Waikiki: Assessing the “Spouting Waters” and Studying Its Effect on Benthic Communities

1. Average % Cover of Native Algae in Both Transects Laurencia spp. Laurencia spp. Pterocladiella Pterocladiella caerulescens caerulescens Padina spp. Crustose coralline Bryopsis spp. Dictyota acutiloba Transect 1 Transect 2 Waikiki: Assessing the “Spouting Waters” and Studying Its Effect on Benthic Communities Kanoelani Steward; Faculty Advisor: Mackenzie Manning Kapi‘olani Community College, Honolulu, Hawai‘i, USA ABSTRACT. Present day Waikiki is the result of a massive transformation of what used to be a flourishing ecosystem. It provided natural resources to a once thriving traditional Hawaiian community where natural streams used to flow to help nourish the land and sea. As a result of this dramatic change, most of these streams have been filled in or diverted. However, there is anecdotal evidence that suggests some flow may reach the ocean via submarine groundwater discharge (SGD) along the shoreline of Waikiki’s beaches. This study sets out to discover sources of SGD in Waikiki in an effort to characterize their influence on adjacent benthic habitats. We hypothesize that these flows could significantly affect the benthic community of marine organisms and coral reefs that inhabit areas adjacent to SGD outflow. In order to locate SGD along the shoreline, we measured fluctuations in the salinity and temperature of the seawater during low tides along the shoreline. Upon locating an area of SGD, the adjacent benthic community was characterized using point-intercept transect snorkel surveys to assess the substrate, coral, and algal composition of the area. Salinity and temperature measurements were recorded along the transect to measure the size of the area these flows may influence. These data will be compared against data collected at a near by control site in Waikiki that is not influenced by SGD. We predict the two sites will differ in community composition and suggest that the influence of SGD is a factor in those differences. This research is significant because it connects the history of Waikiki with the present-day effects of these ever-flowing streams. It addresses the influence of these “spouting waters” to determine the impact to adjacent benthic communities. INTRODUCTION. Our research is focused on detecting freshwater signatures that would indicate possible stream flow into Waikiki, and its influence on adjacent benthic communities. RESULTS. Substantial decreases in salinity (and hence possible sources of SGD) were determined using the following salinity balance equation: (Fs)x + (As)x = actual salinity, where Fs is groundwater salinity, As is the salinity of the ocean, x is their relative percentages, and actual salinity is the salinity detected. GRAPH B. Invasive algal species were the dominant algae throughout both transect lines. QUESTIONS. Do freshwater streams still flow to Waikiki? If so, how are the benthic communities adjacent to these flows affected? HYPOTHESES. We hypothesize that freshwater streams exist at various locations throughout Waikiki as Submarine Groundwater Discharge (SGD). We also hypothesize that this SGD outflow significantly affects adjacent benthic communities. FIGURE 1. Red points indicate substantial decreases in salinity equal to at least 10% groundwater. White lines indicate benthic transects 1 and 2. METHODS. To determine the presence of SGD outflow, a YSI meter was used to measure the salinity (ppt) and temperature (C) of the ocean. A GPS unit was also used to keep record of significant locations. GRAPH C. Algal composition between the two transects varied GRAPH A. Transect 1, the line closer to the storm drain/jetty where SGD was detected, showed a higher percentage of algae. FUTURE RESEARCH. Deploying settlement tiles to qualify and quantify the recruitment of benthic organisms to areas influenced by SGD. Perhaps, the influence of SGD affects the recruitment of organisms in that area and translates to the differences we observe in community structure. METHODS. To analyze the effects of SGD outflow, we conducted two 70m transect benthic surveys using point-intercept quadrats placed every 5m along each transect. ACKNOWLEDGEMENTS. We thank the Kapi`olani Community College STEM Program for institutional support. Funding was provided by NSF TCUP and NSF EPSCoR. This material is based upon work supported by the NSF. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF.