Physiology

Environmental stress affects the function of individual organisms and influences their ability to compete against other species for space, food, and other resources. Since each species will respond differently to a stress, such as high temperatures, even small environmental changes can upset the delicate ecological balance, causing large changes in the structure of marine communities.

PISCO is investigating how marine organisms cope at a molecular, cellular, and whole-organism level to environmental stress caused by variations in temperature, salinity, light, and food supply. Understanding how organisms may respond to stresses caused by climate change and ocean acidification can be an early warning system for managers. This work has allowed PISCO to pioneer the use of a DNA microarray ("gene chip") to evaluate the effects of short-term changes in the environment on the function of organisms. We look at physical responses to these stimuli using three main approaches:

• RNA : DNA measurements indicate whether an organism is growing at a given time. Most animals have a fairly constant amount of DNA (the "blueprints" for growth), and only increase the amount of RNA (the "construction sites" for growth within the cell) when growing. A high ratio of RNA to DNA indicates that a lot of "construction" is going on and the animal is growing. This technique shows how quickly organisms respond to stimulus such as an increase in food supply.
• Heat shock proteins (HSPs) indicate when an organism has become hot or otherwise stressed. The stress damages proteins (used by every function in a cell). In response to the damage, cells produce HSPs which stick to healthy proteins, interfering with their function. By measuring the amount of HSP within the cells of organisms in their natural environment and in the lab, investigators hope to reveal patterns of environmental stress and determine how reliable HSPs are as an indicator of this stress.
• The ratio of carbon to nitrogen (C:N ratio) in plants can indicate nutrient limitations that slow plant growth. Plants require many nutrients to survive, grow, and reproduce but their growth is often limited by the availability of nitrogen and phosphorous. PISCO researchers can examine seaweeds and other plants to understand how their growth is affected by nutrient availability. These studies can show how these plants respond to changes in oceanographic conditions and inform how ocean conditions affect primary productivity on rocky shores.

Using these studies PISCO has found relational evidence between the functions of organisms, and large-scale oceanographic patterns. Results indicate that RNA : DNA and C:N ratios are an effective way to measure recent nutritional fluxes in marine organisms. Heat shock protein (HSP) responses are particularly useful for understanding how marine organisms may respond to a changing climate in which heat stress is likely to increase.

PISCO scientists are leading the way in studying the response of ecologically important species such as mussels, whelks, limpets, grazing snails and sea stars to thermal stress, at local and regional scales. PISCO scientists have demonstrated that HSP levels increase with height on the shore, but that responses differ between sites. While we continue to explore variation in heat shock response to stressful conditions, results thus far indicate that this response will be a valuable tool in understanding and predicting how marine communities will respond to environmental disturbances such as climate change.