Northwest Fisheries Science Center

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Blog on ocean conditions along the Newport Line and the northern CA Current.

Warm water phytoplankton species

By Xiuning Du
April 19, 2016

Figure 1. Diatom Planktoniella sol: Oceanic, most common in tropical and subtropical seas.

While phytoplankton abundance and species richness were low in January 2016, both significantly increased from February (See earlier blog post: Winter phytoplankton bloom) continued to be high in March. The phytoplankton community during this late winter period was numerically dominated by cold-water and cosmopolitan species but the February and March sampling also show a few warm-water forms of phytoplankton that have rarely been spotted in our previous biweekly samplings. Some of these warm water species (see the list below) have been noted from waters of southern and central coasts of California during the EI Niño event of 1957-1958 (Balech 1960, Bolin and Abbott 1962).

Figure 2. Diatom Chaetoceros atlanticus var. neapolitana: oceanic, more southerly in distribution, up to 34,000 cells per liter off southern California and abundant in February and March (Cupp 1943).

A specific ecotype of phytoplankton species is largely observation- and geography- dependent, being associated with specific water mass properties, e.g. ranges of temperature and salinity. Warm-water forms of phytoplankton are more common in the southern portions of the California Current ecosystem compared to coastal waters off Oregon and Washington. Southern species appeared off Oregon is either in southern coastal/offshore water carried north to Oregon through Davidson Current or oceanic offshore water off Oregon advected onshore with wind-driven Ekman transport. Northward transport is common during winter downwelling season when southerly/southwesterly winds prevail along the west coast of US, and is enhanced during EI Niño events. During the past few months, nearly continuous south/southwest winds were blowing off Newport indicating northward and onshore flow patterns dominated on the Oregon coast. Upper water column temperature was constantly above 11°C and increased above 12 degree at the end of March in the inner shelf waters. The nearshore warming in March favored the survival and growth of the warmer water forms of phytoplankton.

Figure 3. Diatom: Chaetoceros didymus var. produberans: neritic, south temperate, rare compared to type.

The observed warmer water species: Diatoms Planktoniella sol (Figure 1), Chaetoceros atlanticus var. neapolitana (Figure 2), Chaetoceros didymus var. produberans (Figure 3), Chaetoceros brevis (neritic, south temperate to subtropical) , Chaetoceros peruvianus (Figure 4), Chaetoceros curvisetus (neritic, south temperate), Chaetoceros lorenzianus (neritic, tropical and temperate, the only exceptional one quantitatively abundant); dinoflagellates Ceratium azoricum (Figure 5), Ceratium platycorne (prefer oceanic oligotrophic waters), Ceratium pentagonum (oceanic, warm temperate to tropical waters) and Dinophysis tripos (warm temperate to tropical waters).

Figure 4. Diatom Chaetoceros peruvianus: oceanic, south temperate to warm seas.

North winds off Oregon blew consistently from 29 March through 10 April suggesting that the upwelling season might have been initiated and spring is upon us. Will these warm water species be completely gone soon? Or they will continue wonder around for a bit longer time or even some new types of warm water forms will show up? A big south-westerly storm has been blowing for the past few days so will that send the ecosystem back to a “winter” state? We will continue our updates.

Figure 5. Dinoflagellate Ceratium azoricum: warm water.

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