Abstract

1. Assessing oyster reef habitat value through naked goby (Gobiosoma bosc) lipid production – A pilot study Terra M Lederhouse, Christopher L Rowe, Lisa Kellogg, & Kennedy T PaynterMarine, Estuarine, & Environmental Science Graduate Program University of Maryland, College Park Abstract Organismal lipid content has been used as an indicator of habitat quality and has potential for use in the development of oyster reef restoration success criteria. Experimental oyster reefs were created in September 2005 in the Severn River, Maryland, to test habitat quality for naked gobies (Gobiosoma bosc). In November 2005, tray contents were sieved and all visible fish were collected. Each reef tray goby population was pooled and homogenized in a coffee grinder. Lipids were extracted from a sub-sample via the soxhlet method. Mean goby percent lipid contents for loose shell, intermediate, and high density reef trayswere 150-200% greater than those from control and low density treatments. No difference was found between control and low density treatments, or among loose shell, intermediate, and high density oysters These findings indicate that the density of oysters on natural un-restored oyster reefs in the Chesapeake Bay (~1 m-2) provides limited habitat and/or ecological benefits to naked gobies. Results Lipid analyses: Significant differences were found between gobies in intermediate, high, and shell treatments and those in mud and low treatments. However, no differences were found between treatments within the two groupings. Figure 2: Lipid % dry mass of naked gobies. n = number of replicates included in analysis, and s = the sample size (number of individuals within n). One fish sample in the mud treatment was excluded due to low mass size that prevented an accurate lipid calculation. Organism abundance: Naked goby abundance was significantly greater on shell and high density oyster habitats than on mud or low density. Significant differences were found between treatments for organism abundances. In most instances, there were no differences between mud and low density treatments, and no differences between intermediate density, high density, and shell treatments. Figure 3: Organism abundance (per m2). Worm abundances were log transformed (log X) to determine differences between treatments. a,b,c,dItems sharing a letter within the same category are not significantly different, Tukey's ANOVA, p < 0.05. Rugosity: Surface complexity in shell, intermediate, and high density treatments was significantly greater than in mud and low density treatments. Figure 4: Average rugosity of each treatment. A measurement of “1” indicates a perfectly flat surface. Items sharing a letter are not significantly different (Tukey’s ANOVA, P < 0.05). Results cont… Correlations: Fish dry weight and % lipid mass were positively correlated with all organism abundances. Table 1: Pearson Product Moment Correlation Coefficients and associated probabilities. “Fish dry weight” indicates the average individual dry weight in grams of naked gobies. “Fish dry weight / m2” indicates the total dry weight, in grams, of naked gobies per square meter. Rugosity was also positively correlated with all organism abundances. Materials and methods Field Studies: Trays were lined with 1 mm2 fiberglass mesh and filled with the following treatments: MUD: Ambient mud SHELL: Loose oyster shell LOW: Low density oysters, ~27/m2 INTERMEDIATE: Medium density oysters, ~120/m2 HIGH: High density oysters, ~240/m2 Each treatment was replicated 4 times for a total of 20 units Trays were placed in a grid near the shore of the Severn River at the U.S. Naval Academy and retrieved 8 weeks later Rugosity (surface complexity) was measured on each tray. Bell wire was manipulated across the surface of each tray. The length of bell wire required to reach across the tray was divided by the length of the tray to determine rugosity. Tray contents were sieved and living resident organisms collected & counted. Lipid extractions: Naked gobies from each tray were pooled, lyophilized, homogenized with a coffee grinder, and a sub-sample loaded into cotton thimbles for extraction. Loaded thimbles were allowed to equilibrate ~18 hours in a dry box with humidity <10%. Lipids were extracted with petroleum ether using glass soxhlets for 6-8 hours. Thimbles were dried at 55°C for ~10 hours, and then allowed to equilibrate for at least 24 hours in a dry box. Percent lipid content, or lipid % dry mass, was determined according to the following: [(I – P) / (I – E)] * 100 = % lipid I = Pre-extraction mass of loaded thimble P = Post-extraction mass of loaded thimble E = Pre-extraction mass of empty thimble Conclusions Positive correlations between naked goby lipid content and all organism abundances indicate that this may be an appropriate metric for determining energy transfer and community health on restored oyster reefs. Increasing surface complexity positively affects community development and naked goby lipid content. Habitat type (presence of hard substrate and of living oysters) may indirectly affect the biomass and lipid content of naked gobies. Figure 1: Tray filled with high density oyster treatment. Tray is 0.3364 m2, and is resting atop sieves used to collect fish & other organisms Ongoing Research Current field studies aim to enhance pilot study results. These experiments are being conducted in the Patuxent River at the U.S. Naval Recreation Center. Experiments will last two months, and will then be repeated. Each treatment is replicated 5 times. Experiment 1: Habitat Effects MUD: Ambient mud SHELL: Loose oyster shell LOW: Low density living oysters (~25 / m2) HIGH: High density living oysters (~180 / m2) Densities were adjusted to more accurately reflect current densities on oyster reefs in the Chesapeake Bay, and intermediate density was excluded. These treatments also represent the range of naked goby habitats in the Chesapeake Bay. Experiment 2: Oyster Effects LIVE: High density living oyster clumps (~180 / m2) DEAD: High density dead oyster clumps (~180 / m2) Dead oyster clumps were created by boiling living oysters, shucking the meat, and re-creating the clump by gluing the shells shut with marine epoxy. Results from this experiment will determine whether living oysters affect naked goby lipid content differently than hard substrate with the same surface complexity.