UCB Moorea Class: Biology and Geomorphology of Tropical Islands

Pineapple farms dominate the agricultural landscape of Moorea, French Polynesia, with over 250 hectares of pineapple farmland. Agricultural runoff has been well known to affect stream ecosystems, in particular, photosynthetic organisms such as diatoms. Few studies have looked specifically at environmental effects of pineapple farm runoff. This study looks at how 1) pineapple farms affect stream chemistry, 2) pineapple farms affect diatom assemblage, and 3) individual effects of herbicides (atrazine and diuron) and fertilizers on diatom populations. No significant differences in stream chemistry or diatom assemblages in farm affected and unaffected areas were observed. Herbicides and fertilizers did not have any significant effects on diatom species richness and abundance.

Animals must be locally adapted to their habitat to optimize use of available resources. In highly variable environments, behavioral change allows animals to optimize resources quickly enough to keep pace with their environment (Luttbeg 1999). The factors that determine the animal's behavior are often difficult to uncover. Coris gaimard (Quoy and Gaimard 1824), a species of wrasse, exhibits different foraging frequencies across its range. This study attempts to determine what biotic factors may affect the foraging behavior. The study compares the behavior of two populations of C. gaimard in two similar lagoons around the island of Moorea, French Polynesia and a population in a previous study done in Japanese waters (Shibuno et al. 1994). Standardized timed observations from Moorea showed an increase in the amount of foraging behavior at the site with a smaller prey base. The behaviors, however, maintained the same relative frequency as the behaviors seen in Japanese waters where the prey base was larger, but had a different species composition. These observations indicate that prey quantity determines the amount of foraging, but the type of available prey determines the foraging strategy. Additionally, C. gaimard engages in heterospecific feeding relationships, but the presence of other foraging species does not significantly affect its foraging behavior. These results indicate that prey populations are a mjor biotic factor in determining foraging strategies.

Surface plankton tows were completed at select reef passes and lagoons over five weeks on the island of Mo’orea, French Polynesia. Differences in zooplankton species richness and abundance were analyzed based on location, salinity, and tide. Reef passes and lagoons varied in the average abundance of zooplankton as well as having different species prevalence. Lab experiments tested individual groups’ tolerance to varying salinity levels that were found in Cook’s Bay. There was a significant drop in copepod and crustacean nauplii populations when exposed to lower salinity levels.

I studied the habitat selection and thermal biology of two cryptic South Pacific skinks (Emoia cyanura and Emoia impar) in order to determine whether or not differences in thermal preference affect habitat partitioning. I measured sun exposure and thermal characteristics of microhabitats selected by each skink, and then quantified preferred substrate temperatures and preferred body temperatures in a laboratory thermal gradient. Compared to E. impar, E. cyanura inhabited areas with open canopy cover, and selected significantly warmer substrates in the field and lab setting. E. cyanura also had a significantly higher preferred body temperature that E. impar. Furthermore, E. cyanura had significantly less variability in preferred body temperature than E. impar. These findings up hold Huey and Slatkin’s (1976) theory on the costs and benefits of lizard thermoregulation, and support the hypothesis that differences in thermal preference provide E. cyanura and E. impar with a mechanism for habitat partitioning.

The growing concern for threatened or endangered species has made conservationists recognize the need to accurately assess the status of small populations. In order to do this, the survivorship and fecundity of each life stage must be established to determine the population’s overall growth rate. A small population of the evergreen tree Calophyllum inophyllum can be found on the island of Moorea in French Polynesia. This tree is an excellent study organism because it has been internationally recognized as an endangered species and its large spherical seeds allow it to be traced easily. It grows along the coast, and the seeds float in water and continue to be viable for over three months. Determining the fate of the seed is one important step in developing useful models for conservation managers. The factors tested are survivorship, loss, and fecundity in the seed to seedling life stage. A seed-sowing experiment yielded 36.24% germination, which is much lower than past germination rates of this tree. The terrestrial crab, C. carnifex, was found to be the primary predator of the C. inophyllum seed, causing a 59% loss of seeds. This high predation loss could be impacting the population growth rate. The long-distance dispersal study provided evidence that the seeds were capable of moving past the reef. This has important implications in the studies of island colonization.

Epiphytes contribute significantly to the biomass of forest canopies; however, in the tropics, epiphytes have been greatly understudied. This study seeks to better understand the effects of forest edge on the distribution of epiphytes as well as describe general characteristics of epiphytic communities on Inocarpus fagifer in Mo'orea, French Polynesia. It was found that species richness was relatively similar throughout the study site. While there was no significant difference between locality on buttress root or trunk of the host tree, moss communities in particular were significantly affected by distance from forest edge and proximity to perennial streams. Ferns were found to be somewhat correlated with their proximity to streams while liverworts and lichens were not greatly affected. Overall, location of epiphyte communities relative to edge or at different heights on the host tree did not play a large role in the establishment of epiphytes.

Studies examining benthic macrofauna of estuaries are becoming more prevalent in the scientific community but none have yet been conducted on the island of Moorea, French Polynesia. The present field study surveyed four estuaries on the island: the Papeahi, Paopao, Urufara and Vaihana Rivers. Organisms were collected and abiotic factors (including sediment type, depth, temperature, water flow, salinity, pH and dissolved oxygen) were measured to find correlations between species diversity and species abundances and the physical conditions that surround them. Abundance of taxa varied considerably among estuaries. Correlations were found between diversity and temperature and between gastropod abundance and depth/salinity. Many correlations reported in previous studies were absent; however this is most likely due to low abundances, small sample sizes and time constraints.

Aquatic invertebrates utilize multiple forms of sensory perception including chemical signaling, to evaluate their surrounding environment. The hermit crab Calcinus latens is able to detect external chemical cues within the complex coral rubble habitat. These discrete chemicals whether emanated from a potential predator, competitor or conspecific are received through chemosensory structures and elicit a specific behavioral response. This study examines the effect of four chemical treatments (control-ambient sea water, predator-Octopus bocki, potential competitor-Saron marmoratus and conspecific-Calcinus latens) on the number of times an individual Calcinus latens is observed in active, exploratory behavior verses stationary, defensive behavior. The results demonstrate a significant difference in the amount of time observed in defensive behaviors by the hermit crabs exposed to the treatment containing octopus chemical cues when compared to the other treatments. Across the four chemical treatments, there was a significant difference in the observed use of six specific behaviors, indicating a patterned behavioral response, unique for each treatment. Additionally, an experiment testing the response of Calcinus latens individuals to artificially introduced treatment species, (octopus Octopus bocki, shrimp Saron marmoratus as well as conspecifics) in which tested individuals could utilize all modes of sensory perception, was compared to the chemically stimulated behaviors. Analysis of the response behavior to chemical cues verses multimodal sensory assessment of actual treatment species demonstrated a statistically significant similarity in elicited behavior which underlines the importance of chemical signaling in modulating the behavior of Calcinus latens within the coral rubble microhabitat.

Invasive species are known to displace native habitat and threaten biodiversity. Lantana camara has invaded over 60 countries and island groups and is one of the top invasive plant species in French Polynesia. Few studies discuss the relationship between L. camara and anthropogenic disturbances, though it is known to be associated with disturbance. I surveyed the major roadsides of Moorea, French Polynesia for L. camara cover in association with environmental factors, resulting in an estimated L. camara roadside area cover of 1.99%. L. camara presence was significantly correlated to roadside habitat types, highest in areas of agricultural disturbance. L. camara presence and area cover were positively correlated to soil moisture and slope. Faunal species richness was higher in areas where L. camara was present. Germination experiments reared no results over six weeks. However, in a vegetative growth experiment, cuttings had greatest height growth over two weeks under the heaviest shaded light treatment. I predict that the current range of L. camara on Moorea could expand to shaded areas with sufficient soil moisture, slope, and intermediate disturbance, conditions typical of higher elevation habitats on Moorea.

The process of succession takes place over a broad range of magnitudes and timescales. Studies of animal succession within short-lived microhabitats are few in number, making it an imporant addition to the ecological literature. The decomposing fruit fo the Tahitian Chestnut tree I. fagifer represents such a microhabitat. In this study, chestnut fruits from the island of Moorea, French Polynesia, were collected at different stages of decomposition, and the invertebrates inside were cataloged and identified to the most specific taxonomic category possible. Pitfall traps were set up at each location where chestnuts were collected in order to ensure that the dynamics of the chestnut habitat were different than the dynamics of the forest floor. Species richness and diversity for the chestnuts and pitfall traps were calculated and compared in order to test for trends of succession. There were no significant differences in richness or diversity for the pitfall traps, but significant differences did occur across stages for the chestnuts. Predictable trends of succession were interpreted from these results, suggesting that some form of facilitative succession was taking place.