CICEET Progress Report for the period 8/01/00 through 1/31/01

Project Title:

Density-Dependent Effects on Grazing and Success for seed Generated Seagrass (Zostera marina L.) Plants.

Principal Investigator(s):

Scott W. Nixon,
Stephen Granger,
Brian Maynard, and
Malia Schwartz

I. Accomplishments

1. Scheduled Tasks

   During the third year of this project we focused on the design and testing of an underwater seeding machine capable of cost-effectively planting eelgrass seeds over large areas. In order to determine the optimum application rate for seagrass seeds we investigated the effects of seeding density on germination and seedling survival. Relying on the results of these experimental plantings we designed the seeding machine to deliver seeds in a range of densities to allow for site specific variations in sediment characteristics. Our prototype machine was to be able to plant seeds at the optimum sediment depth and seed density to achieve the greatest seed germination and the seedling survival. With our first two years of research now complete we have focused our project goals from August 1, 2000 to January 31, 2001 in three areas. First, to finalize the design and construction of a test seeding machine. Second, to investigate various gel mixtures to be used in the application of seeds with the seeding machine. Finally, to use our prototype seeding machine to seed marine sediments in aquarium tanks and several field sites in Narragansett Bay and the coastal lagoons of southern Rhode Island.

2. Progress on Tasks

   The first operational seeding machine was completed in September of 2000. The machine is towed along the bottom opening a furrow as it moves over the sediments. Seagrass seeds, held in suspension by a gel matrix, are pumped from a reservoir in the surface support boat through flexible tubing to the underwater sled. A manifold distributes the gel/seed mixture into several stainless steel tubes mounted behind the tines allowing the matrix to be deposited into the furrow. A weighted pad that is attached to the back of the sled closes the furrow (Figure 1). During our first trials of the sled we determined the correct depth setting for the tines to ensure that seeds were delivered to the sediments at an optimum depth for germination. Additional trials determined the appropriate pump settings to achieve seed/gel delivery rates shown in our experiments to achieve the highest seedling survival.
   




A critical factor to our design was finding a pump that would be capable of pushing the seed-gel matrix into the sediments without damaging the seed itself. To solve this problem we collaborated with the Edhardt Corpaortation in Hackettstown, New Jersey. This company specializes in developing and manufacturing pumps for the food industry. The pumps designed and manufactured by the Edhart Corp. are capable of metering exact amounts of viscous materials with out damaging the contents. The pumps worked well for our application allowing for the precise control of gel application without damaging the seeds as they passed through the pump head. The engineers at the company were instrumental in helping us modify one of their existing pump models (PV 4000) for use in this unique application. They continued their support of this project by allowing us to rent a pump, at a discounted rate, for use in preliminary trials.

The design of our seeding technique relies on a gel based matrix to hold seeds in suspension. Knox gelatin, (Kind and Knox Gelatine Inc. PO Box 927 Sioux City, IA 51102) prepared with seawater, was used as the seeding matrix. As one of our first questions, we needed to determine the appropriate viscosity of the gel. Various gelatin to seawater ratios were tested to developed the consistency which would best hold the seeds in suspension while not restricting the flow of gel to the sled. A ratio of 17:1 (gel, g : seawater ,l) kept at 16^oC was used during our initial aquarium trials in October. However, as ambient temperatures cooled, holding the constant temperature at 16^oC became difficult and the viscosity of gel would change as it cooled. To compensate the ratio was changed to 10:1 and used at a temperature between 0-5^oC . The 10:1 ratio was used for all field trials.

Preliminary trials of the seeding sled in large seawater tanks began in October 2000. Two flow-through seawater tanks each measuring 5.8m x 1.8m x 1m were used as the test tanks. One tank was lined with fine, higher organic (1.7%) sediment indicative of Narragansett Bay while the second was lined with coarse, low organic (0.5%) sediment indicative of Rhode Island Sound. Two seeding runs of approximately 1.5 meters in length took place in each tank. A total of 1000 seeds were to be planted for each run to yield a planting density of 1000 seeds m^-2. Viable ungerminated seeds were selected and added to 500 ml of prepared gel matrix. The seed-gel matrix was pumped through tubing and followed by 1500 ml of unseeded gel to purge the lines. During tank trials the seeding sled was pulled through the tank using a hand winch secured to the tank wall. Speed and distance traveled were estimated using markers placed every 25cm along the run. The test run was terminated when the majority of seeds had been cleared from the lines. At the end of each run all lines were flushed and any seeds remaining were tallied. Concurrently with each tank trial, three replicate control plots measuring 0.024 m² were seeded at a density 1000 seeds m² (24 seeds each). Seeds in each control plots were planted by hand at a depth of 2.5 cm using calibrated tweezers.

Our field tests of the seeding machine began in November 2000. Four sites were selected to include a range of environmental conditions. These sites ranged from more energetic sites in Narragansett Bay to low energy sites in Ninigret Pond (Charlestown, RI). All sites selected were either in or adjacent to an existing eelgrass bed or previous eelgrass restoration site. Planting at a site where eelgrass already exists, would eliminate the question of whether water quality could sustain eelgrass growth and would allow for a better determination of the success or failure of the mechanized seeding technique. At each of the four sites a test plot was located using PVC stakes. At shallower sites the sled was towed manually while at deeper sites the sled was towed from the tending vessel. In this way we would have better control of the delivery rate and the speed at which the sled moved along the bottom. Divers visually monitored the seeding process. Hand signals were used to communicate and control the speed of the sled and the termination of each run. After each run seeds remaining in the line or pump were collected, tallied and the number of seeds successfully planted calculated. Between one to three test runs, depending on site specific conditions, were performed at each location. The gel matrix used was prepared the day before each planting with a ratio of 10:1 (grams of gel : litres of water) and held on ice until the time of planting. Seeds were mixed with the gel matrix just prior to planting. Our goal planting density was 1000 seeds m^-2 and planted to a depth of one to three centimeters into the sediments. Concurrently three replicate control plots (0.024m²) were located at each of the four field sites and seeded at a density of 1000 seeds meter^-2 by hand.

3. Difficulties Encountered

   Our preliminary trials (summer 1999) using seeds held in a gel matrix and applied to the sediments by syringe were very successful with up to 70% germination in some replicates. These initial trials were performed in aquaria and consisted of 60 milliliters of gelatin in each planting. However, during our initial trials of the seeding machine we used up to 50 times the amount of gel that was used in the syringe plantings. Our observations indicate that the increased amount of gel in these planting added an additional organic load to the sediments. Our previous work indicates that persistent anoxia in the sediments can have a negative effect on the germination and persistence of seeds and seedlings. As the period of germination does not end until mid May 2001 the effect of the respiratory demand placed on the sediment by the gel, and its effect on seed germination in our test plots will not determined the spring. However, there are many solutions to reducing the higher sediment oxygen demand. We can easily reduce the amount of gel needed to keep the seeds in suspension or by using other types of gelling material which contain lower amounts of organic material.

4. Anticipated Success in Meeting Project Objectives in Scheduled Project Period

   We do not anticipate any problems meeting the project objectives. We have already completed a number of experiments to determine the correct planting density, depth, and time to achieve optimal germination. We have incorporated this information into the design of a mechanized eelgrass-seeding machine. We have constructed and successfully tested that machine in both controlled aquarium tanks and field sites. We are confident that with additional testing and modifications developed form our first field trials the design of the machine will be successful.

5. Preliminary data

   Testing of the seeding machine began in the October of 2000. Eelgrass seed planted during these initial trials will germinate through the winter and into the spring of 2001 with the germination period ending around Mid-May, 2001. At that time we will revisit all the sites to determine the success of these first plantings.

II. Tasks and activities for next reporting period

1. Tasks for the next reporting period

   We will focus our efforts for the next reporting period on monitoring the success of our initial seeding machine trials. The majority of germination will be complete by the end of May, 2001 at which time we will revisit our test sites. During this period, we will also assist Malia Schwatz in writing and publishing a "How-To" guide for eelgrass seed collection. The pamphlet, as described in our proposal, will give a detailed description of how to collect and hold Zostera marina seeds. Finally, we will produce a manuscript for publication that will describe the results of our first two years of research on the effects of seeding density on the germination and success of eelgrass seeds and seedlings.

2. Work plan to accomplish tasks

   Divers will revisit each test location in late May to early June 2001. The total number of shoot will be counted and the percent germination calculated. A final survey will occur in August 2001 to measure the survival of any new seedlings though the first growing season. We will then incorporate any new information gathered into modifications to the design of the seeding sled or the gel matrix used in the planting.

3. Concerns or difficulties

   We do not anticipate any difficulties in achieving the goals we have set forth for this reporting period.

III. Expenditures

Our expenditures for this project have been within our anticipated budget. We do not foresee any unexpected costs to occur within the next reporting period.