggregations influenced the abundance and distribution of understory microphytobenthic (MPB) organisms (benthic diatoms and cyanobacteria) on an exposed rocky intertidal. Results showed that the settlement of microphytobenthic organisms was modulated by the interaction between the species composition and the density of the seaweed aggregations, with branched morphologies at higher densities having higher particle retention and greater abundance of MPB organisms underneath their canopies.…”

Biophysical Interactions in Fragmented Marine Canopies: Fundamental Processes, Consequences, and Upscaling

“…This is likely driven by differences in hydrodynamic stress attenuation and food availability rather than structural complexity per se (Bell et al, 2013). Canopies of macroalgae with greater structural complexity also promote spatial and temporal patchiness of microphytobenthos, with potential significant effects on the overall productivity of ecosystems (Umanzor et al, 2017). Fragmentation of seagrass canopies also alters their interactions with filter feeders.…”