Tuesday, August 12, 2008

Docks and Eelgrass?

Last week I had the pleasure of heading over to Fishers Island for the annual “Founder's Day” when the Town Board and other “officials” go over to this distant outpost of Southold to discuss the issues. It truly is a beautiful place that everyone should visit at least once. There is one supermarket, one (public) restaurant, one general store/deli…you get the idea.

We had been over to the island to collect seeds the day prior and the weather was nice, but the ride over this day was pretty hairy as the waves really rocked the ferry from side to side. A couple of the less seaworthy on board didn’t fair too well as we passed under Plum Island and hit some real big rollers. I’m glad I didn’t witness anything first hand, but I am told that there were a few green faces in the cabin.

The main reason I was going over, besides the free lunch, was to work with Mark Terry and John Sep of Southold Town to conduct a preliminary dock survey. The Southold Town Board is developing new dock law and wants to establish design standards for Fishers Island based on the unique physical and environmental conditions and needs of the residents.

We knew from our previous work that the Island is one of the last strongholds for eelgrass in the Town, but we have never took the time to observe how the docks and eelgrass interact. We don’t make it a habit of anchoring in and around docks or other structures.

Starting on the east end of the island and working our way west along the north shore, we visited every dock along the way in a small lobster boat provided by a local resident. At each station they measured depths at the end of the dock and took photos for reference. I jumped in the water at most of the docks to look for grass and take pictures so Mark and John could also see what was going on.

Well I can’t say that I was surprised, but it looks like eelgrass can thrive under a dock if the conditions are right. The combination of mostly N/S orientation, clear water and height above the water enabled grass to grow under most of the structures we visited in Fishers Island Sound. There were a couple cases where the dock was wider and lower than a neighbor, or the orientation was such that light was apparently reduced to the point of limiting grass growth. I didn’t snorkel in the harbors as there is very little grass there.

There was also an issue with grass growing under the docks if they extended into a deep water meadow of 10 feet or more. (we need to further investigate this observation to narrow down this depth precicsely). Apparently the combination of water depth, reducing light, as well as the shade of the dock limits growth.

One thing that was a little surprising was the effect of floating docks and boats. All of the floating docks resulted in loss of grass. In all cases the dock resulted in an unvegetated shadow in the grass meadow. In one case the clearing was “L” shaped. However, in cases where there was surrounding grass it seemed to thrive under the walkway leading to the float.

With regard to boats it was fairly clear that the presence or absence of grass was related to depth in the slip. If the water was deep enough the boat did not appear to have an impact. If it was shallow or the boat had excessive draft the impacts included scouring, shading and loss of grass under the vessel.

In some cases the docks also had a boat house or similar structure. In all cases, these structures reduced light to the point that grass could not persist in the shadow.

This was all very exciting and encouraging for our first look. I look forward to getting out there to take a closer look at some of these areas in an effort to refine the design standards. It should also be noted that these observations on Fishers do not indicate how grass and docks will interact on the mainland as there are issues with water clarity and water quality before the impact of these fixed structures is considered...


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