Not all invaders… come from outer space…
Boston Harbor Curley School
Invasive Crabs in the Boston Harbor
Invasive crabs are “exotic” not this kind of exotic…
Exotic species can be animals, plants, or even microbes (microscopic!) Exotic species are not native to the ecosystem Meaning we’re not originally from here
Where are we from? Cows?Rice?Chickens?Apples? Imagine life without these things!
So, how do exotics get here? We introduced some of them on purpose Fact: Over 98% of the U.S. food supply are introduced plants/animals
Or… We introduce them accidentally For example, ballast water is used to stabilize the ship… but can transport a huge aquarium of exotic life! These exotics get dumped into local waters. Ballast water line
Exotic Disaster
When is an exotic invasive ? When it spreads rapidly and out-competes native species A Kudzu invasion blankets all other life
Invasive success : They have HIGH reproductive rates A single female Asian Shore Crab can produce up to 200,000 eggs per year! That’s twice the rate of native crabs
They leave behind their predators and competitors. They play by a different set of rules. Invasive success: Wild boar in the U.S.
Invasives can be harmful… They threaten biodiversity Fact: ½ of all species that are “endangered” have been impacted by invasives Many of these endangered species become extinct
Natural ecosystems support a biodiversity of speciesThe arrival of an exotic like Purple Loosestrife……can alter an entire landscape.
Important Invasives of the Boston Harbor European Green Crab Asian Shore Crab
Impacts of the Invaders European Green Crab Accidentally introduced in 1817 Accidentally introduced in 1817 Consumes large numbers of juvenile soft-shell clams and oysters Consumes large numbers of juvenile soft-shell clams and oysters Eats $44 million worth of shellfish per year! Eats $44 million worth of shellfish per year!
Impacts of the Invaders Asian Shore Crab First recorded in Mass. in 1988 First recorded in Mass. in 1988 Broad diet, disrupts food web Broad diet, disrupts food web Studies show as Asian Shore Crab numbers go up, native crab numbers are decreasing Studies show as Asian Shore Crab numbers go up, native crab numbers are decreasing
Ranges of the Invasive Crabs European Green CrabAsian Shore Crab Boston
What can WE do? What should WE do? These are OUR islands. Become Citizen Scientists!
Not this… This kind of science!
Skills you will need: Ability to identify a crab’s specie and gender Ability to identify a crab’s specie and gender Let’s do it!
Identifying the European Green Crab Five Spines behind each eye Color - can be green, red, yellow, or brown Triangular shaped body
Identifying the Asian Shore Crab Large claws relative to body size Relatively square body Striped legs Three Spines behind each eye
Identifying the native Rock Crab Nine or more Spines behind each eye Color - usually reddish brown Triangular shaped body
Identifying Gender in Crabs Males have the “lighthouse” Females are more circular This rule works for other species of crab too.
Quick Quiz! 1. List two reasons invasive species can be very successful. 2. The European Green Crab has __ spines behind each eye. 3. The Asian Shore Crab has __ spines behind each eye. 4. The native Rock Crab has ___ spines behind each eye. 5. Male crabs have a _____________ shape underneath. 6. Female crabs have a more __________ shape underneath lighthouse circular