Seagrass Ecosystem Services and Their Variability across Genera and Geographical Regions

Abstract

Threats to and loss of seagrass ecosystems globally, impact not only natural resources but also the lives of people who directly or indirectly depend on these systems. Seagrass ecosystems play a multi-functional role in human well-being, e.g. food through fisheries, control of erosion and protection against floods. Quantifying these services reveals their contributions to human well-being and helps justify seagrass conservation. There has been no comprehensive assessment as to whether seagrass ecosystem services are perceived to vary over the globe or amongst genera. Our study compiles the most complete list of ecosystem services provided by seagrasses so far, including bioregional- and genus-specific information from expert opinion and published studies. Several seagrass ecosystem services vary considerably in their (known) provision across genera and over the globe. Seagrasses genera are clearly not all equal with regard to the ecosystem services they provide. As seagrass genera are not evenly distributed over all bioregions, the presence of an ecosystem service sometimes depends on the genera present. Larger sized seagrass genera (e.g. Posidonia, Enhalus) are perceived to provide more substantial and a wider variety of ecosystem services than smaller species (e.g. Halophila, Lepilaena). Nevertheless, smaller species provide important services. Our findings point out data gaps, provide new insight for more efficient management and recommend caution in economic valuation of seagrass services worldwide.

Fig 1. Seagrass meadow exposed during low tide.

Patchy seagrass meadow dominated by Thalassodendron ciliatum during low tide in Zanzibar, Tanzania. Photo credit: Lina Mtwana Nordlund.

Fig 2. Ecosystem services (ES) provided by seagrass—expert eliciting.

Colours represent consensus view of experts’ in each bioregional group. Red represents service not present; grey unknown and green service present. A sum of present, unknown, not present services scores can be seen in the table to the far right per ES and at the bottom for each genus in every bioregion. Bioregions according to Short et al., 2007 [2]:I = Temperate North Atlantic, II = Tropical Atlantic, III = Mediterranean, IV = Temperate North Pacific, V = Tropical Indo-Pacific, VI = Temperate Southern Oceans. At the far left # indicates a number that corresponds to the same ecosystem service in Table 1 facilitate comparisons, and has no prioritization.

Fig 3. Perceived provision of seagrass ecosystem services.

Global A) mean frequency, B) mean frequency per genus, of perceived provision of different ecosystem services of seagrasses. The higher mean the more frequently that service is provided. Data are across bioregion and genera means ± SE. Horizontal bars represent homogenous subsets (Tukey test).

Fig 4. Perceived provision of seagrass ecosystem services among bioregions.

A) mean frequency, B) mean frequency per genus, of perceived provision of different ecosystem services of seagrasses. Large values of mean frequency of ES show that more services are provided. Data are across service and genera means ± SE. Bars with different letters (a and b) are significantly different (Tukey test).

Fig 5. Multivariate relationship among genera and perceived seagrass ecosystem services.

The following numbers correspond to the numbers in Fig 2 and Table 1. Ecosystem service: 1 = Compost fertilizer; 2 = Fisheries habitat; 3 = Food (for humans); 4 = Food from seagrass associated species; 5 = Invertebrate habitat; 6 = Nursery; 7 = Pharmaceuticals; 8 = Raw materials; 9 = Vertebrate habitat incl birds; 10 = Carbon sequestration; 11 = Coastal protection; 12 = Geomorphology as a result of sediment accretion; 13 = Sediment accretion; 14 = Sediment stabilization; 15 = Animal food; 16 = Mariculture (as a habitat/substrate); 17 = Seagrasses as food for animals; 18 = Water purification; 19 = Bequest value; 20 = Cultural artefacts; 21 = Education; 22 = Recreation; 23 = Research; 24 = Spiritual value; 25 = Tourism.

Fig 6. Relationship between mean perceived frequency of ecosystem service and seagrass genera shoot-specific leaf area.

Relationship between mean perceived frequency of provision of ecosystem services by different seagrass genera and mean genus shoot-specific leaf area (size). Note the log10 scale (abscissa).