Fringing Reef Report, Isabella Menezes PDF

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MB2050, Isabella Menezes, 13693525

April 27, 2020

FRINGING REEF REPORT

Fringing reef report MB2050

MB2050, Isabella Menezes, 13693525

April 27, 2020

Introduction

Fringing reefs have one of the simpler structures and form compared to other reef forms. They have very similar characteristics to barrier reefs, except they are attached to a shoreline (Taebi, Lowe, Pattiaratchi, Ivey & Symonds, 2012). Fringing reefs are less common in the mainlands; they occur more frequently around islands. Using the spring line as a starting point, they consist of three different zones; the reef flat, then further out is the reef crest, and last there is the outer reef. Several physical factors influence each zone. Some of these factors include dissolved oxygen, temperature, and salinity. Each of these factors connects to the particular morphological, sedimental, and hydrodynamic conditions. These conditions control the distribution of the species that reside across the fringing reef (Taebi, Lowe, Pattiaratchi, Ivey & Symonds, 2012).

The data collected is from a fringing reef located at Picnic Bay at Magnetic Island. The specific reef flat zone surveyed lies between the reef crest and the spring line of the shore. The water in this location (the reef flat) tends to be shallow, therefore often being exposed during very low tides. Organisms living in these areas get exposed from low tides far more frequently than in other zones. Because of the frequent exposure, they have acquired a set of adaptations that allow them to survive in these harsh conditions. Despite the circumstances, there is still a large number of organisms that thrive on these reef flats of the Fringing reef.

Many factors influence the abundance and distribution of species on the reef flat. These factors include the availability of specific structures (such as hard substrata for sessile fauna), physical gradients, and sediment types. The goal is to examine the marine flora and fauna and distribution of organisms of the intertidal zone. Furthermore, shed light on what environmental conditions determine the distribution, such as sediment type and distance from the spring line.

Fringing reef report MB2050

MB2050, Isabella Menezes, 13693525

April 27, 2020

Materials and Methods: The data collected was gathered from a fringing reef located at Picnic Bay, Magnetic Island (19.9 o S, 146.5o E) north of the city of Townsville. Some transects were placed every 10 meters, with the first transect starting 2m from the spring line. After carefully inspecting each transect, all organisms occupying the area were identified and recorded. The transect was laid out up to 160m while simultaneously recording data to avoid minimal walking on the substratum, minimizing damage and misinformation. The flora, consisting of seagrass species and algae, and sessile fauna (such as coral and sponges) identified in each transect measured as a percentage cover, same method for the substrate found in each transect. Therefore, the substratum type and coral cover added together will result in 100% of the complete transect area. Any other taxa, as well as burrows noticed in the vicinity, were also noted; however, these comments only occasionally had numerical values, so they are not included in the final data. Once all data was collected all along the transects, the data makes up a class set. The data set has been repeated over multiple years of conducting the excursion/study, creating an extensive class data set (Bellwood, O. (2020) MB2050 Subject Manual).

Fringing reef report MB2050

MB2050, Isabella Menezes, 13693525

April 27, 2020

Results Each sampled transect was counted, recorded, and graphed, indicating the quantity and distribution of different species (specifically the fauna). In Figure 1, there is a Linear (Total Species Abundance) trend line that demonstrates a slight increase in the number of species identified along the transect. Sample points to note at 32m, 112m, 122m to 132m as well as 142m show anomalous results. These results conclude a decrease of abundance over distance from the spring line and a slight overall trend that shows an increased value.

Total Abundance of Species 10 9

Species abundance

8 7 6 Horiz. Abundance Total Species Abundance Linear (Total Species Abundance)

5 4 3 2 1 0

2 12 22 32 42 52 62 72 82 92 102112122132142152162

Horizontal Distance (m) Figure 1: Total abundance of species(Fauna) found over the transect.

Fringing reef report MB2050

MB2050, Isabella Menezes, 13693525

April 27, 2020

When looking at the transect line closer to the spring line, there are noticeably softer sediments, such as sand, silt, and mud (Figure 2). After plotting the distance from the spring line against the total percentage cover of distribution of hard sediments and soft sediments, it is clear that there is hardly any sign of harder substratum until passing the 32m mark from the spring line. The harder sediment types include biogenic rubble, dead coral, and coral rubble (sediment types that tend to appear more frequently as the distance from the spring line increases).

Distribution of Soft and Hard sediment 100 90

Pencentage cover (%)

80 70

soft sediment Soft sedimen t

60 50 40 30 20 10 0

2

12

22

32

42

52

62

72

82

92

102

112

122

132

142

152

162

Distance from Spring Line (m) Figure 2: A graph showing both the hard and soft sediment distribution along the transect.

When comparing the Floral(algae) against Fauna(sessile) % cover over each transect line ( Figure 3), there is a clear inverse correlation. Neither is very present until passing the 52m mark on the transect. After this point, the abundance of Floral(algae) and Fauna(sessile) rise in a similar pattern for the next 10 meters until the Floral(algae) cover takes over; this is where the inverse correlation starts appearing as the Floral(algae) cover increases, the Fauna(sessile) cover decreases, and vice versa. This relationship can be observed from 62m and onwards over the transect. After this mark, there is noticeable spikes and drops over the Fauna(sessile) cover.

Fringing reef report MB2050

MB2050, Isabella Menezes, 13693525

April 27, 2020

The inverse relationship displays itself from 82m onwards, with obvious spikes and drops in the sessile cover (from roughly 17% up to 40%, then down to 10% and ends at 68%). The explanation for the significant drops for the Fauna(sessile) cover can be explained by it directly correlating with significant spikes in Floral(algae) cover (increasing up to 30%, then down to 20% then back up to 50%).

Algea vs. Sessile Fauna abundance 70

Percentage Cover (%)

60 50 40 30 20 10 0

2

12

22

32

42

52

62

72

82

92

102

112

122

132

142

152

Distance from Spring Line (m) Horiz. % Cover

Floral (algea)

Horiz. % Cover

Fauna (sessile)

Figure 3: The algae plotted against the sessile fauna percentage cover in each sampled transect.

Plotting all the substratum composition for each transect sample reveals important trends (Figure 4). Between 12m and 72m, the dominant substratum is silt and mud (soft substrata), and after that mark, there is hardly any sign of mud and silt. After hitting the 82m mark on the transect line, hard substrata becomes dominant, consisting of mainly dead coral and biogenic sand, paired with various compositions of live coral and biogenic rubble.

Fringing reef report MB2050

MB2050, Isabella Menezes, 13693525

April 27, 2020

Cover (%)

Total Substratum Cover (%) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 2m 12m 22m

m 32

m m m m 52 62 72 82

m 42

m m 92 102

2m 32m 42m 12 1 1

2m 11

2m 60m 1 15

Horizontal Distance (m) sand dead coral

mud/silt biogenic sand

coral rubble live coral

biogenic rubble

Figure 4: The total cover in the percentage of the substratum.

When plotting soft-sediment substratum cover percentage against seagrass cover percentage, there is a clear correlation between the two (Figure 5). The seagrass starts at very low values closer to the spring line; however, as the soft sediment cover% drops down to 70%, the seagrass mimics this trend as well. The seagrass cover slowly remains partial to the soft sediment as the distance from the spring line increases.

Pecentage Cover (%)

Relationship between soft sediment and seagrass cover 100 90 80 70 60 50 40 30 20 10 0 2

12

22

32

42

52

62

72

82

92

102

112

122

132

142

152

Distance from Spring Line (m) % soft sediment % seagr

Soft sediment Seagrass cover

Figure 5: The relationship between soft-sediment substratum and seagrass cover plotted over the transect.

Fringing reef report MB2050

MB2050, Isabella Menezes, 13693525

April 27, 2020

Discussion In an environment supporting an abundance of life, several factors determine how and what lives in each area of a fringing reef. A clear correlation between distance from the spring line and the distribution of species, also known as zonation, is very present within the survey. Substratum type plays a vital role in how organisms survive in their area. Depending on where they are on the transect, the substratum can be increasingly different. Substratum type is especially relevant for benthic communities, which rely significantly on the substratum in their environment. Because the substratum plays such a vital role for organisms that inhabit the area, it is important to highlight the change in sediment type and composition in a graph to get a clear overview (Figure 2 and Figure 4). It is clear that as the transect gets further from the spring line, the substratum experiences drastic changes, going from soft sediment to a mixture of soft and hard sediment (Figure 2 and Figure 5), opening an opportunity for other communities to flourish. The relationship between Flora(algae) and Fauna(sessile) is another interaction to note. There is little or no sign of their presence until the 52m mark (Figure 3). A possible explanation for this would be that they experience difficulty in growth in these conditions since they must be further away from the beach and for the coral; they need a harder substratum to attach to, which occurs further from the spring line (Tokuda & Ezaki, 2013). After passing 52m on the transect line, the two grow together until they start competing for space, giving an inverse correlation. As the flora(algae) abundance increased, the fauna(sessile) abundance remained either constant or displayed a decreasing pattern. When flora (algae) abundance decreased, the fauna(sessile) abundance would experience a dramatic increase in growth. The dramatic increase can be observed clearly at two points in Figure 3; at the 82 and 102m. Both display an inverse relationship where a decrease in abundance would mean an increase in abundance for the other part.

Competition is another factor to consider when looking at the inverse correlation in Figure 3. McCook, Jompa & Diaz-Pulido's (2001) exemplify this inverse correlation and suggest that there is a competition taking place between the algae and the coral. The research done indicates that coral tissue damage and algal growth are often related. The study does not necessarily point to direct competition between the two species, but rather a case of competitive exclusion of algal growth against areas of healthy coral tissue (pg. 409).

Both algae and sessile organisms are reliant on several resources and substratum for attachment. As seen in Figure 3, in certain areas, some colonies form, where there are drastic variations in the number of Flora(algae) or Fauna(sessile) cover %. The apparent increase of Fauna(sessile) cover at the end of

Fringing reef report MB2050

MB2050, Isabella Menezes, 13693525

April 27, 2020

the transect demonstrates a dominance of colonization over the algae for the reef slope. A common occurrence because algal growth is more common along reef flats (Morrissey, 1980), while Fauna(sessile), including coral, is more likely to grow on reef slopes, exemplified in Figure 3. Reef slopes tend to have deeper water, subjecting the organisms to less air and intense sunlight, more distribution for filter feeders, and more access to the harder substratum (Anthony & Kerswell, 2007). Sessile organisms such as coral are very reliant on deeper water environments to avoid the frequent exposure that organisms experience who reside at the reef flat, as this area is more likely to be exposed at low tide ("FringingReefs - coraldigest", 2020).

The type of sediment dictates the distribution and abundance of an organism. In harder sediments, especially in deeper waters, corals grow more abundantly in a single area. However, at locations where corals do not grow, the seagrass often inhabits. As seen in Figure 4, harder substratum types (such as biogenic rubble and coral rubble, as well as live coral), are much more common further out in the transect, where soft sediments are less abundant.

Soft sediments allow seagrasses to take root that cannot bury their roots into harder substrates (Gambi et al., 2008). However, the seagrass numbers decline when approaching the spring line (Figure 5). The sediment in these areas are often too fine; the roots have difficulty to attach; and, even if they could, there is not enough pore water exchange in the sediment, causing hypoxic conditions which make it difficult for the seagrass to grow (Gambi et al., 2008). As soon as conditions become liveable, the seagrass distribution increases and form a relationship with the sediment type (Figure 5). However, as the end of the transect line gets closer, the seagrass cover % declines. When the substratum is too hard, it is difficult for seagrass to attach, as well as corals often crowd the zone. The seagrass is reliant on the relationship it has with the soft substrata, as well as the zonation on the reef flat. This report has aimed to examine the relationships and tendencies that flora and fauna have in the fringing reef in Picnic Bay at Magnetic Island. It demonstrates how they relate to their preferred substratum type and how the distance from the spring line affects their distribution. A display of trends based on the zonation from plotting different parts of the dataset reveals unique relationships. Relationships between different species and environmental conditions are displayed, such as the comparison between coral and algae. Based on these results, we have a clearer picture of what factors affect the abundance of species that live in fringing reefs.

Fringing reef report MB2050

MB2050, Isabella Menezes, 13693525

April 27, 2020

References (2020). Retrieved 22 April 2020, from https://www.thesea.org/coral-reef-types/fringing-reefs/ Anthony, K., & Kerswell, A. (2007). Coral mortality following extreme low tides and high solar radiation. Marine Biology, 151(5), 1623-1631. doi: 10.1007/s00227-006-0573-0 Bellwood, O. (2020) MB2050 Subject Manual. Fringing Reef - an overview | ScienceDirect Topics. (2020). Retrieved 22 April 2020, from https://www.sciencedirect.com/topics/earth-and-planetary-sciences/fringing-reef FringingReefs - coraldigest. (2020). Retrieved 22 April 2020, from http://www.coraldigest.org/index.php/FringingReefs Gambi, C., Bianchelli, S., Pérez, M., Invers, O., Ruiz, J., & Danovaro, R. (2008). Biodiversity response to experimental induced hypoxic-anoxic conditions in seagrass sediments. Biodiversity And Conservation, 18(1), 33-54. doi: 10.1007/s10531-008-9433-1 McCook, L., Jompa, J., & Diaz-Pulido, G. (2001). Competition between corals and algae on coral reefs: a review of evidence and mechanisms. Coral Reefs, 19(4), 400-417. doi: 10.1007/s003380000129 Morrissey, J. (1980). Community structure and zonation of microalgae and hermatypic corals on a fringing reef flat of magnetic island (Queensland, Australia). Aquatic Botany, 8, 91-139. doi: 10.1016/0304-3770(80)90045-5 Taebi, S., Lowe, R., Pattiaratchi, C., Ivey, G., & Symonds, G. (2012). A numerical study of the dynamics of the wave-driven circulation within a fringing reef system. Ocean Dynamics, 62(4), 585-602. doi: 10.1007/s10236-011-0514-4 Tokuda, Y., & Ezaki, Y. (2013). Attachment structures inRhizotrochus(Scleractinia): macro- to microscopic traits and their evolutionary significance. Lethaia, 46(2), 232-244. doi: 10.1111/let.12013

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