UCB Moorea Class: Biology and Geomorphology of Tropical Islands

Natural and anthropogenic disturbances are changing coral reef systems at local and global scales. In Mo’orea, French Polynesia, it is unsure whether a Pocilloporid-and Poritid-dominant reef represents either a transitional, recovering community or a new, stable community (Pratchett 2010). Understanding the species-specific associations between coral-symbionts and their coral hosts will provide a more precise look at how symbionts contribute to their relationship. To better understand this mutualism, this study combined field surveys with phylogenetic analyses to examine the species-specific association between Trapezia crabs and their Pocillopora coral hosts and ask more broadly if there is an association between environmental variables and a morphological phylogeny of Trapezia. There was a significant association between certain species of Trapezia and Pocillopora (Likelihood ratio, x²=84.49, df=16, p=<0.0001*), whereT. rufopunctata was found most frequently withP. edyouxi (80.75%) andT. serenei onP. meandrina (63.4%) andP. verrucosa (37.50%). Discriminant analyses support that differences between crab communities are largely attributed to the morphological features (coral size and branching depth) of coral hosts. Field observations paired with a morphological phylogeny support a trend where similar sized corals were found to be associated with more closely related crab species. Understanding the degree of species-specific associations allows us to better grasp how coral communities and their symbionts will change with natural and anthropogenic episodic changes

Anthropogenic increases in atmospheric CO₂ compound the rates of long-term changes in the abiotic conditions of the Earth’s oceans. Because many physiological processes, including calcification rate, depend on these physical factors, there is mounting concern over how changes in temperature (T) and the CaCO₃ saturation of seawater will affect marine organisms.  These effects may be particularly relevant during development— many organisms produce protective calcified structures critical for pelagic dispersal and larval survivability.  I investigated how unmitigated increases in oceanic pCO₂ and temperature consistent with climate change predictions affect the embryonic development rate, hatching success, and veliger morphology of the opisthobranch gastropod,Stylocheilus striatus. Embryos were reared in four seawater treatments: 1) control (pH=8.02, T=27°C), 2) high-temperature (pH=8.02, T=31°C), 3) acidified(pH=7.67, T=27°C), 4) acidified high-temperature (pH=7.67, T=31°C). Development times increased under reduced pH conditions, but substantially decreased under high-temperature and acidifiedhigh-temperature treatments, with significant interaction between temperature and pH. The percentage of embryos that hatched into veligers significantly decreased in all three treatments (<70%reductionsin acidified high-temperature conditions).Larval shell size decreased in all three treatments— effects of acidification and temperature were synergistic, causing greater decreases in shell size with significant interaction in acidified high-temperature treatments. Additionally, there were observable deformities in the shell morphology of hatchlings incubated in decreased pH treatments— these deformities were exacerbated by temperature increases. Thus, my results indicate that oceanic conditions congruent with climate change predictions ca. 2100 suppress successful development in encapsulating gastropod embryos, potentially reducing their viability as pelagic larvae.

The importance of disturbance ecology grows as pristine habitat becomes increasingly encroached upon by land use change. This study focuses on the behavior of the burrowing terrestrial crabCardisoma carnifex(Herbst 1794) on the island of Moorea after its semi-permanent burrow was disrupted. In the first manipulation, a set of four disturbance treatments was applied to burrows in sand and dirt substrate to examine recovery time. The second manipulation increased the intensity of the disturbance to see if the crabs’ strategies change. The results showed a significant increase in recovery time with the intensity of disturbance in dirt substrates, but not in sand. There was also a significant combined effect of treatment and substrate type on recovery. The second set of data showed the same set of recovery strategies even as the disturbances were more intense. This shows that these crabs can restore their burrows in relatively low levels of disturbance, but it remains to be seen how they and other species cope with larger scale influences such as urbanization.

Defense mechanisms have been long recognized as an important factor in establishing the development of many organism life histories. As a result, many processes associated with ensuring survivability have been very well established in organisms that utilize defense mechanisms. How these defense mechanisms have shaped the evisceration and regenerative processes of sea cucumber Holothuria leucospilota still remain largely unstudied. In this study it is revealed that Holothuria leucospilota remain very consistent in their modes of evisceration, ejecting the same organs in every evisceration event. The consistency is compounded by the finding that approximately 28% of their body mass is eviscerated regardless of organism size. In terms of organ regeneration, the thickening of the mesentery tissues is apparent at Day 4 and regeneration of the digestive tract at Day 16. Sediment feeding also resumes at Day 16 along with the regeneration of the digestive tract. No regeneration of the left respiratory tree or gonads is observed within the 28-day study. 

Habitat preferences are intrinsically linked to factors that facilitate the survival of a species. The relationship between these factors determines how well a species does in its environment. Often habitat choice is related to the availability of food, presence of predators, and proximity to other viable habitats, amongst other variables. How these variables interact depends on fluctuations in the trophic web of which they are a part.Corythoichthys flavofasciatusis a species of pipefish that occurs in the fringing and back reefs of Mo’orea, French Polynesia. It feeds on zooplankton and occurs primarily on dead coral heads that are covered in algal turf. This study aimed to understand the relationship between zooplankton abundance, habitat quality, and substrate types on the habitat preferences of this pipefish. A field survey of the abundance of zooplankton in different habitats was used to determine if more food was available in habitats that were dominated by dead coral. Results suggest that more zooplankton are found above algal turf than live coral. A survey looking at pipefish abundance and amount of coral available in the habitat suggests that pipefish abundance correlates weakly to the amount of algal turf in the environment. An experiment quantifying color change in light and dark morphs of pipefish was conducted to determine if pipefish were capable of background adaptation, depending on substrate color. The results suggest that these observations were not statistically significant but warrant further research, using larger sample sizes. The findings of this study provide insight into the ecological role of pipefish in coral reef habitats.

Abstract.Much of the recent decline in coral reefs can be attributed to coral disease; however, very little is known about coral immunity. Pink non-nomral pigmented immune response lesions have been seen on massivePoritescoral in Mo’orea. Field surveys were conducted around the island measuring; sedimentation, water flow rate, location in the fringing or back reef and the number ofDendropoma maximumandSpirobranchus giganteusembedded in the coral to test for an association with the immune response. Multivariate linear regression reveals a nearly significant positive association betweenSpirobranchusgiganteusand pink lesions. This study suggestsS. giganteusmay play a role in this immune response or be linked to some other confounding factor. Thus,S.giganteuscould be a potential bio-indicator for coral disease to help aid reef conservation efforts. 

Communities of non- vascular plants called bryophytes grow on limestone and basalt on Mo'orea, French Polynesia. The abiotic properties associated with living on each substrate is not well known, however. This study looks at the soil pH, buffering capacity, phosphate levels and substrate water holding ability associated with each substrate. In general, limestone has greater water holding capacity than basalt and its soils are more basic, have higher phosphate levels and have a greater pH buffering capacity than soils on basalt. This study also looks at the biological impact of these substrate abiotic differences by using multivariate discriminate analysis to compare bryophyte communities on each substrate. Five species are tightly correlated with a particular substrate. Ectropothecium sandwichense and Floribundaria aerunginosa prefer limestone whereas  Calymperes aongstroemii, Taxithelium vernieri, and Ectropothecium sodale, prefer basalt. Because the distribution of these species is highly correlated with substrate in nature, a reciprocal transplant experiment was designed to see if substrate directly affected a specie's growth. Ectropothecium sodale and Ectropothecium sandwichense can, physiologically, grow on either substrate. This suggests that other factors like elevation, predation and community effects might be contributing to the segregated bryophyte communities observed in nature. Understanding the abiotic and potential biotic factors that influence the distributions of bryophytes enables locals, scientists and developers to use these plants as bioindicators of habitat change.

Social structures and population ecology can greatly influence individual behaviors in animal societies. The Common Myna (Acridotheres trisis) is a social, aggressive bird that is known as one of the world’s worst invaders. On the island of Mo’orea, French Polynesia,A. tristisis most often found in pairs and groups. It was anticipated that a pair ofA. tristiswould act as a team to increase foraging and defense efficiency. This study examined aggressive behaviors using behavioral observations ofA. tristisin pairs and groups on two different sites on the island. Food was added to the sites to determine how food availability may affect behavior. The results show that being in a group setting significantly increases aggression. A look at non-aggressive behaviors provided information on the most common behaviors seen inA. tristisboth in groups and pairs. Furthermore, the addition of food significantly increases aggression. The aggressive behaviors seen were increased with group type and food availability. These behaviors could be mediating the invasive nature of this bird.

Abstract.Estuaries are some of the most productive ecosystems in the world; though human development and global warming are threatening them. Zooplankton communities can serve as biological indicators of stresses due to their short lifecycles and sensitivity to environmental shocks, such as salinity changes. Studies have looked at the effects of freshwater shocks in the lab outnumber those that surveyed natural zooplankton distributions change along the freshwater gradient created by outflow from rivers. This study surveys the distribution of various taxa and examines the relationship this has with salinity by sampling zooplankton in Pao Pao River and Opunohu River on the island of Moorea in French Polynesia. In addition, this study tests the ability of copepods native to brackish water in Pao Pao to survive various shocks of increasing or decreasing salinity over time, as well as their response to bright light. Significant differences were found in overall community composition between bays and along the freshwater gradient. Most taxa exhibited strong correlations to salinity levels; some positive, some negative and some parabolic. Sharp rises in salinity appear not to affect copepod survival rates significantly, but abrupt drops do have significant effects. Light seems to repel copepods significantly as well. 

A controlled observation study was used to determine differences in athropod communities on fruits introduced to the island of Mo’orea, French Polynesia, approximately 300 and 1000 years ago respectively: papaya (Carica papaya) and Tahitian chestnut (Inocarpus fagifer), in two regions: an agricultural school and a tropical moist broadleaf forest. Distinct differences in communities existed by fruit and region, and there was interaction between the influence of region and fruit type. Papaya communities showed the most differences by region. Papaya communities had a greater mean number of individuals and taxa than Tahitian chestnut communities. Region did not have a significant effect on the mean number of individuals and taxa, but for both individuals and taxa the forested region showed more variation in the communities found on each fruit than in the agricultural region, perhaps due to greater niche differentiation (competition among species), on the less frequently disturbed site. The most abundant taxa were flies (Diptera) and ants (Hymenoptera: Formicidae). Community differentiation by region appeared to be influenced most strongly by less abundant species, rather than by the most abundant taxa. This study provides groundwork for future studies of tropical relationships between arthropods, land use changes, and fruit, and provides evidence of agricultural impacts on arthropod communities.