LowerVibriospp. abundances inZostera marinaleaf canopies suggest a novel ecosystem function for temperate seagrass beds

Abstract

Seagrasses, a polyphyletic group of about 60 marine angiosperm species, are the foundation of diverse and functionally important marine habitats along sheltered sedimentary coasts. As a novel ecological function with high societal relevance, a role of the leaf canopy for reducing potentially harmful bacteria has recently been hypothesized. Accordingly, we tested whether or not the abundance of general bacteria and more specifically, those belonging to the genus Vibrio were reduced within temperate Zostera marina (eelgrass) meadows compared to adjacent sand flats and sampled 5 sites in the south-western Baltic Sea using SCUBA. Compared to non-vegetated area, we found an average reduction of 39% for all Vibrio and 63% for the potentially harmful V. vulnificus/cholerae subtype based on robust plate counting data on Vibrio selective agar. The underlying mechanism is currently elusive and clearly merits further study. Our results underline the critical importance of seagrasses in maintaining shallow water ecosystem functioning including water quality and provide further motivation for their protection and restoration.

The ecology of potentially pathogenicVibriospp. in a seagrass meadow ecosystem

“…would be less prevalent in the water column above seagrass meadows as compared to unvegetated sites. This was based on the results from two recent studies investigating either several types of pathogenic bacteria (Lamb et al 2017), or pathogenic vibrios specifically (Reusch et al 2021) in seagrass meadows. However, we could not detect such a difference with any of the three analytical approaches used.…”

“…temperature and salinity regimes which are known to influence the growth and environmental prevalence of some Vibrio species (Eiler et al 2006), and could thus mask an effect of seagrass presence. Unlike another recent study from the Baltic Sea (Reusch et al 2021), we did not assess differences in Vibrio abundances on a small spatial scale (over a few meters) in and around individual meadows, but instead sampled sites that were typically several kilometers apart resulting in no information on local environmental variation, which might be of importance. Therefore, despite our findings, we cannot conclusively exclude the possibility that seagrass meadows in our study area function as natural filters that remove vibrios and other pathogenic bacteria from the water column, e.g.…”

“…For example, we chose an enrichment cultivation approach including both peptone water and TCBS agar (Lesmana et al 1985) which may select for certain populations of vibrios yet excluded others compared to other enrichment media, e.g. CHROMagar (Reusch et al 2021). Sequencing of selected colonies also showed that selectivity of methodologies could still be improved and reliable identification requires a combination of techniques.…”

“…In the Baltic Sea, meadows of the dominant foundation species eelgrass (Zostera marina), have been associated with reduction of potentially pathogenic Vibrio spp. (Reusch et al 2021). The mechanisms of such reductions remain unclear, but one proposed mechanism is increased sedimentation rates above seagrass meadows, which may contribute significantly to removal of Vibrio cells attached to particles in the water column, as vibrio often associate with surfaces (Huq et al 1983, Datta et al 2016, Kesy et al 2020).…”

Confidence-driven communication of process mining on time series

“…Recent studies indicate that water temperature and salinity govern the occurrence (and the massive increase) of non-cholerae Vibrios [9]. Although water temperature and salinity seem to play a major role for the occurrence of Vibrios, other factors such as chlorophyll and the occurrence of aquatic vegetation [10,11] associated with a higher carbon content [12] seem to influence the frequency of massive blooms.…”