Proceedings of the 2007 Georgia Basin Puget Sound Research Conference
Session 4C: Seagrass Biology and Ecology
Chair: Sandy Wyllie-Escheverria
Lipid Biomarkers as Proxies of Past Eelgrass Abundance and Organic Matter Composition of Sediment in the Nearshore of Puget Sound, WA
The widespread loss of eelgrass in Puget Sound has ecological implications including loss of essential habitat for juvenile salmon. We developed and applied a multi-index technique using lipid biomarkers for investigating the paleo-occurrence of eelgrass to help determine whether these losses are naturally occurring or have been exacerbated by anthropogenic activities. Specific hydrocarbons, in particular C17 and C19 n-alkanes with an odd-over-even carbon number preference in combination with higher-plant sterols: stigmasterol, fl-sitosterol, and campesterol, are good indicators of eelgrass. Analyses of sediment cores from Westcott and Padilla Bays show variation in these compound concentrations downcore suggesting the biomass of eelgrass has varied over the past 150 years. This interpretation may be confounded by a C19 n-alkane derived from algae, and terrigenous plant sterols suggested by the presence of C27 and C29 n-alkanes. Algae, often but not always, can be identified by a bell-shaped pattern of n-alkanes, C20 and C25 highly branched isoprenoids, or sterols such as cholesterol, desmosterol, and brassicasterol. Compound specific isotope ratios may help resolve these interferences because Z. marina is a C3 plant with some C4 characteristics such as 13C-enriched n-alkanes. Measurements of ?13C for the C17, and C19 n-alkanes from leaves of Z. marina were 12â, in contrast with typical ranges of 18-22â for algae-derived n-alkanes and 20-27â for terrigenous-plant n-alkanes.
Variation in Floral and Seedling Development as Indicators of Seagrass Meadow Condition.
Whereas the condition of seagrass meadows is often linked to variation in the density of sterile shoots, even though these plants flower rarely is floral development, seed viability or the potential of seedling recruitment considered as indicator of the status and health of the meadow. Using field-collected samples and laboratory experiments we describe the potential of these biotic processes as potential indicators of meadow condition. In 2006 floral development after fertilization was assessed at eight sites throughout the range of Zostera marina (eelgrass) within the continental United States. Laboratory experiments, with seeds collected in 2005, were designed to test germination frequency and seedling development of individual seeds from three sites in the San Juan Archipelago in Washington State. Results from the floral condition study indicate differences in seed set due to variation in the rate of abortion among developing seeds across the study populations. We also found significant differences for seed/ovule ratios between sites and habit (perennial vs. annual). Moreover results from laboratory experiments revealed significant differences in germination rates, seedling development and condition of seeds remaining in the sediment. This study demonstrates the importance of factoring sexual reproduction data into programs designed to assess the condition of seagrass meadows.
Population Status of the Seagrass Zostera Marina in the San Juan Archipelago
Zostera marina meadows in the San Juan Archipelago contribute to nearshore biodiversity and productivity and are protected by a no-net-loss policy in Washington State. In 2003/04, retrospective analysis, using historical aerial photos revealed substantial losses had occurred within several small embayments. As a consequence a monitoring study was initiated in 2005 to track population status within the shallow subtidal region at 11 sites as part of a larger project to determine causative factors of population decline. All sites were re-sampled in 2006. At each site, shoot densities, flowering frequency, rhizome internode lengths, sediment grain size and percent organic matter were sampled. In addition, during 2005, leaf tissue was collected and archived for genetic analysis. Shoot density and flowering frequency increased in 2006 but leaf length appeared to correlate more closely with stress level as measured by sediment grain size than with the year. In addition to providing baseline information at the site level, these results can be used to interpret results of genetic analysis. Project objectives are to provide baseline ecological information to guide restoration efforts once factors in decline are known. We demonstrate the value of monitoring at the site level for species under threat in the Salish Sea.
Fish Assemblages Found in Eelgrass Meadows (Zostera marina) of the New Gulf Islands National Park Reserve of Canada
The Gulf Islands National Park Reserve of Canada (GINPRC) encompasses about 35 km2 of near shore marine ecosystems within its boundaries. There are many ecosystems in GINPRC that will require monitoring to ensure for the conservation of ecological integrity. However, one ecosystem in particular, namely eelgrass (Zostera marina), is arguably the most productive and sensitive to a wide variety of land-use and marine activities. In this talk, we present results from an assessment of eelgrass properties, environmental conditions and fish assemblages collected at 16 eelgrass beds during August 2004-2006. Overall, we conclude that fish assemblages in eelgrass beds in the southern Gulf Islands tend to be in relatively poor health compared to other Parks Canada regions on the west coast of British Columbia. We discuss some possible reasons for the observed poor health in the fish assemblages.
Assessing the Ecological Connectivity of Eelgrass Habitats and Protected Areas: a Tail of the Population Structure of the Eastern Pacific Bay Pipefish, Syngnathus Leptorhynchus.
Populations require a network of interconnected habitats to maintain biological processes such as reproduction. Defining the spatial scale and patterns of exchange among interbreeding groups is critical to establish breeding units and population boundaries. Investigating genetic connectivity (dispersal) of individuals among habitat patches is an effective way to measure these population parameters and assess the ability of protected areas to maintain population processes.
Eelgrass habitats play a critical role for nearshore and offshore marine ecosystems as nurseries, spawning habitats, and as habitat for resident species. Locally, significant losses of eelgrass habitat have been documented and ultimately these losses will affect ecological function and species diversity. Monitoring eelgrass habitat function can be achieved by studying populations of such eelgrass specialists as the eastern Pacific bay pipefish, Syngnathus leptorhynchus.
My masters’ research focuses on measuring the ecological connectivity of eelgrass beds by investigating the genetic population structure of Syngnathus leptorhynchus in Barkley Sound, British Columbia. I will present my findings of pipefish population boundaries and breeding units. This will include an assessment of the degree of connectivity (gene flow) of the bay pipefish within and outside of a de facto marine reserve, the Broken Group Islands, Pacific Rim National Park Reserve of Canada. The influence of seascape features on gene flow will also be discussed.