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...
Apparently, climate change might not be such a bad thing. Especially not if you are an exploited species of bivalve. Now I am not trying to be a climate change apologist, but too often we get caught up in this debate and science is 99% of the time on the side saying "It's bad." However, as I have learned in my own research with invasive species, there are always two sides to every coin. A warming ocean could be a benefit to numerous species, probably as many species as it might be of detriment. Obviously, there are a whole suite of ecosystem processes that are also affected, but in certain cases, it might not be so bad. At least not according to a paper in Marine Biology entitled "Strengthening recruitment of exploited scallops Pecten maximus with ocean warming." Its an interesting read. The essential idea is that over a long(ish) time period, the researchers were able to demonstrate a highly significant correlation between increasing temperature and increasing settlement and recruitment of juvenile scallops to a local scallop population. Shifts in recruitment can be attributed to temperature related shifts in feeding, gonad development and larval survival - and this impacts are more apparent in species who use environmental cues to induce development and spawning. Such is the case for many species of bivalves, including scallops, and so a warming ocean could potentially enhance scallop recruitment. There are some stats involved in their methods, but the basic results are pretty simple, over the past decade, scallop landings around the Isle of Man have been increasing. IN addition, mean springtime temperatures have been increasing (which cues development). I know what you all might be thinking, correlation does not equal causation (you know the one, mean global temperature has increased as the number of global pirates has decreased, meaning that the number of pirates somehow influences the climate), but that goes into their methods of using residuals and proxy values and all sorts of things. Basically, recruitment increase isn't significantly related to other things (spawning stock, dissolved oxygen, chlorophyll a), and is strongly related to temperature. They even examined a number of scallops during the three month conditioning period and the GSI - which indicates relative gonad development - was significantly higher in years when temperature was higher. So when temperature goes up, the scallops develop larger gonads and subsequently release more larvae which show up as strong recruitment classes.
So what does this mean for bay scallops? Well, there are plenty of issues with ocean warming and bay scallops - and one of particular concern is predator range expansion and new predators coming into the bay scallops range. In terms of recruitment, we haven't seen any patterns that would suggest this is the case in New York. However, there hasn't been many scallops here to spawn over the past 20 years until recently - due to the restoration efforts - and there needs to be a local spawning population in order to observe any of the patterns described from the paper. That said, bay scallop recruitment is not likely to be effected by ocean warming in terms of larger populations - although timing of first spawn might change, the number of times they spawn might change, etc, but it is my opinion that there are numerous variables that influence the size of recruitment classes in local scallop populations, particularly in the bay, which is already a dynamic environment.
Shephard, S., Beukers-Stewart, B., Hiddink, J., Brand, A., & Kaiser, M. (2009). Strengthening recruitment of exploited scallops Pecten maximus with ocean warming Marine Biology, 157 (1), 91-97 DOI: 10.1007/s00227-009-1298-7
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
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.