Acknowledgements
I am infinitely apprecia2ve of all the support, guidance, and encouragement I have received from my academic director Dr. Richard Walz, who has provided me with a wealth of knowledge and resources to help me complete my academic achievements this semester. Thank you to my incredibly qualified ISP advisor, Dr. Narriman Jiddawi for providing me with advice, knowledge, and connec2ons that have enriched my learning experiences throughout the en2re semester Thank you to my academic coordinator, Said Omar, for your unwavering support and willingness to help me find the materials and knowledge that I needed to be successful throughout the en2re semester, as well as the independent study process. Finally, I must thank the United Republic of Tanzania for giving me permission to perform research in this beau2ful country, as well as the countless Zanzibaris I have met along the way who have provided me with their hospitality, encouragement, and uncondi2onal kindness.
Abstract
A baseline dataset of echinoderm biodiversity of three types of echinoderms Sea urchins, starfish, and sea cucumbers was established at Pange sandbar off the western coast of Unguja island, Tanzania. Over the course of a 28-day study with 10 days of field survey, 2,812 individuals were recorded from 23 different species across ten transects of varying lengths. Two species one starfish and one urchin remain uniden2fied. The overall propor2ons of each type of echinoderm were determined, as well as the propor2ons of individual species. Nearly 75% of all species recorded were of Diadema setosum. Future research is recommended to determine the effects of such a large community of organisms on overall biodiversity at Pange. Another major finding was the evidence of substrate zona2on, as well as the zona2on of Diadema setosum, which was seen in greater abundance in zones farther from shore. In addi2on to the posi2ve correla2on between Diadema setosum individuals and distance from shore, a sta2s2cally significant correla2on was also seen between distance from shore and species richness. Each of these observa2ons were reinforced by strong correla2on coefficients of 0.778 and 0.868, respec2vely.
Data ya msingi inayojumuisha se2 za data za viumbe hai jamii ya achinodamata wa aina tatu za achinodamata, ki2 cha pweza, starfish, majongoo bahari ilianzishwa ka2ka eneo la ufukwe wa Pange upande wa mwambao wa mwamao wa magharibi ya kisiwacha Unguja, Tanzania. Kwa kipindi cha siku 28-upimaji, 2,812 viumbe hai vilionekna kutoka ka2ka aina tofau2 23 tafau2 ka2ka transek2 zenye urefu tafau2. Aina tafau2 za species; moja ni ki2 chapweza na moja ni uyumba, hawakuwezwa kutambulika. The uwiano wa jumla wa kila aina ya achinodamata waliweza kuamuliwa, vile vile uwiano wa jumla. Takriban asilimia 75% wa aina zote ulirekodiwa walikuwa ni “Diadema setosum“ . Utafi2 wa siku za mbele ni kuchunguza athari ya kuwa communi2 kubwa ya aina moja kutokana na bioanuwai ya Pange. Kitu chengine kikubwa ni Pamoja na kuwepo kwa ushahidi wa mgawanyo wa substra2 , vile vile mgawanyo wa Diadema setosum, ambao walionekana kwa wingi ka2ka eneo la utafi2 kutoka ufukweni Kwa kuongezea uwiano chanya baina ya Diadema setosum na masafa kutoka ufukweni, takwimu za uwiano muhimu ulionekana baina ya masafa kutokea ufukweni na aina viumbe hai Kila uchunguzi uliimarishwa kwa ufafanuzi wa coefficient ya 0.778 na 0.868, kwa m2ririko huo.
Introduc4on
Zanzibar is part of one of the world’s major biodiversity hotspots. The Zanzibar archipelago specifically is considered a marine biodiversity hotspot and is home to some of the most pris2ne coral reefs in the world. The Western Indian Ocean (WIO) is home to a variety of aqua2c organisms, from corals to mangroves, to cetaceans. A combina2on of its rich cultural heritage, scenic natural landscapes, and biodiversity makes the Zanzibar archipelago a unique and growing tourist des2na2on among travelers across the world. Tourism inevitably poses some challenges to the preserva2on of the vary en22es which abract tourists in the first place. To adequately address the environmental impacts of tourism, it is important to establish biodiversity datasets as baselines for future comparisons.
Pange sandbar is a rela2vely understudied area of Zanzibar’s coastal waters. Possessing a par2cularly large inter2dal area, the sandbar is an excep2onal loca2on for iden2fying shallowwater echinoderms, of which there are over 440 species in the WIO (Richmond 2002). The primary objec2ve of this research was to record the abundance, distribu2on, and biodiversity of sea urchins, starfish, and sea cucumbers in the inter2dal area of Pange Sandbar. In addi2on to recording these three types of echinoderms, ad-hoc observa2ons were also noted regarding pollu2on, anchor damage, or anything else of significance that may serve as important evidence for how the ecosystem is being affected by human ac2vi2es. Protec2on of Pange Sandbar is detailed under the CHABAMCA General Management Plan, but enforcement is not consistent. Enforcing the protec2on of Pange and the areas around it may seem more worthwhile if research can prove that the area contains robust biodiversity. An intended impact of this study is to mo2vate tourist companies that use the sandbar to develop cleaner prac2ces that may
lessen their impact on the ecosystem Instead of marke2ng Pange for its white sand and blue water, its biodiversity and related educa2on could poten2ally become a major focus of tourist companies
Background
The United Republic of Tanzania is on the eastern coast of Africa and is bordered by Kenya to its north, and Mozambique to the south. The Zanzibar archipelago is situated approximately 25 kilometers from the coast of Tanzania, in the Indian Ocean, at approximately 6 degrees south of the equator. The two major islands of Zanzibar’s archipelago are Unguja and Pemba, with a combined popula2on totaling nearly 3 million (The United Republic of Tanzania 2022). Pange Sandbar is located approximately 3.39 kilometers off the western coast of Stone Town, Unguja. Although uninhabited, Pange, popularly marketed as “Nakupenda”, hosts anywhere from 800-1000 people each day during the high tourism season. These tourism excursions ojen include a seafood meal that is served in single-use plas2c or metal containers and eaten with plas2c utensils. According to Trip Advisor, a “Nakupenda Beach Day Tour” includes, along with food, soj drinks, and bobled water, as well as alcoholic drinks available for purchase (Trip Advisor 2022). Each of these items produces waste that was evident when I first visited Pange on February 18, 2023. Satellite images from Google Earth Pro provide evidence that the sandbar has hosted human ac2vi2es as early as March of 2002, and that visita2on to the sandbar has increased since then. Pange consists almost en2rely of sand, with some large rock forma2ons that become exposed during low 2de. Pange is uninhabited due to its small size
and its dynamic nature. The sandbar is constantly changing shape and size both daily, due to 2des, and annually due to erosion and natural geological and hydrological processes. Pange’s exposed por2on is about 670 meters long but varies depending on the 2dal circumstance. Generally, neap 2des provide the least varia2on between high and low 2des, and occur every two weeks, where Spring 2des produce the highest varia2on between high and low 2des, and hence provide the lowest of low 2des which are ideal for conduc2ng research in inter2dal areas. The shallow inter2dal area of the sandbar’s southern side extends as much as 780 meters south of the exposed sand slope and extends over 1200 meters along the island from east to west.
Pange sandbar lies within the Changuu-Bawe Marine Conserva2on Area, or CHABAMCA. The protected area contains approximately 118 square kilometers and was originally declared as conserved in 1988 (Figure 1) Objec2ves of the CHABAMCA General Management Plan include establishing research, educa2ng the public, providing economic jus2fica2on for the u2liza2on of scarce resources, management improvements, and conserva2on. The CHABAMCA determines resource values based on four categories: biodiversity, scenic, socio-economic, and cultural.
Within the CHABAMCA management plan Pange is recognized as having scenic value, a high percentage of coral cover, as well as being a common roos2ng site for seabirds. The CHABAMCA highlights poten2al problems that stem from tourism at Pange, ci2ng coral damage from anchors and humans, as well as libering and disturbing na2ve fish and bird popula2ons (Richmond 2020). According to tour operators, the prevalence of sea urchins due to the overfishing of their natural predators is a main complaint from tourists who visit Pange. The CHABAMCA proposal declared Pange a No Take Zone (NTZ) and provided a list of ac2vi2es prohibited in all zones of the CHABAMCA (Richmond 2020). An important factor to consider is
how adequate funding may be achieved to ini2ate and sustain the protec2ve measures proposed by the CHABAMCA. The organiza2on acknowledged this reality in their proposal.
Figure 1. The Changuu-Bawe Marine Conserva2on Area (depicted in central hatched area) (Richmond 2020: 6).
A key concept examined in this study is “species biodiversity ”, specifically that of echinoderms within Pange’s inter2dal areas. Biodiversity can range from small-scale gene2c diversity to ecosystem diversity on a much larger scale. Understanding species biodiversity in a par2cular area entails the systema2c recording of which species are observed (species richness), as well as the number of individuals spobed of each species (abundance). Several indices may
be used to quan2fy the biodiversity of a system. The Shannon and Simpson biodiversity indices are the most used formulas that combine species richness and abundance (Morris 2014).
Species biodiversity is incredibly important to the health of ecological systems, and greater biodiversity can create greater resistance in ecosystems to stresses and impacts.
Phylum Echinodermata, rela2ng to the Greek phrase for “spiny skinned”, consists of six living classes, three of which are examined in this study: Echinoidea (sea urchins), Holothuroidea (sea cucumbers), and Asteroidea (starfish). The remaining three classes are Ophiuroidea, Crinoidea, and Concentricycloidea, consis2ng of briblestars, featherstars and allies, and sea daisies. These three classes tend to be harder to record accurately due to their small size and their tendency to nestle into deep crevices. For these reasons, the echinoderms of primary focus in this survey are sea urchins, sea cucumbers, and starfish. Echinoderms are en2rely aqua2c, and are characterized by their radial symmetry, internal calci2c skeleton, as well as their hydraulic vascular systems (Richmond 2002, Amemiya et al. 2005)
Sea urchins, of which there are an es2mated 60 species found in the WIO, can be dis2nguished by their circular shape, and can be flabened or bulbous. The two main types of urchins are regular and irregular, the former having large spikes that extend from the organism at right angles from its skeleton, and the later having thinner, more irregular, hair-like spikes.
Between their spines are small pedicellariae, which can serve protec2ve or hygienic func2ons.
In all urchins, the mouth is contained on the underside of the body and is used for feeding, most commonly with a toothed apparatus called the Aristotle’s Lantern (Richmond 2002). The presence of sea urchins is significant when determining the health of the ecosystem due to its indica2on of overfishing and excessive eutrophica2on (Rowe, Richmond 2004).
Sea cucumbers are soj and long bodied, contain no limbs, and instead have an anterior mouth with 10-30 tentacles used for feeding. A common defense mechanism of sea cucumbers is the release of their long and s2cky Cuvierian tubules, which can easily trap and immobilize predators (Byern & Grunwald 2010). The small building-blocks of a sea cucumber’s internal skeleton are called holothurian ossicles, which are embedded in their dermis layer. Ossicles can have varying shapes and distribu2ons depending on the species of sea cucumber and can only be properly examined when extracted from body the wall by soaking in bleach and then examined under microscope. Approximately 140 species of sea cucumber can be found in the inter2dal waters of the WIO (Richmond 2002)
Starfish generally have 5 arms, some2mes more, extending from the center of their bodies. In the center of their bodies lies most of their major organs, where their undersides contain their mouths through which they consume food through a wide range of feeding strategies. The upper, aboral surface usually contains the anus, and at least one madreporite, which starfish use to maintain seawater reten2on in their water-vascular systems. Unlike urchins, starfish have sessile pedicellariae but are s2ll used for similar cleaning and defensive func2ons.
Types of substrates that may be seen within Pange’s inter2dal area include seagrass beds, rubble/sandy substrate, as well as coral and sponge-covered rocks. Other marine invertebrates that may be encountered at Pange include the following phyla: Mollusca, Crustacea, Nematoda, Annelida, Platyhelminthes, Porifera, and Cnidaria. On our first visit to Pange sandbar as a group, we encountered a rare sea hare called Umbraculum umbraculum, as well as the more common Dolabella Auricularia. We also saw a beau2ful nudibranch species called Phyllidia (fryeria) marindica.
Methodology
Tidal circumstances largely dictated the days in which echinoderms could be surveyed in the inter2dal. The 28-day research period began on Thursday, April 6th , during a spring 2de cycle, with low 2des of 0.30m and 0.23m at 10:28am and 10:47pm, respec2vely. During the research period, only 11 days had low-enough 2des that occurred during reasonable daylight hours; ajer sunrise and at least three hours before sunset. Days with low-2de water-depths over 0.5m were considered inadequate for survey due to considerable challenges with visibility, naviga2ng through deeper water with measuring tools, and keeping important gear dry. Tidal processes also affected the window of 2me where water level was adequate, with water being low enough for an average window of about 3 hours each day.
The predetermined method of survey for this study was to create transects and examine quadrats every 25 meters along each transect. The first of the 11 days was used for planning and prac2cing methods. The tools used on the first day included a 1x1m square quadrat with gridlines, a 30m measuring tape, species iden2fica2on guides, and a notebook for recording. On April 6th, I arrived on the Northeastern side of Pange and walked over to the southern side to examine shoreline features and determine a star2ng point for my first transect. A preliminary transect of 150 meters was examined with quadrats placed in 25-meter increments, totaling 7 quadrats. For each quadrat placed, the echinoderm species observed as well as the number of individuals for each species was to be recorded along with the substrate type. Only one specimen was recorded within the en2re first transect, a single Protoreaster lincki found at 0 meters It was quickly determined that the quadrat method would not provide an accurate
representa2on of the biodiversity at Pange, as only 1 square meter for every 25 meters of transect was being analyzed using this method
A more con2nuous and robust data-collec2on strategy using the T-bar/belt method was adopted for the remaining ten days. For this method, the quadrat was replaced by a T-bar, which is essen2ally a meter-long plas2c rod with a handle that protrudes perpendicularly from the center of the rod. When used properly, this method allows a transect to be analyzed con2nuously from start-to finish over an area equaling 1 square meter x the length of the transect. Substrate type is recorded at the beginning of each transect and at each subsequent change in substrate. The belt-method required a slightly different procedure, where each transect was measured in 20-30 meter segments and the tape was weighed down by a rock placed every 10 meters or fewer depending on the force of current. Once the measuring tape was laid out, straightened, and stabilized, I walked along the line holding the T-bar so that the measuring tape was in the center of my field of view and perpendicular to the bar above it, where .5 meters on either side of the tape lay under the bar. Every starfish, sea urchin, and sea cucumber within the zone underneath the t-bar, including any individuals that were within a foot outside of the transect were recorded. The decision to include individuals that were just outside of the T-bar is due to the varia2ons in current and visibility that made it impossible to precisely determine the boundaries of each transect. Each species observed was assigned an acronym to represent its scien2fic name.
Ten transects in total were successfully completed using the T-bar method, covering a total area of 2,140 square meters (Figure 2). The average transect was 214m long with lengths differing immensely due to constraints from weather, 2me, current, 2des, and equipment.
Transects were placed 53.3 meters apart from each other on average. In order to keep transects straight and perpendicular to shore, two points of reference were used for each transect, one on shore and one on the horizon When running each transect, staying aligned in between the two predetermined points ensured that the transect was as straight as possible and not curving to the east of west.
Transect J, the first of ten transects, was completed on May 7th, using the belt method
Transect J was located on the far east end of the sandbar and spanned 120 meters south of its origin point. See table 1 (appendix) for the lengths of each transect and their dates of comple2on. Ajer collec2ng data from all 10 transects, the Shannon biodiversity index was used to calculate the species diversity using the following formula:
To simplify analysis of the zona2on of organisms, the observa2on area was divided into 18 different zones, represen2ng distances in 20m increments from a common star2ng line along the shore, where each transect originated from. The zone closest to shore was zone 1, represen2ng 0-20 meters, and the zone farthest from shore was zone 18, represen2ng 261-360 meters from shore. The longest transect completed, transect E, contained all 18 zones, 360 meters total, whereas shorter transects contained as few as only 6 zones, or 120m Some zones were surveyed more ojen than others, leading to an uneven number of replica2ons among zones. See table 2 (appendix) for detailed informa2on on each zone.
The differences in number of replica2ons per zone was accounted for when zona2on data was analyzed To provide an average number of organisms per zone, data from each zone was divided by the number of 2mes the zone was replicated For example, zone 1, at 0-20m, was included in 7 different transects, so the total number of organisms recorded within zone 1, 113, was divided by 7, to get an average of 16.14 organisms All data sets from each zone were averaged using this method. From these averages, conclusions were drawn that reflected evidence of echinoderm zona2on.
As an American performing research in Zanzibar, an important considera2on when conduc2ng this study was ethics Because much wealth comes to Zanzibar through tourism and the exploita2on of its natural beauty; many people rely on business opportuni2es centered around tourist abrac2ons like Pange, thus it is extremely important to consider how to facilitate environmental protec2on at Pange, if needed, in a way that protects not only the ecological community, but the human lives which depend on it
Performing a study in a natural environment inevitably comes with risks of damaging the ecosystem. When recording echinoderms at Pange within the delicate inter2dal area for extended periods of 2me, organisms and the overall ecosystem become vulnerable to being stepped on or disturbed. With appropriate planning and aben2on, as well as being careful, unnecessary disturbances were avoided as much as possible. When formula2ng poten2al solu2ons from research outcomes, deep considera2on was paid to any poten2al impacts that conclusions may have on local communi2es. Because this study was taking place in a primarily Swahili-speaking environment, the paper may not be accessible to the people it could impact
the most. A Swahili abstract was developed ajer the end of research, to increase opportuni2es for the public to engage with the literature.
Results
Throughout the ten transects examined over an area of 2,140 square meters, 2,812 individual echinoderms were recorded belonging to 23 different species. Of all echinoderms observed, 94.77% belonged to the class Echinoidea, of which 12 different species were recorded.
Approximately 5.05% of echinoderms were of the class Asteroidea, in which 7 different species were observed. Holothuroidea sigh2ngs of 4 different species cons2tuted a mere 0.18% of echinoderm observa2ons. Images of all observed echinoderm species are featured in Appendix B, species 1-23, or on page 19. Detailed in Table 1 is a breakdown of the 23 echinoderm species that were observed, and their quan22es:
Table 1. Species informa2on
Acronym Scien,fic Name Sigh,ngs Physical Descrip,on
Substrate Echinoidea
DS Diadema setosum 2,047 Black with long, thin needle-like spines. Conspicuous orange and blue anus O@en found in large clusters
EM Echinometra mathaei 460 Black to dark red or purple, or occasionally pale. Medium-length pointed spines
LE Lovenia elongata 53 Light pink to purple heart-shaped, irregular urchin. Short, furry spines that angle backwards with fewer longer, banded spines.
DSa Diadema savignyi 34 Shape and size like DS. Has bright blue paOern radiaLng from body surface Lacking conspicuous anus
TG Tripneustes gra8lla 32 Cake urchin/collector urchin: short, light-colored spines. O@en found covered in rubble and seagrass debris
EC Echinothrix calamaris 12 Long, thin spines, most banded. Anus grey with Lny black and white dots
Sand, rubble, nestled into rock crevices
Sand, rubble, crevices
Rubble, sand, buried to parLally buried
Sand, rubble, crevices
Seagrass patches
Rock surfaces, rubble
MS Metalia sternalis 10
Like LE, but with uniform, short, hairlike spines, and 5 obvious petals
Rubble, sand, buried to parLally buried
TP Toxopneustes pileolus 5 Like TG, but with poisonous flower-like pedicellariae that extend when submerged Seagrass patches
BL Brissus latecarinatus 4 Like MS, but ovular, and with 4 petals Sand
ED Echinothrix diadema 3 Like EC, but without conspicuous anus Spines can have neon-blue or green hue towards base
Esp* Echinothrix species 3
EMe Eucidaris metularia 2
Asteroidea
Like EC, but anus is concaved and appears as a hole in apical area
Small. Medium-length, blunt, brown and white banded spines Bare apical area with pentagonal paOern
LiM Linckia mul8fora 42 MoOled base tones of orange and brown, speckled with purple, brown, magenta, or grey dots. Arm Lps o@en Lnted blue-grey. O@en found with varying arm lengths due to regeneraLon.
PT Pentaceraster tuberculatus 37 Covered in spines, usually with 5 disLnct spines at center, and spines around edges of arms.
LiL Linckia laevigata 22 Similar in shape but slightly thicker than LiM Mostly solid-colored royal blue, or lighter blue and orange.
PL Protoreaster lincki 22
DisLncLve knobby starfish like PT. Always bright with red or orange spines on top of grey to white body.
PM Pentaceraster mammillatus 11 Like PT, but central spots are less conspicuous and blend in with numerous other spines that appear in rows all over the arms and body
LM Luidia maculata 6 Large starfish with 7 tapering arms. MoOled brown, beige, white, and black. Arm edges lined with small, white spines.
Lsp* Linckia species 2 Like LiM, but orange base color is densely covered in red dots. Arm Lps are black.
Holothuroidea
HA Holothuria atra 2 Cucumber-sized. Black, o@en covered in fine coaLng of sand with some bare patches
HP Holothuria pervicax 1 Smaller body with base moOled base of brown, white, grey, and black. ScaOered papillae with rings around each one, like targets. May have Cuvierian tubules ejected.
Sand, rubble
Rock surfaces, rubble
Rock crevices
Rock surfaces
Sand, light to dense seagrass
Rubble, seagrass
Rubble, seagrass
Sand, light to dense seagrass
Sand, parLally buried
Rock surfaces
Sand & seagrass
Underneath rocks, within crevices
AM Ac8nopyga miliaris 1
BV Bohadschia vi8ensis 1
Pickle-sized. Black with fine papillae that appear as small bumps. Orange/red anus. May have Cuvierian tubules ejected.
Thick, loaf-like body. Pale yellow or beige with small, darker papillae May have Cuvierian tubules ejected.
Rubble, crevices
Buried in sand
Substrates men2oned in the right-most column of table 1 are es2mated and averaged.
Figure 3 presents a graphic display of the rela2ve abundances of each echinoderm species, where the overwhelming abundance of urchins, specifically Diadema setosum, is evident.
Figure 3. Pie chart depic2ng the propor2ons of each echinoderm species with sea cucumbers to the middle lej, starfish in the lower lej, and urchin species on the right.
As shown above, a major propor2on of Pange’s echinoderms belonged to species Diadema setosum and Echinometra mathaei Barely visible is the propor2on of Sea cucumbers on the lej side of the figure. Poten2al reasons for so few Holothuroidea sigh2ngs are discussed in the conclusion.
One species of the three types of echinoderms observed is shown in figures 4-6 Because of its major presence at Pange, the Diadema setosum was chosen as a representa2ve for the class echinoidea (Figure 4). Linckia mul>fora was chosen to represent the Asteroidea class due to its varia2on in many of its features, including color and pabern, number of madreporites, as well as the number and size of their arms (Figure 5 & Appendix B species 13) The Bohadschia vi>ensis individual that was observed in transect G showed expelled Cuvierian tubules, which are a unique defensive feature of some species of sea cucumbers (Figure 6)
In addi2on to these three representa2ves, photos of all 23 observed echinoderm species are included in Appendix B.
On average, zones farther from shore contained more echinoderms than those closer to shore. A posi2ve rela2onship between zone and number of individuals recorded was evident when echinoderm data from all transects were weighted and assessed Zones 16-18 contained the most echinoderms with an average of 156 per replica2on, an increase of more than 3-fold from the average of 50.7 echinoderms in zones 13-15 (Figure 7)
Echinoderms per Zone (weighted)
Total Diadema setosum
Adjusted # of individuals
Figure 7 Weighted comparison between total Diadema setosum individuals and the number of total echinoderm individuals per zone Diadema setosum individuals are clearly more abundant farther away from shore. This trend closely aligns with that of the total echinoderms per zone, showing how much the presence of DS contributes to the total number of echinoderms observed. An interes2ng discrepancy to note is how the rela2onship between the zone and number of echinoderms changed quite dras2cally with the exclusion of DS data (Figure 8).
Non-DS echinoderms per Zone (weighted)
Adjusted # of nonDS echinoderms
Figure 8 Weighted number of echinoderm individuals per zone, excluding Diadema setosum
Similar to the peak in the blue line at zone 13 in figure 7, a sharp increase can be seen in the number of non-DS echinoderms in zone 13 This larger number of echinoderms in zone 13 appears to be anomaly and is examined in greater detail within the discussion sec2on. Besides the anomaly of zone 13, it appears that when DS were not included in echinoderm sums per zone, a posi2ve rela2onship between the zone and number of echinoderm individuals was much less apparent This discovery can be related to the trend depicted in figure 7, where it is evident that DS are more prevalent in zones farther from shore. An observa2on that is important to note is that large DS clusters were rarely seen sharing space with other organisms, that is, once DS coverage became very dense, in zones 16-18, other urchins and starfish were only seen outside of the dense clusters Some2mes clusters were so dense and plen2ful that no other organisms were visible in the area.
Species biodiversity was analyzed for the en2re dataset using the Shannon biodiversity index which, resulted in a value of 1.0353.
When analyzing the data as a whole, zones with the greatest species diversity were difficult to pinpoint, as replica2ons among zones differed vastly. However, there was no apparent correla2on between the number of replica2ons and the number of species recorded per zone, with a low correla2on coefficient of 0.277. Despite there being low correla2on between the two variables, the longest transect, E, was chosen to exemplify data trends across all zones to avoid the need to account for inconsistencies in zone replica2ons.
Transect E showcased a posi2ve rela2onship between the zone and number of species present. On average, zones further from shore contained a greater variety of species than zones
closer to shore This conclusion is substan2ated by a strong correla2on coefficient of 0.868 between the two variables (Figure 9)
Species # per Zone Transect E
Figure 9. Number of species observed per zone within transect E
Transect E was also useful in determining substrate zona2on. Zones 1-9 were predominately rubble, with sec2ons 10-13 being predominately sand with some seagrass, and zones 14-19 consisted mostly of coral rubble and sand, with some larger rocks with sponge and coral growths. This is consistent with the prevalence of DS being heavily concentrated towards the zones further from shore, as DS were rarely seen inhabi2ng areas with a large propor2on of seagrass.
The most prevalent starfish species was the Linckia mul>fora, LiM, in which 42 individuals were seen across all transects. Weighted averages of LiM densi2es per zone were calculated and no strong evidence of zona2on was present. A correla2on test resulted in a low coefficient of 0.284. LiM were ojen found with some of their arms tucked and folded into rock crevices. Some2mes individuals were found as only a single arm, with 4-5 other budding arms
undergoing regenera2on (Figure 5 & Appendix B, species 13) An ill LiM individual was observed in Quadrat B in the middle of zone 12 Three of the specimen’s five arms were afflicted with an ailment that was similar in appearance to mold. One of the afflicted arms was longer, with a bleach-white 2p, that looked completely dead and ready to fall off. In the center of the starfish there appeared to be tumor-like growths that extended from the afflicted arms (Appendix C, observa2on 3) Other Linckia species were observed, such as the Linckia laevigata, and an unknown species presumed to be of the Linckia genus, which was labelled Linkia species (Lsp). The two Lsp individuals that were observed were in shallow zones of transects B and C. Each specimen was similar in shape and form as the other Linckia species, but with a different color and pabern, as well as dis2nct, black-2pped arms (Appendix B, species 19)
A second uniden2fied species was specified as belonging to the Echinothrix genus, and hence was named Echinothrix sp Only three Esp individuals were sighted in zones 1, 11, and 10, making it difficult to determine any zona2on trends. Esp looked like the Echinothrix calamaris, but did not have a visible anus, which instead appeared to be concave, like a hole in its aboral surface (Appendix B, species 11)
Ad-hoc observa2ons were recorded informally on an as-needed basis. Some less common organisms that were observed within transects were recorded and their images can be seen in the appendix. Evidence of human ac2vity was also recorded when significant. Waste items such as plas2c plates and utensils were seen, as well as a sweater and a boble of body spray (Appendix C, Observa2ons 5-7).
Discussion
Within the study period, a significant amount of echinoderm individuals and biodiversity were recorded at Pange. At nearly 3,000 individuals, the 2,812 echinoderms recorded is an impressive sum considering the total area surveyed was only 2,140 square meters. This expansive dataset allowed for in-depth analysis of trends among individual species, as well as trends between zones and transects. The Shannon biodiversity index value of 1.0353 indicated good biodiversity of the system. As demonstrated in figure 3, however, species evenness was heavily skewed, with almost ¾ of individuals being DS, and much smaller rela2ve propor2ons of other species, with sigh2ngs of several species being less than 3 individuals across all transects.
In general, data collected shows that zones farther from shore contained more echinoderm individuals. However, this finding seems to be almost en2rely due to a greater presence of Diadema setosum, which was by far the most abundant echinoderm observed at Pange sandbar, making up 72.8% of all echinoderm sigh2ngs. When Diadema setosum data is disregarded, the posi2ve correla2on between echinoderm density and distance from shore nearly diminished.
From this we can conclude that zona2on plays less of a role in overall echinoderm density than it plays specifically for the DS species. Perhaps if species were more evenly populated at Pange, zona2on of other species would be as clear as that of Diadema setosum. When the anomaly of zone 13’s abnormally large non-DS echinoderm density is overlooked, no obvious rela2onship was seen between echinoderm popula2on density and distance from shore. Upon closer examina2on of the data, it appears that several unusually large clusters of Echinometra mathaei were recorded in zone 13 of transect D Echinometra mathaei may have proliferated in that area due to several circumstances, such as a lack of strong current in the area due to nearby
protec2ve rock forma2ons, or a localized algal bloom that provided a substan2al food source.
The large grouping of EM individuals also may have occurred by chance.
The large presence of DS has occurred unlikely due to chance, but instead may be an indica2on of poor ecosystem health. DS tend to be found in coral rubble areas, grazing on algae from dead or weakened corals. The Diadema setosum popula2on at Pange is clearly thriving, which may be due to direct human impacts such as overfishing of their natural predators in the region, or indirect human impacts such as climate change affec2ng aqua2c ecosystem stability (Öndes et. Al 2022).
Diadema setosum was observed in large clusters of up to 50 individuals. The species is very capable of prolifera2ng and taking over large areas (Appendix C, observa2on 2). Areas heavily populated by DS should be closely monitored, as popula2ons may grow exponen2ally quickly and begin to interfere with spaces inhabited by other species Because DS clusters take up a significant amount of space with their long needles, other organisms are rarely seen occupying the same space. If DS con2nues to proliferate at Pange, the effects may be seen in future census data, not only effec2ng echinoderm popula2ons, but those of other inter2dal organisms
Linckia mul>fora individuals were always exci2ng sigh2ngs. The varia2on between individuals in terms of colora2on, stage of life, and substrate abachment was ojen vast. These differences in individuals some2mes made iden2fica2on difficult or incomplete. Linckia species overall tended to be a difficult genus to iden2fy species due to limited in-depth research on Linckia starfish species and their characteris2cs. The unknown Linckia species, Lsp, was iden2fied as a separate species because its unique color pabern and arm 2ps.
The unknown echinothrix species sigh2ngs could have been of sick individuals belonging to Echinothrix calamaris or diadema Or, they poten2ally could have been performing an unknown behavior involving the anus form and inver2ng temporarily. Whether or not these theories are true could poten2ally be proven from the images taken of individuals (Appendix B, species 11).
Transect E proved to be a significant transect due to its length. The transect exemplified species richness as related to zone/distance from shore, as well as trends in substrate zona2on. However, because transect E was the longest transect by far, zones 16-18 each had only one replica2on More replica2ons of these far transects undoubtably would have increased the validity of data collected from these zones. Thus, a recommenda2on for future studies would be to keep transect lengths consistent or focus on a smaller number of zones at a 2me to narrow the focus of the survey.
Though the specific defining factor between different zones is distance from shore, a closely correlated factor is water depth, which increased gradually as the zones moved further from shore. Another factor that differen2ated zones was the substrate, with zones closer to shore consis2ng of mostly rubble, whereas seagrass concentra2on was generally more abundant in the middle zones. It is unknown whether organisms that showed zona2on preferences were favoring par2cular zones due to water depth, substrate type, distance from shore, or a combina2on of mul2ple factors. However, in a very informal observa2on in the case of the Diadema setosum, individuals observed in very shallow water, less than two inches, always seemed to be struggling. Their spines would flaben, and they seemed to be using moving their spines as much as they could, as if using all of their energy to locate deeper water.
Another variable to consider from the data is zona2on along the shore, from east to west. Factors affec2ng this variable may include currents, coastal erosion, and the geography of the area. As seen in figure 2, rock forma2ons differed between transects. For certain species that preferred rocky substrates, such as EM, a preference for rockier regions of Pange’s inter2dal area may be evident, however making the determina2on is difficult, as data is not con2nuous from east to west due to the spacings between transects.
Shortcomings of this experiment that can be improved upon in the future include the precision of marking transects and their loca2ons. GPS determina2ons were imprecise, and therefore figure 2 features only a rough es2mate, at best, of where exactly each transect was placed in rela2onship to shore as well as in rela2onship to surrounding transects. Another difficulty in determining precise loca2ons was the use of the measuring tape, that would blow with the current and make it difficult to keep transects in straight lines. Improvement on methods occurred gradually over the course of the study, perhaps making certain transects more or less accurate than others.
Visibility is also a factor to consider, which differed greatly based on weather and 2dal condi2ons. Some days were rainy, and the water surface was much less clear. On these days, transects were either cut short, or abandoned en2rely. Visibility was also made difficult when the 2de was not at its lowest or within a two to three-hour range around each low 2de. Even though more 2me was spent looking for echinoderms when visibility was poor, some organisms, such as Lovenia elongata, which tends to be buried in the sand, may have been overlooked. Species like LE that are generally less conspicuous may have been overlooked even when visibility was ideal. Other organisms that were less conspicuous included Metalia sternalis,
Luidia maculata, and Eucidaris metularia, each inconspicuous in for different reasons. MS was difficult to spot because it was ojen buried in the sand, or otherwise sand colored LM, although large and conspicuous, was also commonly found buried under a thin layer of sand. EMe was a smaller organism, and lived on rocks and within crevices, ojen tucked underneath overhangs The only 2mes EMe was observed was when a rock was moved or flipped, or when a transect was looked over for a second 2me, which did not always occur.
The extremely small propor2on of sea cucumber spoungs may have been due to their generally inconspicuous presenta2on. The two Holothuria atra species individuals were mostly covered in a thin layer of sand (Appendix B, species 20) Bohadschia vi>ensis was only spobed because its Cuvierian tubules were ejected (Figure 6 & Appendix B, species 23). The rest of the animal was completely buried under the sand. The Holothuria pervicax was on the underside of a rock that was lijed in order to get a beber look at an urchin inside of a crevice. Most of these sea cucumber sigh2ngs occurred by chance, and therefore should be considered only a small propor2on of what could have been seen, had methods been more thorough
One of the most conspicuous organisms observed was, of course, the Diadema setosum, with its long, thin spines that s2ck out of crevices, and its bright blue and orange anus. However, the bright anus was not as helpful for spoung the organism as it was for iden2fying it. Some organisms were less obvious or conspicuous in their appearance, leading to discrepancies in determining the species. Linckia mul>fora, for example, was frequently found as a singular limb, without most of the body present for iden2fica2on. Even when the en2re individual was present, a lack of consistency was observed in the number of legs, as well as the number of madreporites. These two factors are supposed to be key iden2fiers, as according to Mabhew
Richmond’s A Field Guide to the Seashores of Eastern Africa and the Western Indian Ocean Islands, 2011 According to the field guide LiM individuals should have two madreporites on their aboral surface. However, a substan2al number of individuals recorded did not have two madreporites that were clearly visible. Either the organism had only one obvious madreporite, the madreporites were indis2nguishable against the colored dot pabern, or in some cases both madreporites were clearly visible (Appendix B, species 13).
Although it is unlikely that any individuals recorded as LiM were another species en2rely, it is important to consider that misiden2fica2on was possible, and can contribute to skewed data. Not only was LiM difficult to iden2fy with certainty, but Brissus latecarinatus was ojen confused with and recorded incorrectly as Metalia sternalis Before the first BL individual was properly iden2fied as a new species of the survey in zone 1 of transect A, individuals previously recorded that were, in fact, BL, were thought to be MS. It was only when photos were reviewed that these falsely iden2fied specimens were BL, not MS. The issue that arises is that not every specimen collected was photographed. For most observa2ons, only the species name was recorded if I was completely certain of my observa2on. Due to human error and the inability to look back at observa2ons to re-assess iden2fica2ons, some species may have been misiden2fied. In transect E, a Pentaceraster tuberculatus was seen consuming what was first recorded as an MS individual, but upon closer examina2on was determined to be a BL. This figure also displays an interes2ng interac2on between the two organisms, which is not frequently recorded (Appendix C, observa2on 4).
Conclusion
The biodiversity at Pange sandbar is undoubtably vast, but only 2me will tell whether the ecosystem will maintain its rich biodiversity through the coming years, especially as climate change effects increase, and human pressures on ocean ecosystems become greater. Because this study is one of the first of its kind at Pange, the basic census and zona2on data may serve as a benchmark for future studies. Mul2ple conclusions from this survey could be elaborated on in future experiments. The large presence of Diadema setosum could be an early indicator for an ecosystem at risk, but more robust research is needed to confirm the validity of this argument.
The importance of recording abundance, distribu2on, and biodiversity of any group of animals in an ecosystem can have impacts that extend far into the future. On a local level, where Pange’s echinoderm diversity could abract members of the community to the sandbar, as well as form a basis for which educa2onal programs may develop. The establishment of baseline data for echinoderms in this study has the poten2al to be replicated or expanded in countless ways to build a broader understanding of Stone Town Harbor’s threatened ecosystems. Without immediate ac2on, the future of Zanzibar ’s coastal ecosystems and the lives of those who depend on them will be at stake. If Pange can become equally appreciated for its ecological value as it is for its scenic and commercial values, then it may seem more worthwhile to incorporate protec2ve measures to ensure Pange’s longevity.
Recommenda4ons
The large gap in Holothuroidea data can be filled by future studies that examine sec2ons of the inter2dal much more closely in ways such as peering under rocks and examining
substrates closely for evidence of buried sea cucumbers Unfortunately, these methods could cause disturbances to the ecosystem and therefore should be used carefully.
Because the longest transect extended only 360 meters from shore, a large por2on of the inter2dal area remains unstudied Even along shorter sec2ons of the inter2dal zone, 300+ addi2onal meters can be explored all the way to the southern edge of the inter2dal. If the posi2ve correla2on between species diversity and distance from shore con2nues to be supported as data is collected farther out, many more species may be catalogued.
One of the most data-sufficient conclusions made was that DS is incredibly abundant.
Factors that contribute to the abundance of DS can be determined through more extensive survey of Pange’s inter2dal areas that extend even further out than was covered in this study. In addi2on to understanding why DS is so abundant and what can be done to control the popula2on, research that compares the rela2onship between popula2on density of Diadema setosum and echinoderm species biodiversity may provide valuable insight into the effects of DS popula2ons on the greater ecological community. It is not yet known why, or how quickly, if at all, DS popula2ons are expanding, and what the possible repercussions would be for a popula2on explosion of Diadema setosum
This study and similar studies in the future can help emphasize the significance of conserva2on and incen2vize improvements of exis2ng conserva2on strategies. The sooner these studies are conducted, the sooner solu2ons to tourism impacts and environmental issues in Zanzibar can be determined and implemented.
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