2002 Progress Report: Shelter Bottlenecks and Self-Regulation in Blue Crab Populations: Assessing the Roles of Nursery Habitats and Juvenile Interactions for Shelter Dependent OrganismsEPA Grant Number: R827072C027
Subproject: this is subproject number 027 , established and managed by the Center Director under grant R827072
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Alabama Center For Estuarine Studies (ACES)
Center Director: Shipp, Robert L.
Title: Shelter Bottlenecks and Self-Regulation in Blue Crab Populations: Assessing the Roles of Nursery Habitats and Juvenile Interactions for Shelter Dependent Organisms
Investigators: Moksnes, Per-Olav , Heck, Kenneth L.
Institution: University of South Alabama
EPA Project Officer: Packard, Benjamin H
Project Period: January 1, 2001 through December 31, 2002
Project Period Covered by this Report: January 1, 2001 through December 31, 2002
RFA: Alabama Center For Estuarine Studies (ACES) (1999) RFA Text | Recipients Lists
Research Category: Targeted Research
Many marine fish and crustaceans in the young, juvenile stages are vulnerable to predation, and their survival may depend on the availability of habitats that provide shelter from predators. In areas where the supply of the larval stages is high, such nursery habitats may become overcrowded and limiting for juvenile populations, resulting in density-dependent processes that can regulate their numbers. Little is presently known, however, about the processes that can act as regulating mechanisms in juvenile marine organisms.
In the present project we studied the blue crab Callinectes sapidus in the Mobile Bay Estuary, Alabama, an area with a documented, large supply of blue crab postlarvae. The goal of the project was to determine if the availability of seagrass habitats can become a limiting resource for juvenile populations of blue crabs, and to test if competition and cannibalism between juveniles within seagrass beds can be important population regulating mechanisms. We hypothesized that: (1) competition for space or food within grass beds will result in density-dependent emigration from these habitats into unvegetated areas where mortality is higher; and (2) cannibalism between juveniles is common and increases with either cannibal or prey densities. These hypotheses were tested at Dauphin Island Sea Lab and the surrounding area, and assessed on several spatio-temporal scales using both laboratory and field experimental techniques.
We believe this work could significantly improve the basic understanding of recruitment regulation in benthic organisms, and broadly apply to the management of shelter-dependent fishery species. Understanding whether a marine population is limited by the supply of larvae, or regulated by density-dependent processes after settlement is central for efficient conservation and management of marine habitats and organisms. If juvenile blue crabs are limited by nursery habitats, and not by larval supply in the Mobile Bay Estuary, the species may be managed better by protecting the seagrass and marsh habitats in the area than by increasing the regulations on the fishery.
In Year 1 of the project, the results from two extensive laboratory mesocosms experiments did not provide support of the hypothesis that competition within grass beds creates density-dependent emigration from the nursery habitats, but suggested that density-dependent juvenile cannibalism may act as a regulating mechanism. To investigate further the effect of cannibalism and to test the influence of different juvenile habitats on the recruitment of juvenile blue crabs, two field experiments were performed in 2002.
In the first study, a cage experiment was performed to assess the relative importance of postlarval habitat selection and predation on abundance and distribution of juvenile blue crabs among four different habitats: live oysters, seagrass (Halodule wrightii), artificial seagrass, and open mud. The experimental setup consisted of empty habitat patches provided with or without cages that would allow settling megalopae and the smallest juvenile crabs to pass through the mesh but would stop predators. After a period of 3 days, the number of crabs that had colonized the habitats were sampled. High and similar numbers of blue crab settlers (megalopae and first instar crabs) colonized the oysters and natural and artificial seagrass habitats (140-350 settlers/m2), whereas significantly lower numbers were found on the open mud habitat (35-70 settlers/m2). This habitat-specific settlement pattern also was found in cages where predators were excluded, suggesting that active habitat selection at settlement was responsible for the distribution. Similar settlement and survival in the three structurally complex habitats demonstrated that oysters constitute a potentially important habitat for juvenile crabs, and that artificial grass could be used in the second experiment as a substitute for natural grass.
In the second experiment, we enclosed different densities of juvenile blue crabs and assessed density-dependent effects on blue crab recruits (megalopae and first to third instar crabs) that colonized artificial seagrass patches inside the cages. High densities of blue crab recruits colonized the predator exclusion cages (466 recruits m-2 3d-1), whereas densities of recruits were up to seven times lower in cages containing cannibalistic crabs, in uncaged seagrass plots and in natural seagrass. A negative correlation was found between the number of enclosed cannibals and the number of new recruits, suggesting that early juvenile mortality is directly related to cannibal densities, and therefore to the survival of earlier cohorts. Furthermore, proportional losses of megalopae and J1 crabs in cannibal inclusion cages were elevated during periods of high settlement compared to low settlement (70-86 percent and 31-54 percent loss 3d-1, respectively), indicating that the functional response of juvenile cannibals may decrease cannibalism at low prey densities. Laboratory experiments demonstrated that blue crab settlers did not emigrate in response to juvenile cannibals, suggesting that the high loss rates in the field experiment represent settlement mortality.
The study demonstrates that density-dependent cannibalism between juvenile blue crabs can be a major source of early benthic mortality with large effects on local recruitment patterns. These results suggest that juvenile crabs can regulate new cohorts by cannibalizing more efficiently when smaller crabs are abundant, and by creating higher mortality rates on new settlers when cannibal densities are high. This regulating mechanism would limit the densities of crabs within nursery habitats, making the availability of seagrass, marsh, and oyster habitats a critical factor in the recruitment of juvenile blue crabs.
Future activities include the: (1) presentation of the study results at the Benthic Ecology Meeting in 2003; and (2) publication of three manuscripts on the results of the project.
Supplemental Keywords:marine fish, predation, marine organisms, blue crab postlarvae, seagrass habitat, competition, cannibalism, population regulating mechanisms, oysters, artificial seagrass, open mud, ecosystem, seagrass, Halodule wrightii, blue crab, Callinectes sapidus, ecosystem protection, ecology, ecological effects, ecological indicators, environmental exposure, geographic area, water, aquatic ecosystem, coastal ecosystem, coastal environments, estuary, estuaries, estuarine research, estuarine waters, environmental chemistry, chemistry, assessment, indicators, Alabama, AL, artificial reef design, human modifications, fishery sampling., RFA, Scientific Discipline, ECOSYSTEMS, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Aquatic Ecosystems & Estuarine Research, estuarine research, Ecosystem/Assessment/Indicators, Ecosystem Protection, exploratory research environmental biology, Chemistry, State, Restoration, Aquatic Ecosystem, Ecological Effects - Environmental Exposure & Risk, Aquatic Ecosystems, Terrestrial Ecosystems, Habitat, Species, Ecological Monitoring, Ecology and Ecosystems, Aquatic Ecosystem Restoration, Ecological Indicators, marine food web, coastal ecosystem, water use, endangered species, estuaries, watersheds, Blue Crab Callinectes Sapidus, Alabama (AL), predators, coastal environments, Alabama estuaries, ecosystem, environmental indicators, water quality, conservation biology, estuarine waters, nusery habitat, human modifications
Progress and Final Reports:Original Abstract
Main Center Abstract and Reports:R827072 Alabama Center For Estuarine Studies (ACES)
Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R827072C001 Fluorescent Whitening Agents As Facile Pollution Markers In Shellfishing Waters
R827072C002 Red Snapper Demographics on Artificial Reefs: The Effect of Nearest-Neighbor Dynamics
R827072C003 Stabilization of Eroding Shorelines in Estuarine Wave Eliminates with Constructed Fringe Wetlands Incorporating Offshore Breakwaters
R827072C004 Interaction Between Water Column Structure and Reproduction in Jellyfish Populations Of Mobile Bay (SGER)
R827072C005 Effects of Variation in River Discharge and Wind-Driven Resuspension on Higher Trophic Levels in the Mobile Bay Ecosystem
R827072C006 Results of Zooplankton Component
R827072C007 Benthic Study Component
R827072C008 A Preliminary Survey of Macroalgal and Aquatic Plant Distribution in the Mobile Tensaw Delta
R827072C009 Fisheries-induced changes in the structure and function of shallow water "nursery habitats": an experimental assessment
R827072C010 Effects Of Variation in River Discharge and Wind-Driven Resuspension on Lower Trophic Levels of the Mobile Bay Ecosystem
R827072C011 Evaluation of Alabama Estuaries as Developmental Habitat for Juvenile Sea Turtles
R827072C012 Effects of Salinity Stress on Natural and Anthropogenically-Derived Bacteria in Estuarine Environments
R827072C013 The Role of Land-Use/Land-Cover and Sub-estuarine Ecosystem Nitrogen Cycling in the Regulation of Nitrogen Delivery to a River Dominated Estuary; Mobile Bay, Alabama
R827072C014 Environmental Attitudes of Alabama Coastal Residents: Public Opinion Polls and Environmental Policy
R827072C015 Synthesis and Characterization of an Electrochemical Peptide Nucleic Acid Probe
R827072C016 Determinants of Small-Scale Variation in the Abundance of the Blue Crab Callinectes Sapidus
R827072C017 Effects of Estrogen Pollution on the Reproductive Fitness of the Gulf Pipefish, Syngnathus scovelli
R827072C019 A Model for Genetic Diversity Aquatic Insects of the Mobile/Tensaw River Delta
R827072C020 Evaluating Trophic Processes as Indicators of Anthropogenic Eutrophication in Coastal Ecosystems: An Exploratory Analysis
R827072C021 Effects of Anthropogenic Eutrophication on the Magnitude and Trophic Fate of Microphytobenthic Production in Estuaries
R827072C022 Characteristics of Ship Waves and Wind Waves in Mobile Bay
R827072C023 Methods Comparison Between Stripping Voltammetry and Plasma Emission Spectroscopy for Metals in Mobile Bay
R827072C024 Changes in Water Conditions and Sedimentation Rates Associated With Construction of the Mobile Bay Causeway
R827072C025 Cold-Induced Hibernation of Marine Vibrios in the Gulf of Mexico: A Study of Cell-Cell Communication and Dormancy in Vibrio vulnificus
R827072C026 Holocene Sedimentary History of Weeks Bay, AL: Human and Natural Impacts on Deposition in a Gulf Coast Estuary
R827072C027 Shelter Bottlenecks and Self-Regulation in Blue Crab Populations: Assessing the Roles of Nursery Habitats and Juvenile Interactions for Shelter Dependent Organisms
R827072C028 Predicting Seagrass Survival in Nutrient Enriched Waters: Toward a New View of an Existing Paradigm
R827072C029 DMSP and its Role as an Antioxidant in the Salt Marsh Macrophyte Spartina alterniflora
R827072C030 A Preliminary Survey of Aerial and Ground-Dwelling Insects of the Mobile/Tensaw Delta
R827072C031 Natural Biogeochemical Tags of Striped Mullet, Mugil cephalus, Estuarine Nursery Areas in the North Central Gulf of Mexico
R827072C032 Resolution of Sedimentation Rates in Impacted Coastal Environments Using 137Cs and 210Pb Markers: Dog River and Fowl River Embayments
R827072C033 Investigation of the Use of Pulse Amplitude Modulated (PAM) Fluorometry as an Indicator of Submerged Aquatic Vegetation Health in Mobile Bay
R827072C034 Influence of Invasive Plant Species in Determining Diversity of Aquatic Vegetation in the Mobile-Tensaw Delta
R827072C035 The Influence of Shallow Water Hydrodynamics on the Importance of Seagrass Detritus in Estuarine Food Webs
R827072C036 Food Web Interactions, Spatial Subsidies and the Flow of Energy Between the Mobile Bay Delta and Offshore Waters: A SGER Proposal to the Alabama Center for Estuarine Studies
R830651C001 Meteorological Modeling of Hurricanes and Coastal Interactions: A Stability Study For Vertical Pressure Levels
R830651C002 Characterization of Glycoprotein Cues Used by the Parasitic Rhizocephalan Barnacle Loxothylacus texanus To Identify Its Blue Crab Host, Callinectes sapidus
R830651C003 Survey of Diamondback Terrapin Populations in Alabama Estuaries
R830651C004 An Assessment of Environmental Contaminant Levels in Water and Dragonfly Larvae Tissues from the Mobile/Tensaw Delta