Temby 1 Factors That Limit Establishment of Stony Corals Michelle C. Temby Department of Integrative Biology, College of Letters and Sciences University of California Berkeley EAP Tropical Biology and Conservation Spring 2019 7 June 2019 ______________________________________________________________________________ ABSTRACT C orals occupy less than 1% of the surface area of world oceans but provide a home for 25% of all marine fish species. Nevertheless, corals do not get the attention the y deserve in terms of their success as organisms. In my study, I analyze individual coral heads, specifically the genus Pocillopora (tentative identification: Pocillopora elegans ), and their establishments in Cuajiniquil using 3 locations in Guanacaste, Co sta Rica to understand why coral reefs are not establishing at some sites. These sites occur at Bajo Rojo, BahÂ’a Thomas West, and Isla David. I recorded the size of establishing coral heads, the surrounding water temperature where each coral head occurred, the urchin cover in a 30cm radius of each coral head, the bleaching of each individual coral head, the substrate the coral was establishing on, the approximate angle of the substrate, the depth of the coral, and the surge of the water at each site. I foun d several potential factors responsible for the failure of Pocillopora to establish in Cuajiniquil: urchin populations that may compete with corals for substrate, strong surges that may displace larvae, and a range in coral health measured by bleaching obs erved at Isla David and Bajo Rojo. Pocillopora spp . are, however, establishing in larger numbers at BahÂ’a Thomas which may be due to the weak surge, the smaller quantities of urchins, and the good health of individual establishing corals. ______________________________________________________________________________ RESUMEN Los corales ocupan menos del 1% de la superficie de los ocÂŽanos del mundo, pero proporcionan un hogar para el 25% de todas las especies de peces marinos. Sin embargo, los corales no obtienen la atenciÂ—n que merecen en tÂŽrminos de su ÂŽxito como organismos. En mi estudio, analizo cabezas de coral individuales, especÂ’ficamente el gÂŽnero Pocillopora (identificaciÂ—n tentativa: Pocillopora elegans), y sus establecimientos en Cuajiniquil utilizando 3 localidades en Guanacaste, Costa Rica para entender por quÂŽ los arrecifes de coral no son estableciendo en algunos sitios. Estos sitios se encuentran en bajo rojo, BahÂ’a Thomas West e Isla David. GrabÂŽ el tamaÂ–o de establecer cabez as de coral, la temperatura del agua circundante donde se produjo cada cabeza de coral, la cubierta de erizo en un radio de 30 cm de cada cabeza de coral, el blanqueo de cada cabeza de coral individual, el sustrato que el coral estaba estableciendo, el Â‡ng ulo aproximado del sustrato, la profundidad del coral, y la oleada del agua en cada sitio. EncontrÂŽ varios factores potenciales responsables del fracaso de Pocillopora para establecer en Cuajiniquil: poblaciones de erizos que pueden competir con los corale s para el sustrato, fuertes oleadas que pueden desplazar a las larvas, y un rango en la salud medido por el blanqueo observado en Isla David y bajo rojo. Pocillopora spp. son, sin embargo, el establecimiento de arrecifes en BahÂ’a Thomas que pueden deberse a la oleada dÂŽbil, las cantidades mÂ‡s pequeÂ–as de erizos, y la salud del individuo que establece los corales. ________ ______________________________________________________________________
Pocillopora spp. in Cuajiniquil Temby 2 I NTRODUCTION Coral reefs are the most biologically diverse of sh allow water marine ecosystems , yet they are being degraded worldwide by human activities and climate change (Roberts, 2002) . Central American coasts are currently exposed to more pollution, both natural and anthropogenic, than ever before. This has had a devastating effect on most reefs and corals in the tropics. Coral reefs have been deemed the marine equivalent of tropical forests in both diversity and productivity, yet management and conservation of corals are not given the attention they deserve (Guzman, 1991 ) . Stony corals of the world's oceans are divided into two groups: the reef building, or hermatypic corals and the non reef building, or ahermatypic corals. The hermatypic corals are responsible for reef existence. Their success depends on the presence of microscopic algae known as zooxanthellae (Hickman, 2008). Corals have a symbiotic relationship with the colorful zooxanthellae that live in their tissues. When the symbiotic relationship becomes stressed due to increased ocean temperature s or pollution, the algae are expelled from the tissues of the coral. Without the algae, the coral loses its major source of food, turns white or very pale, and is more susceptible to disease ( US Department of Commerce , 2010) During the last few decades, howeve r, severe bleaching events have killed the zooxanthellae of many corals that rely on the microscopic plants for survival. Furthermore, continuous degradation of coral reef habitats is increasing in the eastern Pacific as intense natural disturbance and fre quent human impact devastate corals and reefs of Costa Rica. Surviving individuals for some Pocillopora spp. are extremely small and reef recovery by sexual and asexual means has been significantly reduced (GuzmÂ‡n , 1991). In asexual reproduction within the same colony, the polyps can divide as the coral colony grows (Barnes and Hughes, 1999). Corals can also reproduce asexually when the tips of the branches are broken off. The fragments are distributed by ocean currents and can establish and form a new colo ny at new locations. Corals can reproduce sexually through spawning by releasing buoyant sperm and eggs into the water column. These sperm and eggs are able to fertilize in the water ( Gomez and Pawlak , 2018 ). Recovery of these reefs and establishment of n ew corals in the eastern Pacific are linked to several important biological processes including coral reproduction, availability and location of parent coral populations, dispersal mechanisms, coral predation, and reef framework destruction. My study attem pts to answer the following questions: Why are corals, specifically Pocillopora spp. (tentative identification: Pocillopora elegans ), not establishing in large numbers at some sites in Cuajiniquil? Where are Pocillopora corals establishing prominently in Cuajiniquil? In my study, I examine several hypotheses concerning these questions found in the table below (Table 1). I used a two way ANOVA in JMP to compare variables at three sites. 1. Pocillopora coral in poor health do not grow large enough to create reefs. 2. Sea urchins are so populous in the area that they may be overtaking viable spaces and crevices for establishing corals. 3. The surge at some sites may be too strong compared to others for reefs to form. 4. Substrate for Pocillopora growth may need to be rocky and uneven, but not sandy, for successful coral growth.
Pocillopora spp. in Cuajiniquil Temby 3 5. Extremely shallow depths could lead to a severely bleached or sickly Pocillopora 6. Water temperature that is too warm may prevent Pocillopora reproductive events. 7. Bleach ed Pocillopora coral may prevent reproductive events. 8. Pocillopora corals are not establishing at some sites because larvae are not arriving. Table 1. Eight h ypotheses regarding reasons for fewer coral establishments at some sites. Eight potential hypo theses that could explain the failure of Pocillopora to establish in Cuajiniquil . The potential factors that seem to have the most impact on coral establishment : urchin populations may compete with corals for substrate, strong surges may displace larvae, a nd a range in coral health measured by bleaching may affect some reproduction at Isla David and Bajo Rojo. Pocillopora spp . are, however, establishing in larger numbers at BahÂ’a Thomas which may be due to the weak surge, the smaller quantities of urchins, and the good health of individual establishing corals. MATERIALS AND METHODS The observations included in my study took place from 10 May 2019 to 16 May 2019. I spent a total of 30 hours in the water in those six days and observed and measured over 100 individual corals for the 3 sites. In my study, I analyzed establishing Pocillopora spp. coral heads between 0 20 cm in size. I defined "establishing heads " as individual Pocillopora not connected to any part of another Pocillopora reef or coral. I defined coral coverage as the amount of coral (no matter if it was larger than 20 cm or if it was connected to another Pocillopora reef or coral head) in square m eters in each 30 meter x 2 meter transect (60 square meters). This fraction was then converted into a percentage to be used for results. I surveyed 3 locations in Guanacaste, Costa Rica along the coast of the Santa Elena Peninsula and Cuajiniquil. These si tes included Bajo Rojo, BahÂ’a Thomas West, and Isla David. At Bajo Rojo, I used the leeward exposed side of sedimentary rock for transects 1 through 4. This side contained substrate of mainly rocks affected by bio erosion. On the windward side of the sedim entary rock was one large 40 meter ridge, angled at about 45 degrees that had no corals visible. Both sides of the site had strong surges and the sediment was almost completely underwater. At each site, I found an individual coral head between 0 20 cm in size and placed a weighted tape measure transect 30 meters from the first coral head found (unless coral heads were not found for a transect then the transect was placed randomly ). I then snorkeled along the 30 meter transect and counted the number of sea urchins and coral heads approximately 1 meter on each side of the transect. I measured the size of each coral head and noted the surrounding water temperature (based on my own body temperature change). Temperature was categorized on a scale of 1 (coldest) to 5 (hottest) which was converted into temperature names (1= cold, 2 = cool, 3 = warm cool, 4 = warm, 5 = direct sunlight). I also recorded the urchin cover in a 30 cm radius of the given coral head and assigned a bleach rating on a scale of 1 3 (1 = hea lthy, no bleaching, 2 = some bleaching but zooxanthellae present, 3 = complete bleaching). I then recorded the distance to the next coral head, the distance of the coral head to the shore, and the depth of the coral. I also noted the substrate the coral was on, the approximate angle of the substrate from the horizontal upward from the ocean floo r, and the surge angle of the water at each site. I used a weighted string on a PVC pipe with a protractor to measure the surge
Pocillopora spp. in Cuajiniquil Temby 4 angle (Fig. 1). With the dangled string in the water, I was able to measure the angle at which the surge was dragging it out. Th is measurement served as a proxy for surge strength. Lower angles correlate to weaker surges and higher angles correlate to stronger surges. The highest angle a surge went to was 90 degrees. As part of my study I took photos of each individual coral head. I repeated this entire procedure for 4 transects at each of the 3 site s . Figure 1. Surge angle tool. I used a weighted string on a PVC pipe with a protractor to measure the surge angle. The highest angle a surge went to was 90 degrees. RESULTS Bleach rating vs. size of individual coral head At BahÂ’a Thomas, individual establishing corals ranging in size from 4cm to 20cm mostly had a bleach rating of 1 and few had a bleach rating of 2. None were completely bleached with a bleach rating of 3. At Isla Dav id, an observable visual trend occurred; as size of individual corals increased, bleach rating decreased. The smallest recorded coral at Isla David had a bleach rating of 3 while the largest recorded coral at Isla David had a bleach rating of 1. Corals at Isla David with bleach ratings of 2 occurred at sizes between the smallest and largest corals of Isla David. Finally, at Bajo Rojo, individual establishing corals ranged in size and bleach without following a continuous pattern. The relationship between si ze and bleaching depends on the site (F = 10.9, d.f. = 3, 58, p < 0.0001) (Fig. 2) (Table 2).
Pocillopora spp. in Cuajiniquil Temby 5 Figure 2. Bleach rating vs. size of coral head. The relationship between bleaching and coral head size varied by site. At Isla David, larger corals faced dist inctly less bleaching than smaller corals, compared to Bajo Rojo which had a random distribution and to Bah Â’ a Thomas where bleaching was minimal and appeared unrelated to size. site # transects Avg. # coral heads/transect Standard deviation BR 4 3 1.83 ID 4 1.75 1.5 BT 4 21 9.56 Table 2. Comparison of average number of coral heads per transect for each of the 3 study sites. Four transects were used at each site. This table is helpful for comparing coral occurrence at Bajo Rojo, Isla David, and BahÂ’a Thomas. BahÂ’a Thomas had the most coral heads on average per transect with the largest standard deviation. Percent of coral coverage per transect vs. counted number of urchins per transect The most coral coverage occur red when less than 100 urchins per transect were present. BahÂ’a Thomas sustained coral coverage at a higher percent cover of urchins than the other two sites. At BahÂ’a Thomas, average overall coral coverage was 44.7% and occurred in areas with no more than 350 urchins present in each transect. At Isla David, average overall coral coverage was 3% and occurred in areas of 100 350 urchins. At Bajo Rojo, average overall coral coverage was 4.15% and occurred in areas of 100 200 urchins and 600 800 urchins. The r elationship between urchins and coral coverage also depends on site (F = 8.6, d.f. = 3, 8, p = 0.007) (Fig. 3).
Pocillopora spp. in Cuajiniquil Temby 6 Figure 3. Percent of coral coverage per transect vs. counted number of urchins per transect. Coral coverage is different than the number of coral heads in each transect. Coverage takes into account coral abundance and reef cover if it is available in a transect at a site. The amount of coral coverage is measured by square meters of coral over a 30m x 2m transect. The fraction is then converted into a percentage used in the graph above. Urchin cover is defined as the number of visible urchins I counted over a 30m x 2m transect. I may have missed urchins hidden within crevices of substrates or miscounted urchins crowded together in large quantiti es. Therefore, the number of urchins per transect is an approximation. Total number of coral heads vs. surge angle in degrees per transect More corals were establishing in areas with weak surges. The highest number of individual establishing coral heads o ccurred at BahÂ’a Thomas which had the weakest surge angle of 20 degrees or less. Isla David had surge angles between 35 and 65 degrees, but less than 5 heads occurred per transect. Finally, at Bajo Rojo, the surge was the strongest with an angle between 80 and 90 degrees, and 5 or less heads per transect. At 20 degrees and below, the highest amounts of coral heads were found. Above 35 degrees, less than 5 coral heads per transect were found. The relationship between surge angle and number of establishing c oral heads depends on site (F= 11.67, d.f. = 3, 8, p = 0.0027) (Fig. 4).
Pocillopora spp. in Cuajiniquil Temby 7 Figure 4. Total number of coral heads vs. surge angle in degrees per transect. Some individual coral heads were larger than 20cm in size . It was important to include them in the total number of coral heads per transect to see how well corals were doing overall in different surge strengths. However, those that were much larger than 20cm in size were not counted as "establishing corals" and thus were not included in most other resul ts of the study. Total coral heads for each specific substrate at each of the 3 study sites Finally, I looked at establishing corals and the substrates they occurred on at each site. At BahÂ’a Thomas, most establishing coral heads occurred on sand. BahÂ’a Thomas had more coral heads on multiple rocks, flat rock, sand and rock, and sand than at the other two study sites. At BahÂ’a Thomas, individual coral heads were found on all substrates except for bio erosion rocks. At Isla David, the few establishing coral heads of the site occurred mostly on bio erosion rocks. However, Isla David had fewer coral heads occur (compared to the other 2 sites) on bio erosion rocks, flat rocks, and uneven rock crevices. Individual coral heads at Isla David were only found on bio erosion rocks, flat rocks, and uneven rock crevices. At Bajo Rojo, most establishing coral h eads occurred on bio erosion rocks. More coral heads occurred on uneven rock crevices and bio erosion rocks at Bajo Rojo compared with the other two sites. At Bajo Rojo, establishing corals did not occur on any other substrate other than uneven rock crevic es and bio erosion rocks (Table 3).
Pocillopora spp. in Cuajiniquil Temby 8 Site Substrate BR BT ID uneven rock, crevice 3 1 1 bioerosion rock 8 0 3 multiple rocks 0 13 0 flat rock 0 4 1 on coral 0 1 0 sand and rock 0 8 0 sand and pebbles 0 1 0 sand 0 16 0 Table 3. Total number of coral heads for each specific substrate at each of the 3 study sites. Substrates are ordered from top down by roughest/most uneven to smoothest/most even surfaces. Some individual coral heads were larger than 20cm in size . It was important to include them in the total number of coral heads per transect to see how well corals were doing overall on different substrates. However, those that were much larger than 20cm in size were not counted as "establishing corals" and thus were not included in most other results of the study. Size of individual coral head vs. depth At BahÂ’a T homas, I did not find individual establishing corals deeper than 4 meters. Those that did occur at BahÂ’a Thomas ranged from 4 cm to 20 cm in size. At Bajo Rojo, individual establishing corals occurred between 1.5 and 6 meters and ranged in size from 4 cm t o 20 cm. Isla David had coral heads occur between depths of 2.5 and 4.5 meters and ranged in sizes between 10 to 23cm. Tide was not taken into account with changing depth. I did not find conclusive evidence that coral head size depend ed on the depth at whi ch it was found and no significant interaction between these variables occurred (Table 4). Bleach rating vs. depth At BahÂ’a Thomas, individual corals had bleach ratings of either 1 or 2. No individual corals in the transects used at BahÂ’a Thomas had a bleach rating of 3. At Isla David, individual corals that were establishing between 4 and 5 meters had bleach ratings of both 1 and 3. Individual corals occurring between 2 and 3 meters at Isla David had a bleach rating of either 1 or 2. At Bajo Rojo, the shallowest depth in which I found an establishing coral had the highest bleach rating of 3. In this case only, the bleach rating of 3 meant the coral was sickly. I knew the coral was ailing because it was broken down, lacked a healthy color, and was covere d in algae (Figure 5) . Other individual establishing corals found at Bajo Rojo ranged in both depth and bleach rating. Establishing Pocillopora deeper than 4.5 meters occurred at Bajo Rojo with a bleach rating of 1 or 2; no establishing Pocillopora deeper than 4.5 meters had a bleach rating of 3. Depth was not adjusted for tides. Bleach and depth resulted in a significant interaction that depended on the site (Table 4).
Pocillopora spp. in Cuajiniquil Temby 9 Bleach rating vs. angle of substrate I examined bleach rating vs. the angle of the substrate with respect to the horizontal upwards from the ocean floor for each individual coral head. At BahÂ’a Thomas, only substrate angles of 10 degrees or less occurred. These individual corals on substrates with small angles had bleach ratings of either 1 or 2, none with a bleach rating of 3. At Bajo Rojo specifically, a pattern between angle of substrate and bleach rating did not occur. At Isla David, substrate with angles between 20 to 45 degrees showed an observable visual trend; as substrate angle increase d , bleach rating increase d . This resulted in a significant interaction. However, bleach rating and the angle of substrate may depend on site (Table 4). Bleach rating vs. temperature I analyzed bleach r ating vs. temperature to see the effects of different water temperature on coral health . Temperature was categorized on a scale of 1 to 5 which was converted into temperature names for results (1= cold, 2 = cool, 3 = warm cool, 4 = warm, 5 = direct sunligh t). At BahÂ’a Thomas, individual establishing corals occurred at cold, warm cool, and warm temperatures and only experienced bleach ratings of either a 1 or a 2. Most occurred in cold, warm cool, and warm temperatures with a bleach rating of 1. Three establ ishing corals had a bleach rating of 2 and occurred in warm water. At Isla David, temperatures were either cool or warm. In cool temperatures, the individual establishing corals at this site had a bleach rating of either 1 or 3. In warm waters, the individ ual establishing corals at this site had a bleach rating of either 1 or 2. At Bajo Rojo, a visual trend between temperature and bleach rating occurred; as temperature increase d , bleach rating increased. Depth may also affect these variables . In direct sunl ight, the bleach rating was a 3, which in this case describes a degrading, sickly Pocillopora . Bleaching and temperature at these sites resulted in a significant interaction; bleach rating may depend on temperature, but site may also play a role in the rel ationship between bleaching and temperature (Table 4). Size of individual coral head vs. urchin cover surrounding individual coral head At BahÂ’a Thomas, the largest individual coral head at the site had 0 surrounding urchins. Most individual coral heads at BahÂ’a Thomas ranged in size from 4cm to 20cm and had less than 15 surrounding urchins. At Isla David, individual corals with sizes of 14cm and 15cm were surrounded by 0 to 5 urchins at the time I surveyed them. A t Isla David , i f more than 10 urchins wer e present, as surrounding urchins increased in number, the size of individual establishing corals decreased. At Bajo Rojo, each individual coral, ranging in size from 4cm to 20 cm, occurred when less than 10 urchins surrounded the coral. No significant rel ationship was found between surrounding urchin numbers, coral size, and site location (Table 4). Bleach rating vs. urchin cover surrounding individual coral head At BahÂ’a Thomas, most corals had a bleach rating of 1 and were surrounded by 0 to 25 urchins. Three corals at the site with a bleach rating of 2 had 0 surrounding urchins. No corals at this site had a bleach rating of 3. At Isla David, individual corals with a bleach rating of 1 had 10 to 15 urchins present. Individual establishing corals with a bleach rating of 2 had only 1 urchin present. With 20 surrounding urchins, the establishing coral had a bleach rating of 3. At Bajo Rojo, for all individual coral heads , all bleach ratings occurred with less than 10 surrounding urchins . The relation ship between bleach rating and surrounding urchins depended on the site and resulted in a significant interaction (Table 4).
Pocillopora spp. in Cuajiniquil Temby 10 Size of individual coral head vs. angle of substrate I examined the size of each coral head vs. the angle of the substrate with r espect to the horizontal upwards from the ocean floor for each individual coral head. At BahÂ’a Thomas, only substrate angles of 10 degrees or less occurred in sizes between 4cm to 20cm. At Isla David, a visual trend occurred; as angle of substrate increase d, size of individual coral head decreased. At Bajo Rojo, no clear pattern occurred between the size of each individual coral head and the substrate angle. No significant relationship was found between substrate angle, coral head size, and site location (T able 4). Effect F ratio d.f. P Size of individual coral head vs. depth 2.27 3, 58 0.0899 Bleach rating vs. depth 13.66 3, 58 <.0001* Bleach rating vs. angle of substrate 13.97 3, 58 <.0001* Bleach rating vs. temperature 17.42 3, 57 <.0001* Size of individual coral head vs. urchin cover surrounding individual coral head 2.00 3, 58 0.1233 Bleach rating vs. urchin cover surrounding individual coral head 11.48 3, 58 <.0001* Size of individual coral head vs. angle of substrate 1.55 3, 58 0.2111 Table 4. Two way analysis of variance for all 3 study sites, depth, bleach rating, size, temperature, angle of substrate, and number of urchins in 30 cm radius of individual coral. Significant tests are marked with an asterisk. Size of individual coral head is i n centimeters and depth of coral is in meters. Angle of substrate is in degrees and is measured on the horizontal upward from the ocean floor. DISCUSSION To examine why Pocillopora corals are not establishing in large amounts at some sites and to understa nd where Pocillopora corals are establishing prominently in Cuajiniquil, I compared my hypotheses to my results. In my study, establishing coral heads are defined as individual Pocillopora not connected to any part of another Pocillopora coral or reef betw een 0cm and 20 cm in size. My first hypothesis was that Pocillopora coral in poor health do not grow large enough to support reef growth . Although three quarters of all stony corals sexually reproduce by releasing massive numbers of eggs and sperm into the water (Veron, 2000), bleached Pocillopora coral may prevent some asexual reproductive events . In asexual reproduction, new clonal polyps bud off from parent polyps to expand or begin new colonies (Sumich, 1996). This occurs only when the parent polyp reac hes a certain size and divides. This process continues throughout the animal's life (Barnes and Hughes, 1999). My results from Isla David show that as bleaching increases, size decreases. These results support my hypothesis, showing that smaller corals tha t
Pocillopora spp. in Cuajiniquil Temby 11 are unhealthy, described by high bleach ratings, may lead to less success since asexual reproductive events occur when the parent polyp reaches a certain size before dividing. However, the other two study sites do not show a pattern that supports this hy pothesis. My second hypothesis is that vast quantities of sea urchins may be overtaking available spaces and crevices. Sea urchins settle equally well in the presence of rock surfaces encrusted with coralline algae, rock surfaces away from urchins, and roc k surfaces forming an urchin pocket (Cameron, 1980). At both Isla David and Bajo Rojo, large numbers of urchins may be overtaking crevices and rocky substrates that are not available at BahÂ’a Thomas. This may reduce the ability of corals to cover more than 10% of each transect at these two sites. Since urchins are grazers and scrapers , they typically do not favor sandy substrates. For this reason, it is possible that BahÂ’a Thomas had the most coral coverage of all 3 sites with some of the lowest numbers of sea urchins due to the sandy substrate most corals of the site were establishing on. These data support the hypothesis due to the overwhelming success of the coral reef and the individual establishing coral heads, as well as the lower numbers of urchins in each transect at BahÂ’a Thomas. Although the relationship between urchins and coral coverage statistically depends on site, there is strong evidence to support that large numbers of urchins affect coral establishments by residing in spots on rocky substrat e s that stony coral propagules could settle on, specifically at Isla David and Bajo Rojo. Although surge may bring some food particles to these corals (other than their main food source of zooxanthellae), the surges and currents throughout Costa Rica and Central America are currently exposing corals to a larger range of metal pollution than ever before as a result of the increasing environmental contamination from sewage discharges, oil spills, agricultural chemicals and fertilizers, and topsoil erosion (G uzmÂ‡n and JimÂŽnez, 1992). Not only do strong surges bring pollutants from land to sea, they also seem to play a significant role in the ability of individual corals to settle. My third hypothesis is that the surge at some sites may be too strong, compared to the surge of other sites, for some establishing corals to settle. This hypothesis is supported by my data since the largest amount of individual establishing corals occurred in weak surges with angles of 20 degrees or less. Based on my data, there may b e a maximum capacity of surge strength that establishing corals can withstand without difficulty; at surges 35 degrees and higher, at both Isla David and Bajo Rojo, no more than 5 coral heads were found per transect. This supports the hypothesis that surge strength may have an impact on establishing corals. Rough surges may break coral larvae loose, pull these larvae far from a viable site, or even unsettle establishing corals that are not entirely secure due to their small size or young age. Surge may thus affect coral numbers at some sites if propagules from parent corals are disrupted by strong surges since these propagules may take anywhere from 2 hours to 103 days to settle (Richmond, 1987). The fourth hypothesis was that substrate for Pocillopora growt h may need to be rocky and uneven, but not sandy, for new coral growth. This hypothesis was not supported due to the results from BahÂ’a Thomas (Table 3). Most individual establishing corals at BahÂ’a Thomas, and the most in the entire study, occurred on san d. This was a surprising discovery because , although some establishing corals in the sand at BahÂ’a Thomas were not completely secure to the substrate, all establishing corals on the sand were healthy with no bleaching, aside from one coral in the sand with a bleach rating of 2. This is contradictory to the concept that corals prefer rocky substrate (SECORE Foundation, 2015) since the most corals found on any substrate occurred on sand. These establishing corals may be occurring on sand at BahÂ’a Thomas becau se sand provides an open space for corals to settle and is practically urchin free; urchins do not
Pocillopora spp. in Cuajiniquil Temby 12 prefer to feed or scrape across sand. Furthermore, the surge is weak enough at this site that propagule or polyp disruption may not be a serious issue. These factors may allow large numbers of corals to continue to establish on this smoother, more even substrate. My fifth hypothesis is that extremely shallow depths could lead to a severely bleached or sickly Pocillopora. These shallow waters may heat up at hig h temperatures due the proximity to the surface and to direct sunlight. Although Pocillopora typically occur at shallower depths than other coral species, extremely shallow depths may lead to poor health of a coral and even coral death due to over heating f rom direct sunlight. This was supported by an ailing, unhealthy coral at Bajo Rojo that occurred at 1.5 meters at high tide, the shallowest recorded depth of coral growth at this site. The bleach rating was a 3 and the coral was clearly declining in health with little signs of recovering ( Figure 5 ). However, corals at BahÂ’a Thomas occurring at 1.5 meters or shallower had bleach ratings of 1. This does not support my fifth hypothesis but may be explained by the site; although corals at BahÂ’a Thomas occur at shallower depths than the other study sites, the coast may be protected from direct sunlight and heat by the high mountain of land that surround s the site. However, at both Isla David and Bajo Rojo, the only corals found with a bleach rating of 3 occurred at 4 meters or deeper. Although they do not support my hypothesis, these establishing , completely bleached corals may be outliers; the strong surges at these sites may have unsettled the unhealthy coral at some point in time, possibly rolling them to deeper depths than they originated at. Corals with bleach ratings between 1 and 2 at Isla David and Bajo Rojo occurred at depths between 2.4 meters and 6 meters. These data points support the hypothesis that at reasonably shallow to medium depths (greater than 2 meters and less than 6 meters), corals have low levels of bleaching. At extremes, however, (less than 2 meters and more than 6 meters), it is possible that Pocillopora corals are over heated in extremely shallow waters and are poten tially chilled in extremely deep waters which would effectively hurt or kill the corals . These data help to pose a new hypothesis: extremely shallow waters and extremely deep waters may be a threat to Pocillopora health due to intense temperature variation s. Figure 5 . An ailing, unhealthy coral at Bajo Rojo that occurred at 1.5 meters at high tide. The bleach rating was a 3 and the coral was dying because it was broken down, lacked a healthy color, and was covered in algae.
Pocillopora spp. in Cuajiniquil Temby 13 My sixth and seventh hypotheses are related. The sixth hypothesis examined in this study is that water temperature that is too warm may influence local reproductive events and the seventh hypothesis discussed is that bleached Pocillopora coral may prevent local reproductive events. My hypotheses were supported by results from Bajo Rojo since a visual trend between temperature and bleach rating occurred; as temperature increased, bleach rating increased. At cool temperatures, the bleach rating was 1 while in warm temperatures, the bleach rating of an individual establishing coral was 3. This pattern typically occurs because, at warmer temperatures, zooxanthellae are more vulnerable and more likely to be expelled (Herre, 1999). My hypothesis is not supported b y all three sites, however. This may be explained because, at BahÂ’a Thomas, some corals establishing on sandy substrate may be unsettled on occasion by a surprisingly strong current from a tropical storm, by an animal interaction, or by a boat anchor and m ay be moved into a favorable water temperature zone. In these zones, the corals can resettle, reproduce, and successfully launch the growth of a coral reef in the best possible conditions. Furthermore, since few Pocillopora exist at Isla David, the current establishing corals at Isla David may have been propagules from past corals that withstood events, such as warming water temperatures or tropical storms, that killed off many original corals of the site. The eighth hypothesis discussed is that larvae are not arriving to some sites. This is supported only by one side of Bajo Rojo. For the ridge of the windward side of Bajo Rojo, I hypothesized that coral growth may not be occurring due the possibility that larvae are not arriving to that specific side. On the windward side of the sedimentary rock is an expansive 100 meter by 40 meter ridge, angled at about 45 degrees, where I observed no coral growth. Coral growth may not be occurring on the windward ridge because the surge is too strong, and the windward s ide is not protected from rough waves or direct sunlight. The steep ridge may be missing biofilm, a key inducer of coral settlement that sends out chemical signals to floating coral larvae to settle (SECORE Foundation, 2015). If biofilm is present, then pe rhaps larvae are not arriving to the windward side of Bajo Rojo due to currents and wave action. These factors may be preventing new coral larvae from settling or even arriving on the windward side of Bajo Rojo. The site's leeward exposed side is sedimentary rock and was used for transects 1, 2, 3, and 4. Pocillopora corals may not be establishing in large numbers at some sites in Cuajiniquil due to the strong surges that may displace larvae, the large number of urchins that may take over viable su bstrates and eat newly settled corals, and the range in health that could influence reproductive success of establishing corals experienced at Isla David and Bajo Rojo. Establishing Pocillopora are, nonetheless, occurring in large quantities at BahÂ’a Thoma s potentially due to the weak surge, the smaller numbers of urchins, the overall good health of individual establishing corals , and the abundant sandy substrate . Furthermore, at BahÂ’a Thomas, some corals establishing on sand may be unsettled by forceful st orms, marine animal encounters, or boat anchors, allowing these corals to be moved into a favorable temperature zone. The corals in these favorable and potentially temperate water zones can resettle, thrive, and be naturally selected for if they are reprod uctively fit . These successful corals can then begin the growth of a coral reef. ACKNOWLEDGMENTS I would like to thank the entire Lara family, especially Minor, Minor Jr, and Steven, for not only transporting me between sites by boat, but also free diving with me to find Pocillopora specimens and documenting some of these specimens with me. I would also like to thank Haley
Pocillopora spp. in Cuajiniquil Temby 14 Hudson for her constant help in setting up transects, finding Pocillopora, and free diving at deep depths to document specimens. Thank you to Dhiraj Ramireddy for helping to count sea urchins in transects. Another thanks to my host mother, Flor Lara, for housing and feeding me during the grueling two weeks of diving for long hours each day. Finally, I would like to thank Frank Joyce for h is constant support, his helpful advice on my study, and his underwater camera. LITERATURE CITED Barnes, R. S. K., and R. N. Hughes. "An Introduction to Marine Ecology." 1999, doi:10.1002/9781444313284. Cameron, Ra, and Sc Schroeter. "Sea Urchin Recru itment: Effect of Substrate Selection on Juvenile Distribution." Marine Ecology Progress Series , vol. 2, 1980, pp. 243 Ã 247, doi:10.3354/meps002243. Gomez, A. , Pawlak C. 2018. A Continuing Study of Coral Condition, Occurrence, and Abundance on the Santa Elena Peninsula. EAP University of California, Instituto Monteverde Fall 2018. [Unpublished]. GuzmÂ‡n , Hector M. "Restoration of Coral Reefs in Pacific Costa Rica." Conservation Biology , vol. 5, no. 2, 1991, pp. 189 Ã 195. JSTOR , ww w.jstor.org/stable/2386192. GuzmÂ‡n, HÂŽctor M., and Carlos E. JimÂŽnez. "Contamination of Coral Reefs by Heavy Metals along the Caribbean Coast of Central America (Costa Rica and Panama)." Marine Pollution Bulletin, vol. 24, no. 11, 1992, pp. 554 Ã 561., doi:10.1016/0025 326x(92) 90708 e. Herre, E, et al. "The Evolution of Mutualisms: Exploring the Paths between Conflict and Cooperation." Trends in Ecology & Evolution , vol. 14, no. 2, 1999, pp. 4 9 Ã 53, doi:10.1016/s0169 5347(98)01529 8. Hickman, Cleveland P. 2008. A Field Guide to Corals and Other Radiates of GalÂ‡pagos: an Illustrated Guidebook to the Corals, Anemones, Zoanthids, Black Corals, Gorgonians, Sea Pens, and Hydroids of the GalÂ‡pagos Islands . Sugar Spring Press, 2008. Richmond, R. H. "Energetics, Competency, and Long Distance Dispersal of Planula Larvae of the Coral Pocillopora Damicornis." Marine Biology , vol. 93, no. 4, 1987, pp. 527 Ã 533. Roberts, C. M. "Marine Biodiversity Hotspots and Conservation Priorities for Tropical Reefs." Science , vol. 295, no. 5558, 2002, pp. 1280 Ã 1284., doi:10.1126/science.1067728. SECORE Foundation. "Larval Settlement." SECORE , 31 July 2015, www.secore.org/sit e/corals/ detail/larval settlement.18.html. Sumich, J.L. 1996. An Introduction to the Biology of Marine Life . Vol. 6. Dubuque, IA:
Pocillopora spp. in Cuajiniquil Temby 15 Wm. C. Brown. pp. 255 269. US Department of Commerce, and National Oceanic and Atmospheric Administration. "What Is Coral Bleaching?" NOAA's National Ocean Service , 15 Mar. 2010, oceanservice.noaa.gov/facts/coral_bleach.html. Veron, JEN. 2000. Corals of the World . Vol 3. Australia: Australian Institute of Marine Sciences and CRR Qld Pty Ltd. APPENDIX Figure 6 . Size of individual coral head (centimeters) vs. depth of individual coral (meters).
Pocillopora spp. in Cuajiniquil Temby 16 Figure 7 . Bleach rating of individual coral vs. depth of individual coral in meters. Figure 8 . Bleach rating of individual coral vs. angle of substrate in degrees fr om the horizontal upwards from the ocean floor.
Pocillopora spp. in Cuajiniquil Temby 17 Figure 9 . Bleach rating of individual coral vs. temperature. Temperature was categorized on a scale of 1 to 5 which was converted into temperature names for results (1= cold, 2 = cool, 3 = warm cool, 4 = w arm, 5 = direct sunlight) Figure 10 . Size of individual coral head in centimeters vs. urchin cover surrounding individual coral head in 30cm radius from coral head.
Pocillopora spp. in Cuajiniquil Temby 18 Figure 11. An example of an establishing coral with a bleach rating of 1. This coral is rated a 1 because it is h ealthy with no bleaching . Figure 12. An example of an establishing coral with a bleach rating of 2. This coral is rated a 2 because there is some bleaching occurring. However, zooxanthellae are present.
Pocillopora spp. in Cuajiniquil Temby 19 Figure 13. An exam ple of an establishing coral with a bleach rating of 3. This coral is rated a 3 because it is completely bleached and almost all of its zooxanthellae are gone. Figure 14. An example of coral coverage at BahÂ’a Thomas. Coral coverage is different than the number of individual coral heads. It takes into account reef cover and total coral cover in each transect and is translated into a percentage.
Pocillopora spp. in Cuajiniquil Temby 20 Figure 15. A study site: Bajo Rojo. The lower left hand side and middle portion of the above image were used for Bajo Rojo transects 1 4 of the study. The windward side with no observed coral growth is on the upper right hand side of the above image. Figure 16. A study site: BahÂ’a Thomas. The C shaped coast of the peninsula in the above image was used for Bah Â’a Thomas transects 1 4 of the study.
Pocillopora spp. in Cuajiniquil Temby 21 Figure 17. A study site: Isla David. The closest shore lines to the islands of the above image were used for Isla David transects 1 4 of the study. Figure 18. Measuring of each individual establishing coral head between 0 20cm. A weighted ruler was used to measure the size of each individual establishing coral in the study.
Pocillopora spp. in Cuajiniquil Temby 22 Figure 1 9. A side by side view of establishing coral s with different bleach rating s on a scale of 1 3 from left to right . This coral farthest left is rated a 1 because it is h ealthy with no bleaching . This middle coral is rated a 2 because there is some bleaching occurring. However, zooxanthellae are present. This coral farthest right is rated a 3 because it is completely bleached and almost all of its zooxanthellae are gone.