Several properties tended to show non-linear trends from low to high eutrophication sites (Fig. 2). A) Lost of most, least, and randomly connected species in food webs by eutrophication level from New Brunswick (NB), b) most connected species in food webs by region and eutrophication level from NB, Prince Edward Island (PEI) and Nova Scotia (NS), and c) most connected species in cumulative webs by region and the overall Atlantic seagrass web. Overall, the Atlantic web showed lower %T and higher %B than the regional webs. This causes plants to grow quickly producing more food and then detritus. ( Log Out /  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]. Yes Our study illustrates that food-web structure and functioning of seagrass habitats change with human impacts and that the spatial scale of food-web analysis is critical for determining results. Click through the PLOS taxonomy to find articles in your field. Performed the experiments: MC AS. These food webs were then used to test for differences in food-web structure across impact levels and regions (1, 2), and across different spatial scales of data accumulation (2, 3, 4). here. There was a trend of declining %T in NB, and increasing %I and %H (but not %B) with increasing impact in both NB and PEI (as expected in Table 2). 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). Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada. 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. Higher food-web degradation in PEI may reflect the high impact of farming (mostly potato), with associated high loads of fertilizers and pesticides that partially end up in estuaries ([41], Table 1). This analysis illustrates that the spatial scale at which food-web properties are studied (covering the overall region or different sub-regions) affect food-web topology and the conclusions drawn from resulting analyses. Thus, the length of the food chain, itself modulated by a number of factors, may result in different allocation of biomass among trophic levels (13). Overall, the temperate and St Mark's estuary seagrass webs were characterized by lower fractions of %Omn and %I, a higher fraction of %T, and lower C relative to the other aquatic webs. Dead seagrasses provide food for decomposers like worms, sea cucumbers , crabs, and filter feeders. Seagrass meadows are ecologically and economically important components of many coastal areas worldwide. 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) within regions (2 levels: NB, PEI) we used site-specific food webs in a two-way nested analysis. The grey links represent feeding links. September 17, 2016. The majority of seagrass enters the food chain as . Thus, our results suggest that as seagrass food webs become more degraded they become more vulnerable to the loss of species that highly interact in the web. These multiple stressors may interact with each other, can enhance or dampen each other's effect, and challenge our understanding of eutrophication impacts on coastal ecosystems since their analysis is complex [39], [40]. Affiliations Skipwith Pond, Little Rock Lake) ecosystems [20]. [15], [16], [17], [18]). Relevant permits for our observational and field studies were obtained from national institutions (Parks Canada and the Department of Fisheries and Oceans). Seagrass growth, abundance, morphology and reproductive capacity are dependent upon the availability of nutrients in the plants’ environment. The transect depth was 1.2–1.8 m in NB and PEI, and 2–4 m in NS where the seagrass beds occur at greater depth. We present a detailed characterization of food webs associated with seagrass beds in different regions in Atlantic Canada, and show how these food webs change across a gradient of human impacts associated with eutrophication. PEI webs were characterized by a higher number of fish groups and fewer primary producers and invertebrates. Organic matter leaches into the . 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 , , . ), and bryozoans (e.g. Seagrasses form extensive underwater meadows that support diverse and complex communities, occur on all continents except Antarctica [1], [2], and are valued as one of the most important marine ecosystems [3] because they provide essential functions and services [1], [4], [5]. The grasses, which includes widespread eelgrass and turtlegrass, live entirely submerged, making them distinct from more familiar beach vegetation that is covered and uncovered by the tides. Moreover, within each region there was a tendency towards decreasing S, increasing %I and decreasing %T (except NB) from low to high impacted sites (as predicted in Table 2), but with considerable variability (Table 3). Not all groups were used in all food webs; see Methods S2 for detailed occurrence information. Seagrasses are also home to a number of fish species valued by fishers (as catch or bait) and by aquarists. ( Log Out /  However, the overall changes in food-web structure have not been fully described, and studies available are limited in spatial coverage. To address these gaps, we used a combination of large-scale field surveys and food-web modeling to (i) quantify the main structural features of food webs associated with Z. marina across local and regional scales and human impacts in Atlantic Canada, (ii) assess whether structural differences translate into changes in functioning by analyzing the robustness of food webs to simulated species loss, and (iii) compare the structure of seagrass food webs in Atlantic Canada with other aquatic food webs to determine whether seagrass webs have unique and consistent features. In the marine realm, seagrass beds are among the few ecosystems that provide both habitat and a primary resource for … Trophic information from the literature used to assemble the seagrass food-web networks. Other human impacts, particularly exploitation, occurred throughout the region and no site was located in a marine protected area. No, PLOS is a nonprofit 501(c)(3) corporation, #C2354500, based in San Francisco, California, US, https://doi.org/10.1371/journal.pone.0022591. Is the Subject Area "Food web structure" applicable to this article? In NB, S, SWTL, MaxTL, and the trophic path length (Path) decreased from low to high eutrophication, while %I, the fraction of herbivore species (%H), and the generality (or number of prey per species, GenSD) increased. Although less severe, signs of eutrophication have also been observed in seagrass beds in Atlantic Canada [12], [14]. Daru acknowledged that seagrass isn’t as exciting as sharks or tuna, or as marine mammals such as seals, dolphins, and manatees. SWTL and MaxTL tended to decrease (as predicted in Table 2) from low to high impact in PEI, although his difference was not significant. SIMPER analysis (Fig. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. 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. In Canada, although eelgrass has been recently listed as an ecologically significant species [9], no specific legal protection exists for seagrass communities and very few beds are included in marine protected areas [7]. Scytosiphon spp.) 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. Yes This method calculates a pseudo-F statistic directly analogous to the traditional F-statistic for multifactorial univariate ANOVA models but uses permutation procedures to obtain p-values for each term in the model [29]. Larger animals such as fish and birds consume the mud-dwellers, transferring nutrients further afield. Secondly, we used non-metric multi-dimensional scaling (MDS) and cluster analysis based on Euclidean distances to visualize differences among i) individual food webs with low impact levels, ii) cumulative food webs across regions and impact levels (NB-low, NB-medium, NB-high, PEI-low, PEI-medium, PEI-high) and across regions (NB, PEI, NS, Atlantic), and iii) all aquatic ecosystems. No, Is the Subject Area "Food" applicable to this article? 1b). 1a, respectively). Seagrass provides homes and shelter (3). Post was not sent - check your email addresses! As semi-nomadic animals, dugongs may either travel huge distances in search of specific seagrass or live in the same area throughout their lives. They usually have to travel when their main food, seagras, is in scarcity. https://doi.org/10.1371/journal.pone.0022591.t002. No, Is the Subject Area "Eutrophication" applicable to this article? There are nine species of seagrass found around Rottnest. Change ), You are commenting using your Twitter account. Impact levels were chosen based on previous sampling in NB [12] and nutrient concentrations in rivers and estuaries in PEI (Surface water quality database; Government of Prince Edward Island; Department of Environment, Energy and Forestry; http://www.gov.pe.ca/eef/). All species were identified to the lowest possible taxonomic level (Methods S2). The Future Of Coffee Matters To Us For More Than One Reason. Food chain of sea water (2). ... said seagrass is one of our most valuable ecosystems, helping to sustain the marine food chain. https://doi.org/10.1371/journal.pone.0022591.s002. The result is a reduction in above (blades, sheaths, inflorescences) and below (rhizomes, rootlets) ground seagrass production [4]. A global assessment reported that 29% of the known areal extent … Food-web images were produced with FoodWeb3D, written by R.J. Williams, Pacific Ecoinformatics and Computational Ecology Lab. For example, in Waquoit Bay (Cape Cod, Massachusetts) seagrass beds have practically disappeared over the past century due to nutrient loading [13]. Yes A) Study sites located in New Brunswick, Prince Edward Island, and Nova Scotia (see Table 1 for details). These structural changes translate into functional changes with impacted sites being less robust to simulated species loss. Extinction analyses were performed using the software WebProg-Node Knockouts [32]. 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]. We use free range eggs, bake our own breads, pastries and cakes and have vegan, vegetarian and gluten free options available. To examine whether changes in food-web structure translated into changes in functioning, we explored the potential effect of simulated species removal to trigger cascades of secondary extinctions [32]. No, Is the Subject Area "Predation" applicable to this article? Plankton, algae, and bacteria grow on seagrass stems, providing food for additional organisms. As eutrophication increases there is a reduction in shoot density, decreases in above and below ground biomass, and an overall reduction in the physical complexity of the habitat [12], [14]. broad scope, and wide readership – a perfect fit for your research every time. https://doi.org/10.1371/journal.pone.0022591.s003. A two-dimensional representation was accepted as a good depiction of the data if the stress index was ≤0.1 [28]. We excluded highly mobile species identified with visual census from the quadrat results. Interactions between region and impact level occurred for the vulnerability (VulSD) (Fig. PLoS ONE 6(7): For our food-web analysis, we chose a widely-used binary network approach ([20], [21], www.foodwebs.org) due to its simplicity and few required assumptions and parameters. These direct effects were also observed at our study sites (Table 1, Methods S1, [12], [14]). Our results showed that 75% of all properties in site-specific food webs in PEI followed the expected trend of degradation compared to only 43% in NB, however these ratios differed for cumulative webs (69% in NB, 50% in PEI). 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]. Notably, PEI had much higher L/S, C, and GenSD than NB, and both L/S and C declined and GenSD increased with increasing eutrophication (as expected in Table 2), at least in PEI. The information on trophic links was used to create a matrix of prey-predator relationships. In NB, the low and high levels were grouped, whereas in PEI, the medium and high levels were more closely grouped. 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. Overall, PEI webs were the least robust to species deletion, followed by NB and NS (Fig. [20] and four cumulative food webs from this study (NS, NB, PEI, Atlantic) depicted as temperate seagrass webs. 4d). 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). Like meadows on land, seagrass meadows are highly productive and support extensive food webs. Whereas food-web structure was similar among low-impact sites, increasing food-web degradation was observed with rising impact level indicated by a structural simplification and lower robustness to species loss. Changes in species presence/absence, or local diversity, should be evident as structural changes in the food webs. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. NS webs had the highest number of primary producers and NB webs had fewer groups of fishes, invertebrates, and primary producers. Change ), You are commenting using your Facebook account. https://doi.org/10.1371/journal.pone.0022591.g008. He is at Carson Beach in South Boston, where he found no seagrasses. Unfortunately, seagrass does not get the attention it deserves because most people are unaware of its existence. Overall, our results suggest that food webs that are subjected to a higher degree of anthropogenic impacts are more degraded, simplified, and less robust to species extinctions, patterns that have been previously shown for marine food webs in the Mediterranean [22] and seagrass food webs in Portugal [17]. feeding, habitat, and mortality) as in the groups of generic macroalgae, zooplankton, or demersal fish (Methods S4). For each test, we first assessed skewness and individual correlations between food-web properties by constructing a draftsman plot (matrix of plots of each food-web property against the other), and examining the resulting Spearman rank correlations. During the day, we identified all sessile benthic and epiphytic fauna and flora as well as small, slow-moving, and cryptic macrofauna using 11 quadrats (50×50cm) placed every 5 m along the transect line. Species losses were simulated sequentially by removing 1) the least connected species, 2) the most connected species, and 3) species randomly chosen from 1000 random removal sequences initiated for each food web. These tiny plants and bacteria capture the sun's energy and, through photosynthesis, convert nutrients and carbon dioxide into organic compounds. 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. These results highlight the complexity of bottom-up effects on seagrass food webs. In addition, to test for differences across blocks (4 levels, Fig. Seagrasses improve water quality by trapping sediments, … 5). [17]). Rose Lincoln/Harvard Staff Photographer. Seagrass recovery alters the structure and functioning of the food web and influences the biomass development of seagrass‐associated fauna. Although seagrass communities have been well-studied in the field, a quantification of their food-web structure and functioning, and how these change across space and human impacts has been lacking. 1a). 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. https://doi.org/10.1371/journal.pone.0022591.g001, https://doi.org/10.1371/journal.pone.0022591.t001. https://doi.org/10.1371/journal.pone.0022591.s001. Data from different sites were then aggregated into cumulative food webs for (2) each region and impact level (NB-low, NB-medium, NB-high, PEI-low, PEI-medium, PEI-high), (3) each region (NB, PEI, NS), and (4) the overall seagrass community in Atlantic Canada (Fig. For more information about PLOS Subject Areas, click Most seagrass meadows around the British coast are in a poor condition, say scientists. Yes Wrote the paper: MC AS TR HKL. However, among cumulative food webs, 69% of food-web properties in NB and 50% in PEI followed the expected trend of degradation with increasing eutrophication (Table 2, 4). To test the effect of increasing spatial aggregation on food-web structure, we compared the cumulative regional (NS, NB, PEI) and overall Atlantic food webs (Table 4, Fig. In addition, the comparison of some historical and more recent data highlights important declines of seagrass beds in several locations [23]. Cumulative regional webs are NB, PEI, NS, Atlantic. A secondary extinction is defined as a non-basal species losing all of its prey and a cannibalistic species losing all of its prey items except itself. Citation: Coll M, Schmidt A, Romanuk T, Lotze HK (2011) Food-Web Structure of Seagrass Communities across Different Spatial Scales and Human Impacts. Ecosystem services provided by seagrasses include reducing the number of microbial pathogens in the water, providing food, shelter and nurseries for many species, and decreasing the impact of waves on the shorelines. Basal species, which are those species with predators but no prey (see Methods S2 for specific species), were protected from being removed. Yes The increase in phytoplankton, epiphytic, and free-floating macroalgae reduces the amount of light reaching seagrass for photosynthesis and growth, while the decomposition of dead algal matter enhances oxygen depletion and the development of anoxic sediments [4], [12]. Within Atlantic Canada, seagrass food webs from low impact sites in NS, NB, and PEI showed similar food-web structure suggesting consistent features across local and regional scales, despite differences in localities (such as the connection to the open Atlantic Ocean in NS, open Gulf of St. Lawrence in PEI, and Northumberland Strait in NB) and food-web composition (Fig. 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. Also, ChLen, %Can, VulSD, and %Omn were lower and Path higher in the Atlantic compared to regional webs. Change ), You are commenting using your Google account. Lots of things can damage seagrass, from polluted water to boats dragging their anchors in seagrass meadows. The cumulative Atlantic seagrass food web had 107 trophic groups including 25 primary producers and detritus components, 36 invertebrate, 45 vertebrate groups, and an “import” group to account for import diets into the system (Methods S4). VulSD did not follow the predicted decrease in both regions. 3.1 ). Based on all species identified during field sampling, including primary producers, benthic and pelagic invertebrates, fishes, and other vertebrates, we constructed (1) individual food webs for each study site (n = 16). Because the properties represented different measures (%, counts, etc. PLOS ONE promises fair, rigorous peer review, bio-accumulate in the food chain [17]. https://doi.org/10.1371/journal.pone.0022591.g002. 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]. They consume the detritus material and produce nutrient-rich waste. They also help with coastal stability. Relax and take in our view while enjoying your breakfast, brunch, lunch, dessert or coffee in our restaurant or outside on our decks. We selected twelve sites along the Gulf of St. Lawrence coast of New Brunswick (NB) and Prince Edward Island (PEI), sampled once from 27 July to 8 August 2007, and four sites along the Atlantic coast of Nova Scotia (NS), sampled from 15–20 August 2007 (Fig. In the marine realm, seagrass beds are among the few ecosystems that provide both habitat and a primary resource for associated organisms, and thus may be structurally different from webs that don't contain extensive beds of foundation vegetation. Seagrass detritus is known to be important in food webs of benthic coastal communities, but extensive utilization of buoyant seagrass detritus by planktonic microheterotrophs has not been reported. Trophic transfer of seagrass, however, is not restricted to shallow coastal zones with evidence from the Atlantic indicating that seagrass may subsidize whole food webs (and therefore fisheries productivity) in the deep sea (Wolff, 1976, 1980). We thank Jessica Wysmyk, Alison Battersby and Kate Varsava for support in the field, Jennifer Dunne for assistance with the food-web network approach, Micheal van den Heuvel for insight into the nutrient conditions of PEI estuaries, and Colette Wabnitz for stimulating discussions on seagrass ecology. B) Underwater photos of seagrass beds of NB and PEI (Block 2 and 3 in Fig. Harvard University Post-Doctoral Fellow in Organismic and Evolutionary Biology, Barnabas Daru, researches seagrasses of the world. In PEI, S, %T, SWTL, MaxTL, the mean short-weighted chain length (ChLen), Path, and the fractions of omnivory (%Omn) and cannibalism (%Can) decreased as well, while %I, %H, the fraction of basal species (%B), and GenSD increased from low to high eutrophication. Eutrophication in seagrass webs has been shown to reduce above and below ground seagrass production, decrease shoot density, and increase the abundance of fast-growing phytoplankton, epiphytic and benthic algae [11]. 4c). here. No, Is the Subject Area "Canada" applicable to this article? 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). However, these cumulative webs produce different results from food webs at smaller spatial scales (study sites, region by impact level, or region). The rhizomes can spread under t… If significant differences occurred, a univariate PERMANOVA was conducted for individual food-web properties. Presence (+) or absence (−) is shown for each site for Low/Medium/High impacted sites in each block (1–4) for NB and PEI, and for each site Taylor Head Provincial Park/False Passage/Musquodoboit Harbour/Franks George in NS (a single sign is used when records were the same in all sites). seagrass food chain in relatively undisturbed, low-nutrient catchments and ‘developed’ catchments subjected to a prolonged period of nutrient enrichment. Seagrass meadows provide food and habitat for 1000’s of species such as shellfish, seahorses, manatees, and sea turtles. Here, NS and NB were most similar, PEI was in an intermediate position, and all regional webs were quite different from the overall Atlantic web. From the estuarine group, we separated a seagrass-dominated tropical estuary (Saint Mark's estuary, [20], [27]) that differed from non-seagrass dominated estuaries. We constructed individual food webs for each study site and cumulative webs for each province and the entire region based on presence/absence of species, and calculated 16 structural properties for each web. Regions  =  NB or PEI. 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. ( Log Out /  Our study was conducted in a vast area of eastern Canada (Fig. All analyses were performed using multivariate permutational analysis of variance (PERMANOVA) on the Euclidean distance matrix of food-web properties, which allows for the analysis of more complex designs (multiple factors and their interaction) without the constraints of multivariate normality, homoscedasticity, and having a greater number of variables than sampling units of traditional MANOVA. This has implications for ecosystem management since highly exploited species tend to be highly connected in marine food webs [22], [38]. Previous work has shown that binary network models and more complex biomass and trophic flow models deliver comparable results when analyzing structural food-web degradation, suggesting that both approaches capture fundamental information about how food webs are structured and change under human pressures [22]. 5). Thus the binary food-web network approach chosen in this study captures fundamental processes in the response of food webs to degradation. ), they were all normalized prior to the construction of a Euclidean distance matrix [31]. 1a, Table 1, see below). Seagrass beds have been under assault globally. 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. Results of a Principal Component Analysis (scores of PC axis 1, explaining >50% or variance, Methods S1) indicated a clear impact gradient within each block. 7). Globally, eelgrass beds are subject to natural and anthropogenic impacts that have caused declines, and in some cases, local extinction [6], [8]. Yes Seagrass contriubutes to physical structure of environment. The findings highlight the need to direct limited conservation dollars according to science, with a focus on places where biodiversity is most at risk, said Barnabas Daru, Harvard Herbaria Postdoctoral Fellow in Organismic and Evolutionary Biology, who performed the analysis on the world’s 70 species of seagrass. 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. See Table 2 for abbreviations of food-web properties. Postdoctoral researchers contribute to scientific knowledge akin, perhaps, to the way seagrass contributes to the robustness of a marine ecosystem’s biodiversity: A new analysis of a key contributor to the marine food web has turned up a surprising twist: more unique species in cooler waters than in the tropics, a reversal of the situation on land.

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