The swarm of thousands of red crabs in the Hannibal Bank Seamount near the coast of Panama has left many marine experts excited and bewildered. Why are they here?
The question is legitimate considering that these types of crabs normally reside somewhere in the Gulf of Mexico and are washed ashore on the beaches of Southern and Central California. Thus, this has been the farthest they've traveled and the first time they have been caught on video doing so, explained the researchers.
The truth is nobody knows the reason yet. One, although seamounts are aplenty, less is known about them, and researchers are still in the process of learning more about Hannibal Bank Seamount. Second, the movement and activity of the crabs are simply "bizarre."
However, there are a couple of theories:
Many studies have already associated the appearance of the red crabs with El Nino, especially in the shores of California. It's believed that as temperatures of the sea surface increase by 4 to 7 degrees, the weather patterns in the ocean change, driving these crabs, which can be easily brought about by currents, away from their natural habitat.
Further, researchers who discovered the crabd swarm in the seamount, pointed out that during the time of their discovery, crabs of the same species have been reported washed ashore in California.
However, they don't think that what's happening in these U.S. shores is connected to that of the Hannibal Bank Seamount.
"[I]t is significant that P. planipes can be simultaneously abundant at the two distant locations and at two different habitats," said the research.
Another possible explanation is that the red crabs are looking for food such as zooplankton that are not distributed uniformly in the ocean, but rather appear in patches.
Since the researchers observed that the red crabs did congregate in patches, with up to 78 crabs per square meter (seven crabs per square feet), it's possible the researchers had seen the crabs when they're feeding.
Meanwhile, seamounts, which form during volcanic activities, are a rich ecological resource, which may imply that there could be abundant food supply within the area.
Escape From Predators
The researchers also noted that the area where the red crabs were found was hypoxic, which means the levels of oxygen are quite low that may prevent many marine species from surviving.
"Off Baja California P. planipes is the main prey of large pelagic predators such as yellowfin tuna and skipjack tuna," explained the study.
The crabs are also part of the diet of yellowtail amberjacks, certain types of whales, otters, and a good number of birds, including herring gulls. Moreover, based on the size of the crabs observed, these are more likely adults, which make them even more appetizing to their predators.
In the end, these are theories, and some of them may be debunked later as researchers delve deeper into the phenomenon.