UCB Moorea Class: Biology and Geomorphology of Tropical Islands

Geomorphological changes occur on a range of spatial and temporal scales. In the past, they have been primarily driven by abiotic factors like storm events and wave action. More recently, human impacts have begun to affect geomorphological processes. It is critical to understand where and how humans impact such processes in order to minimize environmental impact of activities like boating and adding infrastructure. I studied human impacts on the formation and continuous alteration of Motu Tiahura, Mo'orea, French Polynesia. By studying velocities, sediment distribution, beach profiles and wave heights in areas with and without human activity, it was found that humans are in fact having a geomorphological impact on Motu Tiahura.

Land breeding sites are important conservation priorities for the preservation of seabirds that cannot breed over the ocean. An example of a seabird that must breed on land is the white-tailed tropicbird (Phaethon lepturus). This bird is frequently seen on the island of Mo’orea in French Polynesia, but little is known about whether this species spends time there for the purpose of breeding. I hypothesized that these birds are breeding on Mo’orea and therefore conducted a study that included (1) observations of group interactions; (2) time budget construction; and (3) number surveys. My group interaction observations revealed courtship behavior previously described by the literature but I observed no definite evidence of cliff‐face nesting. The time budget results showed that the tropicbirds spend a significant portion of their time flying over the land by themselves (73%), and at low elevation near vegetation (61%). The number survey revealed that the birds preferred to be on land at mid‐day and favored one valley, ‘Opunohu, over the 2 others I surveyed. Because of the amount of time the birds spend by themselves and the absence of definite nest site data, I am unable to conclude that white‐tailed tropicbirds are breeding on Mo’orea at this time of year. However, their courtship behavior and extensive interaction with vegetation that may indicate potential nest sites in tree hollows lead me to conclude that Mo’orea could be a land breeding site for this species at other times of year.

Secondary compounds, often found in medicinal plants, are believed to have evolved as chemical defenses for many species. These bioactive chemicals have been shown to protect the plant from their numerous insect predators and pathogens through a wide variety of mechanisms. The purpose of this study is to examine the effect these secondary compounds have on the amount of predation towards medicinal species. Looking at the amount of leaf herbivory and an antifungal bioassay of six species of Leguminosae, the main objective of the study was to find a correlation between predation and medicinal properties. Herbivore feeding preference appeared averse to medicinal leaves, although no relationship between leaf damage and yeast inhibition was found. A feeding experiment conducted using common herbivores inadvertently demonstrated the antifungal properties of the medicinal species, and gave further indication of an herbivore aversion to leaves with bioactive secondary compounds.

Early Polynesians created monumental structures called marae, using coral as a major element in the construction of the ahu. This study will analyze the relative frequency of coral genera found in the ahu of three different royal coastal marae sites on Mo‘orea and evaluate its correspondence to the composition of adjacent coral communities. Volumetric measurements of the ahu and its constituent coral genera composition were calculated. Transects were performed in both the fringing and barrier reefs surrounding the marae sites in order to record size and frequency of the coral genera present there. Some marae site survey results revealed a strong correlation between the usage of coral as a major element of construction in marae, and modern coral genera distribution and abundance in the surrounding fringing reef. The barrier reef environment suffered minimal impact resulting from marae construction. When all coral genera were combined, there was a significant difference in coral composition between marae site reefs and control site reefs. Additionally, coral measurements revealed a positive correlation of increased coral diameter with increased distance from shore. Using coral head size as a proxy for age, the presence of younger coral communities closer to shore may be the long-term result of older, larger corals being collected nearer to shore for use in the constructing of marae.

Color polymorphism has been implicated as an important component of cryptic coloration in organisms inhabiting complex environments. Recent studies have suggested that mantle color variation in Tridacnid clams may serve various functions, including as a mechanism to achieve background matching. The mantle color variation of Tridacna maxima was examined in a series of experiments, including a background-matching photo survey, a predation experiment, and a zooxanthellae count. The results of the photo survey showed a significant correlation between T. maxima mantle and background color. T. maxima which did not match their background experienced a significantly greater rate of predation. Finally, the population of zooxanthellae was seen to increase for the same size of mantle area with age. These results suggest that balancing photosynthetic efficiency and anti-predation needs can be addressed by mantle color variation throughout the lifetime of T. maxima.

Islands of the south pacific are fragile ecosystems, home to native land and sea birds that evolved in the absence of predators. On Mo’orea, French Polynesia the first humans arrived around 600 AD bringing with them invasive vertebrate predators. This study examines one of these predators on Mo’orea by observing swamp harrier (Circus approximans) habitat preference and behavior to determine if it has changed in comparison to its source population. Also it will examine their role in seabird predation on Mo’orea through a series of animal waste sample collections at high elevations. Since swamp harrier introduction in 1885 their habitat preference has not much changed from their Australian source population. The majority of its time and foraging is spent over low vegetation, though some expansion into other habitats has occurred since there are no other raptors on the island with which to compete. Feral cats (Felis catus) are also prevalent on the island and along with the swamp harriers are preying upon the native seabird populations on Mo’orea. Tahiti petrels (Pesudobulweria rostrata) and Audubon's shearwaters (Puffinus lherminieri) are being preferentially eaten by these predators over the invasive songbirds at high elevation. Feral cats appear to be the more significant predator of seabirds and without their control nesting seabird colonies may cease to exist on Mo’orea.

Abstract. Zooplankton is an essential component of every coral reef system, not only because it is the base of many marine food chains, but also because it is an important stage in many marine animals’ life cycles. While by definition plankton is free floating, zooplankton ha been known to move in predictable patterns. This includes a daily diel vertical migration towards the surface at night and back to the depths during the day and fluctuations in abundance over the lunar cycle, usually peaking around the full moon. This study aimed to look at the amount of control plankters have in choosing their horizontal position over the reef by looking at substrate preferences of demersal zooplankton in the fringing reef. It was found that zooplankton emerge in the largest numbers from branching coral followed by coral rubble and sand and in significantly lower numbers from smooth coral. This suggests that demersal zooplankton is able to select the substrate on which it seeks shelter during the day. Little evidence was found suggesting specific taxa prefer specific substrates. The study also compared plankton emerging from the substrate of the reef with those in the water above it. A zooplankton from the genus Lucifer was found to be dominant in the water column above the reef, but was not seeking shelter in the reef substrate during the day. Lastly, fluctuations in abundance were observed throughout the lunar cycle with a peak in numbers occurring 6-11 days after the full moon.

Parasites are ecologically significant organisms and must be understood to properly appreciate nearly any community. Parasitism is one of the most common (if not the most common) lifestyles, and parasites can influence species throughout a community. One group of parasites, the Eulimidae, is a large family of marine gastropods. Unfortunately, eulimids have not been thoroughly studied and host use behaviors have not been well characterized at the specific, or even generic levels. Therefore, this study seeks to describe host preference, host detection and tracking, and dependence on host access for two eulimid species, both sharing the macrohabitat environment. A series of experiments and a field survey showed that Peasistilifer nitidula was host specific, actively located hosts by chemical cues, reattached to hosts quickly, and required frequent access to the host for survival. Conversely, Melanella acicula had a preferred host but parasitized others as well, did not actively pursue hosts by chemical or visual detection methods, reattached infrequently in the short-term, and could survive longer isolated from the host. Using these aspects of host use to compare these co-existing species showed significantly different life histories, and suggests possible niche differentiation between a generalist and specialist species.

Jumping spiders (of the family Salticidae) are found around the globe including on the island of Mo’orea, French Polynesia. Unlike continents, an island system such as Mo’orea often magnifies the effects of an invasive species due to their increased frequency of unfilled ecological niches. In my distributional study most species I encountered were non-native, and in my behavioral study I investigated the potential for correlation between a species’ dominance in elevation-divided habitats and observed aggressive interspecies interactions. A total of 206 Salticidae were collected, 86 of which were utilized in my behavioral study. Of the eight jumping spider species encountered (six known, two unknown) I found there was no strong correlation between a species’ behavior towards other spiders and its distribution. Future studies could be directed concerning how spider behaviors besides interspecies aggression influence the dominance of that species in a given habitat.

Abstract. Humans have continually interacted with and transformed their surroundings. Cordyline fruticosa Chevalier 1919, was among the many plants Polynesians brought with them as they voyaged from western Polynesia to eastern Polynesia. Polynesian culture is historically associated with C. fruticosa, which was centered around the ancient marae, or temples. The distribution of the large, sterile, green leaf variety was studied at marae and contemporary areas such as homes and businesses on Mo’orea, French Polynesia. I expected to find the sacred green variety around marae and the ornamental red varieties in contemporary locations. No C. fruticosa plants were found around marae sites. Contrary to predictions, the green variety of C. fruticosa was more prevalent at the contemporary sites than the red varieties. Local Tahitians were consulted on current attitudes towards and uses of C. fruticosa. These elders indicated that the sacred green variety continues to be utilized in religious, medicinal, and cultural ways, perhaps explaining its prevalence over red varieties.