Thursday, April 5, 2012

The Intertidal Sea Life of Croatia

UPDATE: A very appreciative thank you to Mick Otten (Mick's Marine Biology) for helping identify the species in these photos!

The first time I ever visited Croatia, I fell head over heels in love with it. I went in the summertime, when it's always sunny, the temperature hovers around a dry 25 degrees Celcius, and the water is a crystal clear hue of aquamarine.

I spent hours combing the rocky shore for signs of wildlife, of which I found lots. I spent just as much time snorkelling, examining intertidal echinoderms, crustaceans, anemones, and barnacles.

Intertidal species are those that live near or onshore, where the water level varies drastically with the tide. These animals are fascinating because of the adaptations they have evolved to deal with extreme variation in temperature, water level, and salinity.

A hermit crab poking out of its house to see who's picked it up (Clibanarius erythropus)

The shoreline can harbour many micro-environments throughout the day. Species with limited motility, like barnacles, sea stars, and anemones, may be completely submerged in seawater at high tide, then left totally dry with the hot sun beaming down on them at low tide.

A bright sea anemone (Actinia equina)

In spite of these harsh conditions, the intertidal zone is teeming with life. I must have found some type of animal every meter I explored. Luckily, I had with me a camera, and I was able to capture everything I found.

Spiny sea urchins clinging to a rock (Arbacia lixula)

Empty sea shells that were once home to snails, and possibly hermit crabs (left Hexaplex trunculus and right Monodonta turbinata)

A sea urchin skeleton. Notice the pentaradial symmetry, a trait shared by all echinoderms.

The same skeleton viewed from the top. The small hole is where the anus lies. The mouth is on the ventral side.

A crab hiding in a crevice (Pachygrapsus marmoratus)

A sea anemone, closed for low tide (Actinia equina)

A well-camouflaged crab (Pachygrapsus marmoratus)

A sea snail, firmly clinging to rock (Monodonta turbinata)

The sphynx blenny (Aidablennius sphynx)

Barnacles closed for high tide (Patella species). Fact: barnacles have the largest penis to body size ratio of any known animal, with some penises reaching 40 times the length of the body.

This sea star lost two of its arms, which were regenerating when this photo was taken (Coscinasterias tenuispina)

The sharp spines of a sea urchin offer it good protection (Arbacia lixula)

Marbled rock crab (Pachygrapsus marmoratus)

A crab exoskeleton. Crabs regularly shed their shells as they grow (Xantho species)

Sphynx blenny (Aidablennius sphynx), shrimp (Palaemon genus), and burrowing worms. Update: Mick Otten (Mick's Marine Biology Blog) has informed me that what I thought were burrowing worms are actually a species of green seaweed, Padina pavonica.


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