Zostera marina is a seagrass species, commonly known as eelgrass, that is found on both coasts of the United States, as well as in Europe. Unfortunately, Zostera is disappearing all over the place, including right here in New York. This could have devastating impacts on animals that rely on eelgrass as foraging grounds, or, as is the case with scallops, use it as a refuge from predation. This is its story, as seen through the eyes of an aspiring graduate student...
Although there are a lot of them associating with eelgrass beds in Shinnecock Bay, NY. Nope, I am hunting for baby scallops. Shinnecock Bay has some of the healthiest eelgrass meadows in Long Island, and in some places within the bay, new meadows are forming. This is great, as many species depend on seagrasses as predation refuges and nursery grounds, including my model organism, bay scallops. Why then are there apparently no scallops in Shinnecock Bay? Well, its not exactly that there aren't any, of course, but that there are so few, they might essentially be ecologically extinct. However, restoration efforts in the Peconics and larval monitoring have turned up some pretty exciting results. And, Shinnecock Bay is connected to the Peconics through a canal, whose gates are left open when there is a high tide in the Peconics, allowing water to flow into Shinnecock Bay. This is a potential source of scallop larvae. While the spawner sanctuaries are quite distant from the canal, there is a growing scallop population around Robin's Island in Great Peconic, not far from the canal. And either way, scallop larvae spend up to 2 weeks in the water column, so it is possible for fairly long distance dispersal. So I thought we might see some scallops in Shinnecock Bay. I certainly saw some juveniles last summer, but didn't see any adults, so their survival is likely very low. One reason is probably predation. The same eelgrass meadows that are valuable for scallops is also a valuable habitat for blue crabs and mud crabs, both of which eat scallops like popcorn (or at least I imagine that's how they eat them). And yet, no one has investigate either scallop or blue crab recruitment in Shinnecock Bay, so that's what I am currently doing. My scallop monitoring has already started, and surprisingly (or maybe not surprisingly), I didn't get the results I was anticipating. Instead of the highest numbers of scallops at the site closest to the canal and diminishing numbers with distance, I had two relatively high spat numbers sites, on either side of the Shinnecock Inlet, opening up to the ocean. Could this mean a possible oceanic transport of scallop larvae into Shinnecock Bay? Is this supply-side ecology? There are clearly not large numbers of larvae, but there is a supply, and it's coming from somewhere, but to be honest, I have no idea where. Soon I plan on sampling for blue crabs, whose larval origin I know is oceanic. If they display a similar settlement pattern, perhaps my question will be answered. On a side note, we did collect a lot of other organisms. All together, over 20 different species of organisms came up on the collectors. The most abundant were scallops, mud crabs, blue mussels, jingle shells and slipper shells. But we also saw 2 types of sea squirts, bryozoans, rock crabs, 4 different species of snails, sea stars, urchins, other bivalves (arcs, angel wings and cockles), scaled worms and other polychaetes. Oh yeah, and a few of these things that I have as yet been unable to identify, although my guess is some sort of nudibranch. So yeah, exciting stuff indeed. (scaled worm)
Seriously, I need them... I have scallops, I have mesocosms, I have artificial seagrass, I have mud crabs. Check that, I don't have mud crabs. I need fish and mud crabs! Wow, who thought getting these things would be so difficult... Went out trawling today with a group of elementary school children on the RV Peconic out of the Southampton Marine Station... We caught some interesting fish, and we caught crabs, just not the ones I am looking for. Oh science, why must you be so difficult sometimes!
Ok, on a more serious note, I am sort of freaking out here. I just got scallops on Monday. They are already around 10-11 mm, and soon they will be too big (assume ~2mm growth per week at this time of year, maybe less in a flow through system). So I want to use them ASAP. In addition, Cochlodiniumis blooming again in Shinnecock Bay. If it gets into our seawater system, my baby scallops are toast. Seriously, its bad. Read about it here, or here, or here if you don't want to take my word for it. So theres two reasons why I need to get started quickly, and yet, it seems unlikely that I will have either mud crabs (probably the most abundant crab out there, you would think I can get those easily) or fish to start my tri-trophic interaction experiments. Ideally, I would like to have tautog, scup and toadfish (which have received varying levels of fishing pressure, and each of which will likely have a differing impact on scallops and mud crabs). Ah well. Here's to keeping fingers crossed!
For years, the "supply-side" ecology has been a common theme describing mechanisms for benthic species distributions and densities. In general terms, the amount and extent of a particular organism is driven by the supply of larvae to a given area. This larval supply can thus be seen as driving benthic community structure, especially for marine invertebrates - as their life cycles contain a planktonic larval stage which allows for dispersal over relatively long distances. Thus, many of these populations are considered "open" and their continuation is dependent on some large supply of larvae. This makes sense, and it has been demonstrated many times in the literature. However, this has often been demonstrated on hard bottom communities. Soft bottom benthos don't always display similar patterns. A recent paper by Dr. Megan Dethier from the Friday Harbor Laboratory at the University of Washington, details an experiment conducted investigated very small, post set, infaunal recruits. Sampling these habitats is often difficult due to the 3-D nature of soft sediments. She was able to demonstrate that for a number of taxa she was working with, the strongest recruitment was not in areas where the largest adult populations existed. This suggests that for many of the soft bottom benthos she studied, the supply of larvae is not limiting the adult populations, but rather some post-settlement processes, such as predation, competition or abiotic stressors.
LEWIN, R. (1986). Supply-Side Ecology: Existing models of population structure and dynamics of ecological communities have tended to ignore the effect of the influx of new members into the communities Science, 234 (4772), 25-27 DOI: 10.1126/science.234.4772.25
Dethier, M. (2010). Variation in recruitment does not drive the cline in diversity along an estuarine gradient Marine Ecology Progress Series, 410, 43-54 DOI: 10.3354/meps08636
This is a particularly interesting article, because "supply-side" ecology doesn't always hold true in soft bottom benthos. I have observed this first hand with the scallop restoration work on Long Island. Over 6 years, we have monitored larval supply of scallop spat at a number of different locations, and then each winter and spring, we conduct benthic surveys for juvenile densities. There isn't always a match between sites where we had the highest numbers of post-set and the highest juvenile densities. The main causes for this mismatch is likely to be predation or physical factors.
On another project, I am investigating scallop settlement on artificial seagrass units. I design collectors to mimic seagrass, each collector has 10 artificial seagrass shoots. Half of the collector (5 shoots) is enclosed in a mesh bag (just under 1mm) and the other half exposed to predation. There is an order of magnitude difference between the number of available settlers (those inside the bags) when compared to those actual "recruits" (those scallops outside the bags). This low pattern of surviving recruits holds up regardless of location within the grass mats (either on small or large mats, at the center or the edge). This indicates to me that predation is a major contributing factor structuring the scallop populations, at least in the estuary in which I work, Hallock Bay, Long Island.
Its that time of year again. Scallops have started spawning. Tiny larvae have drifted around and metamorphosed. And now, they are settling out of the water column onto various substrates. I have made this point many times before, but I will repeat it: typically, eelgrass is considered the main suitable substrate for bay scallops, and that their larvae settle out of the water column onto this submerged angiosperm. However, scallop spat appear to be pretty opportunistic settlers, settling on a variety of substrates - both natural and artificial. Some of my colleagues have investigated the settlement of post set on various natural substrates - comparing different abundant macroalgae to eelgrass. This past week we did some diving to look for scallop spat attached to macroalgae in the field. First, I will say it is difficult to spot 1-2mm scallops on a natural surface - they blend in very well! That said, I was able to identify ~25 scallops of the 1-2mm range attached to 3 different types of macroalgae - Codium fragile (my personal favorite and a species I am fully confident is acting as an eelgrass surrogate for many species which rely on eelgrass), Spyridea, and something I call "red puff" algae, because right now, I can't remember its genus. Anyway, we found baby scallops on these three types of algae while diving, measuring the height of attachment and collecting both the scallops (to be measure in the lab) and the algae tuft to return to the lab. We then took wet weight biomass of the algae, and sprayed it down into a sieve (800 um mesh) to see if there were any scallops we missed. All in all, it was a rewarding dive for a variety of reasons, most importantly is that if we are finding multiple scallops on relatively small algae tufts, that is an indication that this years spawning and first set have been very good. This is promising for the scallop population as a whole. Second, it further reiterates that species other than eelgrass can potentially serve as alternative habitats for scallops - and this is important for the restoration efforts along the East Coast. It will allow managers to target some potentially non-traditional areas for restoration. Good stuff!
I am a marine biologist that is currently attending graduate school at the School of Marine and Atmospheric Sciences, Marine Sciences Research Center, of Stony Brook University, New York. I am very interested in marine ecology and have been focusing my studies on bay scallop interactions with their habitats. I plan to investigate various anthropogenic impacts on bay scallop populations for my PhD dissertation. This blog will highlight the details of my graduate research, from bay scallop-eelgrass interactions as previously mentioned, to alternative habitats for scallops, such as Codium, to trophic cascades, and more. Enjoy!
Eelgrass is an important habitat for multiple marine species, including the bay scallop
Scallop on Artificial Eelgrass
This tethered juvenile bay scallop attached itself to my artificial eelgrass...
The decline of eelgrass meadows
Eelgrass, Zostera marina, is a flowering, marine vascular plant that remains submerged all the time. This is quite a feat for vascular flowering plants, and only a few dozen species world wide are capable of growing completely submerged in a marine environment. Eelgrass creates and extremely important habitat, its upright structures and complex root system create a 3-D living space for many different types of animals. It is (or was) the dominant habitat forming SAV (submerged aquatic vegetation) throughout much of the coastal waters in the northeastern United States. Unfortunately, for various reasons, eelgrass meadows have seen drastic declines, and in many locations eelgrass only exists in a mosaic of small patches. This is extremely bad news as many of the important, and formerly important, commercial and recreational fisheries of the northeast US are dependent on Zostera at some part of their life cycle as a nursery and foraging ground. Some of the species are finfish like tautog, bluefish, fluke, winter flounder, porgies, while others are shellfish such as blue mussels, hard clams, oysters, bay scallops, and blue crabs. Many of the aforementioned species support or once supported vibrant fisheries. Many of those fisheries have collapsed, also for various reasons. However, is it possible there is a link between the crash of the fisheries, the decline of Zostera and the failure for recovery on both ends?
Eelgrass, Zostera marina, a temperate seagrass species, providing a vital habitat for numerous marine species
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Scallops in eelgrass
Some adult bay scallops we planted in eelgrass for a free release survival experiment we conducted
If you live in coastal zones, urge your local and state representatives to push for environmental issues that you are concerned about. Ask for more stringent rules regarding the destruction of existing eelgrass. Encourage restoration programs to be set-up. Call your state and national representatives and ask them what they are doing to protect our precious resources. Practice safer boating and know the undersea terrain - i.e., don't drive your boat in very shallow water. Avoid clamming in eelgrass meadows.