<Spot Prawns and Starfish: Understanding Their Interconnectedness>
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Do you appreciate seafood? I certainly do, especially Spot prawns. These large, local delicacies have a brief availability each season, leading to a rush to enjoy them before waiting another year.
The demand for Spot prawns is significant both locally and globally, yet their supply appears to be declining. This raises questions: is it due to overfishing, diseases affecting the prawns, or perhaps the dwindling starfish population?
You might wonder how the loss of starfish could impact the availability of Spot prawns. This article aims to illuminate the interconnectedness of starfish, Spot prawns, sea urchins, and kelp, while highlighting how the decline in starfish due to a wasting disease is impacting the supply of our beloved prawns.
Understanding Spot Prawns
Spot prawns (Pandalus platyceros) are fascinating creatures. They inhabit waters from Unalaska Island in Alaska down to San Diego, California.
In British Columbia, Spot prawns are the largest among seven commercial shrimp species found along the coast. Their size varies significantly; some larger females can reach nearly 25 cm (about 10 inches) in length.
The name "spot prawns" derives from the distinctive white spots that appear on their tails once cooked, alongside unique white stripes on their shells.
Spot prawns typically live for 4 to 6 years and exhibit hermaphroditic traits, transitioning from males to females after two years, which is when they reach their full size, meaning it’s rare to find male Spot prawns on the dinner plate.
Juveniles often inhabit shallower areas and can be spotted hiding beneath the blades of sieve kelp.
In British Columbia, around 2,450 tons of Spot prawns are harvested annually from the waters between the mainland and Vancouver Island. The harvesting season usually starts in May and lasts for 6 to 8 weeks, leading to the popular tradition of enjoying them until the next season arrives.
What is a Spot Prawn?
Wild BC Spot prawns are celebrated globally for their sweet flavor and firm texture. They are caught using baited traps placed on the ocean floor at depths of 40 to 100 meters. Fishermen claim this method minimally impacts the ocean habitat and results in low bycatch levels. However, it's worth noting that this method can potentially damage fragile glass-sponge reefs and coral beds.
Due to high demand, some harvesters resort to using trawl nets, which can cause significant damage compared to traps, especially when dragged over sensitive marine environments.
Now, let’s shift our focus back to the other crucial species involved in the ecosystem of Spot prawns: starfish, sea urchins, and kelp.
The Role of Starfish
The two primary starfish species in this context are the Ochre Sea Stars (Pisaster ochraceous) and Sunflower Stars (Pycnopodia helianthoides). These species are essential for maintaining diverse benthic communities, which include organisms living on or near the seabed.
In 1969, Dr. Robert T. Paine, an ecologist, introduced the term "keystone species" to describe organisms whose removal can drastically alter the community structure. He identified the Ochre Star as the first designated keystone species due to its role as a predator that controls mussel populations, allowing other species to thrive.
Sunflower Stars
The Sunflower Star is another remarkable keystone species. Known as one of the largest predatory sea stars, it can reach up to 1 meter in width and weighs as much as 5 kg. It inhabits both intertidal zones and deeper waters.
Juvenile Sunflower Stars primarily feed on mussels and sea urchins, which in turn consume large amounts of kelp. By preying on these species, Sunflower Stars help sustain healthy kelp populations, benefiting the entire ecosystem.
Starfish Wasting Disease
In 2013, a wasting disease devastated starfish populations along the Pacific coast, affecting over 20 species from Baja California to Alaska. The cause remains uncertain, with various agents, including a specific virus, suggested but not definitively proven.
Some researchers believe that environmental factors, such as organic runoff and climate change, may contribute to the disease's severity. As conditions worsen, the impact on marine ecosystems becomes increasingly concerning.
The Impact on Kelp
The dramatic decline of starfish has led to a rapid increase in mussel and sea urchin populations. In British Columbia, the Green Sea Urchin (Strongylocentrotus droebachiensis) population quadrupled, resulting in significant overgrazing of kelp, reducing the Sea Colander Kelp population by 80%.
This reduction in kelp forests directly affects Spot prawns, which rely on these habitats for shelter and development. Fewer kelp forests mean increased predation on prawn larvae, leading to a decline in adult populations.
As the number of adult prawns decreases, the effort to harvest the same quantity increases, leading to higher costs and prices. In response, fishermen may resort to more efficient yet ecologically harmful methods like trawling.
The cycle continues, with the pressure to harvest more from an already declining population compounding the issue.
Solutions?
Are there solutions to this ecological dilemma? Some scientists speculate that starfish populations may be recovering, though it’s too soon to celebrate.
This raises personal questions about sustainable consumption. Should we advocate for harvest limits on Spot prawns to preserve this valuable resource? I believe that if it benefits the ecosystem, it’s worth considering.
In the meantime, I remain hopeful for a resolution, as my love for Spot prawns endures.
Until next time, Rich
Sources
The insights in this article stem from extensive research, with significant inspiration drawn from an article by marine biologist Sheila Byers in Volume 47 (2019) of Discovery, published by the Vancouver Natural History Society. This publication is an invaluable resource for those interested in natural history.