Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Access to this dataset is restricted until June 2015.  Please contact the PI for further information.

The data are counts of taxa from samples of artificial seagrass (used to simulate eelgrass, Zostera marina L.) in San Diego Bay.  Each line of data represents the total number of individuals from each taxon collected in a 0.25 x 0.25 m artificial seagrass unit (ASU) deployed in San Diego Bay.  The density of individuals per square meter can be calculated by multiplying counts by 16. Taxa are identified to species where possible, but for some (primarily amphipods), identifications are to the family or genus level. 

Experiment #1: Deployments 1 and 2 were part of this experiment, which took place in central San Diego Bay, California, USA. The objective of this experiment on seagrass habitat fragmentation was to determine the interactive effects of habitat loss and structural complexity on epifaunal diversity, abundance, and biomass. Structural complexity was represented by shoot density, which varied across three levels (low SC (160 shoots m-2 = 10 shoots per ASU), intermediate SC (512 shoots m-2 = 32 shoots per ASU), and high SC (1024 shoots m-2 = 64 shoots per ASU). Habitat loss varied over 10 levels, from 0 to 90% loss (specifically, 0, 10, 20, 40, 60, 70, 75, 80, 85, or 90% habitat loss). These variables were fully crossed to allow a determination of how structural complexity influences the relationship between habitat loss and epifaunal community structure. For this experiment, epifauna are crustaceans, molluscs, and other taxa that are residents in seagrass habitat (size range ca. 0.5 mm - 2 cm in body length). The experiment was conducted by creating 30 plots of artificial seagrass (each 2 m x 2 m), each of which was modular such that small sections (known as ASUs, for “Artificial Seagrass Unit”) of each could be removed to simulate habitat loss. Each ASU consisted of a 25 x 25 cm square of black plastic mesh to which were tied 64 artificial eelgrass shoots. Each artificial seagrass shoot was a 1 m long piece of green polypropylene ribbon folded in half and tied to the mesh to form two 50 cm tall simulated eelgrass blades. Plots were laid out in the shallow subtidal zone of San Diego Bay, were allowed to be colonized by organisms for 45 d, and then were experimentally fragmented by removing the appropriate number of modules from each. One month later, samples were collected from each plot. Four ASUs were collected from each plot, rinsed into sieves, and animals preserved in 10% formalin.

Epifauna were sorted in the laboratory using dissecting microscopes. To make sorting more efficient, animals first were sorted into two sizes, those that were retained on a 2.8 mm sieve, and those that were retained on a 0.5 mm sieve. Animals were sorted to species, genus, or family (lowest category possible) using field guides such as the Light and Smith Guide to Intertidal Invertebrates. Training for taxon identification was aided by digital photographs taken for most taxa. Specimens of small, similar looking taxa (e.g. amphipods) were sent to other benthic ecology laboratories for confirmation of identification.

Experiment #2: Deployments 3 and 4 were part of this experiment, which took place near the mouth of San Diego Bay, California, USA, adjacent to Shelter Island. The objective of this experiment on seagrass habitat fragmentation was to determine the interactive effects of predator access and habitat patchiness on epifaunal diversity, abundance, and biomass. The general design of the experiment matched that of Experiment #1, except that all plots consisted of the same structural complexity, and that plots were not fragmented after being colonized (instead, plots were deployed pre-fragmented [10 levels] and were colonized in that state).  Instead of varying structural complexity, predator access to plots was varied by creating three treatments: caged ASUs (full wire mesh cage of selected ASUs to restrict predators, but allow colonization by epifauna), open ASUs (no cage), and cage-control ASUs (wire mesh cages with two sides removed to allow access by predators, but otherwise identical to full cages). Cages and cage-controls were placed over three separate AUSs in each plot for the duration of the soak. To sample plots, three ASUs were retrieved from each plot and handled identically to Experiment 1. For deployment 3, a shoot density of 1024 shoots m-2 was used in all plots. For deployment 4, a shoot density of 106 shoots m-2 was used in all plots.

BCO-DMO Processing:

- added conventional header with dataset name, PI name, version date
- renamed parameters to BCO-DMO standard
- added lab, lat, lon, experiment and deployment columns
- replaced blanks with 'nd' (no data); replaced spaces with under-scores.
- lined up data for all taxa for all expts. by adding columns where needed

Description from NSF award abstract:
In this research project, the investigator will carry out a set of field experiments to determine whether the effects of experimentally fragmenting seagrass habitat on epifaunal community structure are mediated by environmental factors that typically co-vary in marine habitats: structural complexity and predation risk.

Studies in terrestrial and marine systems collectively show that the effects of patchiness depend largely on landscape context, i.e., the characteristics and settings of individual landscapes. Progress in exploring what aspects of landscape context modify effects of habitat fragmentation on ecological processes has been slow. The experiments developed for this research directly address primary questions about the role of habitat structure in moderating ecological processes in a critical nursery habitat, and take initial steps forward to explore three important concepts: (i) how communities respond to the process of habitat fragmentation, rather than simply how communities differ between continuous and patchy areas; (ii) the relative influences of the two major components of habitat fragmentation (habitat loss and increasing patchiness) on biodiversity; and (iii) how co-varying factors in naturally occurring habitats alter faunal responses to large-scale alteration of habitat.

Seagrasses provide critical ecosystem services including the formation of critical refuge and foraging areas for the postlarvae, juveniles, and adults of many species of fishes and invertebrates that feed on diverse assemblages of invertebrate epifauna and infauna. However, disturbances that fragment seagrass habitat are increasingly common and approximately 30% of the world's seagrass habitat has been lost. Disturbances to seagrass habitat may alter feedbacks between plants and invertebrate grazers that influence ecosystem function and may increase susceptibility to species invasions.