SEA Currents: Corwith Cramer
March 18, 2019
I Couldn’t Be More Proud, or, What I Learned From my Students
23° 43.2’ N x 083° 00.6’ W
Ship’s Heading & Speed
Hove to under storm trys’l, main stays’l and fore stys’l for wire maintenance / styrocast at 2018 in the evening.
Winds NE x E Beaufort Force 6, seas building, sky filling with clouds as cold front approaches.
March 18th, 2019; Later in the day and into the evening.
Today we celebrated our scientific achievements as each student shared their oceanographic discoveries with their shipmates. For the last six weeks we have sailed across, immersed ourselves in, and studied this small patch of ocean called the Caribbean Sea; and collectively we have learned so much. Today those efforts offered up their yield as each student presented their final oceanography projects; and I could not be more proud of their accomplishments.
Thanks to Allyssa and Emily B. we learned that sea surface temperature and salinity across the Caribbean is significantly higher this year compared to last year. This is likely due to natural fluctuations in the North Atlantic Oscillation which also changed during the same time period.
Thanks to Emily S. and Lucas we learned that coastal eutrophication (e.g. river runoff, nutrients, and pollution) differs from one island to the next. These island comparisons were based on measurements of phosphate, chlorophyll-a, and bacteria levels in surface waters close to, and further away from, shore.
Jacob taught us about suspended sediments and dissolved organic matter that runs off islands and how these water properties can influence the availability and quality of sunlight reaching coral reefs.
Natalie and Delphine shared their discoveries of zooplankton biodiversity, which according to their observations, varied significantly along our cruise track. Similarly, some zooplankton were only found in our neuston net during the day (such as blue copepods) while others were only found at night (such as stomatopod larvae).
Mariana treated us to a lesson about humpback whale songs recorded on Silver Bank- whale sanctuary and Samana Bay- a region busy with small boat traffic. Differences in note frequency and duration indicate that humpback whales adjust their songs in the presence of boat noise.
June also studied humpback whales and discovered that their song has changed over the last two years. By closely examining spectrograms (a scientific way to visualize sound) she documented subtle changes in frequency and/or duration of common notes and identified entirely new ones.
Skylah, Emma, and Mica teamed up and helped us to better understand the variability in eel larvae (aka leptocephali) and spiny lobster larvae (aka phyllosoma) abundance and distribution. This year we collected very few leptocephali or phyllosoma larvae; and based on their close examination of past Sea Semester cruises they confirmed that this was indeed an unusual occurrence. The unprecedented dearth of these critically important species is troubling and deserves further research.
Vuk taught us about different species of pelagic Sargassum (a drifting algae found only in the North Atlantic and Caribbean) and where we found them along our cruise track. Notably, distribution patterns this year were very different than earlier Sea Semester cruises.
Alle and Julia delved deep into the Sargassum ecosystem and discovered that different species of Sargassum harbor different species and amounts of associated mobile fauna, which can include a variety of shrimps, crabs, polychaete worms, fish, etc. Differences in Sargassum inhabitants were attributed to variations in Sargassum species ‘architecture’ - essentially offering more or less habitat for small critters to hide.
Mark wondered if the oasis of the Sargassum ecosystem provided a boon to local food webs and examined the correlation between marine mammal and seabird sightings with the amounts of Sargassum observed and collected in our nets. Though no correlation was found all enjoyed Mark’s humorous poster presentation.
Asia explored the vast amount of coral reef data we collected and learned that the abundance and diversity of coral, fish, and invertebrates varied considerably from one island to the next. This was not a function of sea surface temperature and salinity as both variables were nearly uniform across our sites, however, significant correlations were observed with variation in nutrient concentration and the amount of chlorophyll-a.
Brison explored the trophic structure of each coral reef and confirmed a well standing relationship between the abundance of herbivorous and carnivorous fish. However, his data also revealed subtle differences between the reefs that may be correlated with over-fishing pressure on each island.
Allison shared her observations of coral cover in relation to sponge abundance, a known competitor on the reef for space; as well as the abundance and diversity of reef invertebrates that use coral structure as a habitat. Though the hypotheses were sound no significant relationship was observed suggesting that other factors must be at play on the reefs we surveyed.
And finally, Andrew studied the soundscapes of each coral reef by deploying a hydroacoustic recording device called a Sound Trap loaned to us by NOAA – New England Fisheries Science Center and our soundscape/whale expert Sarah Weiss (see earlier blog post by Sarah). Andrew learned that the most obvious sounds one can hear on the reef besides breaking waves are the chorus of snapping shrimp and the occasional scrapping sounds of parrotfish feeding on coral and calcareous algae. Each reef sounded different suggesting a new means to assess the health and biodiversity of coral reef environments.
Through a collective effort we have learned far more than each of us could have done on our own; a testament to the teamwork approach embodied by SEA and the mutual respect among shipmates and scientists, each taking care in the collection of the data.
Officially the scientific mission of C284 has reached a successful conclusion!
Thanks to the ship SSV Corwith Cramer for taking us there and keeping us safe. Thanks to the captain and professional crew for their support of the scientific mission. And finally, thanks to all students for their hard work and diligence, thanks for teaching me so much, many thanks for all the data!