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A comparative analysis of marine invertebrate phyla biodiversity at Dunwich, Minjerribah (North Stradbroke Island) across three years
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Kate Lant 2021
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Abstract | |
Understanding changes in diversity patterns across phyla is critical to understand the vulnerability and adaptability of marine organisms to environmental changes. Moreton Bay has an array of diverse tropical and temperate marine invertebrates, making it an ecologically significant system (Davie and Hooper et al, 1998). Autonomous Reef Monitoring Systems (ARMS) have been deployed at Dunwich, Minjierribah (North Stradbroke Island) since 2019, for periods between 2 and 12 months, allowing sessile marine invertebrates to settle and grow on the plates. Images of plates deployed for periods of 4 months in 2019 and 2021, and 2 months in 2020 were analysed to asses the diversity of phyla between the plates. Upon initial inspection, 2021 plates showed limited diversity, with coverage of white colonial ascidian genus Didemnum spp. dominating, present in large colonies. Shannon's diversity index was calculated for all the plates, to compare the differences across years, hypothesising that 2021 would show significantly less biodiversity than 2019 and 2020. The hypothesis could be accepted, because significant differences in the diversity was seen for 2019 vs 2021 and 2020 vs 2021. The results indicate the relationship and sensitivity that marine communities have with the surrounding environmental variables, including salinity, temperature and pH (Medupin., 2019). Wide scale environmental difference between the years may account for the changes seen, such as flooding events during the deployment of the 2021 plates, increasing sedimentation and limiting growth capabilities. Further, the effect of invasive species becoming more significant, as native species lack the ability to adapt to changes in their environment (Evans., 2017).
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Introduction | |
Marine invertebrates are critical to global biodiversity, and provide significant and cascading contribution to ecosystem (Collier, Probert and Jeffries., 2016). They exhibit huge diversity, not only in their morphology but in all aspects of their lifestyle and life history. Moreton Bay, Queensland, is no exception to this, supporting huge numbers of sessile and sedentary marine invertebrate diversity within all major phyla, seen in Figure 1 (Davie and Hooper, 1998). Within Moreton Bay, the Queensland museum reported over 3000 species of macro invertebrates emerging within Moreton bay (Hooper, 2021). It is vital to understand and maintain the diversity of marine invertebrates, because they are key indicator of water quality in the area, and are vital to stimulate primary productivity, feeding the Moreton Bay food web (Tibbets et al., 2018)
Numerous factors influence the diversity of these invertebrate populations, including water pollution, destruction and degradation of habitats, wide-ranging effects of climate change, and the introduction of invasive species. The invasive colonial ascidian Didemnum perlucidum, has been a problem for native species in the Gulf of Carpentaria, moving down the east coast to Moreton Bay (Stark et al., 2014). This species encrusts on, and completely overgrows native species due to its fast reproduction capabilities, sexually and asexually through the entire year (Zhan et al., 2015). Consequently, eradicating entirely, or even controlling the further spread of this invasive species is not currently achievable (Qld Gov., 2021). Further, human disturbance is prevalent in Moreton Bay, with jetties, marinas and constant boat disturbance in areas such as Dunwich.
Intense urbanisation, land clearing and construction of dams and water impoundments are some of the land changes that can hugely effect waterways, that connect to Moreton Bay (Tibbets et al., 2018). Land clearing causes increased amounts of run off into water ways during periods of heavy rainfall, where increased amounts of nutrients, pesticides and insecticides enter the water. Entire structures of marine communities can be altered, including the species richness and diversity, where some organisms are not adapted to harsh environmental conditions, such as increased acidity (Dauer et al., 2000). Many ascidians, within phyla chordata, have the ability to survive in increased acidity and temperature. Particularly of concern for native invertebrates in Moreton Bay is the increased ability of invasive species to tolerate significantly higher temperatures. Meaning that climate change, and the progressive warming of waters will disproportionately negatively effect native species (Hooper, 2021; Evans et al., 2017 ).
To study these marine communities, and understand the fascinating changes occurring, the University of Queensland has been deploying Autonomous Reef Monitoring Systems (ARMS) since 2019 at numerous different locations around the bay. These settlement plates are hard substratum, which create the ideal substrate for sessile invertebrate larvae in the plankton to attach onto, and begin growing (Medupin, 2019). Ten plates are stacked on top of each other, providing multiple levels for invertebrates to grow and reproduce.
Previous comparative studies using the ARMS plates focused on differences in growth of specific species across a spatial range (gbri.org, 2019 and 2020 research). Because this was the third year collecting ARMS plates data, the opportunity to run a comparative analysis across a temporal range, at one location could be done for the first time.
Initial visual comparison indicated that the biomass of invertebrates on the 2019 plates was high, there was barely any free space, and it was covered by an array of different organisms. Compared to the 2020 plates, they was less coverage, but the diversity was still there. 2021 however lacked diversity, and showed only high biomass for the ascidians. From initial inspection, the plates were predominantly covered with both colonial and solitary ascidians, with many of the 2021 plates seeming to be completely engrossed by the invasive white colonial ascidian Didemnun spp., leaving no space other invertebrates to grow. From the visual assessment, a research aim and hypotheses could be formed. The aim of this research was to analyse the biodiversity on the plates, and complete statistical analysis to identify if 2019 and 2020 showed significantly higher biodiversity than the 2021 plates. Therefore, the hypothesis was that 2021 would show significantly less biodiversity than both the 2019 and the 2020 settlement plates.The null hypothesis of this is therefore that there would be no significant difference in diversity between any of the three years. Further, it was hypothesised that phylum Chordata would be the most dominant phyla throughout all three years.
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| Figure 1 |
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Materials and Methods | |
Data Collection
ARMS plates were deployed from One Mile Jetty at Dunwich. Images of top and bottom sides of all of the ARMS plates from 2019, 2020 and 2020 had been uploaded to the gbri.org.au website. Dunwich was the location chosen, and because the only data from 2019 for Dunwich was for 4 months, the short term plates deployed in the consecutive years were used for comparison. The plates analysed were the 2019 Dunwich plates, deployed for 4 months (20/11/18 - 13/3/19) and the Dunwich_Short plates from 2020, deployed for 2 months (22/01/20 - 18/03/20) and 2021, deployed for 4 months (4/11/20 - 3/3/21).
Data Analysis
To count biodiversity, it was decided to do this by phyla and not by species, because detecting individual species through analysis of images would not be consistent or reliable. Commonly the shannon's diversity index (SDI) is used for species counts, but has successfully been used for taxa and family levels, so applying it to phyla level in this study is appropriate (Morales et al., 2019).
For each plate, an SDI was calculated by counting the number of different species seen present per phyla for one plate (Figure 2). So, an individual SDI was calculated in excel for plates, from ARM 1 and ARM 2 from 2019, 2020 and 2021. There were cases where some images were missing for the 2021 data.
To understand the changes in community composition across the years, the phyla counts for each year were totalled, to create pie charts to visually represent the phyla composition, and diversity.
Statistical Analysis
The Shannons diversity index was calculated using 10 phyla, Porifera, Arthropoda, Nematoda, Cnidaria, Mollusca, Bryozoan, Annelida, Platyhelminthes, Chordata and Echinodermata. Figure 2 shows an example of how this was calculated using excel. Then using Rstudio, t.tests (not paired) between each three years were conducted to see if there was any significant differences between the Shannon diversity index across years.
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| Figure 2 |
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Results | |
Shannons Diversity Index
The 2019 diversity index show the highest, with a maximum of 0.92, minimum of 0.13, and a mean of 0.67. 2020 had a maximum of 0.78, minimum of 0.23, and a mean of 0.57. 2021 had a mean of 0.34, with a maximum of 0.57, and a minimum of 0.13. Figure 1 illustrates the outcome of the t.tests, showing that there was a significant difference between the diversity for 2019 and 2020 (p value = <0.001)
Community Composition
Constructing pie charts, from totalling the counts per phyla for years was done so that the changes in the composition of phyla could be compared across the years. All of the pie charts, (Fig 5 - 7 )indicate that phylum chordata have the highest percentage of composition in all years, followed by Porifera. 2021 shows the highest percentage of chordata, with 42% of the diversity accounted for by this phylum.
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| Figure 7 |
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Discussion | |
The results of this comparative study support the hypothesis that 2019 and 2020 would show significantly higher diversity than 2021, and the null hypothesis can be rejected. The species composition was also analysed, to show that phylum chordata was the dominant phyla across all years. These results indicate that wide scale environmental changes are occurring, that are significantly effecting the composition and diversity of marine invertebrate communities at Dunwich.
Phylum chordata dominates the plates in all years, which supports the initial hypothesis. There are numerous reasons for the dominance of this phylum over others. Firstly, based on community ecology, and community structures, there are often a few species/phyla that are dominant, in relatively high numbers, seen as the genus Didemnun within chordata, and solitary ascidians , as well as Porifera in high numbers, Figure 8 is an example of some of these dominant species (Hale et al., 2021; Dauer et al., 2000). As well as lots of species at lower numbers, that creates a diverse population, which is seen in 2019 and 2020 (Arindom, 2021). Further, the dominance of phylum Chordata, where other phyla seem to be lacking, on the 2021 plates, does suggest that the environment could be becoming more extreme. Ascidians, unlike many other marine invertebrates can withstand changes in pH, salinity and temperature, making them such a successful inhabitant of numerous different environments globally (Zhan et al., 2015).
Environmental and anthropogenic changes pose large, possible detrimental impacts on marine invertebrate communities (Stark et al., 2014; Tibbets et al., 2018). In 2019, the total annual rainfall average was 764 mm, well below the 1049 mm average, and the annual streamflow in the Brisbane river was classified the lowest it had been in 12 years (BOM, 2019). This therefore suggests that little disturbance would have been occurring in terms of changes in acidity and salinity related to increased runoff during heavy rainfall. If 2019 had a more stable surrounding environment in the bay, with less fluctuation then it could explain why diversity is so high during this time, allowing numerous different invertebrates to settle and grow. Further, at the end of 2020 south east Queensland experienced flooding, which would in turn cause large amounts of run off into the bay, due to agriculture/ housing land clearing, causing dramatic increases in sediment entering the waterways (BOM, 2020; Tibbets et al., 2018). Extreme weather events such as flooding put intense pressure on ecosystems, and change/deplete the water quality significantly (Tibbets et al, 2019; Death., 2009). The increased sedimentation causes a decline in availability of light, necessary for benthic processes, so that these marine invertebrates can feed small particles through filtration (Hale et al., 2021; Narayan et al., 2015). During the period that the 2021 plates were deployed, water clarity, as a result of the flooding would have declined, and high levels of fine sediments and new available nutrients would have increased the pelagic productivity. However, this would be in the pelagic zone, not in the benthic zone, where the marine invertebrates settled on the ARMS plates could utilise this as a food source.
Further anthropogenic events impacting the Dunwich ARMS plates is general recreational activities, and boating that occur at One Mile Jetty, disturbing the communities. Previous research indicates that there is a clear trend moving away from anthropogenic disturbances of increased marine benthic biodiversity (Stark et al., 2014)
There are several limitations that impact the validity of interpretations that can be drawn from this study. To access all data to complete a temporal comparison, images have to be used, because it is not possible to analyse the plates from past years in person. Therefore, analysing the true content of plates is not possible. Analysing images is difficult, and locating and categorising the presence or absence of phyla, and counting exactly how many different species per phyla were present is not possible just through image analysis. Further, on the images it is much easier to see some phyla compared to others, which will negatively influence the direction of results. Phylum chordata, the ascidians are large in both colony sized for colonial species, and individual solitary ascidians are also large, and much large than other phyla. So, it is much easier to count presence of this phylum, opposed to counting presence of phylum Echinodermata, for example.
Future research would be enhanced by analysing the plates in person not through image analysis, and therefore being able to identify to the species level, to assess species diversity, rather than phyla diversity, however, this was out of the scope of this research. Future research need to focus on temporal comparison, so that it can be done successfully, rather than extrapolating temporal results from data that was not designed for this specific study. Future research could also focus on comparisons of AMRS plates deployed for different times. This would allow ecological succession to be monitored, as earlier succession stages there are more generalised fast breeding species, which was clearly seen by the abundance of ascidians. Where as later succession, more specialised species being to reproduce slowly, and this could be interesting to understand the diversity in years, over longer time scales.
This comparative study shows insight into the changes occurring in the invertebrate communities at Dunwich across three years. This research shows the direct link between invertebrate populations, and the external environmental changes that significantly impact upon the diversity of these communities. As changes continue to occur, both wide scale environment, and small scale communities, populations will change, as organisms either adapt or fail to adapt to their surrounding environment. It is vital that these communities stay diverse and abundant, and any loss of diversity will greatly effect ecosystem services. Future research should continue to understand changes across large scale, and even small scale time frames, such as biodiversity changes during winter months, to monitor the presence and absence of particular phyla, and their ability to adapt to increased environmental and anthropogenic changes.
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| Figure 8 |
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Acknowledgements | |
Thank you to Sandie and Bernie for guidance on this report, and to those who deployed and collected the ARMS plates, making this research possible.
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References | |
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