Friday, May 29, 2015

Aquatic Life Dazzles in May‏

Mink on rock in Chesnut Creek
For me wetlands have always been very special places.  I am not quite sure why that is although we all have our favorite habitats.  I spent a lot of time while young roaming along a creek in GA and these memories have stayed with me until now.  The animals of aquatic habitats are generally more limited in their distribution than terrestrial species and show many special adaptations in life cycles.  

Twelve spotted skimmer
Dragonflies are very primitive insects and highly predaceous both as aquatic larvae and adults.  Despite their ability to migrate long distances as adults, they are required to find wetlands to breed.  Two distinctive odonates in our farm ponds are the male twelve spotted skimmer and blue dasher, both of which are more colorful than the females.  

Blue dasher dragonfly
Males set up territories along the shorelines and await the arrival of females.  The aquatic larvae subsequently emerge and metamorphose into the radically different adults.  Such a metamorphic life style allows the adults and young to avoid competition for food.  But it is a difficult process fraught with danger.  
Dragonhunter
I found a dragonhunter soon after it emerged from the larval skin and it was bright green!  This tiny T Rex of dragonflies eats other odonates.  The green color is quite unusual and is thought to be the color of the copper based blood pigment, hemocyanin, showing through the transparent cuticle of the still developing body and wings.



Fishfly
This time of year there are quite a few dark insects with white markings flying near the New River that are a strange type of critter called a fishfly (Nigronia) related to the dobsonflies. They have an aquatic nymph, the hellgrammite, familiar to fishermen as a good bait and for their ability to bite hard!  This aquatic predator may live for three years before emerging as an adult which lives only a short time, during which it mates and lays eggs.  

 
Female bullfrog
A very obvious aquatic amphibian predator is the bullfrog, well known for its loud call and willingness to eat anything that will fit into its mouth.  This is a female, which is obvious from the small size of the ear drum (about the diameter of the eye).   Males have larger ear drums, the better to hear their male competitors for territories and females.   Bullfrogs remain near ponds and their tadpoles mature in water, but there is little competition between the life stages since the young are mainly herbivorous.  

Rainbow trout
An aquatic predator that likely eats tadpoles is the rainbow trout, which is an introduced or exotic species in the east since it originated in the western US.   It is widely planted in streams because of its status as a game species, despite the damage it does to native stream ecology.  This includes competition with the native brook trout.  It is interesting how differently managers view trout compared to exotic species of plants which are often ruthlessly exterminated.  

Northern water snake
An aquatic snake that eats fish and amphibians is the northern water snake, a very wide spread generalist. The queen snake that can occur in the same streams has a very different diet specializing on recently shed crayfish.  This type of extreme limitation in diet is quite remarkable and raises the question of why this would happen.  Apparently a specialist can become so efficient at feeding on one group of prey that are not eaten by other snakes that it occupies an alternative niche and thus avoids competition.  

Queen snake
The queen snake has also become even more aquatic than other fresh water snakes- I found that its skin is more permeable to water and likely also to oxygen than any other snakes, including sea snakes.  So it is a most unusual species despite its normal external appearance.

A top predator in our streams and lakes is a large weasel, the mink.  They are semi-aquatic, foraging in water and on land nearby.  They are quite ferocious and will kill prey even larger than themselves.  Our neighbors tell stories of their attacks on chickens.  I see them in our yard often but their lives are shrouded in mystery for the most part.

So enjoy the remarkable fresh water species in our lakes, ponds, streams and rivers.  Their lives are fascinating and reveal the extreme variation in life cycles which can occur as species adapt to exploit the environment and minimize competition and predation.

Bill Dunson 
Galax, VA and Englewood, FL 

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