Ecology

A potential Ulva grazer

Ulva are early-successional algae, quickly taking over new substrate on boulders that are cleared by storm disturbance.Ulva-barnacle communities are often the first to thrive in newly disturbed areas, and Ulva and its cousin Enteromorpha (also in the order Ulvales) are generally the first macroalgae to colonize open substrate.Their opportunistic success can be attributed to their simple morphologies and fecundity.Some species of Ulva are able to release spores daily.   In Ulva species, between 20 and 60% of their overall biomass can be allocated monthly to reproduction, depending on the season.So many reproductive cells in the water helps Ulva insure dispersal as well as mating.Sometimes the number of gametes or spores released can actually discolor the water and significantly increase the chlorophyll a concentration in the water column.Because of this, it has recently been hypothesized that marine macrophytes such as Ulva species might contribute food to the phytoplankton in addition to their traditional role in detritus-based food chains.  

High rates of photosynthesis give reproductive Ulva cells the selective advantage of being able to subsidize high respiratory costs associated with motility, as well as the ability to grow rapidly upon attachment to the substrate.  Reproductive cells of Ulva fasciata have similar photosynthetic rates to adult vegetative cells, higher respiration rates, and increased irradiance.  Late successional species do not show such properties.Even low rates of photosynthesis in Ulva’s spores and gametes can extend their viability and dispersal range. Consequently, this contributes to their success over algae with shorter-lived or physiologically less competitive reproductive cells.  

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