https://doi.org/10.1371/journal.pone.0022591, Editor: Steven J. Bograd, National Oceanic and Atmospheric Administration/National Marine Fisheries Service/Southwest Fisheries Science Center, United States of America, Received: February 25, 2011; Accepted: June 28, 2011; Published: July 21, 2011. In Boston Harbor, vast seagrass beds have now dwindled to a bare remnant, roughly 750 acres of the 16,000 acres once thought to cover the harbor. But for anyone who cares about the health of marine animals, he said, the role of humble seagrass at the beginning of the marine food chain is key. 1a, Table 1, see below). Impact level  =  Low: white, Medium: grey, High: hatched bars. Transects (50 m long, 4 m wide) were deployed parallel to the shore inside (10 m from any edge) the seagrass bed to visually census highly mobile macrofauna during day and night high tides. However, we also observed changes in food-web structure with increasing human impacts in both NB and PEI, although the responses were not always consistent between the two regions (see the discussion below). Although there was variability among study sites and regions, there was a general decrease in C/N and increase in chlorophyll-a as well as an increase in annual algae biomass along the impact gradient (Methods S1). Food chain of sea water (2). Changes in species presence/absence, or local diversity, should be evident as structural changes in the food webs. Univariate PERMANOVA on each food-web property revealed higher number of trophic groups (S) and short-weighted trophic level (SWTL) in PEI than NB (Fig. here. Exposure conditions and mean carbon to nitrogen (C/N) ratios in seagrass tissue, annual and filamentous epiphytic (on seagrass blades) and benthic algal biomass (g/m2), and chlorophyll-a concentrations in the water column (µg/L) (±SE) are reported for each site. Among the multiple anthropogenic impacts on seagrass beds, eutrophication has been identified as a major cause for seagrass declines around the world [4], [6], [10]. Two detrital groups, suspended detritus and deposited organic matter, were also used and a group to account for import diets into the system. Post was not sent - check your email addresses! / Organikos. ( Log Out /  https://doi.org/10.1371/journal.pone.0022591.g006. Motivated by extensive field surveys and literature information, we analyzed the structural features of food webs associated with Zostera marina across 16 study sites in 3 provinces in Atlantic Canada. Seagrass In The Food Chain. Seagrass beds provide important structure, functions, and services to coastal ecosystems, yet how these differ across different spatial scales and change with human impacts has not been rigorously quantified. Lots of things can damage seagrass, from polluted water to boats dragging their anchors in seagrass meadows. Declines in seagrass beds have frequently been the result of a combination of anthropogenic and natural impacts [7]. September 17, 2016. In addition to nutrient loading (Table 1), our study sites may be affected by other factors, such as chemical pollution, land clearing and construction, and fisheries, as well as changes in the marine and terrestrial fauna that are using seagrass beds [12]. Changes in seagrass beds can alter the structure and function of associated ecosystems and the goods and services they provide to humans [12], [15], [16]. Since oceanic nutrients can vary over large spatial scales [19] an important next empirical step is to consider how interactions such as those within Zostera marina food webs could change at larger scales. We found no differences in food-web properties among all study sites with low impact levels in NB, PEI and NS (PERMANOVA, pseudo-F2,5 = 0.77, p = 0.75) and no clear regional grouping in the MDS ordination (Fig. The information on trophic links was used to create a matrix of prey-predator relationships. Most seagrass meadows around the British coast are in a poor condition, say scientists. Eelgrass, Zostera marina, is the most widely distributed seagrass species in the world and dominates coastal and estuarine habitats of the temperate North Atlantic, including Atlantic Canada [5], [7]. The resulting enhanced turbidity, overgrowth, shading and oxygen depletion due to enhanced decomposition can then lead to increasing canopy patchiness or, in the extreme, complete canopy loss [4], [12], [13]. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. We used a significance level of α = 0.05 yet mention levels up to α  = 0.1 because expected changes in food-web properties are generally small yet may still be biologically relevant. However, when we tested for the effect of region and impact level among NB and PEI sites, we found a significant effect of region (pseudo-F1,6 = 2.49, p = 0.02) but not of impact level or their interaction (p>0.50). They consume the detritus material and produce nutrient-rich waste. All of these factors may have altered the site-specific response to eutrophication and may explain the variability we observed in our results. Our results also show that the spatial scale of study is an important factor for food-web analysis. These results may inform conservation criteria and future management plans of coastal areas in Atlantic Canada since they provide reference directions of degradation of temperate seagrass beds in the region. The majority of seagrass enters the food chain as . Eutrophication can favor different primary producer groups [4], [11], [15], [37] in different coastal ecosystems, which may depend on site-specific abiotic and biotic conditions. However, these cumulative webs produce different results from food webs at smaller spatial scales (study sites, region by impact level, or region). The leaves and upright stems of … Similar conclusions regarding the importance of the spatial scale of study were drawn in an analysis of data collected in several streams at various spatial scales [44] and more generally in other ecosystems [45]. Our study was conducted in a vast area of eastern Canada (Fig. These results coincide with several changes described for three food webs constructed along a gradient of eutrophication in the Montego estuary in Portugal [17], although in Montego estuary seagrass beds had disappeared at highly eutrophied sites due to the severity of impacts. In the last century, up to 92% of the UK’s seagrass has disappeared as a result of pollution, runoff from the land, coastal development and damage from boat propellers and chain moorings. To test whether changes in food-web structure translated into changes in functioning, we analyzed the robustness of food webs to simulated species loss. We also used a one-way analysis on the low impact sites only comparing regions (NB, PEI, NS) and to test for large-scale differences in common food-web properties among the six groups of aquatic ecosystems (marine, estuarine, lotic, lentic, seagrass-tropical and seagrass-temperate). Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada. Photo courtesy of Wikimedia Commons, Seagrass beds have been under assault globally. PEI sites also showed a decrease in the fraction of top predators, lower fractions of omnivory and cannibalism, and a shorter trophic path length. Despite this, seagrass habitats around the world are also among the most human impacted marine ecosystems [6]. The MDS analysis used random starting configurations and 1000 runs with real data. 4d). No, Is the Subject Area "Eutrophication" applicable to this article? https://doi.org/10.1371/journal.pone.0022591.g003, https://doi.org/10.1371/journal.pone.0022591.t003. Although comparable in overall topology, the temperate seagrass food webs differed from other, previously characterized, aquatic ecosystems except a tropical seagrass-dominated web from the Saint Mark's estuary in Florida [20], [27], [32]. Changes in trophic relations in seagrass food webs due to eutrophication have been studied using stable isotopes, trophic guilds, gut contents, and trophic models (e.g. We use free range eggs, bake our own breads, pastries and cakes and have vegan, vegetarian and gluten free options available. 5). ), brown (e.g. Extinction analyses were performed using the software WebProg-Node Knockouts [32]. In the marine realm, seagrass beds are among the few ecosystems that provide both habitat and a primary resource for … These structural changes translate into functional changes with impacted sites being less robust to simulated species loss. Globally, eelgrass beds are subject to natural and anthropogenic impacts that have caused declines, and in some cases, local extinction [6], [8].

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