Benthic Organic Enrichment Research Articles

Aquaculture organic enrichment of marine sediments: assimilative capacity, geochemical indicators, variability, and impact classification

Benthic organic enrichment at 2 high-flow Atlantic salmon Salmo salar farms and at a low-flow mussel Mytilus edulis farm was studied to assess the capacity of local physical and biological processes to assimilate organic waste inputs. Geochemical metrics served as proxies for detecting potential biological effects. High-flow sites are generally predicted to assimilate organic enrichment by flow- and wave-induced waste dispersion and metabolic processes. However, a decrease in porewater dissolved oxygen was detected out to 100 m at the salmon farm with cohesive sediments and to approximately 1000 m outside the farm with permeable sediment. Sediment oxygen consumption was responsive to the vertical flux of organic matter, resulting in hypoxic conditions. An increase in total free sulfides (H2S + HS- + S2-) in porewater was restricted to the immediate vicinity of both salmon farms. Despite exhibiting a high degree of small-scale patchiness, benthic effects were greatest at the fish farms during the pre-harvest period, regardless of season. Natural organic enrichment at the mussel farm constrained the assimilative capacity for biodeposition, resulting in substantial free sulfide accumulation. Sediment free sulfide analysis at a wide array of fish and shellfish farms showed that the ion-selective electrode method that is widely prescribed for regulatory aquaculture monitoring gave biased readings relative to methylene blue colorimetry and direct UV spectrophotometry. The ecological quality status classification system was extended to include quantitative relationships between a wide range of geochemical and biological variables employed worldwide to monitor and regulate the effects of benthic organic enrichment.

Temporal change in the spatial distribution of visual organic enrichment indicators at aquaculture sites in Newfoundland, Canada

Growing salmon in sea cages results in the deposition of uneaten feed and wastes which can smother organisms, increase biological oxygen demand, and alter seafloor communities. At some sites with mainly hard-bottom substrates, opportunistic annelids and mat-forming bacteria are used as visual indicators of aquaculture waste and are monitored via drop camera imaging. Additionally, high organic matter sedimentation rates can result in the proliferation of microbes that release gas; this offgassing could also serve as a useful visual enrichment indicator. Little is known of how the distribution of opportunistic annelids, microbial mats, and offgassing might change over time and space, although coverage has important repercussions in some regulatory schemes. Here, we explore spatiotemporal distributions of offgassing, bacterial mats, annelids, and epibenthic taxon richness based on existing video-monitoring data collected along transects at four Newfoundland aquaculture sites in 2011–2012. A high degree of spatial and temporal patchiness was observed at both fallow and production sites, and combinations of time, transect, and distance to cage explained the distribution of bacterial mats, annelids, and taxon richness. Expected successional patterns resulting from organic enrichment or remediation were evident in some patches. Offgassing was observed only at fallow sites and may signal a distinct and persistent phase in organic matter degradation. Results highlight the spatial heterogeneity of benthic organic enrichment indicators across transects at Newfoundland aquaculture sites, with indicators appearing to form a mosaic of patches undergoing different stages of enrichment or recovery.

Detecting Indicator Taxa Associated with Benthic Organic Enrichment Using Different Video Camera Orientations

Sutherland, T.F.; Sterling, A.M.; Shaw, K.L.; Blasco, N.N.J., and Bradford, M.J., 2019. Detecting indicator taxa associated with benthic organic enrichment using different video camera orientations. Journal of Coastal Research, 35(2), 467–479. Coconut Creek (Florida), ISSN 0749-0208.Two video cameras mounted on a remotely operated vehicle (ROV) were used to generate paired forward-facing (FF) and downward-facing (DF) observations of benthic epifauna along 10 single transects at eight marine finfish aquaculture sites in British Columbia, Canada. The abundance of mat-forming primary indicators of organic enrichment, such as sulphide-oxidizing bacteria and opportunistic polychaete complexes (OPC), were quantified through percentage coverage estimates. Coverage estimates for sulphide-oxidizing bacteria were strongly correlated between the FF and DF orientations across all substrate types. The occurrence of OPC was limited to a single mixed-substrate site, which provided the strongest FF vs. DF relationship within this study. In contrast to sulphide-oxidizing bacteria, epifaunal abundance (count data) revealed strong relationships between camera orientations for fine sediments and mixed sediments and a weaker relationship observed for vertical rock wall environments. Similar observations occurred for estimates of both sessile (dominated by plumose anemones) and motile taxa guilds comprising the total epifaunal community. Weaker relationships associated with the rock wall substrate are likely due to alternating blackout periods experienced by each camera orientation as the ROV passes vertical or ledge habitat zones. Overall, a combination of FF and DF video orientations may provide more robust abundance estimates for settings that are characterized by various substrate grades and structural and/or mat-forming taxa.

Influence of salmonid aquaculture activities on a rock-cliff epifaunal community in Jervis Inlet, British Columbia

Benthic video surveys were carried out at two marine finfish aquaculture and associated reference sites in Jervis Inlet (JI), British Columbia. Substrate composition, epifaunal diversity, mat-forming taxa (primary indicators: opportunistic polychaete complexes (OPCs) and sulfide-oxidizing bacteria) and waste pellets were quantitatively assessed. Hard-bottom substrates were dominated by rock wall, skeletal sponge matrix, graded bedrock, rock-veneer, and cobble. Aquaculture waste outputs (modelled depositional carbon fluxes and observations of waste feed/faecal pellets) were correlated with benthic organic enrichment indicators (OPC and sulfide-oxidizing bacteria). Sulfide-oxidizing bacteria varied in abundance up to a modelled depositional carbon flux of ~2gCm−2day−1 where it sustained 50% areal coverage. Glass sponges revealed an inverse relationship with aquaculture waste outputs and sulfide-oxidizing bacteria. Plumose anemones and shrimp showed a low frequency of occurrence at reference sites; however, they were abundant within the near-field zone of the aquaculture sites associated with a higher modelled carbon flux. Future research should focus on the response of various taxa to depositional gradients and their potential role as secondary indicators of aquaculture activities associated with rock-cliff communities.

Development and preliminary validation of a multi-trophic metabarcoding biotic index for monitoring benthic organic enrichment

Sea-based fish farms are associated with strong, benthic enrichment gradients and routine monitoring is usually required by regulation. This has traditionally been based on benthic macrofaunal communities, which is reliant on taxonomic expertise, and turn-around times can be slow, limiting opportunities for adaptive management. Environmental metabarcoding is a powerful high-throughput sequencing-based technique that can identify and quantify benthic assemblages. Previous studies have demonstrated relationships between specific taxonomic groups (e.g., bacteria, foraminifera) and anthropogenic effects. However, the absence of fixed categorical scales makes the use of data challenging for routine biomonitoring. In this study, we analysed 105 sediment samples collected over three years from three salmon farms spanning two separate bioregions. Environmental DNA and RNA (eDNA/eRNA) metabarcoding of three taxonomic groups (foraminifera, bacteria, and general eukaryotes) was undertaken in parallel with traditional macrofaunal and biochemical analyses, which were used to calculate an Enrichment Stage index for each sample. The most abundant 200–250 Operational Taxonomic Units in each taxonomic group were assessed and assigned to Eco-Groups. These bioindicator taxa were then used to develop a Metabarcoding Biotic Index for each taxonomic group individually and in combination (multi-trophic Metabarcoding Biotic Index). The weakest relationship was between the foraminiferal Metabarcoding Biotic Index and Enrichment Stage (eDNA/eRNA, R2=0.731–0.850), whereas strong correspondence was obtained between the multi-trophic Metabarcoding Biotic Index and Enrichment Stage, or when just bacteria and eukaryotes data were combined (eDNA/RNA, R2>0.900). The strong relationships obtained between the multi-trophic Metabarcoding Biotic Index and Enrichment Stage confirms that this method has the potential to complement or even replace current fish farm biomonitoring techniques in the near future.

Particulate waste outflow from fish-farming cages. How much is uneaten feed?

Particulate wastes drive benthic organic enrichment from cage fish farming. Differentiation between faeces and uneaten feed estimates at cage level are of great value to both economize the feeding process and reduce waste. This study estimates the particulate waste outflowing cages at different depths and orientations, and the wasted feed component by combining in situ measurements and modelling. Particulate matter flux (PMF) was greater vertically through the cage bottoms (60.89%), but lateral outflow was also substantial (39.11%). PMF occurs all around the cages, and the influence of the mainstream current was low. Wasted feed was greatly variable, reaching high values (about 50% of supplied feed. The self-application of feed wastage monitoring and estimates by fish farmers is recommended to improve sustainability.

A Re-assessment of Narragansett Bay Benthic Habitat Quality Between 1988 and 2008

The first bay-wide synoptic survey of benthic habitat quality in Narragansett Bay, Rhode Island, USA, was conducted in August of 1988. Twenty years later, we revisited the same sampling locations as the original survey using similar sediment profile imagery technology and analysis tools. Like estuaries throughout the US, increased temperatures and reductions to anthropogenic nutrient inputs have cumulatively affected Narragansett Bay in the intervening 20 years. To understand how these changes may have influenced benthic organic enrichment and habitat quality, we compared the prevalence and spatial arrangement of benthic biotopes (i.e., biotic and abiotic benthic descriptions) between 1988 and 2008 surveys. Biotopes dominated by Ampelisca spp. tubiculous amphipods increased >fivefold between 1988 and 2008, and expanded into the more urban, anthropogenically stressed Providence River estuary. Ampelisca beds occurred at critical boundaries in organic enrichment and habitat quality in both years and indicated the quantity of organic matter reaching the benthos. In general, benthic biotopes reflect the degree of benthic-pelagic coupling and are an important link between estuarine water quality and other marine life. As estuaries globally cope with the effects of increased warming and legislated anthropogenic nutrient reductions, rapid assessments of benthic biotopes will be critical for understanding changes to whole-estuary condition as a result of these cumulative stressors.

Empirical relationships describing benthic impacts of salmon aquaculture

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 1:33-46 (2010) - DOI: https://doi.org/10.3354/aei00005 Empirical relationships describing benthic impacts of salmon aquaculture B. T. Hargrave* 561 Balmy Beach Road, Owen Sound, Ontario N4K 5N4, Canada *Email: hargraveb@rogers.com ABSTRACT: Benthic organic enrichment due to sedimentation of waste feed and fecal matter released from salmon and other marine finfish aquaculture facilities has traditionally been measured by observing changes in benthic macrofauna assemblages. Sediment oxygen consumption, dissolved nutrient fluxes and variables such as redox potentials (normalized to hydrogen potential, EhNHE) and dissolved ’free’ sulfides (Σ S2–, HS–, H2S) (S) are also sensitive chemical indicators of benthic enrichment effects. Hypoxic or anoxic sediments are formed when high rates of organic matter (OM) sedimentation stimulate anaerobic metabolic processes such as sulfate reduction. General changes in EhNHE, S, OM flux and indices of macrofauna diversity in sediments as a result of increased organic enrichment around salmon aquaculture sites have been described in numerous studies. Some of the results are summarized here in empirical regressions that relate changes in sediment chemical and benthic biological variables to increased OM supply. The equations are descriptive of the data for salmon aquaculture sites where the studies were performed and further investigations are required to determine if the relationships provide general quantitative expressions for changes in sediment geochemical conditions and macrofauna community structure due to benthic organic enrichment. KEY WORDS: Sediment organic enrichment · Redox potentials · Sulfides · Sulfate reduction · Macrofauna · Diversity Full text in pdf format PreviousNextCite this article as: Hargrave BT (2010) Empirical relationships describing benthic impacts of salmon aquaculture. Aquacult Environ Interact 1:33-46. https://doi.org/10.3354/aei00005 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 1, No. 1. Online publication date: June 30, 2010 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2010 Inter-Research.

Predicting aquaculture-derived benthic organic enrichment: Model validation

A sediment trap validation study was conducted near the commercial sea bass and sea bream fish farm in order to assess the predictive capability of a particle tracking deposition model. The validation procedure consisted of two distinct phases. First, the deposition of particulate waste (i.e. fecal pellets and excess feed) was measured near a single net pen containing 19 tons of sea bass. Afterwards, the model quality was determined by statistical comparison of predicted and observed values. Goodness of fit analysis indicates that the model successfully accounts for more than 75% of variance in the observed deposition. At 5% significance level, predictions do not underestimate or overestimate observations and there is no bias. Mean absolute relative error of ±48.9% compares favorably to other published deposition models. Obtained results affirm the reliability of particle tracking techniques in modeling the aquaculture-derived benthic organic enrichment.

Benthic organic enrichment from suspended mussel ( Mytilus edulis) culture in Prince Edward Island, Canada

The effects of increased biodeposition within mussel ( Mytilus edulis) farms on the benthic environment were investigated using surface sediment samples collected from 11 coastal embayments in Prince Edward Island (PEI), Canada. The degree of organic enrichment, determined using geochemical indicators (total free sulfides (S), redox potentials (Eh NHE), water content (WC) and organic matter (OM)), was significantly greater in mussel leases compared to reference sites located both outside lease boundaries and in inlets not used to culture mussel (MANOVA, p < 0.001). Post-hoc tests showed that mean WC and OM, Eh NHE potentials and S concentration were all significantly different between lease and reference sites ( p ≤ 0.009). Temporal changes in organic enrichment conditions were detected by comparing our 2001 data to those previously reported from a 1997 survey of the same sampling sites (MANOVA, p < 0.001). This multivariate effect resulted primarily from a 39% increase in mean S concentration between 1997 and 2001 ( p = 0.029). Surface sediment variables at reference sites were similar between years. Benthic conditions were discriminated along an oxic–anoxic enrichment gradient using multidimensional scaling analysis. Mussel lease sites sampled in 1997 were clustered within predefined oxic sediment classifications along with the majority of reference sites, but were grouped farther along the enrichment gradient in 2001. The significant increase in hypoxic and sulfidic sediments within mussel farms between 1997 and 2001 is consistent with the 43% increase in PEI mussel production—a classic response to excessive organic biodeposition in shallow coastal inlets with relatively low dispersive capacity.

Influence of mussel aquaculture on sediment organic enrichment in a nutrient-rich coastal embayment

Effects of mussel Mytilus edulis aquaculture on benthic organic enrichment were deter- mined in Tracadie Bay, a shallow, nutrient-rich embayment in Prince Edward Island, Canada. Water content (WC), inorganic grain size (GS), organic matter (OM), redox potentials (EhNHE) and free sul- fides (S) in the upper 2 cm of sediment were measured at 58 stations throughout the inlet to evaluate spatial variations between lease and non-lease locations. MANOVA results showed that mean (±SD) values for WC (64.8 ± 12.7%), OM (9.8 ± 4.3%), and S (1794 ± 771 µM) were significantly (p < 0.005) higher and EhNHE lower (-51 ± 78 mV) within mussel leases (n = 24) vs. non-lease areas (n = 34). Negative regressions between S and GS and positive regressions between EhNHE and GS at lease and non-lease locations had similar slopes but intercept values were significantly higher for S and lower for EhNHE (p < 0.007) for lease locations. EhNHE and a Benthic Enrichment Index derived from EhNHE, OM and WC were inversely related to S. K-means clustering and multi-dimensional scaling showed that geochemical variables could be used to group stations into categories of benthic organic enrich- ment within mussel lease and non-lease areas characteristic of oxic-hypoxic sediments described by measures of S and EhNHE.

Use of the size fractionation of the macrobenthic biomass for the rapid assessment of benthic organic enrichment

A new biomass index for monitoring the impact of marine fish cage farming on the benthic environment was evaluated at seven commercial fish farms in the eastern Mediterranean. At each farm, stations near and further away from the cages were sampled for macrofauna and geochemical variables during July 2001, and March and October 2002. Benthic samples were sequentially sieved through 1.0 and 0.5 mm mesh screens and a biomass fractionation index (BFI) was estimated as follows: biomass having passed through 1.0 mm and retained on 0.5 mm sieve only/total biomass (biomass retained on 1.0 mm + 0.5 mm sieve). BFI was quantitatively assessed and compared with the geochemical faunistic and management practice data. BFI was found to decrease consistently with distance from fish cages and particularly after 10 m from the edge of the cages. At all farms, BFI was found to be significantly correlated with distance, redox potential and organic carbon. Multiple regression analysis showed that BFI incorporates various components of sediment geochemistry (sediment grain size and total organic carbon) as well as distance and feeding rates. Although BFI needs to be further tested in different geographic locations and under different management practices, the results seem to be promising for long-term monitoring programmes since it provides a simple and inexpensive solution for assessing the effects of benthic organic enrichment due to fish farm activities.

The use of meiofauna as an indicator of benthic organic enrichment associated with salmonid aquaculture

Sediment chemistry and meiofaunal samples were collected in the Broughton Archipelago, British Columbia, to examine the relationship between sediment variables and meiofauna diversity across near- and far-field gradients surrounding several finfish aquaculture operations. The sediment variables examined consisted of free sulfide concentrations, redox potential ( E NHE), organic content, and sediment grain size. A strong trend between sediment texture and organic content was observed across all sampling locations, which reflected a wide range of sediment types (sand–silt) that exist within the Broughton Archipelago. The abundance of certain meiofaunal groups (kinorhynchs, crustaceans, polychaetes) declined in an asymptotic fashion with increasing free sulfide concentrations, an indicator of benthic organic enrichment. Within these relationships, low meiofaunal abundances occurred in fine sediments associated with higher organic contents. Although other groups (nematodes, foraminifera) showed a slight decline in abundance with increasing organic enrichment, a high amount of variability in abundance was observed at high free sulfide concentrations, rendering these groups not suitable as indicators of organic enrichment. This study reports both horizontal and vertical trends in meiofaunal distributions relative to free sulfide concentrations. The abundance of nematode and crustacean taxa decreased with sediment depth as well as increasing sulfide concentration, while polycheate abundance increased with increasing free sulfide concentration. The ratio of nematodes to copepods was also shown to represent the degree of organic loading associated with aquaculture operations and its application as an indicator of benthic impact is discussed.

Benthic impacts of fish farming: Meta-analysis of community and geochemical data

A number of 41 papers dealing with the benthic effects of fish farming were reviewed and the values of the variables studied were extracted to be used in a meta-analysis of effects. The papers used covered a wide range of farmed species, geographic regions, management practices and specific site characteristics (e.g., depth, exposure, and sediment type). Therefore, the total data-set may not be considered as biased towards a particular set of conditions as is often the case with data collected in a single study. More than 120 biological and geochemical variables were monitored, occasionally using different sampling and analytical protocols for the same variables. The rank correlation analysis between all possible pairs of variables in the data set showed a large number of significant positive or negative correlations, reflecting the response of these variables to benthic organic enrichment. The use of stepwise regression showed that most biological and geochemical variables are determined by a combination of distance from the farm with bottom depth and/or latitude. Results of stepwise regression, repeated separately for each type of sediment, showed that although the general pattern was similar among different types of sediments, the coefficients varied considerably indicating changes of the distance affected by settling particulate organic material for different sediment types. The overall conclusion is that the complicated interactions between variables and the lack of data, such as current speed, induce difficulties in setting common or uniform environmental quality standards for benthic effects of fish farming and these should take into account the existing considerable differences between geographic regions, depth zones and sediment types.

Assessing benthic impacts of organic enrichment from marine aquaculture

Benthic observations were carried out at 22 stations in the Western Isles region of the Bay of Fundy on the east coast of Canada to evaluate impacts at salmon aquaculture sites. Eleven sites were located under salmon net-pens and 11 sites (reference or control locations) were at distances > 50 m from net-pens. Total S- and redox potential (Eh) in surface sediment and benthic O2 uptake and CO2 release were sensitive indicators of benthic organic enrichment. High variability between replicate measurements of sediment gas exchange could reflect spatial patchiness in sedimentation of fecal waste and food pellets under fish pens. Biomass of deposit feeders was significantly increased at cage sites but total macrofauna biomass was similar at cage and reference locations. Surface sediment water content, modal grain size, pore water salinity and sulfate, and total biomass of macrofauna were the least sensitive indicators of enrichment.