The zooplankton community in the Bay of Gibraltar under tidal influences and recommendations for future monitoring studies
The Strait of Gibraltar is known as the gate between the North East Atlantic and the
Mediterranean Sea with still expanding heavy marine traffic, utilising the port in the Bay of Gibraltar. This can lead to a heavily modified waterbody, with an increase of pollution and nutrient input. The water masses in the Bay of Gibraltar are modulated by strong winds, currents and tides, creating an inflow of Atlantic waters during the rising tide and an eastward stream of outflowing waters during the lowering tide.
Zooplankton is a key player in marine ecosystems, linking the energy transfer between primary production and higher trophic levels. Because zooplankton directly responds to variability in their environment, their dynamics are affected by anthropogenic pressures and hydroclimatic changes, which can be monitored by regularly sampling zooplankton in the water column. In the Mediterranean Sea zooplankton is well and widely studied, with temporal and spatial studies in numerous regions around the Sea. In the Bay of Gibraltar however, zooplankton has been essentially overlooked, which has implications for assessing and maintaining good environmental status in the waters of the Bay.
The aim of this study was to create the first baseline study of zooplankton distribution in the Bay of Gibraltar, while observing the tidal influences. Before, a critical literature review was conducted to identify gaps in knowledge and emerging trends in the study of zooplankton in the Mediterranean Sea region, which confirmed the presumption of a lack of zooplankton studies in the Gibraltar area and revealed among other things the ZooScan image analysis methodology and normalised biomass spectrum theory as emerging trends in the Mediterranean waters. With the collected and digitised zooplankton data a learning set for the Bay of Gibraltar was created using the web application EcoTaxa, the final precision and recall rate of the learning set proved high, which makes it suitable for usage in future monitoring studies (under the condition of using the same image analysis methodology). The zooplankton community in the Bay was taxonomically diverse, showing spatial patterns with differences in predominating taxa and highest total abundances in the head of the Bay. The influence of the tides and currents created differences in environmental and biological conditions, with the low tide indicating increased water temperature, dissolved oxygen and zooplankton abundance. The inflow of water during high tide decreased water temperature, dissolved oxygen and zooplankton abundance and the currents flush eggs and smaller species in and out of the Bay. The surface waters in the Bay of Gibraltar are therefore a heterogenous system with various prevailing environmental and anthropogenic influences that need to be measured to interpret the zooplankton dynamics. Total abundances ranged from 81.5 ind. m3 outside of the Bay during high tide, to 250.8 ind. m3 at the head of the Bay during low tide. Copepods generally dominated the zooplankton community, however, on the east side of the Rock of Gibraltar the copepod community was overtaken by Cladocera. Evadne and Penilia showed differences in their distribution between high and low tide sampling and their dominant appearance might mirror a regime shift in the Mediterranean that has been observed in other regions and can be related to an increase in water temperatures. Acartia and Paracalanus dominated the copepod community at all stations. While the abundance of Acartia was stable throughout the inflow and outflow of water masses, Paracalanus abundance grew with the lowering of the tide, possibly because of different migration behaviours. The proposed methodology for future zooplankton monitoring studies in the Bay of Gibraltar provides many benefits (such as saving time and simplifying the taxonomic identification). Some aspects however, need to be reconsidered; for a representative presentation of the zooplankton community it is recommended to sample more layers of the waterbody, using at least two nets with differences in their mesh size to sample smaller and larger zooplankton species. The timing of sampling needs to be adapted as well, to precisely measure the influences of in- and outflowing waters, and a wider range of environmental factors at the time of sampling need to be measured in the future. This study is the first to give a taxonomic overview of zooplankton in the Bay of Gibraltar and with the proposed methodology forms the basis for initiating long-term zooplankton monitoring in the Bay of Gibraltar. Regular monitoring could create many opportunities, such as measuring and maintaining good environmental status and detecting potential threats: a regime shift in the Mediterranean, an introduction of foreign species through the ballast waters of shipping and uncontrolled proliferation of microalgae.
Primary Supervisor: Dr Awantha Dissanayake
Secondary Supervisor: Dr Astrid Cornils, Alfred Wegener Institute
Microplastic survey of abundance and characterisation across the shores of Gibraltar: A marine management issue
Microplastics are a severe pollutant found globally throughout previously pristine marine environments, across all beaches to the deep sea. Microplastics (MPs) are plastic debris smaller than 5 mm and are categorised as either primary or secondary MPs. Primary microplastics are deliberately manufactured to a small size to be used in industry, to create larger plastic items, or in cosmetics or cleaning products. Secondary microplastics occur from the fragmentation and degradation of larger items of plastic. Plastic pollution can have a damaging impact on marine organisms and human health through ingestion and tourism due to aesthetic reasons. As a new, rapidly growing area of research, novel methods of MP research are still being tested, meaning there is a lack of standardised protocols and definitions. Comparison of results across the world is therefore complex. Furthermore, there is a defined difference in the funds available for microplastic research conducted in Western countries compared to developing countries with developing countries lacking the resources or expertise to complete large-scale, temporal research, making the literature from Developed countries more abundant. Research on microplastics has taken place in beach sediments, seabed sediment, water surface, water column and in the deep sea. Trends in research have shown that microplastics are being found in sediments worldwide with their abundance strongly increasing. The aim of the current study is to create a cost-effective, feasible methodology for use by NGOs and Citizen Scientists across the globe, creating harmonisation in results on the state of microplastic pollution worldwide, whilst producing a baseline of microplastic abundance data in Gibraltar.
First, a critical literature review determined the best definitions, methodology for sampling, identification techniques and presentation of results. A pilot study was implemented to trial the methodology and a refinement stage took place. The final methods were executed around the shores of Gibraltar in October 2021. A total of 120 replicates across seven sites were sampled from the top 3 cm in a 25 x 25 cm square area. Microplastics were visually identified, enumerated, and categorised by form, colour, shape, and size into five distinct groups: fragments, fibres, films, foams, and pellets. A baseline of data was identified on the abundance and characterisation of the microplastics present in Gibraltar. Results presented Gibraltar with an average of 39.54 ± 51.67 items per m2 across all the sites with fragment being the most common category. Inside the Bay of Gibraltar has a higher abundance of microplastics, containing 82.4 % of the total microplastics found. The results were elevated owing to Camp Bay’s pollution level; holding over half the microplastics found (N = 188, 60.26 %). Forensic analysis was executed to determine the source of microplastics in Camp Bay and two different sources were identified: paint flakes from the seating area surrounding the beach and rubber fragments originating at a nearby play park with fall protection flooring. Urgent action is required from the Government of Gibraltar in Camp and Little Bay areas and recommendations have been made for better marine management, including researching an alternative to painting every year, replacing the fragmenting fall protection in the play park, and replacing the crumbling stairs in Little Bay. The findings from the present research form the first ever comprehensive baseline study of microplastic abundance and characterisation in beaches in Gibraltar while implementing a feasible, standardised method. Recommendations are proposed for research to be continued over temporal and spatial scales, conducted at multiple times of the year for a period of several years to assess trends in the data. The implications for marine management are discussed within.
read more about Bethany’s research here.
Keywords: microplastic, sediment, characterisation, analysis, paint, marine management.
Primary Supervisor: Dr Awantha Dissanayake
Secondary Supervisor: Dr Jaime Davis
Patella ferruginea distributions at the Western side of Gibraltar, the future threat of sea level rise and a novel method for morphotype identification
Patella ferruginea (Gmelin, 1791) is the most endangered marine macroinvertebrate along the Western Mediterranean rocky shores, where its relative abundance has declined drastically. Anthropogenic pressures have been deemed the number one threat this species faces and has been associated with high mortality rates. Patella ferruginea has two distinct morphotypes, Rouxi with a taller and more symmetrical shell and Lamarcki with a flatter and asymmetrical shell. The species is being protected by two international directives Annex IV of the EU Habitats Directive and Annex II of the Berne and Barcelona Convention and local Nature Protection law (Gibraltar Government’s Nature Protection Ordinance No. 2608) in Gibraltar where this study takes place. Climate Change and Sea level rise has been an important subject when it comes to the future of survival of any marine associated species. Three different sites within the West side of Gibraltar were assessed for the examination of the distribution of the species and its two morphotypes, along with two aspects of the crypsis element the species presents (visual and crevice), the threat that is sea level rise (SLR) for the population in the three sites and in general Gibraltar. A novel method is introduced as well for the identification of the two morphotypes using photographic material and fractal analysis as a measure to reduce human disturbance to Patella ferruginea and recommendations were made for the further conservation of the species. Our results show high number of individuals across two sites with accessibility of a site and the level of pollution in the area being the major driving force for distribution. Vibrations cause by construction sites and airplanes have also been identifies as a driving force. The morphotype distribution was based on the exposure of each site to the elements but also to the height (elevation) of each site with numbers of Rouxi morphotypes decreasing in higher sites. Visual crypsis was attributed to the protection against predators, and sea level rise has been linked with high mortality rates across all possible scenarios. The novel way of identifying the two different morphotypes of Patella ferruginea was successful, and several conservation points were raised.
read more about Petros’s research here.
Keywords: Patella ferruginea; Morphotypes; Rouxi; Lamarcki; Conservation; Climate Change; Sea Level Rise; Threats; Methodology; Fractal; Gibraltar;
Primary Supervisor: Dr Awantha Dissanayake
Secondary Supervisor: Dr Darren Fa
In conjunction with:
Stephen Warr: Department of Environment, Sustainability, Climate Change and Heritage
First marine litter assessment in Gibraltar: low-cost and easy to replicate methodology
The UN General Assembly recognized marine litter as a global problem in 2001. Marine litter can be defined as “any persistent, manufactured or processed solid material that is discarded, disposed of, abandoned or lost in the marine environment (MSFD, 2008). It is estimated that more than 150 million tonnes of plastics have accumulated in the world’s oceans, while 4.6-12.7 million tonnes (Jambeck et al., 2015) are added every year. Marine litter causes harm to the environment, to the fauna, to the economy and even to human health. Yet, there is still much speculation among researchers, policymakers and planners about how to tackle marine litter. Monitoring marine litter is fundamental to better understanding and developing ways to mitigate marine litter. There are marine litter mitigating initiatives that the European governments are committed to, such as the MSFD protocol, which provides a guideline to standardise marine litter assessment. Standardisation is also necessary for the expression of results, allowing the results to be compared and repeated. Most marine litter assessments reviewed were studies done in Europe, specifically in the Mediterranean, although it is important to stress that the literature review was only conducted in English. The average litter abundance in all studies was 0.74 items per square metre. Gibraltar is a British Overseas Territory located bordering the south of Spain, having coastline in the Bay of Gibraltar and in the Mediterranean. It is a small population peninsula that has a lack of studies and science about it. To conduct the first marine litter assessment in Gibraltar, a low-cost and easy-to-replicate method was used, with the use of snorkelling equipment and footage capture (action camera). Developing this accessible method to 3 standardise marine litter assessments and provide a baseline marine litter abundance and characterisation data for the sites assessed All of Gibraltar’s seven beaches were assessed, resulting in an abundance average of 0,00028 items per square metre, ranking Gibraltar as having the cleanest marine environment in all studies reviewed. There was a significant difference between the abundances of the Bay of Gibraltar and the Mediterranean beaches, respectively with averages of 0.18 and 0.02 items per square metre. The reason for this might be related to the proximity of anthropogenic sources of litter. A finding that supports this hypothesis is that the Western beach is the most polluted beach, as well as the closest one to the Spanish border, where many anthropogenic interventions generate litter. The cleanest beach of Gibraltar was Camp Bay. Plastics corresponded to 72.6% of all items recorded, and most of them were located on the intertidal sand (63.7%). To mitigate marine litter and its impacts in Gibraltar, some actions can be taken, such as raising awareness of the cause, continuing the historic ban of single-use plastics, reinforcing the current ban policies, adding or relocating litter bins to facilitate access to it, expanding marine science education for outside the schools, creating projects such as marine citizen science, offering adequate disposal location to the dispose of construction litter, and the implementation of frequent marine litter monitoring to better understand its sources in order to address them for a more effective strategy.
Key words: marine litter, marine debris, assessment, survey, Gibraltar, low-cost, replicable
Evaluation of Environmental and Anthropogenic Drivers of Selected Limpet Populations in Gibraltar: Featuring the Effects of Oestrogenic Hormones
Osteogenic compounds (oestrone, E2, and EE2) are a type of sex hormones found in both male and female organisms, however, is characterized as a female hormone as it aids the development of female characteristics and reproductive system. Oestrogen is released though sewage treatment plants (STPs) due to inefficient infiltration as their non-polar and hydrophobic nature allows the pass of the compound into the environment and exposing organisms causing extreme biological effects. Limpets are a type of filter-feeding molluscs habiting rocky shore environments close to anthropogenic contact. As they are filter-feeders/ grazers, they absorb all toxins, and chemicals they are exposed with, and bioaccumulate at a rapid rate due to their limited ability in excreting contaminants. Oestrogen infiltrates the environment, exposing limpets to high concentrations, and are susceptible to bioaccumulating the hormones within their fat content. Effects of oestrogen found in other species within the same and other taxonomic groups, indicted exposure to oestrogen increases Metallothionein (MT) and Vitellogenin (VTG) biosynthesis. Metallothionein is responsible for the organism’s growth, sex, and size; thus, stimulation induces the rapid size and growth, and has the potential in being responsible of sex change in hermaphroditic limpets. Vitellogenin is a type of protein present in females responsible for the creation of egg yolks. Upon oestrogen exposure, literature indicates males are producing the protein at high levels although not naturally produced in normal circumstances. Males with long-term exposure to the hormone develop premature eggs within their testis displaying intersex/ imposex characteristics. Gibraltar is U.K. overseas territory situated on the most southern tip of the Iberian Peninsula. The country is only 3 miles (5 km) in length, and does not have their own municipal sewage treatment plant. The country sewage is discharged at random times from Europa Point. The present research project samples limpets at three different sites around Gibraltar: Sandy Bay, Europa Point, and Western Beach. Four limpet species were counted and measured for their size Cymbula safiana, Siphonaria pectinata, Diodora aspera, and Patella ferruginea (the endangered Mediterranean limpet). C. safiana, and P. ferruginea are both hermaphroditic limpets with the size threshold of ~5cm, whereas S. pectinata, and D. aspera are dioecious species (organisms possessing only one sex). Results indicated larger overall sizes and increased number of P. ferruginea at Europa Point. It could be the result of long-term increased oestrogen concentration in the source of discharge; thus, limpets grew larger, and as for the hermaphroditic species, turning females.
Sandy Bay prompted similar result to Europa Point, with a smaller number of P. ferruginea. However, the data collected was during the beginning of bathing season, and limpets are extremely susceptible to human collection. However, overall, there was large biodiversity, containing all 4 species. There was the least amount of biodiversity, and smaller sized limpets in Western Beach. Western Beach is situated on the very most north-western portion of Gibraltar, at close proximity to the airport runway (just south of the beach) and close to the Spanish city La Linea de la Conception. Western Beach is also located at Algeciras Bay, sharing the same waters as ports, refineries, polluted rivers, and broken Spanish sewage systems, redirecting the flow into the bay. The results in Western Beach could have been skewed as there are numerous different factors that could potentially harm and halt the growth of Limpets. However. S. pectinata dominated Western Beach indicating higher levels of pollution. The species are the most tolerant to unhabitable environments.
As for the endangered P. ferruginea, there were the highest number of individuals found at Europa Point, where the source of discharge is located. The larger number of individuals and increased size indicates that sewage contain oestrogen is a possible factor in prompting the species’ growth. Possible conservational methods are discussed in aiding the repopulation of the species with further research.
Since the present research project was conducted in the natural environment, there are too many interfering factors that could inhibit and skew the final result. To further the research, it is recommended to conduct oestrogenic testing using YES assay in the natural environment to indicate actual concentration levels if present. It is also recommended to conduct the research in a laboratory environment to prevent external factors from interfering with the result. The research project is Gibraltar’s primary assessment in determining the drivers of limpet population and is one of its kind in discussing conservation methods utilising hormones.
The Effects of Hypersaline Desalination Effluence on Benthic Communities in Gibraltar’s Camp Bay
Water scarcity is an increasing concern globally, and salt water desalination is a solution that many locations take to mitigate the lack of potable water. Gibraltar is one such area.The Ministry of Defence (MoD) has a desalination facility and the effluent is an open pipe outflow along the rocky shoreline in Camp Bay. Literature on the environmental impacts of desalination effluence is limited overall, and almost non-existent on rocky shore habitats. Salinity, dissolved oxygen, and temperature data were taken to identify a rudimentary area of impact. A quadrat survey of sessile species found in subtidal and intertidal zones was performed, along with an underwater camera survey of motile fish species. It was found that the intertidal and subtidal communities had significant differences within the 15 m around the effluent outflow.The greatest contributors to the difference of the intertidal communities were U. lactuca and Chthamalus spp., with the U. Lactura, found in the area right next to the effluence.The subtidal main contributors were the invasive R. okamure and A. armata, with almost none of these two species being found within 15 m of the effluent point.The intertidal and subtidal species abundance follow the intermediate disturbance theory. Additionally, the Labridae family of fish were found to be of higher abundance near the desalination outflow. Echinoderms were of low abundance throughout the whole site, but were found within 15 m of the effluent point.The area of impact is very small due to the natural tidal, wave action, and currents of the area.
Implication for coastal water quality and human health: the potential for colonisation of epiphytic faecal bacteria (Escherichia coli) on Rugulopteryx okamurae
Water is intended for a variety of applications, including a range of recreational activities, transportation, food production, as a repository for sewage and industrial waste, and ecological protection, among others. Water is a vital natural resource that is required for living. However, it is home to one of the smallest harmful bacteria, Escherichia coli, and is utilised in the monitoring of water quality as an indicator of faecal contamination. Researchers discovered that E. coli uses different surfaces like algae for protection and nutrients. At the surface of macroalgae, E. coli communities interact and form epiphytic partnerships, which, in the case of Rugulopteryx okamurae, the level of interaction has not yet been discovered. Rugulopteryx okamurae is a non-native macroalgae that has rapidly expanded in the Strait of Gibraltar, and its potential to encourage the growth of E. coli is enormous. Interactions between macroalgae and bacteria appear to be essential phenomena that require a fuller understanding by those interested in microbial water quality research and management. Trends in research have shown that bacterial colonies are being found on the fronds of algae worldwide, with their abundance strongly increasing. The purpose of this study is to establish a baseline for the presence and abundance of E. coli on the surface of R. okamurae on Gibraltar beaches whilst examining the antimicrobial properties of R. okamurae. Following the comprehensive literature review, a pilot study was conducted to evaluate the sampling and analysis methodologies’ weaknesses. The final procedures were implemented, and data was collected through snorkelling from the three beaches (Camp Bay Beach, Sandy Bay Beach, and Western Beach) of Gibraltar. Water temperatures and 33 algae and 30 water samples have been collected from the end of May until mid-July in 2022. Microbiological analyses were undertaken to determine the baseline of E. coli and total coliform colony abundance on the surface of R. okamurae and within the water column. Results presented the greatest abundance of bacteria at Wester Beach in water samples, resulting in an average of 158 ± 111.65 CFU mL-1 total coliform, from which E. coli has an average of 49.66 ± 51.74 CFU mL-1 . Similarly, the highest bacteria abundance in the case of algae surface samples was found at Western Beach, resulting in an average of 3.11 ± 4.10 CFU g-1 and E. coli 0.22 ± 0.44 CFU g-1 . Then, results of bacterial abundance reported by the agency in charge of water quality monitoring were compared with results from the present study. Antimicrobial analyses were executed to 6 determine the antimicrobial activity of R. okamurae due to the absence of an inhibitory zone, it was revealed to have no antimicrobial properties. Rugulopteryx okamurae’s antimicrobial activity must be identified by more specific and comprehensive testing. Recommendations have been made for higher water quality monitoring standards, including total coliform analyses and other multi-pathogen testing. Findings from the present research form the first ever comprehensive baseline study of bacterial abundance on the surface of Gibraltar’s algae, R. okamurae. Recommendations are made for research to be continued over temporal and spatial scales and conducted at various times of the year. Recommendations have been made to the government on the implications of Western Beach pollution, which is to develop a sewage treatment strategy.
Keywords: water quality, macroalgae, Rugulopteryx okamurae, faecal bacteria, Escherichia coli.
Health status and characterisation of Gibraltar’s maerl
Maerl beds form heterogeneous, three-dimensional habitats for numerous species, housing high levels of biodiversity and species richness across the globe. There is a global lack of knowledge on the distribution and conservation status of maerl, despite the algae’s important ecological role. Therefore, this research project set out to characterise and assess the health status of the maerl present in the north west of BGTW. A new, standardised methodological framework was developed to assess the overall health of the maerl deposit by differentiating between maerl the organism and the maerl habitat. To assess the former, a colour-based visual analysis was performed, as well as size quantification of rhodoliths >4.75 mm and the distribution and coverage ratio of the deposit. The latter was examined through the analysis of a biodiversity characterisation and sediment composition.
The maerl in the north west of BGTW has a critical health status, as 92.2 % of it is dead, high levels of surface erosion and unusual colourations were observed, and rhodoliths were small in size. The habitat health was labelled as intermediate, based on the species richness values, signs of nursery function, high number of Terebellidae (n=233), and sediment composition. The maerl-forming species Lithophyllum racemus and Lithothamnion cf. corallioides were found to be present in the study site. The following sources of pollution were hypothesised to be causing the critical health condition of the maerl: disturbances caused by boats and a nearby runway, sewage effluent and storm water drains, coal residue, and the presence of Rugulopteryx okamurae. Four recommendations were subsequently made to the HM Government of Gibraltar:  to incorporate the maerl as a Benthic Habitat under Descriptor 1 and 6 of the Monitoring Programme for BGTW;  to research the current sources of pollution causing critical health;  to protect the maerl from further degradation under MSFD Criterion 6.1; and  to consider the Spanish sewage effluent as a potential source of eutrophication.
Assessing the Presence and Abundance of the Finger-Shaped Sea Pen (Veretillum cynomorium) Within the Bay of Gibraltar
Sea pens, within the order Pennatulacea, are globally distributed corals that are found in soft sediments. Multiple sea pens living in close proximity to each other form habitats known as sea pen meadows, which provides shelter and nutrients to fish larvae and invertebrates. Within the United Kingdom and other regions of the north-eastern Atlantic assemblages of sea pens and burrowing megafauna can be classified and protected as “sea pen and burrowing megafauna” biotopes. Despite their importance as ecosystem engineers and widespread distribution, little is known about sea pens, especially within the waters around Gibraltar. In this study, the abundance of the finger-shaped sea pen (Veretillum cynomorium) was assessed within the eastern Bay of Gibraltar through footage collected while diving. The average abundance of V. cynomorium obtained through photo quadrats within the sea pen fields at the sampled depths (9 – 20 m) was 4.23 visible colonies/m2 and 7.36 total colonies/m2 (burrowed + visible colonies). The abundances obtained within the thesis are greater than any other V. cynomorium abundance found within the Mediterranean Sea, indicating that Gibraltar is a hotspot for Veretillum cynomorium and possibly other sea pen species. Since Gibraltar is a United Kingdom Overseas Territory and is less than 27 km away from the Atlantic ocean, one of the sampled locations (Spanish Barge 4) can be argued to be the “sea pen and burrowing megafauna” biotope, making this the first possible classification of such a site within the Mediterranean Sea. Due to the importance of sea pens and their abundance within the Bay of Gibraltar, the researcher of the thesis suggests that V. cynomorium should be included as an important species and habitat within Gibraltar’s marine assessments, and that the abundant sea pen fields are monitored and protected in the future.
A Description of Prokaryotic Picoplanktonic Communities and their Relationships with the Physio-Chemical
Ingrid Tissot van Patot
Wastewater-fertilised algae raceways have recently drawn attention as a potentially sustainable source of biogas and a cost-effective form of sewage treatment. Howeverthe complexity and instability of microbial communities in algae raceways often results in bloom collapse, compromising their feasibility as a sustainable source of energy. Project PRODIGIO is an EU-funded project aiming to develop an early-warning signal to help anticipate when a collapse is imminent. PRODIGIO maintains two raceways southern Spain, one fertilised by wastewater, another by fertilisers. Raceways were sampled from 15 April 2021 to 29 November 2021 and the genetic data and environmental variables were analysed. This dissertation focuses on prokaryotic picoplankton community dynamics and the biogeochemistry within the outflow samples of the wastewater algae raceway, aiming to understand causes and effects of community changes in relation to biogeochemical variables. ANOSIM and SIMPER analysis was run on the environmental and ASV datasets to determine how average monthly community compositions and physiochemical environments differed. Spearman’s Rank correlation was run on the environmental dataset, which showed collinearity among variables affected by seasonality (temperature, PAR, Fv/Fm). DO was controlled in the raceway to prevent impacts on biomass production, decoupling it from natural relationships with temperature and nitrate. Though nitrifying bacteria were not abundant, the presence of nitrification and denitrification was confirmed when comparing ammonium concentrations in the inflow vs outflow samples. It is possible that nitrifying bacteria were not shown in abundance in the picoplankton dataset due to the exclusion of larger size fractions. Two phyla; Actinobacteria (Actinomycetota) and Proteobacteria (Pseudomonadota) were most dominant throughout the culturing period. The influence of sewage on community dynamics within the raceway was apparent by the presence of several pathogenic genera such as Mycobacterium, Legionella and Aeromonas. Overall, the wastewater raceway plays host to a complex microbiome influenced by both environmental and biological factors.