UCB Moorea Class: Biology and Geomorphology of Tropical Islands

Seawater pH measurements across different reef settings in Cook’s Bay (Moorea, French Polynesia) taken during October and November 2008 were compared and related to circulation and community composition in the reef flat, fringing reef, lagoon and bay. pH is thus an easy measure of seawater carbonate chemistry, which can be altered by community metabolism. Current velocity and percent cover of coral were greatest across the reef flat, yet no significant difference in seawater pH was found between the algal ridge and the lagoon. However, pH variations were discernible between the surface water from the fringing reef, which had the highest percent cover of algae, and water sampled at depth in the lagoon and bay. This study thus brings a better understanding of pH differences within a reef ecosystem and can serve as a benchmark for monitoring ocean acidification.

Free living corals are and important part of coral reef ecosystems. The members of the coral genus Fungia (Scleractinia, Fungiidae) exist as individual, free living, polyps. Fungiid corals can move actively, though expiation of body tissue, or passively, via being carried by strong currents. It was observed that fungiids were often found in close proximity to one another in the shallow reefs of Moorea, French Polynesia. This study set out to determine if fungiids were aggregated and if so, to test three factors which may be contributing to these aggregations; fungiid size, substrate preference and current speed. Furthermore, the effect of current on the rate at which fungiids can remove sediment from their bodies was tested. It was found that fungiids are aggregated. These aggregations consist of individuals of similar ages. Aggregations are found in branching corals much more often than expected and on sand much less often than expected. Aggregated fungiids are found in areas of lower current speed than solitary fungiids. Finally, high current speeds increase fungiids ability to remove sediment from their bodies.

Plants often depend on other organisms to pollinate their flowers in order to successfully reproduce. On an island, plants face multiple challenges to establish and persist, especially if the plant depends solely on a specific pollinator not present on the island. A pollination and reproduction study was conducted on Scaevola taccada, a widespread coastal shrub, on the island of Mo’orea in French Polynesia. The pollinator community of S. taccada was composed of eight insect species, with the recently introduced honeybee, Apis mellifera, being the most frequent floral visitor. Both site and wind speed were found to have significant effects on visitation rate. A high percentage of successful seed set from pollinator-exclusion studies suggested S. taccada may be able to successfully self-pollinate. The length of flowering times was found to be significantly associated with successful seed set, with flowering times serving as an indicator for successful pollination events. With the ability to outcross and to self-reproduce, S. taccada has adapted to persist on a changing island environment.

Islands have been shown to be highly vulnerable to the invasion of non-native plant species. The island of Moorea, French Polynesia, is both geographically isolated and lacks a high diversity of native plant species, factors that promote the invasion of non-native plants. Disturbed areas, such as roadsides, have also been closely associated with the colonization and spread of non-native and invasive plants. Roads are particularly important vectors of alien plant invasions, aiding in dispersal and likely serving as starting points for edge effects. The present study considers both the alien and native flora in tropical secondary forests adjacent to paved vehicle roads, dirt vehicle roads, and backcountry hiking trails on Moorea, French Polynesia. The composition of total and alien plant species, level of invasion, and significance of edge effects were analyzed between the three corridor types. Significant differences in the alien plant compositions and level of invasion were found between the corridor types. Dirt roads were found to be the most invaded, followed by paved roads and then hiking trails. Two plant species, W. trilobata and A. falcatoria, showed dramatic edge effects into the adjacent forest; however, only the spread of W. trilobata was significantly affected by corridor type, with paved roads showing the greatest effect.

This study was conducted on Mo'orea, French Polynesia to investigate and record the impacts of ecotourism on two populations of himantura fai, pink whiprays or pink whiptail stingrays. Two sites were chosen each with varying impact to rays. Photographs and recordings were made and analyzed. Thirty eight individual rays were identified, 29 from one site and 8 from the other. Five kinds of scarring were described and compared between the two. It was found the more dense ray population was more injured and impacted and habituated to humans. The higher frequency of injury suggests a lower quality of life and indeed a negative impact from ecotourism. A mock mark and recapture study was done using the Lincoln-Peterson method. The population estimates were 30 and 8, suggesting the 29 and 9 rays identified are the entire populations. No rays were seed at both sites, which suggests site fidelity.

Since the 1960’s the crown-of-thorns starfish, Acanthaster planci¸ has devastated coral reefs. There are many competing theories about the causes for these outbreaks of A. planci. One of the leading theories is that it is an anthropogenic cause. As a result, Marine Protected Areas (MPA) may be a way to protect coral reefs from outbreaks of A. planci by removing anthropogenic effects and allowing the reef to protect itself. Coral reef health was assessed using fish population diversity, percent live coral reef coverage and density of A. planci. Lowest live coral reef coverage was 42.97% with 80.70% the highest. Highest Simpson’s 1-D diversity index value was 0.47 for outside of a MPA with 0.82 the highest index value for a site inside an MPA. Density of A. planci were found to be 12.5 per hectare, which is below outbreak densities. No significant differences were found in any metrics for inside or outside MPAs.

Herbivory plays an important role in shaping coral reef community structure. Herbivores consume algae on the reef, helping to prevent coral dominated reefs from “phase shifting” to algae dominated ones. Here I examine how the presence of an herbivorous sea urchin, Diadema savignyi, influences algae growth on Porites sp. coral heads using inclusion and exclusion cages. Corals were either caged with D. savignyi or no D. savignyi, or not caged at all. Treatments were applied for 25 days and percent algae cover was estimated weekly while algae length was measured on day 25. After 25 days, variation in algae cover and algae length were not significantly associated with D. savignyi presence. Corals kept in the presence of D. savignyi had the same amount of algae as corals that D. savignyi had been excluded from. These results are identical to a similar experiment that was performed in the laboratory in which corals were placed in a tank either with or without D. savignyi. These results suggest that at the current time, D. savignyi does not have a strong impact on reducing algae growth in the coral reefs of Moorea, French Polynesia. This may be due to the health of the reef, the ability of live corals to prevent new algae settlement and growth, or the presence of superior fish herbivores.

Crown of thorns starfish (Acanthaster planci Linné 1758) are notorious coral reef devastators; they decimate coral populations, thus changing the coral reef habitat and killing many organisms that depend on the coral. Culcita novaeguineae (Muller and Troschel 1842), or cushion stars, are corallivores and generalists that live in Pacific reefs. Because C. novaeguineae and A. planci have similar food preferences, the presence of crown of thorns may change cushion stars’ eating habits. This study explored cushion star ecology and their laboratory feeding preferences in the presence and absence of crown of thorns. Laboratory experiments were conducted with three coral food choices (Porites sp., Acropora sp., and Monopora sp.) and algae covered rock. Cushion stars only ate Acropora sp. and Monopora sp. in laboratory experiments. They found among all three of those coral genera in the field and were rarely found near Pocillopora sp. Crown of thorns presence had no significant impact on the food choice in the lab or substrate choice of cushion stars in the field. General laboratory trends indicate cushion stars ate more frequently and preferred rock as substrate in the presence of crown of thorns.

While secondary compounds are produced by plants in low abundance, these bioactive compounds are essential to human survival for their medicinal applications. These same compounds are crucial to plants, having evolved as defense mechanisms against herbivory. Chief among the theories of plant responses to herbivory, the Optimal Defense Theory (ODT) hypothesizes that plants will allocate defenses in direct proportion to the risk of a particular plant part to herbivory and the value of that part in terms of loss of fitness to the entire plant. Through insect damage assessments and antimicrobial assays, this study investigates the correlation between herbivory and medicinal activity and whether or not the within-plant ODT is followed in three ethnobotanically useful Malvaceae species, Thespesia populnea, Hibiscus tiliaceus and Hibiscus rosa-sinensis. All three plant species demonstrated an inverse relationship between herbivory and medicinal activity. Variation in secondary composition data from both insect damage assessment and antimicrobial tests supported the ODT.

Hermit crabs interact with each other in a variety of ways involving spatial use (aggregations, migrations), housing (shells), mating, recognition of conspecifics, and food. To test if isolation from conspecifics affects the behavioral interactions of hermit crabs, crabs of the species Coenobita rugosus (Milne-Edwards 1837) of Mo’orea, French Polynesia were isolated from each other for two days, four days, six days, fifteen days, and twenty-two days. They were kept in individual opaque containers with separate running seawater systems to prevent them from seeing or smelling each other. Afterwards, the hermit crabs were put into a tank two at a time and their behavior was recorded and compared to the behaviors of non-isolated crabs. Behaviors looked at fell into two categories: 1) “social” interactions, meaning that the crabs reacted to each other’s presence, and 2) “nonsocial” interactions, meaning that the crabs either ignored each other’s presence or actively avoided behavioral interactions with other crabs. Results indicated that although “social” behavior showed a slight decreasing trend over time, it was not significant; however, the amount of “nonsocial” avoidance behavior seen increased significantly the longer crabs were isolated.