Showing posts with label hermit crab. Show all posts
Showing posts with label hermit crab. Show all posts

7/2/12

Nikumaroro at Night

This is blog entry posted from the field during the 2012 Phoenix Islands Marine Protected Area (PIPA) Expedition. The Phoenix Islands are an isolated island chain more than 1,000 miles southwest of Hawaii. They are part of the island nation of Kiribati, which partnered with the New England Aquarium and Conservation International to create PIPA in 2008. Today it is one of the world's largest marine protected areas and a UNESCO world heritage site. This voyage is part of a regular series of scientific expeditions to investigate coral health and study ecosystems and biodiversity.

This post is from Kelton McMahon, post-doctoral fellow at WHOI and KAUST after the first day of diving near Kanton Island. Read all of Kelton's posts here. Pictures by Keith Ellenbogen.


No matter what you do for a living, how old you may be, or how experienced you are (or think you are), the desire to explore seems to transcend all. We spent two full weeks taking photos, collecting samples, and surveying species distributions and abundances on the reefs fringing the Phoenix Islands.



But like the thousands of photos we’d taken since arriving, our view of the reef was only a snapshot of the diversity and complexity that the ecosystem had to offer. As the sun set behind Nikumaroro Island, we donned our dive gear for a night dive exploration.

A flounder resting on an old coral head

The reef gets a complete makeover at night: new species, new colors and a new perspective of how the system operates. Some species are just settling down for a good night’s sleep. A green sea turtle sits on a sandy patch of bottom, holding its breath long enough to catch a few Z’s. Take a look under a nearby coral ledge and you may find a parrotfish encased in mucus cocoon.

Neon fusilier tucked in for the night amidst the Montipora coral


At the same time, an entirely different suite of animals are just waking up. A neon fusilier fish changes into its night colors for a evening cruising the reef. Meanwhile, a few large solitary shadows glide along the outskirts of our lights looking for a snack.

Don't let the fuzzy, turf-algae and sediment-covered shell fool you - there's a brightly colored hermit crab inside!

Diving by the narrow scope of an underwater flashlight has a way of emphasizing the tiny creatures that come out at night. As we scan the reef with our light, a myriad of iridescent eyes light up. As my light passes over a colorful hermit crab it freezes. Move the light away and he picks up his shell to scurry along his path. Bring the light back and he freezes once again freezes. It reminds me of playing red light-green light as a child.

Shrimp-tastic

Under the next coral ledge, we see two banded coral shrimp sifting through particles in the water column. It’s hard not to imagine that we’ve stumbled upon an old married couple on a dinner date. As the dive comes to an end and we float suspended above the reef on our safety stop, a larval octopus dances in our lights.

Back aboard the skiff, we cruise towards the Nai’a under a blanket of stars. Along the side of the boat, a pod of bottlenose dolphins rides our bow wake. As they crisscross paths below us, they trail plumes of green bioluminescence like jets in an airshow. It was the grand finale to yet another amazing exploration of the Phoenix Islands.

10/13/09

The Slow and the Spineless

The Phoenix Islands "Greatest Hits" highlights continue...

#4: PHOENIX ISLANDS REEF INVERTEBRATES

The invertebrates of this trip deserve to be in the top 10; but on this blog thus far, they've barely received an honorable mention. Mea culpa! Because of the scientific interests of the expedition members, invertebrate diversity attention has been taxonomically-eclipsed by the coral invertebrates, the remarkable fishes, and the algae. But, invertebrate diversity is important and interesting, and I'm not the only blogger who thinks so! Check your backbone at the door and go visit Chris Mah's Echinoblog, as well as The Other 95% (written by Kevin Zelnio and Eric Heupel) if you like inverts. Full disclosure: I do not know all of the taxonomic identifications of the critters posted here, so I invite you to join me in this adventure (semi wiki-style)! If you post the ID in the comments section below, I will amend the blog to include the correct ID and give you credit for the match. :-)

Without further ado, allow me to introduce a few of the "the slow and spineless" Phoenix Islands critters. Most of these images will enlarge when you click on them.


The Christmas Tree worm is aptly named for it's shape (photo above by David Obura). They also come in all sizes and colors (see shots below).


Spirobranchus giganteus on Porites lobata corals (photo: R. Rotjan)

Time for a little echinoderm shout-out (for more, check out Chris Mah's blog here). You may not realize it, but echinoderms are a whole lot more than just sea stars! But, we'll start with a Linckia spp. on the left (not sure which one, any guesses? Also, anyone notice anything a little unusual about this Linckia? Count the arms...). But, sea cucumbers (holothurians) are also echinoderms (photo on the right). New England Aquarium Researcher Tim Werner works on these. I think this one is an Actinopyga spp., and Tim Werner has confirmed that it is A. mauritiana. Thanks, Tim!

 
Linckia spp. sea star and holothurian sea cucumber (photos: R. Rotjan)


Phoenix Island Sea Urchins (photo: R. Rotjan)

Above are two more echinoderms - a Diadema spp. and an Echinometra spp. sea urchins; I think! Let's go check out some more inverts. There are two focal invertebrates in the photo below. The one to the left is an echinoderm (a Culcita novaguinae seastar). But take a look at the invert on the right-- definitely NOT an echinoderm.


Culcita novaguinae cushion star(left) and Tridacna spp. clam (right) (Photo: R. Rotjan)

The photo below shows a bunch of molluscs (Tridacna spp. clams nestled amidst the coral). The photo above shows a clam also - on the right side, next to the cushion star. Chris says that all of these clams are Tridacna maxima. Thanks, Chris!


Tridacna spp. clams (Photo: R. Rotjan)

Molluscs are great; they include clams, mussels, snails, octopus, and squid. They also include nudibranchs, which are shell-less snails like the one below. I think this nudibranch is a Phyllidia spp.; any other ideas?


Nudibranch (Photo: R. Rotjan)Below is another confusing photo. There is no mollusc in the photograph (only a crustacean), but the crustacean is using a snail shell. Yup, it's a land hermit crab (Coenobita perlatus).


Coenobita perlatus hermit crab (photo: R. Rotjan)

Hermit crabs are very interesting creatures, and they are very picky about their shell choice. While we're on the topic of crustaceans (e.g. shrimp, lobsters, crabs), check out this terrestrial land crab (often called a sally lightfoot). Eric Heupel suggests that it might be Graspus tenuicrustatus.


Sally lightfoot crab (Photo: R. Rotjan)

Back to my favorite group--the cnidaria (e.g. corals, jellyfish, anemones). Below are some beautiful hydrozoans. These animals have the appearance of a feather, but the branches have polyps (just like corals).


Hydroids (Photos: R. Rotjan)

Of course, corals will always have my heart. Hard corals, scleractinians, have been featured on many posts here already, and are the main focus of our reef recovery attention. The reason why? Well, hard corals may be slow and technically spineless, but they are the backbone of coral reefs. They have calcium carbonate skeletons that create the complex reef structure. In an earlier post, we showed you lots of dead coral skeleton covered by crustose coralline algae. That skeleton is made by the coral animal via a symbiosis with a photosynthetic algae and provides shelter for most of the other organisms on the reef. To see more about the symbiosis, check out the Blue Impact Tour and click on "color changing corals".

 
Acropora table coral closeup and colony 

But the main point here is that coral animals and their calcium carbonate skeletons create the complex structure of reefs.

So spineless? Hardly. These inverts are themselves the backbone of coral reefs. No bones about it.

-Randi-

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