Marine Respiration : The Effects of Temperature , Light , and Body Size on Pacific Zooplankton and Reef Goby Collected 2 - 10 o N Latitude

Methodology for conducting respiration studies on marine zooplankton and a small goby fish were established and implemented using a Unisef microrespirometer on the open ocean. Specimens were collected from 2-10oN latitude. Oxygen consumption for all animals at ambient temperatures ranging from 26-28oC in both light and dark conditions were measured. Although the amount of testing depended on the availability of animals and their survival, temperature change was stimulated on a goby and hyperiid amphipod. Euphausiids and phronemids collected from 26-28oC were also measured. Rates of oxygen consumption were calculated using Excel and analyzed with Anova statical programming. An increase in temperature, both through stimulation on an individual level and with increasing ambient temperature resulted in an increasing rate of oxygen consumption. Light conditions significantly increased euphausiid respiration. These two factors provide insight into the metabolic effects of diel migration and changing ocean temperatures. Additionally, the zooplankton follows the trend of larger size having a lower metabolic rate. Using the methodology introduced and tested in this experiment, future studies will be able to replicate and expand the implications of this study to better understand the physiology of marine animals, diel migration, community respiration, and the impact of the ocean on the global carbon cycle. Summers, M. Stanford UniversitySEA Cruise 211 Page 2 Introduction Oceanic respiration plays a major role in the global carbon cycle and contributes to the ongoing debate of whether the oceans function as a source or sink of carbon.. Understanding of respiration at the community level is extremely limited and much less is known about the physiology of individual organisms and how they are effected by environmental conditions. Within the pelagic food web, zooplankton are a key intermediate between lower primary producers and higher trophic levels. In the oceans, zooplankton biomass is predicted to be over 21.5 x 10^9 pounds, greater than that of other consumers (Ikeda, 1985). Contributing to both top-down and bottom-up models of the food web, zooplankton are important in controlling phytoplankton growth (Harris, 2000) and organic particulate flux from their grazing provides fuel for benthic communities and contributes to the sink of CO2 (Harris, 2000). The balance between primary production and respiration has recently been challenged based on surface level measurements of microplankton oxygen consumption (Giorgio et al., 2002). Results have indicated that respiration may exceed levels of production in oligatrophic areas of the ocean (Giorgio et al., 2002). Current estimates of photic level respiration stem from only the most productive and metabolically active areas, leading to over-estimates of approximately 1.2gCm^2/d or on a global level, 143GtC/yr (Giorgio et al., 2002). In zooplankton and fish metabolism, the conversion of food to energy requires oxygen. Oxygen consumption, referred to as respiration, can therefore be used to estimate metabolic rate. Since laboratory studies have shown that 42-72% of food ingested is converted through metabolism, understanding metabolic rates can be used to understand the total energy required and expelled by zooplankton (Ikeda, 1985). The extent of these implications are limited however, since Lampitt et al. found that Oithona nana consumes more than double the amount of food it needs to maintain its metabolism (1982). Summers, M. Stanford UniversitySEA Cruise 211 Page 3 Zooplankton occupy a variety of lifestyles and possess a great diversity of body sizes, eating behaviors, and lifecycles. Zooplankton range in size from 2-20 um. Zooplankton are detrivores, herbivores, omnivores, carnivores, and mixovores (combination of autotrophy and heterotrophy). They move and obtain their food through a variety of mechanisms, such as flagella, ion transport, peristaltic contractions, and swimming appendages (Harris, 2000). Such diversity in trophic position, feeding mode, swimming variety, and diel migration behavior implies a wide range of respiration levels among zooplankton taxa. Prior research has indicated that body size, temperature tolerance, developmental stage, and physiological state such as feeding or swimming play a role in the level of respiration. Other factors include food availability, temperature, salinity, and oxygen saturation (Harris, 2000). Another factor could be seasonal variations in respiration that have been attributed to the amount of food available, with respiration rates being lowest during periods of oligatrophy (Lampitt et al., 1982). Also, densities of animals or crowding in experimental chambers is thought to play a role in respiration of animals that experience high population densities at certain parts of the year (Zeiss, 1963). Likewise, the overall energetics of diel migration are not well understood. The energy expended depends on the amount of activity involved as well as the environmental conditions of temperature and pressure experienced (Torres et al., 1983). Oxygen consumption by marine zooplankton and small fish has been difficult to record due to both the small size of the individuals and distance from shore laboratories. Moreover, the environmental conditions associated with tropical climates has been understudied, especially in the Pacific Ocean. Although temperature has been seen to be a major component to respiration rates, few studies have explored marine respiration above 20oC. In tropical areas, sea surface temperatures range approximately 16 degrees from the surface to a depth of 500 m (Scripps Institute of Oceanography, 1963). Based on CTD data from our cruise track, animals that migrate vertically, usually within the first 200 m, may experience temperature fluctuations from Summers, M. Stanford UniversitySEA Cruise 211 Page 4 28-7.5oC degrees. Likewise, as climate conditions vary seasonally with El Nino events and continue to gradually warm, animals are subjected to a greater range of temperatures. The main goal of this study was to explore the utility of using a microrespirometer to obtain accurate measurements of metabolic rates of zooplankton and small fish on a moving ocean vessel. The purpose of this study was to explore the respiration of different zooplankton groups in varying conditions along a cruise track of 18 degrees to 4 degrees north. This paper aims to 1. establish a method for measuring the oxygen consumption of marine zooplankton and small fish, 2. evaluate the effects of temperature and light and dark conditions on the rate of oxygen consumption, 3.measure rate of oxygen consumption differences on an individual level. This analysis can begin an understanding of how animals will cope with varying climatic conditions. Based on prior knowledge, this experiment was expected to show animals respiring at a higher rate with increases in temperature and activity level. Regardless of latitude and temperature conditions at the site of conditions, animals of the same species were expected to respire at the same rate. Additionally, animals that migrate vertically were predicted to have different rates of oxygen consumption in light or dark conditions. Metabolism was also expected to decrease with increase in overall size.