Evaluation of modified Sphyrion tags for marking Caribbean spiny lobsters, Panulirus argus

Jennifer Dijkstra¹* and Julian Gutt.^{2 1}Department of Zoology, University of New Hampshire, Spaulding Life Sciences, 46 College Road, Durham, NH 03824, USA; ²Alfred-Wegener Institute for Polar and Marine Research, Columbusstrasse, Postfach 120161, D-27515 Bremerhaven, Germany.

M. B. Doerries* and C. L. Van Dover. Department of Biology, College of William and Mary, Williamsburg, VA 23187, USA; e-mail mbdoer@wm.edu.

Chemosynthetic deep-sea communities of the Mid-Atlantic Ridge have been described as having two biogeographic provinces based on preliminary species lists and the distribution of two vent mussel species: Bathymodiolus azoricus in the north (Menez Gwen, Lucky Strike, Rainbow) and B. puteoserpentis in the south (Snake Pit, Logatchev). As a part of a quantitative study of species composition and community structure at comparable habitats across these sites, replicate samples of mussel-bed fauna were collected at Logatchev, the southern-most known site on the Mid-Atlantic Ridge. Preliminary visual observations indicate Logatchev has a high biomass, dominated by ophuroids, compared to other vent sites on the Mid-Atlantic Ridge. Further analysis of samples will estimate species richness, evenness and composition, aiding our ability to define biogeographic provinces on the Mid-Atlantic Ridge. Through quantitative and comparative methods of sampling and examining habitats common to most vents, the information collected from Logatchev and other sites will contribute to our understanding of the underlying processes that lead to the development of chemosynthetic biogeographic zones, their ecological and geographical constraints, and the processes leading to divergent community structures.


The interaction of spatial variation and post-settlement density dependence in the intertidal porcelain crab, Petrolisthes cinctipes

Megan J. Donahue.* Section of Evolution & Ecology, University of California, Davis.

In marine populations, variation in larval supply and post-settlement density dependence interact to determine benthic population size and spatial distribution. Petrolisthes cinctipes is a widely-distributed, intertidal porcelain crab with planktotrophic larvae. Like many marine organisms with planktonic larvae, P. cinctipes exhibits high spatial variation in larval supply and local adult density. In this study, I demonstrate two sources of post-settlement density dependence in Petrolisthes cinctipes: gregarious settlement and intraspecific competition. Using density manipulation experiments in the field, I quantify the positive influence of local adult density on settlement rate. Using field and laboratory experiments, I demonstrate the negative effect of density on individual growth rate in all but the largest size class of P. cinctipes. Finally, I offer a framework for understanding how spatial variation in larval supply and local density will interact with these sources of density dependence.

Sponge dynamics in nearshore hard-bottom communities of the Florida Keys

Scott Donahue* and Mark J. Butler IV. Department of Biological Sciences, Old Dominion University, Norfolk, VA 23529, USA.

Sponges, octocorals, and stony corals are the dominant sessile fauna within hard-bottom communities in Florida Bay, FL (USA). The sponge component of these communities has been cyclically decimated from as early as 1844, but most recently experienced a mass die-off of nearly all sponge species in south-central Florida Bay in 1991 and 1992, apparently in association with phytoplankton blooms. Our sponge transplant studies over the past two years suggest that conditions in these formerly impacted areas have recovered sufficiently to permit the survival and growth of several sponge species. However, continued episodic blooms and the proposed restoration of the Everglades hydroperiod have the potential to impact the sponge community in these areas in the future. Therefore, we are investigating the potential role of several sponge taxa in the maintenance of hard-bottom habitat via their influence on local hydrodynamics and the recruitment of sponges and other sessile fauna. Our preliminary evidence suggests that large physical structures such as sponges enhance scouring of the bottom adjacent to them, with potential impacts on local sediment depth and larval settlement. Thus, we are currently examining the recruitment of sessile invertebrates on artificial substrates placed at varying distances around different sponge taxa.

Meredith Dorner,* Scott Santos, Gemma May, and Mary Alice Coffroth. Buffalo Undersea Reef Research, Department of Biological Sciences, State University of New York at Buffalo, Buffalo, NY 14260, USA; telephone (716) 645-2718.

Sea anemones within the genus Aiptasia are distributed worldwide and typically harbor symbiotic dinoflagellates. Aiptasia collected from Japan (A. pulchella), Hawaii (A. pulchella), Eilat (A. pulchella), Bermuda (A. pallida), and Puerto Rico (A. pallida) all harbored zooxanthellae belonging to Symbiodinium clade B, as determined by restriction fragment length polymorphism of nuclear small subunit (n18S)-rDNA. In contrast, A. pallida from the Florida Keys usually host Symbiodinium belonging to clade A. Sampling in Florida in the winter has revealed some individuals which possess Symbiodinium from clades A and B. Two hypotheses are proposed to explain these observations: (1) The Aiptasia sp. found in the Florida Keys are a different species than those found in other areas sampled. (2) The cladal variation observed among the Florida Keys Aiptasi sp. is in response to environmental variation. An ongoing study is evaluating the influence of the environment on this symbiosis by sampling Aiptasia sp. from the Florida Keys each month as well as conducting experiments to determine the effects of light and temperature on zooxanthella clade.


Hitchhiking hydroids: assessing the relationship between the coquina clams Donax and the hydroid Lovenella gracilis

Joanne R. Dougherty* and Michael P. Russell. Department of Biology, Villanova University, Villanova, PA 19085, USA.

The coquina clams in the genus Donax are dominant members of the infaunal community of high-energy sandy beaches. Donax are often found in association with an epibiotic hydroid, Lovenella gracilis. This tufted brown hydroid uses the external posterior end of living clams as a substrate. The significance of the relationship between the clam and the hydroid has not been studied extensively, however some workers suggest that the L. gracilis forms a symbiotic relationship with the clam. I plan to investigate the effect of L. gracilis on the population biology, life history, and distribution of Donax by quantifying the effect of the hydroid on clam growth and rates of predation by gastropods. I will also document the seasonal variation in the association of the hydroid with Donax over the next year. Preliminary field data suggest that there is a size-specific relationship between the clam and the hydroid in that larger clams are more likely to have hydroids, however, the hydroid has been observed on recently settled juveniles as small as 2 mm in length.


Dispersal and recruitment in terrestrial versus marine environments: the benthos is not just an underwater landscape

C. Ashton Drew* and David B. Eggleston. North Carolina State University, Marine Earth & Atmospheric Sciences, Jordan Hall Box 8208, Raleigh, NC 27695, USA.

Existing landscape ecology theory has primarily been developed within terrestrial systems and has not been adequately tested in marine environments. The assumptions and methods appropriate for modeling terrestrial systems might not apply in marine environments. While terrestrial organisms generally move through a landscape, most marine organisms can utilize hydrodynamic currents to disperse over a landscape, requiring a three-dimensional conceptualization of movement patterns. We use a cellular automata model to compare recruitment success resulting from various terrestrial versus marine dispersal strategies within patchy environments. We likewise evaluate how recruitment success of a given dispersal strategy responds to landscape changes. The modeled dispersal strategies are: (1) terrestrial, where an individual may move in any direction based upon habitat preference; (2) passive marine, where an individual cannot move against or perpendicular to the current; and (3) active marine, where an individual can move in any direction but the current significantly biases potential movement. A highly successful recruitment event has a high number of settlers in suitable habitat (maximum survival) and results in a broad spatial extent of recruit distribution across the landscape (spreading risks associated with random environmental perturbations). We conclude: (1) differences in individual dispersal strategy can lead to significant differences in recruitment success within similar landscapes, and (2) the dispersal patterns and overall recruitment success of each strategy responds predictably to changes in landscape structure. We conclude with a presentation of how these modeled results can be combined with remotely sensed landscape mosaics to predict recruitment success marine species with varying dispersal capabilities, including: Nassau grouper (Epinephelus striatus), Caribbean spiny lobster (Panularis argus), Queen conch (Strombus gigas).


Assessing changes in photosynthetic parameters in response to varying environmental stimuli using chlorophyll a fluorescence

Mark D. Driscoll,¹* Florence I. M. Thomas,¹ and Kevin S. Beach.^{2 1}Department of Biology, University of South Florida, 4202 E. Fowler Ave. Tampa, FL 33602, USA; ²Department of Biology, University of Tampa, 401 W. Kennedy Blvd, Tampa, FL 33606, USA.

In recent years, several new technologies have been developed that have the potential to drastically change the way eco-physiologists carrying out experiments in situ and in the laboratory. The use of chlorophyll fluorescence has emerged as an important tool in the investigation of photosynthetic pathways. Measurements of specific photosynthetic parameters (e.g. quantum yield, saturation irradiance [I_k], inhibition irradiance [I_]) have been used to evaluate changes in photosystem configuration and operation in response to variable environmental conditions in terrestrial and marine (e.g. seagrasses, corals, macroalgae) systems. These studies have primarily focused on determining how the photosystem responds to changes in light regime. In addition to light, it has been shown that changes in the rate of chemical diffusion through the benthic boundary layer can affect primary production. The thickness of this boundary layer is reduced in high velocity flow, and increased at low velocities, effectively changing the nutrient flux to the organisms surface in response to hydrodynamic variations (e.g. tides, waves). Using a diving PAM (pulse amplitude modulated) fluorometer, we tested the photosynthetic responses of macroalgae (Caulerpa racemosa, and C. sertulariodes) to changes in hydrodynamic regime and irradiance in the laboratory and field. The use of chlorophyll a fluorescence in these experiments allows for a direct measure of photosystem response with a minimum interruption of water flow or blockage of irradiance. Changes in photochemical (Pq) and non-photochemical (NPQ) quenching, saturation irradiance (I_k), inhibition irradiance (I_) and the maximum electron transport rate (P_max) were measured. Results indicate that photosynthetic responses vary with changes in physical and environmental regimes.


The when, where and why of alternative states in rocky intertidal landscapes

Steve Dudgeon,¹* Christin Slaughter,¹ and Peter S. Petraitis.^{2 1}Department of Biology, California State University, Northridge, CA 91330-8303, USA; ²Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018, USA.

The mid intertidal zone of rocky shores in the Gulf of Maine is characterized by 4 conspicuous taxa, Ascophyllum nodosum, Mytilus edulis, Semibalanus balanoides and Fucus vesiculosus, that serve as foundation species of the respective assemblages that each dominates. At sites between the extremes of water motion on rocky shores, either barnacle-mussel beds or stands of rockweeds can dominate the same physical environment and may represent alternative states. Our empirical evidence of spatial scale dependent patterns of recruitment and mortality supports this hypothesis, but variability in succession among sites suggests that the potential for alternative states may be site-specific. To understand why at some sites communities can switch, but elsewhere cannot, we have developed a spatially-implicit community-level model consisting of these 4 species. Model parameters are based on empirical data taken from populations of each species in the Gulf of Maine or Nova Scotia, including ours on scale-dependent recruitment and mortality. The model assumes an area of 500m² and runs on a per month basis over several years following an ice scour event. As Petraitis and Latham (1999) hypothesized, a switch between states requires scale dependent rates of processes: without it, an established assemblage is resilient and maintains dominance even following clearings >100m²(i.e., site-specific factors determine outcome). Alternative states occur when recruitment and mortality are spatial scale dependent. However, Ascophyllum resists invasion and is stable following clearings up to 12.25 m² in area (4 m in diameter). In simulations of clearings between 4 and 12 m in diameter a switch to barnacles and Fucus vesiculosus occurs, in agreement with our empirical data on Swans Island over the past 5 years. Successful invasion by mussels requires clearings ≥12 m in diameter. The model accommodates both the alternative state and site-specific outcomes observed at different locations on New England rocky shores.


Biodiversity and ecosystem function: the consumer connection

J. E. Duffy,* J. P. Richardson, and K. France. School of Marine Science/VIMS, College of William & Mary, Gloucester Point, VA 23062-1346, USA.

Proposed links between biodiversity and ecosystem processes have generated intense interest and controversy in recent years. Most empirical studies have focused on grassland plants and aquatic microbial systems, with little attention to potential consequences of changing animal diversity. Theory suggests that changing diversity in multi-level food webs can have effects on ecosystem structure and function qualitatively different than those mediated by plants. We are addressing consequences of changing consumer diversity and food web architecture experimentally using eelgrass-beds as a model system. Here we report results from two mesocosm experiments (see Paul Richardson’s poster for tests of mesocosm realism), one in summer and one in fall. The first exposed eelgrass to each of six mesograzer species singly, in random combinations of three, and to all six species together. Epiphyte accumulation, total benthic biomass, benthic community structure, and grazer secondary production differed strongly among grazer species, and total grazer impact was correlated with grazer diversity. The diversity trend resulted from a sampling effect, however, i.e., the most diverse grazer treatments were more likely to include the most voracious grazer species. In the second experiment (fall), we measured impacts of predators (juvenile blue crabs) on food webs varying in diversity at the intermediate (grazer) trophic level. Grazer treatments differed in susceptibility to predation and, thus, in their damping effect on cascading impacts of crabs on plants (see Melanie Spring’s talk for details of the cascade). Comparison of the two experiments and field abundance patterns suggests that more diverse grazer assemblages exert more consistent pressure on plants due to seasonal asynchrony in population cycles among grazer species. Evaluating impacts of biodiversity loss on ecosystem function requires a more systematic expansion of the scope of current experimental research to multi-level food webs.


Measuring microphytobenthic production and consumption using a spectrophotometric method

A. L. Dunsmuir* and J. Cebrian. Dauphin Island Sea Lab, 101 Bienville Blvd, Dauphin Island, AL 36528, USA.

Measuring oxygen production and/or consumption by microphytobenthic communities is often a difficult task. These measurements are normally taken in-situ or in laboratory incubation chambers with an oxygen probe, which normally requires significant water movement to be accurate. This can be achieved by using either a stirring probe or magnetic stirrers within the chambers. The need for stirring often incurs significant cost. Moreover, it can result in substantial bias due to experimental error. A new spectrophotometric method to measure oxygen production by phytoplankton has recently been developed. The method is fast, precise and effective. It also performs over a wide range of concentrations, from anoxic to over-saturated environments, and it has been shown to out-perform classical techniques such as the Winkler titration. However, the new method has yet to be applied to microphytobenthic communities. Here, we use the new method to derive in-situ measurements of oxygen production and consumption by temperate microalgal communities, and evaluate its performance in relation to measurements taken with an oxygen sensor and stirring probe. Our study confirms the new method is faster, more efficient and more sensitive.