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The Asian Shore Crab: Introduced Pest as Aquarium Animal and Food Source

Asian Shore CrabsIn 1988 a small crab showed up on the New Jersey shore, apparently discharged there along with bilge water from ships that had visited the Western Pacific.  Deceptively innocuous, by the mid 1990’s the Asian shore crab (Hemigrapsus sanguineus) was the dominant inter-tidal crab in an area stretching from Maine to North Carolina. In the space of 3-5 years, it became the most common crab at several estuaries that I visit…at one, hermit crabs and sand shrimp have virtually disappeared.

Asian shore crabs seem to co-exist more peaceably with one another than do native species…those pictured here were found under a single small rock.  I wonder if, in contrast to other crabs, newly-molted individuals are not attacked by neighbors. 

Making the Most of an Invader

There is, however, a silver lining to this environmental cloud…the crabs make a nutritious addition to the diets of many aquarium fishes and invertebrates.  Many fishes consume small crabs whole, and they can be broken up for smaller fishes.  Freshwater fishes ranging in size from guppies to peacock bass will enjoy an occasional crab meal as well.

Shore crabs thrive for weeks in damp seaweed under refrigeration and can be frozen for future use.

Collecting Crabs and other Marine Animals

Inshore Lizard FishAsian shore crabs inhabit tide-pools, jetties and salt marshes.  They forage as the tide recedes and are most easily collected at low tide, when they shelter below rocks and other cover.  A wide variety of sizes (please see photo), suitable for nearly any size aquatic pet, can be gathered in no time at all.

While searching for shore crabs, keep your eyes open for shrimps, worms, mussels and other small creatures.  All are useful aquarium foods, and many make very interesting display animals (shore crabs are unprotected, but check local regulations regarding others).

An Unusual Visitor from the South

Seining and setting out minnow traps will improve your catch, and the sea never fails to provide wonderful surprises.  Last summer an inshore lizardfish (Synodus foetens) showed up in my net (please see photo).  I’ve had only limited success with them in captivity and so released this one after taking some photos.

Shore Crabs in the Aquarium

As is my way, I tried my hand at keeping Asian shore crabs in captivity, and was pleasantly surprised.  Although in nature foraging is tied to the tidal cycle, captives abandon this strategy and soon appear at all hours (in contrast, native fiddler crabs that I have kept became active according to an internal clock – feeding and retiring in groups, despite the absence of a tidal influence).  Shore crabs feed ravenously on any and all plant or animal based fish foods.

I set up a group in a large estuary exhibit at the Brooklyn Children’s Museum, and they have done quite well there.  The crabs forage underwater and on rocks protruding above the surface, and co-exist with sand shrimp, striped killifish and other natives (in a small aquarium, they should be monitored closely for aggression).

Crab Alternatives

Please check out our extensive selection of frozen and freeze-dried  fish foods.  Many contain whole marine animals, and are an excellent addition to the diets of aquarium fishes and invertebrates.

Further Reading

Information about this and other introduced marine animals and plants is posted at http://www.seagrant.uconn.edu/INVID.HTM.

Please write in with your questions and comments. Thanks, until next time, Frank Indiviglio.

Caribbean Fish and the Gulf Stream

Cory here. The invasion of the Volitan Lionfish (Pterois volitans) has many concerned for the future of fish populations in the Caribbean and off the waters of Florida. The lionfish are swallowing native baby fish at an incredible rate, leading experts to believe this will begin to thin fish populations. Along with commercial fishing, the future is beginning to look bleak. The lionfish have spread throughout the eastern waters of Florida and are even being found along the shore of New York and Long Island. Wreck divers off of the North and South Carolina waters are finding an abundance of Lionfish. How can this be, a warm water fish in the cold waters of the Mid Atlantic and New England Coasts?

The answer is the Gulf Stream. The Gulf Stream is a current that starts in the Gulf of Mexico, flowing around Florida and up the East Coast of the United States. The current begins to flow further off shore of New England, passing the Southeastern shores of Newfoundland and out into the Atlantic Ocean. The current transports warm water from the Caribbean, the whole way to Europe. The Gulf Stream has a large impact on coastal temperatures not only along the east coast, but in Europe.  Along with the warm water are tropical fish, which also make the trip along the Atlantic coastline.

There have been Spot-fin Butterflies (Chaetodon ocellatus), juvenile Blue Angels (Holacanthus bermudensis), and even small Barracuda spotted by divers off the coast of Rhode Island. In the north, during the fall, divers and snorkelers go in search for tropical species for personal and public aquariums. The sad part of this all is tropical fish caught in the stream will inevitably die as they are carried into cooler waters. Some of the best fishing from North Carolina and northward can be found off shore in the Gulf Stream where water temperatures can be close to 20 degrees higher just 150 to 200 miles offshore. Here Tuna, Wahoo, and Mahi can be found throughout most of the year. The clarity is just as amazing as the temperature difference, going from no visibility to over 100 feet in just 50 miles or so.

Typically, large or adult specimens are not found far from their native waters, because they can swim against the current, which averages around 4 MPH. Normally, juvenile fish or larvae are found due to immaturity, or the inability to fight the push of the current. The biggest question yet is how do these fish make it to the coastal waters of New England, which is 200 to 400 miles away from the Gulf Stream? The logical reasoning at this point is that they are carried toward the coast in small warm water eddies that break off the main current.  Otherwise, the juvenile fish would have to swim hundreds a miles away from warm water into the colder water to only die a month or two later.

Conservation Update: Oriental Weatherfish (Dojo Loach, Misgurnus anguillicaudatus) established on the Iberian Peninsula; Food Trade Decimating Reef Fish off Southeast Asia

Hello, Frank Indiviglio here.

Two articles addressing fresh water and marine fish conservation issues were published this week:

Oriental Weatherfishes in Spain

According to an article in Biological Invasions, the Oriental Weatherfish (native to eastern Russia, south and Southeast Asia) is now well established throughout Spain’s Ebro River delta, and has a foothold in the Onyar River as well. This is of particular concern because over 80% of the Iberian Peninsula’s freshwater fishes are already considered to be threatened, with introduced species outnumbering natives in most rivers.

Last year, studies of the eel fishery in the Ebro River revealed that 8.2 tons of non-target fish, representing 17 species, are captured along with each ton of eels (elvers) harvested.  Approximately 40% of these fish perish before they can be released.

Fishes of the Coral Triangle

Reef fishes are becoming increasingly popular on restaurant menus throughout Southeast Asia and mainland China.  Particularly hard hit are species native to the waters bordered by Malaysia, Indonesia, Papua New Guinea, the Philippines, East Timor and the Solomon Islands.  Known as the “Coral Triangle”, this region is home to 75% of all known species of coral.

According to a recent Conservation Biology article, spawning aggregations of local species have declined by 79% in recent years, largely due to over-fishing.  Groupers, 26 species of which are endangered, have suffered the most.  Conservation efforts are complicated by the large number of countries having interests in these waters.

Thanks, until next time, Frank Indiviglio.

For further information on the natural history and captive care of weatherfishes, please see:


Invasive Species update: Volitan Lionfish



They came from foreign waters. With stealth, appetite, and agility on their side, they’ve become one of the most successful invasive species in recent history, and realistically, the invasion has only just begun. Their deadly and dizzying beauty is of little consolation to those following the invasion of the Volitan Lionfish.
About a year ago, Dave posted a blog on lionfish as invasive species and the responsibility of aquarists to not release non-native species into waterways. Brandon has followed up with similar articles on some other invasive non-native species, too. Just this week I came across 2 more recent articles about the lionfish invasion, this time about populations established in the Caribbean and off the coast for Florida. I wanted to bring you the articles and an update, as the problem is only getting worse as we could have predicted.

Both articles pinpoint the beginning of the problem as six specimens that escaped into open waterways from a Miami waterfront aquarium that was smashed during hurricane Andrew in 1992, though it is highly likely that there were other contributions, too. It is becoming a serious concern as the predators multiply, their numbers in the thousands, and devastate native populations. The articles liken the invasion to a plague of locusts. NOAA studies show that the populations in some areas have increased tremendously, from 22 per hectare in 2004 to 200 per hectare in 2008. The predators are having a huge effect on commercial fish populations and populations of herbivores that keep algae and other marine vegetation at bay, especially on reefs.

As the drama unfolds, it really is compelling to read about, and it will be interesting and scary to see what will happen in the next couple of years if there are no solutions found to keep the populations in check. Scientists are scurrying to find natural predators of lionfish to aid in control, and they’re encouraging fishermen and restaurants to utilize them as entrees. It’s open season on these fish in many places, but with such huge numbers and range, the outlook is bleak for control…disturbing on so many levels.


Until next time, Patty


An Invasive Species Account: Purple Loosestrife

Please welcome back Brandon Moyer with another entry on invasive speciesPurple Loosestrife

The next species I would like to present to you in my exploration of invasive species is one that is notorious among biologists across the country. Though it is quite beautiful in bloom, it is known as a super invasive plant species that disrupts habitats and displaces many native species of fish as well as insects, birds, and other small mammals.

The species is Lythrum salicaria, and it may be something you see every day without even knowing it.  It is known by over ten common names including spiked loosestrife and purple lythrum worldwide, but is best known by the name Purple Loosestrife in the United States. Purple Loosestrife was first introduced into North America through several different vectors; as an ornamental plant for ponds and gardens, as an herb used in cooking and medicine, and through ship ballast water. The origin of Purple Loosestrife is unknown, although its current range is vast. It is very hardy, has spread across Asia and Europe, only limited by the extreme cold of the upper northern hemisphere.

Purple Loosestrife spreads in two ways. One adult plant (4+ years of age) can produce over two million seeds in a single season. These seeds tend to float which aids in dispersal. Their rhizomes, commonly known as runners, can grow up to a foot a season. New plants can spring from these rhizomes, which compounds the number of seeds produced each season.

In several biology and ecology courses I had taken at Millersville University, L. salicaria was a popular example of an introduced species that has taken a strong foothold in a new environment. The dense clusters of roots and rhizomes choke out the roots of other plants around the loosestrife, increasing the area in which it can spread and smothering native plants. Their leaves decompose in the fall when the weather begins to cool and detritivore activity decreases, leading to nutrification of infested waterways. Its thick undergrowth deprives native animals like turtles of areas to bask, but is not dense enough to protect other animals from predation.

Today you can see purple loosestrife almost anywhere you see water in the eastern United States including bogs and drainage areas around warehouses and malls. It can be found in every state except for Florida, Hawaii, and Alaska. Conventional methods of eradicating the invasive, including herbicides and burning, are ineffective. One interesting method of control, considered biological control, is introducing other non-native species that prey on the invasive species. In the case of Purple Loosestrife, leaf beetles, root boring weevils, and flower and seed eating weevils have all been introduced to help stop the spread of the weed.
In any case, control is necessary to protect the complex ecosystems of the wetlands that Purple Loosestrife dominates.  You can help by first learning to identify loosestrife, then using methods to control the spread of this invasive species if you find it on your property by digging, pulling, spot spraying or cutting the plants while they are in bloom and before they seed, usually June-Early August.  Remove the plants and cuttings in plastic bags so they degrade, or incinerate the remains of the plants in a contained area.  It is not recommended that they be composted.  Also, avoid certain cultivars of garden loosestrife and their seed, though they may not be invasive varieties, many may be able to cross pollinate with the invasive species.

For more information on Loosestrife visit the following sites:

Image referenced from Wikipedia http://en.wikipedia.org/wiki/Image:Purple_loosestrife2.jpg, first posted by Megger and used under the GNU Free Documentation License

Thanks Brandon,

Until Next Time,