The Right Blue

Hawaii's Gold Lace Nudibranch

by B. N. Sullivan

Continuing our series on nudibranchs (see previous post on Exotic Underwater Nudies...), today we present the Gold Lace nudibranch (Halgerda terramtuentis). This pretty mollusc is endemic to Hawaii -- that is, it is only found in the waters around the Hawaiian Islands.

It has a pale yellow translucent body overlaid with a lacy network of irregular yellow-orange lines, and a solid yellow-orange line bordering the entire edge of its mantle. It also has little bumps, called tubercles, all over its body, which are a lighter color -- almost white on some individuals.

As if its body were not pretty enough, take a look at those accessories: Its tree-like gills and its rhinophores -- those sensory organs protruding from its head -- are white with black speckles.

While these little critters are found only in Hawaii, they are fairly common here. Both of the individuals pictured on this page were photographed at Puako, Hawaii, where the species is plentiful along the area known as the first dropoff, where they live in small cavelets and in rocky areas. We see them most often at relatively shallow depths -- less than 10 meters/30 ft.

I took both of the photos on this page inside a small cavelet. The individual in the photo above was crawling along the ceiling of the cave, and got dislodged by our exhaled bubbles. On impulse, I snapped a shot of it as it floated downward through the water, and amazingly, it turned out to be a pretty good 'species ID' shot! The second photo is more naturalistic. Because the nudie is crawling across a red encrusting sponge, you can get an idea of its 'see-through' translucence.

Gold Lace nudies are small -- usually between one and two inches (up to 5 cm) in length. They are carnivorous, but they don't "bite." They feed on sponges and other soft organisms.

This nudibranch was officially identified relatively recently - in 1982 - by Hans Bertsch and Scott Johnson of the University of Hawaii. (Many nudibranch species have been officially recorded in the scientific literature since the 1800s.)

By tradition, the scientists who officially discover a species get to name it. This creature's species name has an interesting story. Terramtuentis means "looking at the earth with care." The name was given in honor of a group of Earthwatch volunteers who assisted Bertsch and Johnson with their research.

Ocean Abstract: Sea Fan Macro

What: Detail of a Gorgonian sea fan (Acabaria erythrea), with polyps open

Where: I took this macro photo in the Red Sea
near Sharm el-Sheikh, Egypt

[Click photo to enlarge.]

My previous Wordless Wednesday posts.

What is the difference between 'endemic' and 'indigenous' species?

by B. N. Sullivan

When I write about the creatures we have come to know, I nearly always identify both their common name, and their scientific name, and of course I tell our readers where the creatures live. In some instances, I may also mention that a creature is 'endemic' to a certain place.

A reader recently asked, "Does endemic mean the same thing as indigenous?"

The answer is, "Not exactly." Let me explain.

When we say that a species is indigenous to a place, we mean simply that it occurs there naturally. It is a native. But a species can be indigenous to a number of places at once.

In contrast, if we say a species is endemic to a place, we mean that it occurs naturally only in that place. It is a native to an exclusive or limited area. It is not widely distributed, and won't be found naturally anywhere else.

Most species inhabit specific areas of the world, but not the whole world. When people think about animals on land, they intuitively know this. They know, for instance, that giraffes exist naturally only in Africa, and that the polar bears live naturally only in the Arctic. They would not expect to see a giraffe wandering around wild near Hudson Bay, nor would they expect to see a polar bear in Kenya. Yet there are many animals that are much more widely distributed than giraffes or polar bears. Think of squirrels -- or rats!

In the sea, it is the same. Some marine animals (and plants) occur naturally only in the Caribbean, or the Mediterranean, or Hawaii, for example. Other species are found in a wider range of places.

Here in Hawaii, we have a high percentage of endemic species, compared to other places in the world. This is true both on land and in the ocean. Because the island chain is so geographically isolated -- separated from other land masses in every direction by thousands of miles of open ocean -- there has been less opportunity for species from elsewhere to wander here spontaneously and establish themselves. Likewise, it has been difficult for many species that have evolved here in Hawaii to make their way to other areas of the world.

The photos on this page show examples of fish species that are found in Hawaiian waters. The first photo on this page shows a fish called the Saddle Wrasse (Thalassoma duperrey) being serviced by a smaller fish called the Hawaiian Cleaner Wrasse (Labroides phthirophagus). Both of these species are endemic to Hawaii. They occur naturally nowhere else in the world. Each has 'cousins' of the same genus in other regions. Some of those cousins look quite similar, but they are not anatomically identical. I took the photo at Puako, Hawaii.

The second photo shows a small squadron of Moorish Idols (Zanclus cornutus). These fish are indigenous to Hawaii -- they occur here naturally -- but they are not endemic. They also occur naturally elsewhere in what is known as the Indo-Pacific region and the tropical eastern Pacific. Indeed, we have seen them and photographed them in quite a number of places. These four were photographed at Honaunau, Hawaii.

When we speak of an animal's provenance, there is a third category that is important: the introduced species. Introduced species are those that do not occur naturally in a given place. They are brought there -- introduced -- from somewhere else. Sometimes this happens accidentally (as when a caged parakeet escapes), or when an animal hitch-hikes to a new location on a ship or plane, and manages to establish itself there. In other instances, animals are introduced deliberately, for a variety of reasons. Here in Hawaii, for example, there are a number of game birds that were intentionally introduced decades ago for the benefit of sport hunters. Other species were intentionally introduced as a food source.

In the third image on this page are some Bluestripe Snappers (Lutjanus kasmira), photographed at Puako, Hawaii. These fish were intentionally introduced from the Marquesas in the 1950s as a food fish. As so often happens, their introduction had unintended consequences. Some people in Hawaii do fish for them, and we do see them for sale in some fish markets, but they are not exactly prized. Worse, they have proliferated greatly and they compete with other, more valuable fish. It is also believed that they have contributed to the depletion of the population of a particular kind of crab upon which they prey.

So, to review: Endemics are native to, and live naturally, only in one place; indigenous species are native, but may be more widely distributed; introduced species are 'immigrants' of a sort.