UCB Moorea Class: Biology and Geomorphology of Tropical Islands

Suspension feeders are sessile marine organisms dependent on plankton and organic particles transported by the water column for food. This study focused on the distribution of four suspension feeders (Dendropoma maxima, Spirobranchus giganteus, Heteractis magnifica, and Tridacna maxima) in Mo’orea, French Polynesia based on current, suspended particle abundance, and substrate type. Both D. maxima and S. giganteus were more frequently present at the site with highest current flow and suspended particle abundance. The positive correlation between current and suspended particle, or food, abundance suggests that a stronger current transports more organic particles to a set location than a weaker current. In comparison, H. magnifica and T. maxima abundance and occurrence were not related to current. This is because they are less reliant than D. maxima and S. giganteus on the current for suspension feeding. In comparison, all four species studied showed substrate preference. The distribution of the suspension feeders studied showed varying dependence on current and substrate type. Since suspension feeders regulate primary production by consuming plankton, their distribution and abundance greatly affects marine food chains. Understanding coral reef food chains is vital for comprehending the niche suspension feeders’ fill in coral reef ecosystems.

Defensive animal behavior is often a tradeoff between the energetic costs of defense and predator avoidance, with most animals choosing actions with the lowest energetic expense to evade their predators.Pholcus ancoralisis an introduced spider to Mo’orea, French Polynesia. I studied its defensive behaviors, with an emphasis on whirling, an energetically costly behavior which involves continual gyrations of the body. Different instars as well as females carrying egg sacs were disturbed with tactile, vibratory, and air movement stimuli to determine if larger instars and females with eggs have a higher whirling duration and frequency of defensive behaviors.P. ancoralisalso faced the potential spider predatorsThorelliola ensifera(Salticidae),Tangaroa tahitiensis(Uloboridae), andLeucauge granulata(Tetragnathidae) in a laboratory setting to determine if a higher whirling duration and higher frequency of defensive behaviors would lead to increased survivorship. The tactile stimulus elicited the greatest frequency and duration of whirling fromP. ancoralis. Adult pholcids had the highest whirling frequency and duration out of all the instars, with egg-carrying females displaying an even greater response than other adults. Third and younger instars chose to retreat significantly more than adults, suggesting a change in defensive strategies during development. Whirling was not associated with a higher survivorship ofP. ancoralisin the presence of potential predators, although repelling the predator and dropping away from it was. Thus, whirling is not an appropriate response toT. ensiferabecause it is conspicuous, energetically expensive, and does not promote survivorship. The inefficacy of whirling in this study suggests that this behavior may have arisen to defend against other salticids or other native natural enemies whichP. ancoralisescaped upon its introduction to Mo’orea.

Benthic invertebrates are vital not only for the place they hold in the trophic web of the marine ecosystem, but also for the incredible diversity that they add to the world. This is especially true of the dorid nudibranchs (family Dorididae), a group of specialist predators that are also the most diverse family in a clade of shell-less gastropods. Little work has been done on the roles that environment and behavior play on distribution patterns of dorid nuidbranchs. By carrying out habitat surveys, I found that two species of dorid nudibranchs (Chromodoris lochiandChromodorissp.) occupy different habitats in Cook’s Bay. Behavioral interaction tests showed that both species orient more reliably toward conspecifics than toward allospecifics.C. lochihas a greater propensity to aggregate thanChromodorissp. These findings indicated that the distribution patterns are a result of both habitat preference and aggregation behaviors. Further inquiry into these two areas is needed to make additional conclusions on the forces driving distribution. Information in this area is necessary to inform future conservation decisions. 

The tropical sea urchin genus Diadema, is considered one of the most significant and abundant. Their population dynamics greatly influence the health of coral reefs. Diadema have anti-predator behavior and defenses that help them to maintain a stable population. I investigated the limited spatial vision in Diadema savignyi, by testing their directional orientation to a target representing a crevice space used to hide from predators. This is the fourth sea urchin echinoderm to demonstrate evidence of spatial vision, the first for the genus Diadema. Furthermore, my results demonstrate that D. savignyi use their spines to filter light to improve their spatial vision. D. savignyi which had their spines removed lost their spatial vision. However, in starting closer to the target, D. savignyi still oriented without spines, suggesting spatial vision is still possible. In a field and lab study on the emergence times of D. savignyi, I found that D.savignyi may use daylight levels as a cue in their nocturnal emergence, usedto avoid their diurnal predators. The pervious understanding that Diadema react and process light supports my evidence of the role of light in emergence. My results illustrate mechanisms for which D. savignyi specifically are able to avoid predators, but also suggest the presence of such mechanisms in other sea urchins. In understanding these mechanisms of defense, it is possible to better understand the maintenance of sea urchin populations and thus their role in coral reef ecosystems.

 The role of mutualisms among invasive species in facilitating invasions remains relatively unexplored. Yet such interactions have high potential to alter intact community composition and function due to their positive fitness effects on the species involved. The following study explores an interaction that evolved independently among naturalized hibiscus and invasive ants and Hemiptera that colonized the island of Mo’orea, French Polynesia centuries apart.  For this study, a geographic survey was conducted across 7 plots, which revealed the relationship to be present across a broad range of habitats. Manipulative field experiments were also ran in order to classify the association as a mutualism, parasitism or commensalism. These experiments quantified changes in abundances and behaviors of ants and Hemiptera in response to different availabilities of sugar resources to ants. Results from these field experiments support the hypothesis that the relationship is indeed a mutualism, where all players receive a net benefit from their association with one another. The resultant finding that this is a geographically widespread mutualism among invasive species contributes to the study of invasion meltdowns. The discovery of the success of this invader-invader mutualism in an intact ecosystem contributes to a growing body of research on the role of synergistic effects of multiple species invasions in invasion meltdowns.

Social structure is key to a species' biology and ecology. Relations within a population can have important ftness consequences, but only recently have researchers been able to explicitly measure and quantify these relationships through network modeling. Social network analysis is the study of social groups as networks of nodes connected by social ties. In this study, network analysis is implemented to determine that there is a social structure within an aggregation of Himantura fai at feeding excursion sites. An ethogram defning H. fai behaviors is compiled. A sum of interactions network is subdivided into fve behavior networks to allow for further quantifcation of the relations within the aggregation. Size, color, and sex are found to be correlated to dominance, and an order of dominance is determined, with large females at the top and the smaller of both sexes at the bottom. To address the confounding factor of human presence at the study sites, the effects of feeding excursions on H. fai behavior are investigated. The variation and frequency of interactions between individuals increase with the presence of a feeder, but the amount of time spent interacting with at least one other individual is unaffected by human presence. Overall, this study investigates the effects of feeding excursions on H. fai behavior and utilizes a relatively new analytical tool to determine the social structure of H. fai.

The hermit crab Dardanus pedunculatus and the sea anemone Calliactis tricolor engage in a mutualistic relationship in the tropical reef ecosystem of Mo’orea, French Polynesia. This mutualism is shaped by the pressures on D. pedunculatus individuals to acquire actively and compete for C. tricolor in the wild. D. pedunculatus exhibits a consistent trend in behavior when competing for and placing C. tricolor on its gastropod shell. Since C. tricolor seems to be a valuable resource to D. pedunculatus, this species engages in intraspecific competition. Experiments were designed to examine the behaviors of D. pedunculatus under laboratory conditions when competing for and placing their symbiont. D. pedunculatus individuals steal C. tricolor from one another, with larger D. pedunculatus dominating in these encounters. In contests between two D. pedunculatus individuals, competition is also based on size dominance. The size of the cheliped of the left-handed D. pedunculatus is the most strongly correlated to winning a fight for C. tricolor. The placement of C. tricolor follows a distinctive symmetrical pattern on the shell of D. pedunculatus. By equally distributing C. tricolor, D. pedunculatus could possibly be protecting itself from attack coming at any angle. These behaviors stem from the benefits that both organisms derive from their union. Understanding the behavioral patterns linked to this symbiotic relationship helps to examine the broader web of interactions that build the complexity of reef ecosystems.

The process of plant recolonization takes place over a broad range of magnitudes and timescales. Studies of recolonization in tropical forest ecosystems are few in number making it an important addition to the ecological literature. To determine the effect of propagules and biotic factors such as sunlight, substrate and clearing level on the recolonizaton of plants, previosly-cleared plots were paired with adjacent, unmodifed plots in the forest. Species were identified in the plots and their abundance and presence or absence was compared to determine if one factor was more significant than another.The effect of propagules from the adjacent plot, sunlight availability and level of clearing were important determinants in what species were able to recolonize. Substrate did not show variation. Various biotic and abiotic factors are identifiable as determinants in recolonization but the complexity of interactions in tropical forest ecosystems makes predictions challenging.