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University of California, Santa Barbara |
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University of California, Santa Barbara |
Progress to date:
Our research addresses the important issue of mitigation of adverse effects of OCS (Outer Continental Shelf) oil and gas related activities on surfgrass (Phyllospadix spp.) communities. Phyllospadix is an important structure-forming plant in the intertidal and shallow subtidal zones that is impacted by a number of activities associated with offshore oil and gas production. With funding from Santa Barbara County and the MMS - UC Coastal Marine Institute Program, we gathered much needed information on the reproductive ecology of Phyllospadix and we identified the most appropriate life stages of surfgrass for use in restoration. The primary objectives of our current MMS - UC Coastal Marine Institute funded research are to: (1) test the feasibility of various techniques of outplanting laboratory reared seedlings to the field and evaluate their usefulness in restoring damaged surfgrass populations, (2) collect information on the growth and survivorship of naturally recruited surfgrass seedlings for use in estimating the time required for restored populations to fully recover, (3) test the feasibility of transplanting plugs of adult plants as a viable means of restoration and compare their performance (growth and survivorship) to that of laboratory-reared seedlings outplanted to the field.
1) Testing various outplanting techniques:
Our first attempts of outplanting laboratory-reared seedlings to the field involved manually attaching seedlings to various species of macroalgae that surfgrass most commonly recruit to in nature. Using forceps an investigator grasped the seed of the seedling, and hooked one of its barbed arms onto a branch of the alga, in a manner that attempted to mimic the attachment of seeds in the wild. Approximately 1,000 laboratory grown seedlings were attached using this method in both intertidal and subtidal habitats. This technique proved to be very tedius (especially in subtidal habitats) and no outplanted seedlings remained attached more than a couple months. Following these results we switched our efforts to attaching seedlings to artificial substrates in the laboratory and outplanting these seeded artificial substrates to the field. We have tested two different substrates: braided nylon string and braided nylon netting. In both cases, an opening is made in the braid by untwisting it one half turn. One of the arms of the seed is inserted into the opening and hooked onto one of the braids. The opening closes upon relaxation of the braid locking the seedling in place. Many seedlings can be securely fastened to the strings and nets relatively quickly using this technique. The seeded strings and nets are then transported to the study site in coolers and fastened to the reef using marine epoxy.
Over 2,000 seedlings were attached to 20 cm long nylon strings and outplanted to intertidal and subtidal habitats between 10 Dec 1998 and 7 Jan 1999. Our previous outplant experiments indicated that survivorship of seedlings was higher in areas of reduced algal cover. Consequently, strings were outplanted to areas with dense algal cover and to areas where algae had been removed to test the effects of algal canopies on seedling survivorship. Data on survivorship (# remaining) and growth (# leaves per seedling and mean leaf length) are collected monthly. Preliminary results show mortality was initially high in the first month following outplanting with little mortality thereafter. Survivors showed substantial growth with increases in both leaf number and leaf length.
The improved survivorship of outplanted seedlings on braided nylon led to additional tests in February and March 1999. Here nylon netting was used as the artificial substrate to better examine the effects of seedling density on survivorship. Nylon netting with 1.5 cm square mesh was cut into 20 cm x 20 cm squares and used as the outplant substrate. Determining the effects of density on seedling survivorship is critically important in evaluating the effectiveness of using outplanted seedlings to restore damaged populations. Therefore, seedlings were outplanted at three densities uniformly distributed over the net: high (105 seedlings per net) medium (20 seedlings per net) and low (5 seedlings per net). T he nets were seeded in the laboratory and outplanted to both an intertidal and subtidal site in areas where algae had canopies had been removed and in areas that were scraped to bare rock. Scraped rock was tested because many disturbances frequently remove all vegetation. A total of 1560 seedlings were outplanted for each tidal zone (n = 6 nets for each zone, density, and algal treatment combination). As in our other experiments, data on survivorship (# remaining) and growth (# leaves per seedling and mean leaf length) are collected monthly. We initiated an additional experiment in May 1999 to test whether seedling survivorship varied with the size of outplanted net . Large (20 X 20 cm) and small (10 X 10 cm) net substrates each containing 10 seedlings were outplanted in pairs to our experimental subtidal site (n = 10 nets for both sizes). The nets were attached to areas on the reef where algal canopies had been removed which enabled them to be placed flush against the rock. This experiment was motivated by our belief that smaller pieces of netting are easier to handle and can be attached more securely to the bottom, which could facilitate higher survivorship of outplanted seedlings.
2) Growth and survivorship of naturally
recruited surfgrass seedlings
Twenty five seedlings that were presumed to have recruited three previous winter (Jan – Mar 1998) were mapped and measured on 8 November 1998 at our intertidal site More Mesa. Data on the number of leaves, average leaf length, total length and number of bifurcations of the rhizome, and depth of sand are collected monthly for each of the individuals. Like many of our intertidal sites there has been substantial movement of sand at this site and the young plants are frequently buried by as much as 30-40 cm of sand for periods up to several months. In addition to providing information on growth of established seedlings, the data collected at this site will provide much need information on the degree to which surfgrass seedlings can withstand burial by sand.
3) Adult transplants
In June 1999 thirty plugs of
adult plants were collected from healthy stands of surfgrass in the intertidal
at Coal Oil Point and transplanted to adjacent areas of bare rock. Because we were interested in determining
whether size of the plug influenced its ability to become established we
transplanted small (rhizome length < 5 cm) and large (rhizome length > 5
cm) plugs in a paired design. Unlike
previous restoration attempts that glued the plants directly to the reef we
pulled the leaves of a transplanted plug through a piece of nylon netting and
then glued the netting to the reef in a manner that kept the rhizome of the
plug firmly pressed against the rock. A similar experiment is being set up at
one of our subtidal sites in July 1999. Survivorship and growth (number of
leaves and area of reef covered by rhizome) will be measured monthly. Data obtained from these adult transplant
experiments will be compared to those collected from experiments involving
laboratory-reared seedlings outplanted to the field. An advantage of
transplanting adults over outplanting laboratory-reared seedlings is that
restoration could take place year round.
A disadvantage of transplanting adults is the (presumably) short-term
damage caused by removing small portions of established populations. Plans are
underway to examine the time required for established populations to fill in
gaps created from collecting plugs of different sizes.