The influence of nutrient inputs and habitat isolation on consumer-resource interactions in seagrass

Background/Question/Methods

Species’ distributions often depend on dispersal, and high spatial connectivity can facilitate the movement of individuals among habitats.  Traditionally, marine systems have been thought of as open and thus connected.  However, habitat degradation can lead to isolation of habitat in marine systems.  In particular, seagrasses are experiencing high rates of loss due to nutrient enrichment in bays and estuaries.  Nutrient enrichment alters trophic relationships, produces habitat patches, and leads to seagrass diebacks.  Most investigations of habitat fragmentation in marine systems, including those focused on seagrass, have focused on patch size, with few studies examining how patch isolation affects seagrass communities and trophic relationships. We examined the interactive influence of habitat isolation, nutrient inputs, and consumer effects on seagrass epiphytes and macroalgae using artificial seagrass units placed at varying distances from a contiguous seagrass meadow. 

Results/Conclusions

We found that nutrient inputs and grazer exclusions significantly increased the macroalgae cover over seagrass, but did not increase epiphyte biomass on the seagrass.  Epiphytes were significantly lower in abundance and had significantly different community assemblages in isolated plots of seagrass.  We also found that effects of predators were significantly greater in isolated plots of seagrass than meadow plots.  Our results demonstrate that habitat isolation can significantly alter both species’ abundance and community composition in marine systems.