The GOMCES crew has been back on terra firma for about two weeks now, giving everyone some time to reflect on this summer’s survey. Although we have yet to delve into the data analysis, when asked how the survey went, our first response is usually something along the lines of “It seemed like a ‘slow’ year.”
So, what does a “slow” year look like? That is a great question. While we don’t have a concrete answer yet, here are some observations that coincided with what seemed like a “slow” year.
First, let’s start with the physical setting. Many of these physical setting characteristics did not change among the survey years. For example, we surveyed many of the same transects this year as we have in past years, covering a similar range in depths/distances from shore and seafloor habitats. However, the physical properties of the water column are variable. These properties are also key components of the ecosystem, setting the stage for patterns of growth, survival, transport, and/or reproduction for many organisms.
As you may recall, we use a conductivity-temperature-depth (CTD) meter to measure several key physical properties. Comparable data are also available from monitoring buoys anchored at several locations within the Gulf of Maine. As it will be some time before we process our CTD data, we pulled water temperature data for three different buoys from the NERACOOS website to give us a general picture of what was going on with the physical oceanography this summer. The buoy data are displayed below, along with a map of the buoy locations for orientation. The blue line depicts the average temperature from 2001-2015, the yellow window shows the range in observed temperature values from 2001-2015, and the brown lines and points are the observed temperatures for the particular year of interest.
A sample of 2015 and 2016 water temperatures recorded at three monitoring buoys within the Gulf of Maine.
The buoys tell us that in general 2016 has been a fairly warm year so far in the Gulf of Maine, with warmer water temperatures at depth (and at the surface) than the 2001-2015 mean water temperatures. That being said, there is some considerable variability around the mean – especially towards the southwest Gulf of Maine and Massachusetts Bay area. Although a plot of water temperature at one depth and a few different buoy locations doesn’t tell the full story about if the entire water column is “warmer” or “colder” than previous years, it does seem like overall conditions were warmer during this summer’s survey than years past (2015 data are shown for comparison).
Ultimately our project is focused on evaluating how such physical oceanographic changes affect the distribution and abundance of the biological organisms living in the coastal region. During this summer’s survey, there did seem to be considerable differences in the species we encountered and their abundances compared to past years. One of the most obvious differences was the number of gelatinous zooplankton we caught in the zooplankton ring nets and observed from the boat.
Gelatinous zooplankton are notoriously hard to sample with ring nets given their delicate bodies. So, instead of true counts, our biological oceanographer scores the sample from 0 to 10 based on how much gelatinous material is in the sample, with 0 being none and 10 being a lot. We are in the process of mapping these scores to compare with the earlier years (2015 example shown below). Already, though, the data suggest that gelatinous zooplankton abundance was down considerably compared to previous years, with most of the ring net tows scoring 0 or not much higher. In contrast, abundances of other zooplankton species, and especially the star-of-the-show Calanus finmarchicus, appeared to be on par with previous years. (You may remember from previous years’ blog posts that C. finmarchicus is a very large, fatty copepod that serves as a very important food source for many of the Gulf of Maine’s denizens, from juvenile fish to large baleen whales.)
2015 map of relative gelatinous zooplankton abundance throughout the coastal Gulf of Maine.
In addition to being a slow year for gelatinous zooplankton, 2016 was also slow for the marine bird and mammal team. In total, the number of individuals observed in many of our marine bird groups were lower in 2016 than in 2015 or 2014. This includes species like Wilson’s storm-petrels, Great shearwaters, Arctic and Common terns, Atlantic puffins and Razorbills. Across the board, our preliminary data processing suggests that we encountered fewer individuals of these species in 2016.
Along with lower total observation numbers, we also failed to encounter a tern or alcid foraging flock. In both 2014 and 2015, the marine bird and mammal crew observed at least a few of these foraging flocks, comprised of multiple species and at least 25 or more total individuals. With the exception of the shearwater foraging flock observed on the first day (keep in mind that these birds are currently “wintering” here and will soon return to their southern hemisphere breeding colonies to start their own breeding season), the crew did not come across any other foraging flocks in 2016. Of course, missing a foraging flock might just be a case of wrong-time/wrong-place. However, when combined with fewer total observations, it definitely contributes to the perception that 2016 was a “slow” year.
Where does that leave us? Well, a quick recap. 2016 appeared to be a “slow” year. Water temperatures seemed to be warmer than long-term averages, and especially, warmer than 2015 (which was a fairly cool year). Gelatinous zooplankton were less prevalent, while other zooplankton species, including Calanus finmarchicus, appeared to be similar in abundance to previous years. Total observation numbers of key marine bird species were lower than the past two years and we didn’t see as much foraging activity. We’ll also add that we saw fewer marine mammals and Mola molas (Ocean sunfish) in 2016 (remember that Mola molas eat primarily gelatinous zooplankton!).
There are many possible explanations for these yearly differences. Although it might just be a case of poor timing on our part, patterns may emerge during data analysis that will give us insight into the reasons behind the interannual variability. Right now, what really seems to be sticking out is the difference in the relative abundance of gelatinous zooplankton. That being said, we might be a bit biased since correlating the low gelatinous zooplankton year with lower marine bird/marine mammal observations and activity would strengthen our growing idea of the important (and underappreciated) role that gelatinous zooplankton may play in the Gulf of Maine food web. In any event, we are all excited to confront our knowledge of the Gulf of Maine coastal ecosystem with the data we have collected over the next few months.
Thanks for following along this summer! We hope to have some updates as we continue with our analysis. Additionally, although we are at the end of this project’s funding, we are hoping to secure funds for additional future surveys to keep this important effort going!
The Gulf of Maine Coastal Ecosystem Survey 