Aspects of ecology and algal physiology in Hawaii's rocky intertidal zones

Abstract

Intertidal zones are vulnerable to anthropogenic impacts that result from human populations concentrated near coastal waters and while the impact on temperate rocky intertidal systems is much studied, comparatively less is known about these habitats in the tropics. To bolster knowledge and facilitate conservation efforts this dissertation investigates aspects of ecology and algal physiology in Hawaii's rocky intertidal zone. I describe an intertidal zone with a flora and fauna well suited for a tropical environment. Assemblages of tidepool fishes and benthic organisms vary among sites and are vertically structured across narrow shores; consistent with the hypothesis that abiotic or biotic factors vary. A survey of nitrogen concentration and isotopic composition in two species of algae collected in nearshore waters along southwest O'ahu provides evidence that much of this algal community is supported by land-based nutrients. In addition, I use infrared thermography to examine thermal ecology on a tidally driven shore. I found that temperature varies over fine-spatial scales and changes rapidly with tides and waves and organisms either 1) associate with cooler habitats 2) tolerate hotter surroundings or 3) have characteristics allowing them to remain cooler than their surroundings. To examine the affect of temperature on physiology, thermal tolerances of 9 species of reef algae were tested in the laboratory. These species are robust to short doses of heated seawater; maintaining rates of photosynthesis up to 35°C. Results from a photosynthetic survey conducted with pulse amplitude fluoremetry documents an intertidal algal community that is high-light adjusted with the ability to respond to daily fluctuations in supraoptimal irradiances. In situ measurements and manipulations reveal that microtidal fluctuations (+1 m) combined with early morning timing of low tide, limits exposure to intense solar radiation and temperature, and facilitates the physiological performance of common reef algae. This is in contrast to temperate shores where algae experience reduced rates of photosynthesis from extended periods of aerial exposure. This dissertation advances methods in intertidal ecology, provides a baseline on which to measure future change, and has important implications for predicting the impacts of ocean warming and eutrophication on the eco-physiology of tropical reef algae.