We left the safe harbor of Newport under sunny skies and headed out to conduct our biweekly sampling yesterday afternoon. The forecast was for windier conditions than we generally prefer, but we hadn't been out since Oct 4th, so we were eager to sample as far offshore as the weather allowed.
In mid-October, we had our first substantial winter storm with 40 kt south winds and 23 foot seas.
These winter storms mix the water column, and we generally get warmer water conditions across the shelf with little zonation compared to the summer upwelling that strongly stratifies the Oregon shelf with cold nutrient rich waters inshore and warmer oceanic water off the continental shelf.
We arrived at our first sampling station and we were astonished at how clear the water was- an indication that little phytoplankton were blooming. Our plankton nets came up clean, but our sieves were still filled with tiny organisms, Ctenophores, and lot's of Porcellanid crab larvae.
As we moved farther offshore, the water became even clearer. There were many young krill (furcilia) at our sentinel station- NH-5. Unfortunately, after we pulled the bongo on board, the Captain said we'd have to turn around, but not because of weather as we were intending, but because the boat was overheating. This was a good call, because as we were making our way back to Newport, the engine became very hot and we had to transit very slowly back home. We were thankful we were only 5 miles offshore instead of 25 miles off when this happened.
The live plankton sample we brought back to the lab revealed what appeared to be a shift in the zooplankton community. At first glance, the most noticable difference was the absence of female Calanus copepods that have been very abundant all summer. Further investigation will tell us just how much the community has changed.
The CTD data showed that the near bottom temperatures at NH-5 were just above the long term average and the low oxygen we were seeing in August and September had completely dissipated from the strong winds and large seas we encountered mid-October.
We'll be headed out in early November, sampling out to 85 miles offshore. Stay tuned as we see how the ocean changes during this fall transition time.
Tagged: NH Line
We've been sampling a grid of stations each June since 1998. These stations span from Newport, Oregon, to the northern tip of Washington State and extend from 1 to 30 miles offshore. Although each June is unique in some aspects, June of 2017 was the strangest we've yet encountered in many ways.
The first thing we noticed was the pyrosomes that were in high abundance, everywhere. Pyrosoma atlanticum are colonial pelagic tunicates, and reports were coming in of high numbers of them in areas mostly further south of where we sample. But we were catching them for the first time off of northern Washington!
Moreover, catches of many of our fish species were quite different than an average year (some more abundant, some less so). The juvenile salmon that are the focus of this study were very scarce - one of the lowest in the 20 years of the time series.
However, warm water species, such as Pacific pompano and jack mackerel (a potential predator on juvenile salmon) were found in high numbers. All of these things point to a much altered ecosystem in this region, and do not bode well for salmon returns.
Due to the unusual nature of these findings, we engaged in multiple outreach efforts to get the word out. More info on these findings can be found at the Associated Press and the NW Fisheries Science Center website.
Large diatom blooms were common all summer and into early September at our long term continental shelf station NH-5 (five miles offshore of Newport). However, towards the end of September, a shift in the phytoplankton community occurred, changing from a diatom dominated community to one with more dinoflagellates. The largest change then was an increase of dinoflagellate species diversity and a decrease in diatom diversity.
On a sunny morning on October 4th, we conducted a short cruise to NH-5. The clarity of the water from the boat and a clean zooplankton net after being hauled through the water indicated the disappearance of a phytoplankton bloom. Upon further analysis under the microscope, we actually saw a mixed composition of diatoms and dinoflagellates in the sample. A few species of diatoms, Cylindrotheca closterium, Proboscia alata and Leptocylindrus danicus, were relatively abundant compared to other diatom species. Also, smaller dinoflagellates were abundant and the diversity of larger dinoflagellates, such as Dinophysis and Protoperidinium, was relatively high.
Pseudo-nitzschia, the diatom that produces domoic acid, has been persistently present throughout the summer, however they were rare in this recent sample (Figure 1).
In contrast, harmful dinoflagellates were present in the net tow sample. Alexandrium catanella (Figure 2) is known to produce saxitoxins which can contaminate bivalves (e.g. mussels) and possibly lead to paralytic shellfish poisoning at low cell concentrations. We also observed the dinoflagellate species Dinophysis acuminata, D. fortii (Figure 3), D. rotundata and D. parva that occur offshore Newport. Some of these species produce okadaic acid and dinophysistoxins, which cause diarrhetic shellfish poisoning. Concentrations of Dinophysis species were low on Oct 4, but it will be important to monitor whether these concentrations increase.
Shifts in the physical conditions
These observed transitions of phytoplankton species composition and abundance, and harmful algae closely followed changes of the coastal wind direction, magnitude and persistence. North/northwest winds (upwelling favorable) significantly weakened after early September while southerly winds (downwelling favorable) occurred two to three times for 5 to 6 days in the last month. Phytoplankton species have in turn responded to these seasonal changes of the coastal winds and the underlying physical processes.