Steven Murray

Recent Publications

Current Students

Recent Graduates

Home

Susan Frisch (Email: susanfrisch@hotmail.com)

Spring 2003 Master's Thesis: Taxonomic diversity, geographic distribution, and commercial availability of aquarium-traded species of Caulerpa (Chlorophyta, Caulerpaceae) in southern
California, USA

Fourteen taxa (ten species) of Caulerpa were identified from retail aquarium outlets in southern California, USA. Seaweeds were sold in 58 % and species
of Caulerpa in 52 % of the 50 stores visited between November 2000 and
August 2001. Caulerpa serrulata var. hummii (18 %), C. taxifolia (14 %), C.
racemosa (14 %), and C. racemosa var. lamourouxii (14 %) were the most
common taxa. The fourteen aquarium-traded Caulerpa taxa are distributed
worldwide. Only two (C. ashmeadii and C. microphysa) are confined to the
tropics whereas 12 have distributions that extend into temperate seas. These
temperate components to their distributions indicate that, if introduced,
multiple taxa of aquarium-traded Caulerpa might be capable of establishing
invasive populations in southern California or other temperate waters. The
widespread availability of Caulerpa taxa, including many with distributions
ranging from the tropics to temperate waters, demonstrates that the aquarium
industry is potentially a significant source for Caulerpa introductions.

Everett Yee (Email: eyee@fullerton.edu)

Fall 2002 Master's Thesis: Effects of temperature on activity, food consumption rates, and gut passage times of three seaweed-eating species of Tegula (Trochidae) from central and southern California

Herbivorous ectothermic snails may experience difficulty obtaining sufficient nutrients, limiting their ability to sustain populations under sub-optimal sea temperatures. I hypothesized that, at different temperatures, activity, consumption rates, and gut passage times of three Tegula species would correspond with temperatures characteristic of their geographic distributions: T. brunnea (cold water), T. aureotincta (warm water), and T. funebralis from warm and cold waters. Activity and consumption rates of T. aureotincta increased with temperature; of T. brunnea's were highest at 19 ºC and lowest at 11 ºC; warm-water T. funebralis' were lowest at 11 ºC; and food consumption of cold-water T. funebralis was fastest at 15 ºC but activity was highest at 23 ºC. Temperature affected gut passage time of only T. aureotincta. Temperature's effect on activity and consumption rates might influence the northern limit of T. aureotincta. T. brunnea's activity and consumption rates were not hindered by warmer temperatures. Widely separated T. funebralis populations may be adapted to regional conditions.

Teri Denis (Email: tpdenis@attglobal.net)

Fall 2002 Master's Thesis: Effects of human foot traffic on the standing stocks, size structures, and reproduction of southern California populations of the intertidal rockweed Silvetia compressa (O. Fucales)

Rocky intertidal habitats in southern California often receive large numbers of visitors and are exposed to high levels of human foot traffic. I hypothesized that experimental trampling treatments would decrease the canopy cover, reduce total biomass and reproductive biomass, and alter the size structure of southern California populations of Silvetia compressa, a habitat-structuring seaweed. I hypothesized that the amount of trampling damage would vary among sites exposed to different levels of natural and visitor disturbance. To test these hypotheses, I randomly located 15 plots (0.35 m sq) in the Silvetia assemblage at three sites known to receive different levels of disturbance. At each site, 5 plots served as controls while 10 received monthly trampling treatments of either 150 or 300 steps (429 steps / m sq or 857 steps / m sq) for 16 consecutive months. These treatments were much less intense than those employed in most previous trampling studies yet resulted in significant impacts to Silvetia populations at all three sites. I found that Silvetia cover, total biomass, and reproductive biomass, and the size structures of trampled populations had shifted to include higher frequencies of smaller Silvetia thalli. Most damage to Silvetia thalli appeared to be inflicted by the first 150 steps of trampling. Additionally, damage to Silvetia populations varied among sites and was greatest at Monarch Bay, the site receiving the least amount of natural and visitor disturbance. My results indicate that the simple act of walking across the shore can damage and change the structure of Silvetia populations and that the amount of injury varies among sites exposed to different levels of disturbance.

Jill Moeller (Email: jillmoeller@hotmail.com)

Spring 2002 Master's Thesis: Seasonal and spatial patterns of reproduction and recruitment in a population of the intertidal rockweed Silvetia compressa (Fucales)

Reproduction of the Crystal Cove Silvetia compressa population peaked during late fall and early winter based on receptacle and conceptacle and densities and numbers of early post settlement (EPS) phases collected on outplanted disks. Receptacle densities increased from mid summer through late fall and reached a maximum in November. EPS phases were found on disks between November and May and reached greatest densities in November. EPS settlement varied spatially and was much greater beneath S. compressa fronds than at shore elevations above or below the S. compressa assemblage. The majority of EPS settlers were found on smooth disk surfaces outside the reach of the adult canopy but occurred in disk pits when placed within the reach of canopy fronds. The majority of juvenile thalli (<20 mm) were found attached to rock substrata located beneath S. compressa fronds. Survivorship of young thalli at elevations above and below the S. compressa assemblage was very low. Calculations based on egg densities during the November period of peak receptacle production indicate a million-fold EPS mortality from zygotes to small, field thalli. The very low recruitment success observed for S. compressa is consistent with previous observations of its slow recovery following the mortality of adult thalli in southern California.

Jayson Smith (Email: jaysmith@ucla.edu)

Spring 2002 Master's Thesis: The effects of bait collection and trampling on a southern California Mytilus californianus community

Southern California rocky shores are heavily visited by humans who frequent the rocky intertidal zone for aesthetic pleasure, tidepooling, fishing, and collecting. At sites used by recreational fishers, the effects of foot traffic combined with the collection of mussels for bait may reduce mussel cover and create mussel-free gaps. To test this hypothesis, mussel cover and gap frequency in mussel beds were determined at sites receiving various levels of fisher use (low, moderate, and high use). Results indicated a trend of decreasing mussel cover with increasing fisher activity. In addition, the effects of trampling and bait removal on mussel populations were experimentally tested. Twenty-four 0.5 m x 0.7 m plots were randomly established in a mussel bed and subjected to monthly combinations of trampling (0, 150, or 300 steps) and simulated bait removal (0 or 2 removed mussels). Even during a period of high natural disturbance associated with the 1997-98 ENSO, plots receiving treatments experienced significantly greater reductions in mussel cover, mass, and density than controls. These results indicate that visitor foot traffic and bait removal by fishers can significantly reduce mussel abundance and impact southern California mussel beds.

Laurie Sato

Fall 2002 Master's Thesis: Density, size structure, and reproductive characteristics of intertidal Tegula gallina and T. funebralis (Trochidae) populations on southern California rocky shores

The densities and size structures of Tegula funebralis and T. gallina populations were studied at eight southern California sites, four of which were longstanding marine reserves. Snails found at these study sites were characterized by smaller mean shell diameters (MSDs) and lower frequencies of larger sized individuals compared with snail populations residing at higher latitudes. Among site variation in snail densities and MSDs appeared to be associated with site-specific characteristics, including habitat size and accessibility to visitors instead of reserve status. Gradients in MSDs, aspect ratios, shell thickness, and gonadal production occurred as a function of tidal position in the Dana Point T. gallina population. Snails of both sexes were larger, had higher aspect ratios, thicker shells, and increased gonadal production long a downshore direction. A population shift in the relative abundance of T. funebralis and T. gallina over the past two decades was found and may be correlated with warming regional sea temperatures.

Janine Kido (Email: jkido@fullerton.edu)

Fall 2002 Master's Thesis: Variations in the structure of Lottia gigantea Sowerby (owl limpet) populations among and within sites on southern California rocky shores

The structure of Lottia gigantea populations was studied at eight southern California sites. Greater mean sizes and higher frequencies of larger-sized individuals were found at sites difficult to access, several of which were long-standing reserves. Mean sizes were comparable to those reported for sites where high collecting pressure exists. Structure of populations inhabiting open rock surfaces was compared with populations in small patches within mussel beds. Lower densities and higher frequencies of larger-sized animlas were found in open rock habitats. Larger limpets exhibited greater gonadal mass and were mainly female. Patch habitat limpets showed reduced growth and produced less gonadal mass. Age determinations indicated larger limpets were long-lived. Collecting of larger limpets can shift populations towards those dominated by smaller limpets with lower gonadal production. Because L. gigantea maintains grazing territories, reduced abundances of larger individuals and changes in population structure caused by collecting can reduce available open territory resulting in cascading effects in intertidal communities.