Wednesday 11 April 2012

Are PSP toxins preventing the recovery of North Atlantic right whales?

A review of: Doucette, G. J., Cembella, A. D., Martin, J. L., Michaud, J., Cole, T. V. N. and Rolland, R. M. 2006. Paralytic shellfish poisoning (PSP) toxins in North Atlantic right whales Eubalaena glacialis and their zooplankton prey in the Bay of Fundy, Canada. Marine Ecology Progress Series, 306, 303-313.

Harmful algal bloom incidents are on the rise and these blooms can have great impacts on marine food webs, even being known to contribute towards marine mammal mortalities. They are therefore of special interest when monitoring endangered species, such as the western North Atlantic right whale, Eubalaena glacialis, the current population of which stands at just 300-350 individuals.

E. glacialis has been protected for over 70 years, but it is still approaching extinction. Contributing factors to this include a significant decline in reproductive success and a decline in general health. The cause of these factors is still being investigated but little attention has been paid to the effect of exposure to marine biotoxins. One of the most likely biotoxin threats is Paralytic Shellfish Poisoning (PSP) toxins, as the whale feeding grounds overlap with the distribution of the Alexandrium dinoflagellates which produce PSP toxins. E. glacialis’ primary food source is the calanoid copepod, Calanus finmarchicus, which is known to feed on Alexandrium. This presents a direct path of trophic transfer for the toxin to be consumed by E. glacialis. Not a lot is known about how PSP toxins could affect marine mammals, but it has been suggested that sub-lethal effects on respiratory physiology may lead to abnormal diving and feeding behaviour. In turn, this could be detrimental to body condition and most importantly, ability to reproduce. The aim of this study was therefore to investigate the possible presence of PSP toxins in E. glacialis in their summer feeding grounds, the Bay of Fundy. This could indicate a risk of toxin exposure and prompt further, more detailed research into the effects which the toxins may have on the health and reproduction of E. glacialis.

16 faecal samples were collected opportunistically using fine-mesh dip nets, representing at least 11 actively feeding right whales. The whales encountered were also identified by direct observation and photography. Faecal samples were linked with whale ID to determine age, sex and reproductive history. 48 zooplankton samples were collected using towed mesh nets. The contents of one net were filtered and preserved in 4% formalin-seawater solution, used to determine copepod composition and concentration. Samples were taken from the second net for PSP toxin analysis. Phytoplankton was collected using a surface bucket and all phytoplankton >5µm was identified and counted. Shellfish were collected by the Canadian Food Inspection Agency (CFIA) as part of a routine marine biotoxin monitoring program. Toxin levels for Mytilus edulis were assessed for PSP-related toxicity. E. glacialis faeces and zooplankton were extracted and tested for the presence of PSP toxins and the corresponding faeces and zooplankton samples (in space and time) were compared using high performance liquid chromatography and fluorescence detection. Data analysis was then performed to test for an association between variations in Alexandrium cell counts and PSP shellfish toxicity, and yearly rates of right whale calving and inter calving intervals.

PSP toxins were detected in all whale faecal samples with concentrations ranging from ca. 0.05 - 0.5 µg STX eq g-1 wet weight. PSP toxins were found in 40/48 samples of zooplankton, with concentrations ranging from ca 0 - 0.68µg STX eq g-1 wet weight. The calanoid copepod, Calanus finmarchicus, which is the primary food source of E. glacialis, was found to be dominant in the mesozooplankton community across all samples. The toxicity values for the common mussel, Mytilus edulis, ranged from 100 - 1000µg STX eq (100g)-1. This exceeds the regulatory limit for harvesting of 80µg STX eq (100g)-1. Concentrations of Alexandrium spp found within samples varied between ca. 100-200 cells 1-1. Maximum counts recorded for this genus form 1988-2003 ranged from 240-90700cells 1-1. PSP toxin levels were found to vary from 41-816µg STX eq (100g)-1 between 1992-2003.

The findings of this study show that the highly endangered cetacean, Eubalaena glacialis, is being exposed to great levels of PSP toxins by ingestion. This exposure if primarily though a single zooplankton vector, the calanoid copepod, Calanus finmarchicus. The zooplankton toxicity levels suggested in this study are likely to be underestimates since samples were diluted, but these estimated are already high. The daily exposure these whales face is comparable to a lethal oral dose in humans and these findings suggest that it may pose a significant threat. The PSP toxin composition for faeces differed greatly from that in the zooplankton prey which may suggest a considerable alteration of the PSP toxins within the whale. The mechanisms for this remain unclear, but this may lead to a decline in net toxicity following ingestion of the toxins. Sampling and analyses over several years in many more locations will be needed in order to assess the toxin exposure and better understand the metabolism of the toxins by C. finmarchicus and E. glacialis populations. Significant correlations were also found between maximum Alexandrium counts and calving rates lagged by 4 years, and PSP shellfish toxicity levels and calving rates delayed 6 years. It may be possible that if the toxin negatively affects critical physiological processes, feeding and diving behaviour will be compromised. This could affect the general health and population fitness, and therefore affect reproductive abilities and calf survival. In an already severely depleted population which is approaching extinction, these factors could contribute to a lack of recovery and further population demise.

4 comments:

Matt Amos said...

Hey,

If the toxins are affecting the population fitness is there actually anything that can be done about it? Or are they just screwed?

Samantha Bowgen said...

Considering their population is down to 300-350 individuals, with no sign of recovery currently... yea it is possible that they're screwed.
It hasn't been proven yet that the toxin affects the populations fitness. But this study is pointing out that little study has been done on the link between the toxin and the whales recovery, and it clearly needs to be as such high levels are present.
If the toxins are what is causing the lack of recovery by affecting reproductive ability and calf survival... There are methods of control which could be put in place in feeding or breeding areas. If the toxins were definitely found to threaten an already endangered species, control methods would be justified. Habitat alteration could be look into - is increased nutrient loading causing Alexandrium blooms? Shellfish populations may be reduced - they would naturally remove large amounts of phytoplankton from the water. Efforts could be made to enhance the populations. On the small scale, barriers might be useful, filters, pumps...
Chemical and mineral compounds can be used to kill or inhibit the toxic algal cells, but they could also harm co occurring algae and other organisms - more harm than good?
The link needs to be firmly made between the non-recovering population and the toxins... then methods can be introduced. But its definitely possible that it may be too late..

Lee Hutt said...

Hi Sami

You mentioned that faecal samples were collected opportunistically, I am curious about what that involved. I imagine someone swimming behind the whales with a little net. I do not know much about Whales so I was also wondering how they matched Whale I.D. to their age and reproductive history?

Samantha Bowgen said...

Hello Lee

It’s not too far off what you imagine! The whales frequently defecate, usually just before diving or during courtship activity. The collection was opportunistic, as they would literally wait to come across faecal matter, or follow whales until it happened. It was best to sample it just after the whale had defecated, as then they could ID the whale, and match it to the sample. The faeces is buoyant and remains on the surface for quite a while, so collection is simple. Also sampling took place in the Bay of Fundy, which is of reasonable enough size to make this process easier.
As for matching whale ID to their age and reproductive history... They had access to the North Atlantic Right Whale Catalogue, which quite helpfully has over 25 years worth of data on the life history of individual whales. This made identifying whales by observation or photography much easier, and the toxin content of the faeces could then be matched. :)