Seagrass epiphytes increase appeal to marine herbivores

Candela Marco-Mendez from the University of Alicante along with colleagues from Spain & the USA has recently published some research on the effect of seagrass epiphytes for herbivore grazing preferences. In other words: do marine epiphytes make seagrass nicer or nastier? The seagrass species studied were Posidonia oceanica and Cymodocea nodosa.

Posidonia oceanica: one of the two studied seagrass species. Photo: Wikipedia.

The herbivores studied were the sea urchin Paracentrotus lividus and the fish Sarpa salpa which are both important herbivores in the study site of  Cabo de las Huertas in the Western Mediterranean. The urchin and fish are commonly observed in shallow seagrass meadows and rocky bottom oceans. 

Seagrass herbivores from the Western Mediterranean. Top: the sea urchin Paracentrotus lividus. Bottom: the fish Sarpa salpa. Photos: Wikipedia.

The team undertook tethering experiments, herbivore abundance and feeding observations, food choice experiments and epiphytic community analysis.

Here are a few key results:

• Both herbivores showed a preference for the seagrass Cymodocea nodosa but it was especially favoured by the sea urchin 
• The authors state that this preference could be related to a range of factors including: differences in seagrasses nutrients, chemical and structural defenses and epibiotic load (Marco-Mendez 2015)

• Overall both herbivores showed preference for "epiphytized" leaves (new word there!)

• The authors state: "our study confirms the role of epiphytes in mediating seagrass consumption and preferences especially for Paracentrotus lividus (sea urchin) whose diet is indicated to be greatly supported by epiphytes"

Sarpa salpa tucking into some epiphyte-laden seagrass. Photo: www.kennaecodiving.net/

The seagrass epiphytes likely increase the nutritional value of the seagrass. The authors conclude by saying that their study "indicated the complexity of seagrass-herbivore interactions and suggested that final seagrass consumption rates are not only determined by food preferences, but also by factors that could influence herbivore behavior by changing their priorities such as predation risk and/or home-range mobility."

In summary, the seagrass-epiphyte-herbivore relationship is a complex one but this research has done a great job of highlighting the ecological role of epiphytes in a very different, non-forest, habitat.