UCB Moorea Class: Biology and Geomorphology of Tropical Islands

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.

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.

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.

Island systems are especially vulnerable to the possibility of introduced species becoming invasive and crowding out native flora. Human disturbances such as clearing, development, grazing and agriculture have been known to facilitate the establishment of such disturbance-tolerant species. Cocos nucifera has been cultivated extensively on the lowland areas of the island of Moorea, French Polynesia since the 1800s and as coconut production become less profitable over time, plantations have been gradually abandoned as landowners look to more lucrative efforts. Plantations of varying ages of abandonment can be seen in different stages of succession around the island. Vegetation surveys were done on six sites (in three age classes) to assess the presence and abundance of native and invasive species and to study the changes in community structure over time. Decrease in groundcover and increase in aerial cover seem to indicate the pattern of succession most accurately. The number of invasive versus non-invasive and native versus non-native species did not change significantly as plantations aged.

The terrestrial biota of the French Polynesian archipelago presents a unique opportunity for study due to a relatively poor understanding of its biology. Among the terrestrial invertebrates, the Apoidea are one of many taxa with incompletely documented biodiversity. This study investigated the diversity of the bees on the island of Mo'orea, part of the Society Islands in French Polynesia. Across a range of elevations, I collected 239 individual bees and observed the floral visits of an additional 266 bees. The visited floral species were recorded to assess apoid use of floral resources, and vegetation surveys of collection sites were conducted to assess the available floral community. A total of five genera of bees were found on Mo'orea, including two which are recorded for the first time in the Society Islands. This study suggests that introduced species, rather than native species, comprise the bee biota of Mo'orea, with the longest established species seemingly introduced at or around the time of colonization by early Polynesians. With the exception of the genera Lithurgus and Megachile, bee genera were found to rely predominantly on non-native floral resources. Floral visitation predilection by Mo'orean bees may prove to further the spread of introduced and invasive floral species.

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.

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.

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.

The island of Moorea, Society Islands (French Polynesia) provides a unique opportunity to examine patterns of spider diversity on a small high volcanic island. I collected spiders at a range of elevations (0~900m) and habitats (disturbed coastal, streamside, mid-elevation ridges and high mountains). This allowed me to map distributions and look at differences in spider assemblages. Specimens were identified to family level. I found a total of 30 different morphospecies. A total of 1738 spiders were collected (using sweep netting and active searching) represented by 12 families, 16 determined genera and 12 determined species. My survey revealed that streamside and coastal communities had the greatest overall biodiversity while having the lowest native diversity. Mid-elevation ridges and high mountains had lower overall diversity but higher native biodiversity. Differences in overall diversity may be due to variation in structural differences between these habitats. In the future, more extensive surveys of the spider fauna need to be done to determine whether structural diversity, elevation or vegetation type is most responsible for different distributions of biodiversity. The spider fauna of Moorea is dominated by nonnative species. As anthropomorphic disturbances on the environment increase, more efforts should be directed towards conservation of mid-elevation ridge and high mountain sites which possess more native species.