What it takes to be a successful Invader

Invasive species have received a lot of bad press, but let’s face it, some of these alien species really have what it takes to make it!  One example of a highly successful invasive species is the Round Goby, a native to central Eurasia including the Black Sea and the Caspian Sea.

Male Round Goby in black spawning coloration

Male Round Goby in black spawning coloration

Identifying an alien

Recently a graduate student in Michigan sent a request for identification of a fish skull.  When I saw the skull on a photo that the student attached to the inquiry my first thought was that this is a species I haven’t seen before.  I was thinking to myself, “in my mind I’ve got a fairly good catalog of all the native species that are found in the Great Lakes, so this one is probably exotic”.  Furthermore, I examined the teeth and the rest of the skull picture, and found features that are similar to the marine blennies and gobies that I’m familiar with; quite possibly a Round Goby.

OSUM 104701, Neogobius melanostomus skull

OSUM 104701, Neogobius melanostomus skull

When one observes the teeth of a Round Goby skull, it becomes readily apparent that they are eminently suited to catching prey: numerous, closely packed and somewhat curved teeth. Once the fangs are sunk into the prey’s body it would be difficult to wriggle out of the goby’s maw.  Speaking of the “maw”, the width of the Round Goby’s head and mouth are somewhat disproportionately large in comparison to the size of the body.  This aspect of the anatomy amplifies the capacity of the fish to suck in its prey.  By opening the mouth quickly a vacuum is created, which when combined with the sudden forward lunge that the goby employs toward the prey, improves the likelihood of successful capture.

Neogobius melanostomus are extremely aggressive and will challenge fishes larger than themselves, outcompeting native fish for preferred habitat as well as preying on other fish’s eggs and young.

What makes the Round Goby so successful?

Round Gobies are found primarily in the benthic zone of the water body, from the bottom of shallow areas down to 70 feet in depth.  They prefer areas where there is plenty of cover such as around rocks, sticks and logs.  The species has been found to tolerate polluted conditions, which enables it to occupy areas that less tolerant species cannot live in. This increases their opportunities to grow into a large population that aids in overcoming the other species in less polluted areas.  Another aspect of their biology that enhances their prowess is a highly developed lateralis system, a fishes’ sensory system conveying environmental information to the brain and making them an effective competitor and predator in dark, murky conditions as well as in clear daylight.

High productivity is a hallmark of an effective invader.  A mature Round Goby female is able to produce over 3,000 eggs, the older the female the more eggs they produce.  The male uses posturing and coloration (see the photo above) to attract females to its nest, often mating with more than one female.  The females spawn up to six times in a season, which lasts all summer long from April through September. Let’s do the math: a female could produce 18,000 young in just one year, that’s a lot of Round Gobies!

Although the deleterious effects of this intruder are considerable in scope, as some research here at OSU has shown, one must nonetheless admire their capabilities.  But we should keep in mind that without our assistance it is doubtful that Round Gobies would have spread so far and certainly not so quickly.  Their ability to tolerate euryhaline conditions, a wide range of salinities, facilitates their natural spread under normal conditions over a much longer time. It has allowed them to survive in the ballast waters of vessels and occupy new areas when the ballast is flushed.

Although they are best known from the Great Lakes they are now found in the lower reaches of larger rivers and have been captured in the Illinois River drainage, presaging their invasion of other Mississippi River tributaries.

map of Round Goby invasion in Great lakes regionBut thus far the most dramatic spread of the Round Goby has occurred in the Great Lakes of North America where a lack of effective competitors facilitated their occupation of new territories.

Northern Europe, too, has suffered from a Round Goby Invasion as shown in these maps and the potential for their spread in Europe is estimated to be much greater. You can follow them on AquaMaps, enter genus “Neogobius” and species “melanostomus” to obtain a map showing their predicted spread.

map of Round Goby invasion in Europe


Because they are not tasty to humans it is hard to truly appreciate this fish from any perspective other than that of their successes as invaders. But to a larger, piscine predator they must indeed be tasty as they have become a substantial part of native gamefishes’ diet.  And for Lake Erie water snakes, as well as aquatic birds like gulls and cormorants, Round Gobies are a major new item on the menu.  Indeed, Round Gobies are so abundant in Lake Erie that frustrated anglers often complain that the pesky little perciforms are the only thing they can catch.

The Round Goby is here to stay, and changes wrought by their incursion will reverberate for decades across the Great Lakes at least. Have you caught one yet?


About the Author: Marc Kibbey is Associate Curator of the Fish Division at the Museum of Biological Diversity.

What does it mean to be a moss?


Mosses are the most diverse group of bryophytes with a myriad of assorted characters, some which are characteristic of mosses in general and some that differentiate mosses from one another.

As with all plants, mosses have two stages of their lifecycle, one stage that produces spores, the sporophyte, and one stage that produces gametes (eggs and sperm), the gametophyte. When the sperm fertilizes the eggs, the resulting embryos grow into the sporophyte. Likewise, in a cyclic fashion, spores produced by the sporophyte grow into the gametophyte. In mosses, the sporophyte is attached to and dependent for food (not green and photosynthetic) upon the green gametophyte.

Photo of the habitat of the pale plait moss, Calliergonella lindbergii. The green mat on the forest floor is gametophyte.

Habitat of the pale plait moss, Calliergonella lindbergii. The green mat on the forest floor is gametophyte.


In mosses, the gametophyte is green, has stems and leaves, and is the most noticeable stage of the lifecycle, i.e., the stage that you would generally observe as you take a walk in the woods.



The gametophyte stage is the stage the exhibits poikilohydry, the ability of mosses to dry to surrounding conditions without dying, and then begin metabolic activity when the environment becomes moist. To retain moisture as long as possible, mosses possess characters to prevent water loss.

One of the most conspicuous methods that mosses utilize to conserve water is to change the position of their leaves when the plants are dry versus wet. When dry the leaves often curl or press together, or move closer to the stem. With moisture, the leaves become wide spreading, allowing for maximum interception of light for photosynthesis. The change in leaf configuration between wet and dry conditions changes the entire look of the plant. You can imagine the aggregation this causes bryologists. They need to double their recognition skills to identify one moss species!


Photo of plants of Bryum caespiticium, an acrocarpous moss, i.e., plants that are upright with sporangial stalks borne at the tips of the plants.

Plants of Bryum caespiticium, an acrocarpous moss.


Variation in characters of the gametophyte often differentiates groups of mosses from one another. For example, mosses are either acrocarpous, upright plants that produce the sporophyte at the apex of the plant,


Photo of the pleurocarpous plants of the necklace chain moss, Leskea gracilescens, showing the branched growth form and sporangial stalks that originate from branches.

Pleurocarpous plants of the necklace chain moss, Leskea gracilescens.



… or pleurocarpous, branching plants that bear sporophytes on side branches.





The sporophyte is usually composed of a stalk with a sporangium at the tip. Sporangia are the containers that produce spores, and vary in structural appearance between major groups of plants. In mosses the sporangia are round structures that are usually attached to a stalk, with the stalk attached to the gametophyte.

Photo of the knothole moss, Anacamptodon splachnoides, with leafy green gametophyte and a sporophyte composed of a brown stalk and sporangium attached.

The knothole moss, Anacamptodon
, with leafy green gametophytes and sporophytes composed of a brown stalk and sporangium attached.


Photo of plants of the low bristle moss showing peristome teeth spread to reveal green spores. The sporangia of this moss does not have stalks.

Plants with sporangia of the low bristle moss, Orthotrichum pumilum.


Occasionally the stalk is very short or vestigial, causing the sporangia to be nestled within the leaves of the gametophyte.









The apex of the sporangium possesses a cap that protects the spores until they are fully developed and ready for dispersal. Underneath the cap is the beautifully intricate part of the moss sporangium, the peristome. The peristome is a ring of ornamented teeth around the opening of the sporangium that helps to disperse spores into the air stream by curling in and out of the sporangium as the humidity changes.



Sexual reproduction in plants, the production of gametes and spores, results in genetic variation in the offspring, but it is not the only means of reproduction in mosses. Asexual reproduction, the production of clonal propagules that are exact copies of either the gametophyte or sporophyte, occasionally occurs on moss gametophytes.


What does it mean to be a moss? Small, intricate, and full of wonderful variation!


About the AuthorDr. Cynthia Dassler is Curator of Cryptogams (small plants that produce spores) at The Ohio State Herbarium (OS) in the Department of Evolution, Ecology and Organismal Biology.

All photos courtesy of Bob Klips.

“(S)he got legs,” a look at mite legs


Mites are notorious for not following the “rules.”  For example, we generally teach that you can separate Insects from Arachnids by the number of legs, 3 pairs in insects, 4 pairs in arachnids. Simple, right?  Mites are arachnids, and most have 4 pairs of legs, but not all


And of course legs can get highly modified for various (known or unknown) purposes


About the Author: Dr. Hans Klompen is Professor in the Department of Evolution, Ecology and Organismal Biology & Director of the Ohio State University Acarology Collection.