Yes, there are many species of sea slugs that can be found in the waters around the Hawaiian Islands. Sea slugs, also known as nudibranchs, are a group of shell-less marine gastropod mollusks that inhabit tropical and temperate oceans worldwide. Hawaii’s reefs and shorelines provide ideal habitat for nudibranchs, which thrive in the warm, nutrient-rich waters.
Some of the most commonly seen sea slugs in Hawaii include the leaf sheep nudibranch, the blue dragon nudibranch, Berthellina citrina, the Hawaiian bobtail squid, and various species of dorid nudibranchs. Nudibranchs come in a dazzling array of shapes, sizes, and colors, making them fascinating sights for snorkelers and divers. Here is a closer look at some of Hawaii’s sea slug species.
Common Sea Slugs of Hawaii
Leaf Sheep Nudibranch
The leaf sheep nudibranch (Costasiella kuroshimae) is a species of sea slug that gets its name from its leaf-like appearance. It has a dark green upper body with ruffled leaf-like edges outlined in black. The underside is lighter green with black spots. Leaf sheep nudibranchs are found throughout the Hawaiian Islands from the intertidal zone down to depths of 100 feet or more. They feed on sponges and can grow to about 2 inches in length.
Blue Dragon Nudibranch
The vibrant blue and black colors of the blue dragon nudibranch (Pteraeolidia ianthina) make it one of the most recognizable sea slugs in Hawaii. The blue dragons have wing-like cerata on their upper bodies that resemble a mythical dragon. The underside of their foot is bright yellow. They are prolific breeders and can be found year-round in Hawaii, especially on reefs with abundant hydroids, which are their preferred food source.
Berthellina citrina
Also known as the lemondrop nudibranch, Berthellina citrina is a vividly colored species found in Hawaii’s shallow reef environments. They have an oval-shaped yellow upper body with blue or purple edges and orange rhinophores (chemosensory head structures). The underside is white or pale blue. Berthellina citrina feed on sponges and can grow to about 1.5 inches long.
Hawaiian Bobtail Squid
The Hawaiian bobtail squid (Euprymna scolopes) is a small species of cephalopod mollusk found in Hawaii’s coastal waters. Unlike true squid, the Hawaiian bobtail squid only reaches about 2 inches in length. They have a rounded mantle, large eyes, and 8 short arms equipped with suckers. Their most distinctive feature is a bulbous ink sac that gives them a “bobtailed” appearance. Hawaiian bobtail squid are nocturnal hunters that bury themselves in the sand during the day.
Dorid Nudibranchs
Dorid nudibranchs make up one of the largest groups of nudibranchs, with over 3,000 species worldwide. Many different dorids are found in Hawaiian waters, including species in the genera Glossodoris, Chromodoris, and Hypselodoris. Dorids can be identified by their flower-like gills on their upper backs. They come in elaborate colors and patterns that act as camouflage. Dorids prey on sponges, hydroids, bryozoans, and other fouling organisms.
Sea Slug Life Cycle and Adaptations
Sea slugs have a complex life cycle well-suited to their marine environment. Here are some key facts about their biology and adaptations:
- They hatch from tiny eggs laid in gelatinous spirals or masses.
- After hatching as larvae, they go through a process of metamorphosis to reach their adult form.
- Most nudibranchs live only one to two years.
- They are hermaphrodites, meaning each individual has both male and female reproductive organs.
- They lack a protective shell, but their bright colors warn potential predators that they may be toxic.
- Special cells called nematocysts in their cerata can sting predators.
- They breathe through gills or absorb oxygen through their skin.
- Their eyes are simple and can generally only detect light and dark.
These adaptations allow nudibranchs to thrive in Hawaii’s reef ecosystems where they find ample food sources and sites for egg laying.
Where to Find Sea Slugs in Hawaii
The best places to find sea slugs and nudibranchs in Hawaii include:
- Reef environments – Search in rocky intertidal areas, coral reefs, tide pools, and hardbottom substrates around the islands.
- Wreck sites – Sunken boats and planes provide surfaces for slug food sources to attach.
- Harbors – Manmade structures in busy harbors attract all kinds of marine creatures.
- Night dives – Nocturnal species can be found feeding at night.
Popular spots for nudibranch viewing include Hanauma Bay on Oahu, Kealakekua Bay on the Big Island, Molokini Crater off Maui, and Kauai’s south shore reefs. Anywhere with healthy coral growth is likely to support a variety of sea slug species.
| Island | Good Spots for Sea Slug Viewing |
|---|---|
| Oahu | Hanauma Bay, Pokai Bay, Black Point, Pupukea Tidepools |
| Maui | Molokini Crater, Honolua Bay, Ahihi Bay, Maluaka Beach |
| Big Island | Kealakekua Bay, Kahaluu Beach, Honaunau Bay, Puako tidepools |
| Kauai | Poipu Beach, Tunnels Beach, Koloa Landing, Kealia Beach |
Conclusion
In summary, there is an impressive diversity and abundance of sea slugs and nudibranchs that inhabit the waters surrounding the Hawaiian Islands. These aquatic gastropods fill an important ecological role as predators and prey within Hawaii’s marine ecosystems. Their bright colors and unusual shapes make them a favorite of underwater photographers and scientists. With coral reefs in decline worldwide, it is important to protect Hawaii’s marine habitats to ensure the survival of these fascinating and vulnerable sea creatures. Getting out with a mask and snorkel or scuba gear opens up a world of colorful nudibranch spotting and appreciation in Hawaii.
