Kenneth S. Norris Rancho Marino Reserve

29 Nov, 04 PM - 29 Nov, 04 PM

The factors that determine the geographic range limits of individual species are still poorly understood and existing hypotheses have focused on the role of both biotic and abiotic factors. The aim of my project is to quantify how the ecology and life history of L. gigantea vary throughout its range (Mid-Baja to northern CA) and examine whether the observed variations relate to changes in physical and coastal oceanographic processes. In particular I will measure latitudinal variations in the growth rate, abundance, fecundity and mortality of L. gigantea and also estimate patterns of gene flow between populations. I will then quantify the relationships between these variables and latitudinal fluctuations in habitat temperature, the nature of the habitat (e.g. composition of the substrate) and food availability. By examining the relationship between ecological and environmental variables and quantifying how these change from the center of the range to the range margin I will be able to test the roles of biotic and abiotic factors in determining the range limits of L. gigantea. L. gigantea is commonly harvested by humans (Roy et al, in press). Therefore, I will attempt to quantify how human impacts are affecting the population biology of this species throughout its range. I will quantify the effects of human impacts by comparing protected sites (e.g. reserves) with sites that have unrestricted access and by comparing field data with those from museum collections (see Roy et al, in press). The Kenneth-Norris Rancho Marino UCSB reserve is an ideal field site because it contains a good population of Lottia gigantea. METHODS: In Kenneth-Norris Rancho Marino reserve and at every field site for this project I will be employing the same field techniques. The duration of the field work at the reserve will be from winter 2003 ? 2007. GROWTH RATE: At each field site, I will tag approximately 2-3 populations of Lottia gigantea using very small Bee tags (The Bee Works Co.) with a non-toxic super glue adhesive. I have defined a population of Lottia gigantea as the number of marked individuals inhabiting an area effectively isolated from adult migration to other patches of Lottia gigantea (e.g. a rock surrounded by water or other physical barriers). Individual colored bee tags are numbered and are approximately 2.4mm in diameter. Depending upon the color of the shell of individual limpets (could be black, brown, greenish, or white), I will apply each bee tag in correspondence with the color that most closely matches the color of the limpet. This will cut down on the probability that individual limpets will be singled out by potential predators (shore birds) and reserve visitors. Limpets do not need to be taken off of the substrate in order to tag them; therefore, I will cause very little disturbance by tagging. I will measure all tagged individuals (length and width) to the nearest 0.1mm using Vernier calipers every 2-3 months for four years. Growth rate of Lottia gigantea is density dependent (Wright, 1985; Kido, 2000). Therefore, I will also quantify the density of limpets in the marked population. Where possible, I will monitor one population at a mid tide location, and another 1 or 2 populations in the high intertidal. I will tag approximately 150 individual limpets of all different sizes between the two populations (deviations would be due to variations in population size). HABITAT TEMPERATURE In order to determine how temperature fluctuates from one site to another along the coast, I will install temperature loggers next to marked populations of Lottia gigantea. The HOBO Water Temp Pro will be the temperature logger of choice. I will roughly cut a piece of plexy glass to the shape of a logger (~4 inches long) and attach it to the substrate using sea goin? poxy putty (permalite plastics Co.) next to a marked population. I will then attach the logger to the plexy glass. The logger will record temperature data once every 2 hours and I will download the data during periodic visits. FOOD AVAILABILITY Since limpet growth rates may vary based on differences in food resource availability (Kido, 2000; Daly, 1975; Stimson, 1973), I will determine the algal abundance / thickness around each population at various times throughout the year depending upon the growing season of the algae. I will sample the microalgae inside or immediately adjacent to an area with marked individuals. I will use a hammer and chisel to scrape off a known area of algae and a small portion of the underlying rock (~3.5 cm2). I will then transport the rock chips back to the laboratory and store them in the dark in a freezer until the pigments are extracted and analyzed with a spectrophotometer. ABUNDANCE AND SIZE FREQUENCY DISTRIBUTIONS To determine the abundance of Lottia gigantea at each field site, I will establish a few transects in areas of available habitat. Transect length and the number of quadrats sampled will vary depending on the amount of habitat available. I will measure the size frequency distribution of Lottia gigantea at each field site by measuring the length of approximately 300 ? 500 individuals (where available). Measurements will be made at each site on all animals > 15 mm encountered. Animals < 15mm will be excluded from the surveys because individuals of this size can?t be consistently distinguished from other small limpet species. FECUNDITY In marine invertebrates, fecundity usually scales positively with size. A number of authors have shown this pattern for Lottia gigantea (Kido, 2000; Daly, 1975; Wright, 1985). In order to measure fecundity, one must sample individuals just before they spawn. There is good evidence that at least in northern Baja and southern California, Lottia gigantea spawns in early ? mid February (Daly, 1975; personal observation). Therefore, I will sample individual limpets of all size classes at each field site sometime from late January to mid February. I will create a gonad somatic index (GSI = gonad weight/ [body weight ? gonad weight] x 100) for each limpet. Specimens can then be placed into different size classes and plotted against mean GSI to determine the relationship between local fecundity and size. These values can then be compared with other limpet populations along its geographic range. In order to get a good estimate of local fecundity I need to collect approximately 25 animals of different sizes from each field site (Daly, 1975; Kido, 2000). I will collect unmarked limpets from available habitat at points all throughout the field site. The sampling of limpets shouldn?t have an impact on the local health of the populations at the reserve because so few individuals are actually being taken. It is essential to determine the local fecundity of Lottia gigantea at the reserve because it will provide for a useful comparison of fecundity between other less protected sites in California. These comparisons will be helpful in determining if humans are having an impact on the reproductive ecology of Lottia gigantea. I will not sample individuals at the reserve until the next spawning season (~January 2004). The animals collected for this portion of the study can also be used for molecular analysis (microsatellites in prep.) to determine the amount of gene flow between different populations. In addition, the shells can be used for sclerochronological analysis, which helps to determine the age of the limpet. Therefore, no portion of the animal will go to waste. SEX ALLOCATION Lottia gigantea is a protandrous hermaphrodite (Wright and Lindberg, 1982). The majority of the large individuals are female and most of the small individuals are male (Daly, 1975; Kido, 2000; Wright and Lindberg, 1982). It has become increasingly important to determine the sex ratio of Lottia gigantea populations because of the potential impact humans have had on this species. Since larger animals (mostly females) are preferentially taken from the intertidal, the sex ratio of the local population may have become increasingly male skewed. Alternatively animals in impacted populations may be changing sex at smaller sizes than previously determined. Unfortunately, there are no secondary sex characteristics available to tell male Lottia gigantea from female, and so it is difficult to determine the sex ratio of a marked population without sacrificing a proportion of the animals. Wright and Lindberg (1979) describe a potentially non-fatal method of sex determination for Lottia gigantea. This technique involves inserting a syringe with a hypodermic needle into the gonad of an animal and extracting a small amount of the gonad onto a microscope slide. The sex can usually be observed by the color of the gonads (white = males; darker/spherical = females) with the naked eye, or with the help of a hand lens. If done correctly, this method will result in a very low mortality rate. I am currently practicing this method on animals in the field and in the lab from different locations around San Diego. Once this method is perfected, then I will consider using it on the animals at the reserve in the upcoming seasons of this field study. LITERATURE CITED Daly, G.P. (1975). ?Growth and reproduction in the marine limpet Lottia gigantea (Gray) (Acmaeidae). M.S.. Thesis. San Diego State University Kido, J (2000). ?Variations in the Structure of Lottia gigantea (Owl Limpet) populations among an within sites on southern California rocky shores.? M.S. Thesis. California State University, Fullerton Roy, K., Collins, A.G., Becker, B.J., Begovic, E., Engle, J.M. (in press) ?Anthropogenic impacts and historical decline in body size of rocky intertidal gastropods in southern California.? Ecology Letters Stimson, J.S., (1973) ?The role of territory in the ecology of the intertidal limpet, Lottia gigantea.? Ecology 54(5) 1020-1030 Wright, W.G. and Lindberg, D.R., (1979) ?A non-fatal method of sex Determination for pattellacean gastropods.? J. Mar. Biol. Ass. U.K. 59, 803 Wright, W.G. and Lindberg, D.R., (1982) ?Direct observation of sex-change In the Pattellacean limpet, Lottia gigantea.? J. Mar. Biol. Ass. U.K. 62(3) 737-738. Wright, W.G. (1985) ?The behavioral ecology of the limpet Lottia gigantea: Interaction between territoriality, demography, and protandric hermaphroditism.? Ph.D. thesis Scripps Institution of Oceanography

Visit #995 @Kenneth S. Norris Rancho Marino Reserve

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Under Project # 857 | Research

University of California San Diego - Ecology, Behavior, Evolution. Division of Biology

graduate_student - University of California, San Diego

Reservation Members(s)

Phillip Fenberg Nov 29, 2002 (1 days)
Phillip Fenberg Nov 29, 2002 (1 days)
Phillip Fenberg Nov 29, 2002 (1 days)

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