The Spectral Waters of Gorge Harbour

The semi-contained waters of Gorge Harbour have always had a higher algal density than the open Strait of Georgia. Occasionally, concentrations are so great, the appearance of the ocean water changes dramatically, so that even the casual observer becomes fascinated and, more likely than not, concerned. It is not well understood what brings on algal blooms of such intensity that the clear blue waters turn cloudy with colors of great spectral variety. Only rarely are "Red Tides" truly red. More common hues are green, brown and orange. (And it is worthwhile to remember the old saw : "not all red tides are toxic - not all toxic tides are red".)
The occurrence of algal blooms usually follows a natural rhythm : during the winter months waters remain clear, even as they receive a lot of run-off from the land, with erosional loads of mud and dissolved minerals. In the springtime, as daylight hours lengthen and the sun's power increases, diatoms are the first (phyto-)planktonic organisms to respond, by taking advantage of the high silica content in our granite-surrounded waters to build their fragile shells (frustules) and to multiply rapidly. A few types of diatoms, when present in sufficient density, pose a problem to fish farms. The following image shows a number of very spiny species (Chaetoceros spp., Asterionella japonica), which lodge in the gill tissues of fish and can cause extreme irritation leading to suffocation :


The truly spectacular blooms, though, are caused by different microorganisms, notably dinoflagellates and ciliates, and they tend to happen later in summer.

A "Blood Tide" of biblical proportions occurred in June of 2004, generating considerable local excitement :


The responsible organism was the ciliate Myrionecta rubra, which is classified as zooplankton (as opposed to phytoplankton ; the distinction between animal and plant is often difficult, if not outright inappropriate, in the world of unicellular plankton, where some species can be both - heterotroph and autotroph - at the same time) :


While this microorganism is non-toxic and does not affect the edibility of shellfish, most people dislike oysters that "bleed" red. Others claim that Myrionecta adds a pleasant peppery flavour.


Spectacular blooms of Noctiluca scintillance occurred in the summer of 2007, turning large areas of Gorge Harbour (as well as outlying bays and inlets) into "Cream-of-Carrot" soup :


The responsible organism is a large (>1mm) athecate (naked or without shell) balloon-like dinoflagellate. Individuals don't show much color, but at densities of at least one million organisms per liter, the water turns orange.
Noctiluca blooms are relatively common.


Noctiluca are non-toxic and oily to the touch : they are excellent food for clams and oysters. After the summer of 2007, shellfish were exceptionally plump and tasty.
As the name Noctiluca ("night light") suggests, their presence in the water often causes spectacular bioluminescence.
The image above also shows three specimens of Protoperidinium crassipes : typical thecate (shelled) dinoflagellates.

In September of 2007, Gorge Harbour experienced a brief brown-colored bloom of the thecate dinoflagellate Gonyaulax grindleyi (a.k.a. Protoceratium reticulatum) :


The white scum at the water's edge consists mainly of barnacle exuviae  -  a harmless phenomenon, recurring three times or more every year, as barnacles go through their growth-stages and discard their old skins.


Several individuals of Gonyaulax grindleyi, some dead (colourless) or dying, are visible in above image. The structure of the thecae is clearly discernible.
Blooms of this species have proved toxic in some localities, though no adverse effects have been reported from BC waters.
This is the group which contains Alexandrium catenella (formerly known as Gonyaulax catenella), which causes shellfish harvest closures due to its ability to induce paralytic shellfish poisoning (PSP) in mammals, after having been ingested. The toxin does not harm the shellfish themselves. Gorge Harbour and the west side of Cortes Island have not suffered any PSP outbreaks for the past several years.

Here is an electron-micrograph of the notorious dinoflagellate (note the similarities to the previous species) :


A small (10µ) flagellate (Heterosigma carterae) produces blooms regularly and has caused mortality in farmed fish due to toxicity. It does not appear to affect shellfish.
Gorge Harbour experienced this bloom in June 2008 :


The tiny flagellates look like pale-green potatoes under the microscope (the two flagellae, which propel each individual, are too thin to be seen) :


The year 2009 was characterized by unusually clear water conditions. No plankton blooms, visible to the naked eye, were observed in Gorge Harbour.

It is questionable whether the presence of artificially high concentrations of cultured shellfish represent a direct causative link to the occurrence of blooms. Plankton is shellfish food, and it has been well documented that water, after having passed through a set of oyster rafts, is much diminished in its plankton content.


This micrograph is of the gut content of a beach oyster, representing a small sample of the variety of planktonic organism that are on its menu. Incidentally, Rhizosolenia is another diatom irritating to fish gills.

Oyster feces are the end product of algal blooms, not their origin. The accumulations of fecal matter below shellfish rafts undoubtedly affect the bottom dwelling organisms, possibly negatively. But it is unlikely that plankton blooms are caused that way. Fishfarms can not be used for comparison : there nutrients (not to mention pharmaceuticals) are imported and added to the water, changing the trophic balance dramatically. Unless shellfish farmers start feeding their stock, their growing operations subtract nutrients from the water, rather than add to it. Subtraction of nutrients also changes the local trophic balance, quite likely to the disadvantage of indigenous sub- and intertidal biota (this is one aspect of the larger problem caused by exotic invasive species).

A very helpful and accessible publication is Nicky Haigh's Harmful Plankton Handbook. This slim (50 pp.) ringbook focusses on fishfarm operations, but contains good general sections.

The Stewards of Gorge Harbour is a not for profit organization dedicated to the health, welfare and development of Gorge Harbour. The content on this site are the opinions of the members and are in no way intended to defame or incite. We make an effort to provide information based on facts. Copyright 2010.