The Hoodwinker Sunfish

 This month’s post is reminiscent of last month’s, more about toxins. However, let’s start with something different.

The Ocean Sunfish, genus Mola, is odd-looking—it looks somewhat like a fish that has been cut in half. In addition, these species contain many superlatives. They are one of the largest bony fishes, reaching 3.3 meters and 2740 kg (6000 lbs). Females possess a remarkable reproductive capacity, producing more eggs than any known vertebrate, a staggering 300 million at a time. The little fish fry are tiny. The fry can grow up to 60 million times its original weight before reaching adult proportions, arguably the most extreme size growth of any vertebrate animal. In 2016, researchers sequenced the genome, discovering several genes that might explain its fast growth rate and large body size.

Figure 1. Drawing of an adult 

Ocean Sunfish, Mola mola.

The Hoodwinker Sunfish, Mola tecta, is a species of Sunfish that has only recently come to light, discovered in 2015. This discovery has opened up new research and exploration. So in early June 2024, when a Hoodwinker Sunfish washed up on Oregon beaches, there was a sense of excitement. 

The Associated Press headline read:

Rare 7-foot fish washed ashore on Oregon’s coast garners worldwide attention 

It is a terrific chance to study this rare species.

Not so terrific, the likely cause of the fish’s demise is garnered from another headline.

Oregon officials close entire coast to mussel harvesting due to shellfish poisoning. 

The concern was due to high concentrations of toxic plankton species. For humans, one danger is Paralytic shellfish poisoning, or PSP, which is caused by saxitoxin, a naturally occurring toxin produced by algae, according to the Oregon Health Authority. Similar outbreaks, which have been getting more frequent, have been occurring regularly in Florida.

In 2021, a red tide event off the coast of Florida resulted in thousands of dead fish washing up on beaches, even killing a few manatees. Thus, the likely cause of the Hoodwinker Sunfish’s demise is toxic algae. Toxic algae blooms are known as harmful algal blooms (HABs). Great, just what we need—another acromyn.

Getting technical:

Over the last decade, there has been a noticeable increase in the occurrence and intensity of red tides and other harmful algal blooms (HABs) worldwide. Several factors contribute to this increase:

The primary driver of increased red tides is nutrient pollution, particularly from agricultural runoff, sewage, and industrial waste. Excess nutrients, especially nitrogen and phosphorus, provide a rich environment for algal growth.

Rising sea temperatures due to climate change create favorable conditions for many types of harmful algae. Warmer waters can enhance algal growth rates and extend the growing season. Increased coastal development and land use changes can lead to more runoff and pollution entering coastal waters, further promoting algal blooms. Alterations in ocean currents and water circulation patterns, sometimes linked to climate change, can influence the distribution and frequency of algal blooms.

Species of interest

The Gulf of Mexico, particularly along the Florida coast, has seen a marked increase in red tide events caused by Karenia brevis. These events have become more frequent and severe, with substantial ecological and economic impacts. Large-scale blooms of Pseudo-nitzschia, which produces domoic acid, a potent neurotoxin, are a big issue for the Pacific coast.

Coastal regions in Europe and Asia have also experienced more frequent red tides. For example, the East China Sea has seen increased red tide events, which have significantly affected fisheries and aquaculture. In China, the toxic dinoflagellates include Prorocentrum donghaiense, Azadinium poporum, and Alexandrium tamarense. This last is related to the major cause of red tides on the US northeast coast, Alexandrium catenell.

Algal blooms in Oregon, where sunfish were found, are common in freshwater; Oregon recently closed freshwater lakes due to algal blooms with species that produce microcystins. The problems in the marine environment of Oregon are, at least, a little less common. The culprits in the Oregon marine bloom are likely Alexandrium catenella, which causes paralytic shellfish poisoning, or the potential for Amnesic Shellfish Poisoning (ASP) caused by domoic acid via Pseudo-nitzschia. Those are the likely species involved, but at least 50 other toxin-producing species cause problems.

I hate acronyms and am trying to avoid using them. However, TABs, for toxic algal blooms, is a much better acronym than HAB, for Harmful Algal Blooms. Harmful sounds wimpy, while toxic sounds nasty.

Though blooms occur naturally, they are much more frequent due to human factors. A few steps can prevent many toxic algal blooms. 

The most important point is that nutrient pollution, particularly agricultural runoff, is the primary driver of increased red tides. We must regulate the application of nitrogen and phosphorus on agricultural fields to prevent death by red tide.

Sources and Further Reading

News story about the fish:

https://www.msn.com/en-us/news/us/rare-7-foot-fish-washed-ashore-on-oregons-coast-garners-worldwide-attention/ar-BB1nPlQi

News story about the toxic plankton.

https://apnews.com/article/oregon-coast-shellfish-poisoning-06068473aeb8984efb8fdb3cdae20659

Pan H, Yu H, Ravi V, et al. 2016. The genome of the largest bony fish, ocean sunfish (Mola mola), provides insights into its fast growth rate. GigaScience 5 (1): 36.