Monday, August 17, 2009
Too much of a good thing?
On days like today there is no excuse for not getting out in the field. Although we were down two staff, it was still possible for Kim and I to get out and do what we needed to do. It was either that or stay in the office and catch up on paperwork (me) and webpage updates (Kim).
With a skeleton crew there was only so much that we can do efficiently so I decided we would focus on scouting for new planting sites around Plum Island that we have been trying to complete for the last few weeks and monitoring some older test planting sites in the area.
After a quick call to the homeland security folks on Plum Island we were on our way to visit the cool, deep and high velocity waters of eastern LIS. I won't go into any detail here, but suffice it to say that our scouting was a success and we did find at least one promising looking site on the north side of the Plum Island. This matches up with some earlier observations from April or May. I would have to look back and check the date, but it doesn't matter at this point. We may be planting this site as soon as tomorrow, weather and staff permitting.
The other, and frankly more interesting part of our day, was to monitor some test plantings from this summer. If things make it through August, we can usually be assured that water quality and temperature are not limiting. It's too early to determine if disturbance will be limiting, as this kicks in in the fall and winter, but if the plants don't make it through the summer, there is nothing to monitor and no potential for success, so we have to start somewhere.
Our sites today included two sites on the south side of Plum Island and one on the north side of Great Gull Island. The first two are part of our Suffolk County Eelgrass Restoration Initiative and the third is part of our National Fish and Wildlife Foundation Long Island Sound restoration project. As always, we couldn't do any of this work without the generous support of our funding partners!
First, I have to say that the plants looked great at both sites and it looks like we have some very promising large-scale planting candidates for the coming fall, but we did make one interesting observation. There we incredible numbers of Lacuna vincta snails on many of the plants. I'm not talking about normal numbers, but what appeared to be overwhelming numbers. We like these snails and actually will move them to a completely unvegetated site (one that has no algae to act as an alternative host for these grazers) to help clean off the epiphytes and biofilm on transplants (we're just about to do this for some plantings near Duck Pond Point in LIS), but these were almost at an alarming density.
I don't think this is a bad thing at all, but these little guys were definitely causing some grazing damage to the leaves and sheaths of many of the plants. I do remember seeing a fairly high density on some plants early on at our St. Thomas Pt. restoration site where we have had considerable success so maybe this is just the way it always is during this time of year and I just missed it..or maybe the crazy weather this year has spawned a bumper crop of snails...who knows? I will have to look back at the photos to see what time of year this occurred, however. (Editors Note: I did take a look back at shots from a couple other restoration sites over the years and, in fact, August showed the peak density for Lacuna snails. Some plants appeared to have densities rivaling those seen in the pictures here, but it still seems that we're a little higher this year than in previous years. Also, there was very little, if any, indication of heavy herbivory damage in these earlier photos from other LIS planting sites.)
It is also possible that when the eelgrass is at a low density and there are a large number of snails on the nearby macroalgae, the snails may prefer the eelgrass and leave the algae to preferentially feed on the eelgrass epiphytes and, yes, the leaf tissue! Since there are so few eelgrass plants, the snail density reaches what appears to be a saturation point on many of the plants.
If this is the case what is causing it? I just don't know right now. However, I still believe that the presence of snails, even at these very high densities, are better than no snails. At the Duck Pond Point site in LIS, there is no macroalgae and therefore no snails except for a couple that came along for the ride when we transplanted. Here the plants look fairly good, but there is a heavy layer of epiphytes that must be decreasing overall productivity. Once we deliver some snails to these plants, the problem should be solved.
With each season we learn more about the natural cycles underway in the waters around us. Not every year is the same, but trends have emerged. I hope that with this knowledge we can improve our ability to successfully plant eelgrass. So far, so good, but everyday in the field teaches us something new.