• by Dr. Sarah Oktay, Director, University of Massachusetts Nantucket Field Station •
Well, I wish I was reviewing a 1979 Neil Young and Crazy Horse album (although that would be a bit weird and not all that timely), but in fact I am talking about the rust tide which has reared its ugly head once again in Nantucket Harbor. You can easily see it from shore in the Wauwinet area as a series of rusty brown stains that tarnish the surface of the water in pools and streaks. This is from an algae bloom which tends to be located east of Pocomo in the slower to flush Head of the Harbor area. Last week I took a sample of water in a rust tide patch to corroborate some of the algal species and this week we will sample it again to verify if it is primarily the same species that has been tormenting us in the past, the dreaded Cochlodinium polykrikoides. Sometimes due to a combination of factors, the algae species present can “bloom” or increase rapidly in numbers, tinting the water and causing adverse impacts. The phenomenon is not that different from the way cancer cells multiply in tissue: something triggers a beneficial growth situation such as introducing more food, a change in temperature, or something else metabolically advantageous that causes these organisms to multiply out of control.
This infamous rust tide is caused by a dinoflagellate called Cochlodinium polykrikoides which is a small unarmored (some dinoflagellates have “armor” or plates of cellulose) 2-8 cell organism with flagellas which are little whip like tails that aid in locomotion and feeding. Some dinoflagellates like C. polykrikoides are mixotrophic; that is they both have chlorophyll and can photosynthesize, and they eat other organisms on those days that they don’t feel like cooking. Dinoflagellates often contain chlorophylls a and c and fucoxanthin (along with other pigments that give them a reddish color) and they have two flagella for swimming through the water, one of which is contained in a spiral groove on the body. C. polykrikoides is, in this case a pretty typical run of the mill marine planktonic dinoflagellate species that can be a heartless killer which is not really its fault considering it has no heart.
Today a group of graduate students from the School for the Environment at UMass Boston are sampling the harbor for chlorophyll-a (green pigment found in cyanobacteria and the chloroplasts of algae and plants) and nutrients and metals for a bay scallop project and they’ll be able to see some of the associated chemistry. Over the past several years Dr. Peter Boyce and the newly minted Dr. Valerie Hall have been able to monitor juvenile scallop (spat) behavior and mortality in spat bags placed in various locations in the harbor and they have observed up to a 40% mortality rate for juvenile spat in areas known to have large rust tide events- sometimes even before the bloom becomes apparent with the naked eye which may mean that the effects can occur at relatively low concentrations. At about the same time as we started to see called C. polykrikoides in the harbor (sounds almost like a soap opera), a microbiologist who specializes in marine bacteria and algae funded by our local Nantucket Biodiversity Initiative arrived on island to sample some of the filamentous cyanobacteria known as Lyngbya majuscula that has occurred in increased concentrations on eelgrass in the harbor. Dr. Pia Moisander (UMass Dartmouth) has been investigating “brown tide” organisms for several years in Buzzards Bay and she was awarded a small grant by the Nantucket Biodiversity Initiative back in 2011 to look at cyanobacteria in Hummock Pond and this year to measure L. majuscula. Dr. Moisander measures temperature, chlorophyll-a concentrations (which correlate to phytoplankton densities), associated salinity (amount of ocean water) and zooplankton assemblages (who is around to eat the smaller plankton) to see what if any linkages can be found to these chemical parameters and the appearance of the nuisance and toxic cyanobacteria and algae. Scientists have established that these algae blooms occur in harbors impacted with excess nutrients (more than background levels) that originate from a variety of sources from road runoff to septic systems and fertilizers.
Bay scallops are filter feeders and eat plankton (which could include some inadvertent cannibalism) in the water column. Siphons bring water over a filtering structure, where food becomes trapped in mucus. Next, the cilia on the structure move the food toward the mouth. Then, the food is digested in the stomach and digestive gland. Waste is passed on through the intestine and exits via the anus not unlike how we package and ingest food. Adult scallops have developed enough to swim away from contamination and also exclude some toxic particles during feeding by clapping their shells hard to release gill clogging particles and feeding more slowly, sometimes even ejecting toxic particles. Juveniles do not have that luxury and they are often a little higher in the water column too where toxic algae are more likely to proliferate. The adults are on the sea floor where low oxygen levels can affect them, but algal blooms like Cochlodinium polykrikoides tend to be in surface waters.
The rust tide has been a problem for the Cape Cod area for close to ten years. From the web site: http://buzzardsbay.org/red-tide-psp.htm “In September 2005, we received the first report of a Cochlodinium Bloom in Buzzards Bay, sometimes referred to as “Rusty Tide”, to distinguish it from the PSP related “Red Tides.” Cochlodinium blooms may have occurred previously in Buzzards Bay, but if so, they were not widely reported. We have received reports of these Rusty or Rust Tides in every subsequent year. For example, in August 2012, Cochlodinium blooms were widely reported in the northern half of Buzzards Bay, both in bays and offshore, in late August. ….. The 2005 bloom subsided a few weeks later after waters cooled. Unlike the Alexandrium dinoflagellate (the famous red tide ones), C. polykrikoides does not contain neurotoxins that affect people. C. polykrikoides originally had been considered a Harmful Algal Bloom (HAB) species simply because in high concentrations in contained systems, it caused the death of fish by consuming all the oxygen in the water……. However, more recent studies have concluded that Cochlodinium polykrikoides in fact exhibit a pronounced chemical toxicity (Gobler et. al, 2008; Harmful Algae 7(3):293-307). Tang and Gobler (2008, Harmful Algae, 8(3):454-462) documented that juvenile bay scallops experienced “100% mortality during 3 days exposure to cultures at cell densities an order of magnitude lower than raw bloom water.”
In the paper “Characterization of the toxicity of Cochlodinium polykrikoides isolates from Northeast US estuaries to finfish and shellfish” [Harmful Algae Volume 8, Issue 3, February 2009, Pages 454–462], researchers Ying Zhong Tang and Christopher J. Gobler from the School of Marine and Atmospheric Sciences at Stony Brook University described the concentrations and timescales in which mortality was observed for juvenile bay scallops (underlined parts are my additions for clarity):
“Bioassay experiments demonstrated that 24 h exposure to bloom waters (>5 x 104 cells ml-1) killed 100% of multiple fish species (1-week-old Cyprinodon variegates, adult Fundulus majalis, adult Menidia menidia) and 80% of adult Fundulus heteroclitus. Microscopic evaluation of the gills of moribund (dying) fish revealed epithelial proliferation with focal areas of fusion of gill lamellae, suggesting impairment of gill function (e.g. respiration, nitrogen excretion, ion balance). Lower fish mortality was observed at intermediate C. polykrikoides densities (103 –104 cells ml -1), while fish survived for 48 hour at cell densities below 103 cells ml-1. The inability of frozen and thawed, or filtered (0.2 mm)-bloom water to cause fish mortality suggested that the thick polysaccharide layer associated with cell membranes and/or a toxin principle within this layer may be responsible for fish mortality. Juvenile bay scallops (Argopecten irradians) and American oysters (Crassostrea virginica) experienced elevated mortality compared to control treatments during a 9-day exposure to bloom water (>5 x 104 cells ml-1). Surviving scallops exposed to bloom water also experienced significantly reduced growth rates. Moribund (dying) shellfish displayed hyperplasia (increase in cells), hemorrhaging (copious discharge of blood), squamation (scaliness), and apoptosis (programmed cell death) in gill and digestive tissues with gill inflammation (sounds painful) specifically associated with areas containing C. polykrikoides cells. In summary, our results indicate C. polykrikoides blooms have become annual events on eastern Long Island and that bloom waters are capable of causing rapid mortality in multiple species of finfish and shellfish.” So in relatively plain English, the damage is done by way more than simply reduced levels of oxygen and can occur in natural bloom concentrations. What doesn’t kill the scallops causes them to grow slower in bloom waters with physical damage to their tissues. It does take some time for the effects to be terminal.
Other papers2 that have been published over the past 6 years show multiple incidences of mortality for juvenile bay scallops in high concentration blooms. Fish suffer even more, with almost 100% mortality in concentrated blooms. Fortunately we have not been seeing fish wash up on our shore, but the occurrence of this rust tide is now a fairly common part of August. According to Dr. Peter Boyce (pers. communication), it first appeared in our harbor August 10th this year.
Last but not least is answering the question: How did these organisms manage to travel here from Asia? In Tang and Gobler’s recent 2012 paper “The toxic dinoflagellate Cochlodinium polykrikoides (Dinophyceae) produces resting cysts”: [Harmful Algae Volume 20, December 2012, Pages 71–80] we learn that “While harmful algal blooms (HABs) caused by the toxic dinoflagellate Cochlodinium polykrikoides have been known to science for more than a century, the past two decades have witnessed an extraordinary expansion of these events across Asia, North America, and even Europe. Although the production of resting cysts and subsequent transport via ships’ ballast water or/and the transfer of shellfish stocks could facilitate this expansion, confirmative evidence for cyst production by C. polykrikoides is not available. Here, we provide visual confirmation of the production of resting cysts by C. polykrikoides in laboratory cultures isolated from North America.” So they got over here in shellfish and ballast water and manage to hide out in resting cysts in the seafloor, popping up to torment us whenever conditions are right. Lovely.
The good news is that fish can swim out of effected areas and that dead cells don’t seem to be very dangerous unlike some byproducts of other harmful algae blooms which can still be toxic when the creature that created it is dead. Fish and bivalves placed in concentrated solutions of dead or frozen dinoflagellates did not die. And adult scallops in cultures of C. polykrikoides tend to be smaller, but don’t die from short term contact at the concentrations we see in the harbor. But we should not be seeing any rust tide at all, and the only way to avoid this is to reduce our nutrient footprint. Actions that would help include fertilizing less and more thoughtfully (right time of year, correct time of day, not before rainstorms), not overwatering, and upgrading our septic systems. Our economy in the winter and our way of life as well as quality of life depend on an algal bloom free harbor.
The Town of Nantucket is extremely proactive and professional in their stewardship of the bay scallop populations. Our shellfish biologist, Tara Riley and her team of assistants have significantly upgraded the shellfish hatchery, providing super productive and efficient phytoplankton grow rooms to feed the millions of tiny scallop larvae that they grow out into juvenile scallops that can be successfully released. A quick summary of some of their work can be found on their website: http://www.nantucket-ma.gov/131/Shellfish-Biologist. I support their efforts to upgrade and improve the building they work in as should you.
Resources used for this article:
1) Harmful Algae 01/2009; DOI: 10.1016/j.hal.2008.10.001
2) Gobler et al. Characterization, dynamics, and ecological impacts of harmful Cochlodinium polykrikoides blooms on eastern Long Island, NY, USA
3) Others listed as above