Send us a photo of your activity to email@example.com or share with us on social media @SmithsonianSMS by using #myseagrassfoodweb WRAP UP Such differential changes in primary producers can then translate into site-specific changes in food-web structure. Seagrasses are considered ecosystem engineers. 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. 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. 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. Material exchange, biodiversity and trophic transfer within the food web were investigated in two different types of intertidal seagrass beds: a sheltered, dense Zostera marina bed and a more exposed, sparse Z. noltii bed, in the Northern Wadden Sea. Also, ChLen, %Can, VulSD, and %Omn were lower and Path higher in the Atlantic compared to regional webs. Efforts were made to sample and include as many organisms in the food web as possible with the aim of preventing bias towards higher trophic level organisms in our models. 86 0 obj << /Linearized 1 /O 88 /H [ 743 269 ] /L 310304 /E 9525 /N 14 /T 308466 >> endobj xref 86 17 0000000016 00000 n Discover a faster, simpler path to publishing in a high-quality journal. Ulothrix speciosa), polychaetes (Spirorbis spp. On the other hand, recreational fisheries may be important factors at some sites as fishing for invertebrates is a common practice in Atlantic Canada . Food webs from high impact sites were less robust to species deletion than those from medium or low eutrophication when the most connected or random species were deleted for NB and PEI (Fig. We also found an increase in lower-trophic level groups (higher fraction of herbivores and intermediate consumers), grazers and detritivores such as gastropods and small decapods (higher ratio of prey per species). seagrass beds and the food webs that they support. To perform this analysis we used the cumulative food webs by region and impact level (NB-low, NB-medium, NB-high, PEI-low, PEI-medium and PEI-high, NS-low) and by regions (NB, PEI, NS, Atlantic). Seagrasses form extensive underwater meadows that support diverse and complex communities, occur on all continents except Antarctica , , and are valued as one of the most important marine ecosystems  because they provide essential functions and services , , . 3). Cumulative regional webs are NB, PEI, NS, Atlantic. These direct effects were also observed at our study sites (Table 1, Methods S1, , ). Therefore, they only succeed in clear, shallow waters. 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. 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). Moreover, eutrophication impacts were not consistent between NB and PEI. Overall, seagrass food webs from high impacted sites were less robust than those from medium or low impacted sites to simulated species loss, and the impact was higher when deleting the most connected species compared to less connected or random species. 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. Several properties tended to show non-linear trends from low to high eutrophication sites (Fig. Neighboring areas may show significant differences in food-web organization driven by local or regional factors that are overlooked when data are integrated and only cumulative food webs are studied, as commonly done (e.g. 1b). The increase in linkage density, connectance, and the ratio of predator to prey species contrasts with our initial predictions, and shows the specific structural impact of the increase in primary producers, herbivores, and intermediate species, as well as the changes in the three-dimensional structure of the seagrass beds. 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. 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. Eelgrass - Zostera Marina. 0000001012 00000 n In this hypothesis, both seagrass-dominated and algal-dominated states are maintained by positive feedback loops, mediated by food-web interactions, which make them resistant to perturbation. 7). Data were first √-transformed to avoid over-domination of very common groups . Study sites by region, block and eutrophication level. Overall, PEI webs were the least robust to species deletion, followed by NB and NS (Fig. Relevant permits for our observational and field studies were obtained from national institutions (Parks Canada and the Department of Fisheries and Oceans). These results highlight the complexity of bottom-up effects on seagrass food webs. tomentosoides), and sea mat (M. membranacea). Electra pilosa, Membranipora membranacea). 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). 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. 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. For each of the 18 food webs in 6 groups, we extracted eleven common food-web properties for structural comparison. All our study sites maintained seagrass canopies and thus did not represent extreme levels of eutrophication. Yes All analyses (PCA, MDS, PERMANOVA, and SIMPER) were performed using PRIMER with PERMANOVA+ (v. 6, PRIMER-E Ltd., Plymouth, UK). Analyzed the data: MC AS HKL. 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. 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. SIMPER identified eight food-web properties as contributing the greatest to these differences (Fig. The seagrass habitat was restored by planting seeds in unvegetated plots. PLOS ONE promises fair, rigorous peer review, A higher number of trophic groups were necessary to describe PEI food webs, followed by NS and NB (Fig. These results are comparable to previous studies simulating the loss of species , : more secondary extinctions occur when removing highly connected species, followed by random, and less connected species. 4c). 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.  and four cumulative food webs from this study (NS, NB, PEI, Atlantic) depicted as temperate seagrass webs. 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 . ). VulSD did not follow the predicted decrease in both regions. Not all groups were used in all food webs; see Methods S2 for detailed occurrence information. Different coloured dots represent trophic groups from different trophic levels with black = primary producers, dark to light grey = secondary producers, and the lightest grey being top predators. Epiphytes on seagrass consisted of red (e.g. 0000001181 00000 n ), brown (e.g. 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). 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). Properties that were skewed to the right or left were log(x) or reverse (log(c-x), where c > max x) transformed, respectively. It is also the best option for small sample sizes (<4 replicates, ). 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 , . Primary Producers. The larger circles indicate sites by region, and 1, 2 and 3 indicate the position of the main characterizing trophic groups (primary producers, invertebrates and fishes) along the two principle components. 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). We selected the unrestricted permutation of raw data procedure for p-value calculation because it generally has a Type I error rate close to α for multivariate models and is an exact test for univariate models. No, Is the Subject Area "Eutrophication" applicable to this article? 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. No, Is the Subject Area "Canada" applicable to this article? 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. 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 . For example, in Waquoit Bay (Cape Cod, Massachusetts) seagrass beds have practically disappeared over the past century due to nutrient loading . Honors Biology. ), yet may unintentionally omit site-specific food-web differences. No, Is the Subject Area "Marine ecosystems" applicable to this article? Temperate Atlantic seagrass webs are similar to a tropical seagrass web, yet differed from other aquatic webs, suggesting consistent food-web characteristics across seagrass ecosystems in different regions. Food Web Project. a. Interestingly, seagrass food webs from PEI were less robust to species loss than those from NB and NS, which may be related to the overall greater degradation observed in the PEI webs. Functional group richness for site-specific webs had a mean of 62 (4.4 SD) groups (Table 3). Seagrasses grow both vertically and horizontallytheir blades reach upwards and their roots down and sidewaysto capture sunlight and nutrients from the water and sediment. 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 , . These studies found important changes in the trophic positions of organisms and trophic flows subjected to high levels of nutrients. Caribbean Sea), estuarine (e.g. 0000004946 00000 n MDS ordination of cumulative food webs showed a clear distinction between regions (NB, PEI) (Fig. 0000000743 00000 n 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. Principal Component Analysis (PCA) of trophic groups used to develop food webs by study site was used to examine each of the 16 individual food webs. To test whether changes in food-web structure translated into changes in functioning, we analyzed the robustness of food webs to simulated species loss. Our study was conducted in a vast area of eastern Canada (Fig. 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. However, the overall changes in food-web structure have not been fully described, and studies available are limited in spatial coverage. For more information about PLOS Subject Areas, click 1a, Table 1, see below). position within the bed (edge vs. exterior) may reduce diversity and food web complexity through various mechanisms (reviewed in 15). 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. Growth of epibiota provides food for grazing and foraging marine life, which in turn attracts larger predators – creating a complex food web. Changes in species presence/absence, or local diversity, should be evident as structural changes in the food webs. Each point represents a study site within a Province (NB = New Brunswick, PEI = Prince Edward Island, NS = Nova Scotia) and impact level (Low, Medium, High). , , , ). Yes Since oceanic nutrients can vary over large spatial scales  an important next empirical step is to consider how interactions such as those within Zostera marina food webs could change at larger scales. Although often overlooked, seagrasses provide coastal zones with a number of ecosystem goods and services. In NB, there was also a decline in SWTL, MaxTL, ChLen, and %Omn from low to high, while responses in PEI were more variable. 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. Cumulative or aggregated food webs are useful to represent and compare food-web structure of larger regions (NS, NB, PEI, Atlantic). Overall changes in individual food-web properties were small (Table 3), as expected given the number of species in the webs and that changes relate to presence/absence only. Because the properties represented different measures (%, counts, etc. Citation: Coll M, Schmidt A, Romanuk T, Lotze HK (2011) Food-Web Structure of Seagrass Communities across Different Spatial Scales and Human Impacts. Food web structure and food sources are important determinants of the dynamic stability of food webs. 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. A two-dimensional representation was accepted as a good depiction of the data if the stress index was ≤0.1 . Alexander Tewfik, Joseph B Rasmussen, Kevin S McCann, Simplification of seagrass food webs across a gradient of nutrient enrichment, Canadian Journal of Fisheries and Aquatic Sciences, 10.1139/f07-071, 64, 7, (956-967), (2007). 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. Seagrass beds abound with marine life, so it's critically important that we protect the seagrasses that grow in Scottish waters. More information on the sites and how they are managed can be found at NatureScot’s Sitelink and on the Marine Scotland web pages for some sites. 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). Five marine mammal and 16 bird species were added to the food webs based on our own and published field observations and distribution ranges (Methods S2). Chesapeake Bay), lotic (e.g. Other human impacts, particularly exploitation, occurred throughout the region and no site was located in a marine protected area. We also created a new group for our temperate seagrass food webs (NS, NB, PEI, Atlantic) based on our own data. 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. However, smaller organisms such as infauna are more difficult to sample and there is less information regarding feeding behavior, thus our food web represents the higher trophic level organisms with better detail. , is the Subject Area `` food '' applicable to this article )..., they generally receive little protection even if they are key habitats among points... 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Study food-web structure was similar among low impact sites across regions we obtained species- and region-specific information.
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