Written by Sean Beckwith, Web Content Developer for USF CMS
The briefing included a weather forecast of mostly clear skies and calm seas—not the deciding factor on my decision to confirm participation on the oceanographic cruise to collect fish eggs across the West Florida Shelf (WFS), but a very nice bonus.
This year, 2019, begins a 15-year monitoring program funded by the Florida RESTORE Act Centers of Excellence Program. Dr. Ernst Peebles is principal investigator of the study, Spawning Habitat & Early-Life Linkages to Fisheries (SHELF), along with co-investigators Dr. Mya Breitbart, Dr. Steven Murawski, Dr. Christopher Stallings, Dr. Kevin Boswell (Florida International University), and Dr. James Locascio (Mote Marine Laboratory).
The 11-day cruise was split into two legs, with a day at port for refueling, re-gearing, and switching out members of the scientific party. I took the opportunity to join Leg 1, which returned Sunday, the 11th, after completing the northern half of the WFS sampling path.
Captained by Ryan Healy of the Florida Institute of Oceanography, the R/V Hogarth set sail Tuesday morning (the 6th) for Station 1, located 50 miles west-southwest of the mouth of Tampa Bay. Several hours later we lowered the Bongo plankton nets into the water, towed for 15 minutes and retrieved our first samples – hopefully containing a bonanza of fish eggs.
It’s incredibly challenging to determine where fish actually spawn. Researchers can’t be everywhere all the time, watching the fish spawn. Also, identifying juveniles (and then extrapolating back to where they likely spawned) is controversial because the eggs can float long distances. So, until the recent advent of new techniques (using DNA), identifying fish eggs was tedious to impossible.
Plastic jars screw into the tapered ends of the conical nets to collect the organic material, which will be capped and stored for later analysis in the lab. But first, the nets must be washed down with a seawater hose as the wench operator hoists them onto the back deck of the Hogarth.
Fish eggs are tiny and transparent, so the naked eye cannot be trusted to catch every egg that might be gripping the insides of the Bongo nets. The nets are systematically washed from top to bottom to rinse all the eggs – as well as phytoplankton, zooplankton, jellyfish and anything else that wound up passing through the open mouths of the towed Bongo nets – into the collection jars. To make space in the one-liter jars for preservatives, seawater is poured back out of the jars through the sides of the nets and the bio-matter is carefully ushered back into the jars with the seawater hose. The key is to wind up with jars that are about 50% full of seawater and organic material so that preservatives can be added from chemical work stations inside the ship’s scientific lab. Of the two jars collected with each tow, isopropanol (rubbing alcohol) is added to one, filling it to 100%, and 50 mL of formaldehyde is added to the other (a 1 to 10 ratio of formaldehyde to sample).
Fish eggs nearly all look alike – that is, most species spawn eggs that are small and clear, a somewhat daunting and most definitely painstaking challenge for scientists trying to identify them by microscope. A more reliable method is to utilize DNA-barcoding, a process which looks at the soup of genetic material extracted from samples and categorizes it by the specific species of fish present. One limitation, though, is that this method provides presence/absence of various fish species for a given sample location, but it cannot tell you the abundance of eggs for a particular species.
The planned cruise path calls for 68 stations, but weather, boat and gear sometimes alter plans. Hitting as many of the stations as cruise time allows, the scientific party returned the samples to the laboratories at CMS for processing. With an array of sampling locations, the group of researchers hope to understand what species are spawning where on the WFS. This year’s cruise is in August to target the spawning period of reef fishes (like snappers), while next year’s cruise will occur in spring to target grouper spawning.
On Leg 1, the coastal sampling stations brought us close enough to see beaches, trees, and buildings at some of the Panhandle locations, like Pensacola and Cape San Blas (near Apalachicola). The scientific crew worked day and night, splitting into two 12-hour shifts starting at noon and midnight. While each shift saw their fair share of jellies collected in the Bongo nets, the night shift definitely saw more dolphin action.
During some of the late-night net tows, Atlantic spotted dolphins shot across the surface of the water, chasing flying fish that broke from their school and took flight. Standing on the bow at the start of one of the night shifts, I had the privilege of watching a pod of dolphins surf the bow waves for nearly an hour as I talked with a fellow cruise participant. It was remarkable to see how easily they could manage the waves and maintain their position; even the calves kept in perfect unison with their mothers.
Although the focus of the cruise was on microscopic fish eggs (not dolphins), one deep water station was added to the cruise plan to allow for a CTD cast to measure salinity and temperature at various depths, as well as retrieve water samples.
Brianna Michaud, a Ph.D. candidate and student of Peebles, is chief scientist for this year’s sampling cruise. One particular stretch of sampling stations in the cruise path crosses over Desoto Canyon, a 900-meter deep submarine valley that works its way from the coastal waters off of Pensacola out into the depths of the Gulf of Mexico. Michaud chose one spot along this transect to perform two CTD casts, collecting water at 700, 400, 200, 40 meters, and at the surface. She hopes the water samples will tell us how naturally occurring chemicals change with depth and how those chemicals can be used to trace the transfer of nutrients through the food web. A form of recycling appears to be occurring in the vertical direction, and Michaud will use measurements of the naturally occurring chemicals (stable isotopes) to see how vertically migrating species (like the lantern fish seen in a sample from the same area) may be transferring nutrients from the depths back up to the surface.
Joining Michaud to round out the scientific party on Leg 1 were fellow students from the College of Marine Science, Garrett Miller and Ian Williams; from the USFSP program for Environmental Science and Policy, Geography and Sustainability, Sebastian DiGeronimo, Abby Blackburn and Andrea Rodriguez Campos; from the USF Tampa program for Environmental Science and Policy, Nicole Seiden; and from Eckerd College, Grace Koziol. And, none of this would have been possible without the crew of R/V Hogarth, keeping everything in working order, on course, and serving up tasty meals three times a day.
With the new DNA-barcoding method, the 15-year monitoring survey will provide a much more robust picture of where the fish are spawning, which has powerful implications for the sustainability of Gulf fisheries. After the lab work and data crunching wraps up, I look forward to hearing the results of samples collected on both cruise legs.