Tag Archives: kelp

Street Urchins

Sometimes dinner turns into a mob and bites back.

Well at least that’s what it looks like…

In a shocking turn of events a common sun star (starfish species) was gobbled up by a group of sea urchins (their natural prey species) at a research station in Sweden. Which is just a little bit out of character for the vegetarian lawnmowers that are sea urchins – although make no mistake they can vacuum up a kelp forest if given half the chance.

Although the ‘why’ as to what drove the sea urchins to turn on the starfish (a case of hunger perhaps, or an attempt to remove the threat of predation) remains unclear, the interesting thing is that although the sea urchins have a comparatively simple nervous system (they don’t even have a true brain), they are still able to execute an organised form of attack. This attack strategy has been termed ‘urchin pinning’ by the research team and is usually instigated by one individual that starts the ‘attack’ and is then joined by the other sea urchins who begin munching away at the starfish. They start at the tips and moving inwards, leaving the starfish unable to get away…

The original research article can be found here: https://doi.org/10.1111/eth.13147

A note for sensitive readers: Although many starfish were harmed in the making of this comic they are expected to make a full recovery (physically at least).

Populations Can’t Grow without Homes

Sea otters are one of many charismatic¬†species found along the California coast, yet recovery doesn’t seem to be helping them. Is it something about their habitat that is preventing population growth? (Image Credit: Mike Baird, CC BY 2.0, Image Cropped)

Gaps in kelp cover may threaten the recovery of California sea otters  (2018) Nicholson et al., Ecography, DOI:10.1111/ecog.03561

The Crux

In the 18th and 19th centuries, the fur trade was a massive industry in North America. As a result, many species were hunted and trapped to near extinction. The California sea otter (Enhydra lutris) was reduced in population to less than 50 total individuals. The enactment of the Internation Fur Treaty allowed the species (and others) to come back from the brink of extinction, and they now number over 3200 individuals and are spread across 525km of the California coast. Interestingly, although the population is recovering, it has not bounced back as quickly as other protected mammals living in the same habitat. The California sea lion, for example, has a maximum population growth rate more than twice that of the sea otter (11.7% compared to 5%).

Despite the remarkable recovery of the species, the sea otters occupy less than a quarter of their historic range and have not expanded along the coast in 20 years. The authors of this paper wanted to investigate what it is about the sea otters and their habitat that is slowing this population’s growth rate and spread along the coast.

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