DIVE DRY WITH DR. BILL #579 : THE OTHER KELP CRAB
Sightings of a large shark at our harbor mouth a while back did little to "dampen" my desire to night dive that evening. I had two things going for me. First, I was carrying a camera. You never see anything that spectacular while carrying a camera, only when you dive without one. Second, I meditated prior to the dive focusing on seeing this shark. You almost never see what you are looking for. I felt pretty secure I'd be perfectly safe.
Indeed, not a single shark appeared before my eyes or camera. However, I was not even ten feet down when I caught an interesting sight out of the corner of my eyes. There was a crab clinging to a kelp blade as it swirled around in the surge. Even though I had only a momentary glimpse, I knew this crab was not just the ordinary variety I encounter in the dive park at night. In fact, it was a northern kelp crab (Pugettia productus) rather than the southern kelp crabs (Taliepus nuttallii) I see on almost every night dive.
I did a quick 180 using a strong kick from my good German legs (and American fins), and relocated the blade with the kelp crab on it. It was quite small, about the diameter of my thumb, and difficult to film due to the surge whipping the young giant kelp plant around and around and around. I almost got seasick trying to keep it in my camcorder's viewfinder!
The northern kelp crab differs significantly in shape from the southern kelp crab. It's carapace (which "houses" the body) is shaped like a policeman's shield: a broad forward section with several obvious, pointed spines along the edge. The southern kelp crab's carapace is more globular in outline, narrowing towards the front and lacks the obvious spines. The northern species I filmed was olive in color but may also be greenish brown to maroon depending on its food source. The southern kelp crabs in the dive park are all a beautiful red color. Northern kelp crab male may reach a carapace width of over 3 1/2 inches with the females being slightly smaller.
Northern kelp crabs range from Alaska to Asuncion Point in Mexico while the southern species is from from Santa Barbara to Magdalena Bay in Baja. Thus both overlap here in SoCal. The northern species frequents rocky shores and kelp forests, and may be found as deep as 950 ft.
Food for this species consists largely of algae, frequently the larger kelps including giant kelp, feather boa kelp and certain species of Sargassum. They may also feed on red algae. The color of their exoskeleton is known to be dependent on the type of food they are munching. At times when their preferred algae is scarce such as warm El Ninos, they may eat barnacles, mussels, hydroids or bryozoans. Traveling up the food chain, they must fear predators like cabezon, sculpins and sea gulls as well as sea otters in the northern part of their range.
It is reported that during fall the northern kelp crab migrates to deeper water where they group together and mate. The newly extruded eggs are bright orange, but turn red and later a grayish-purple before they hatch. There may be as many as 80,000+ depending on the size of the female. Eggs may be seen carried by her under her broad telson ("tail") almost any time of year and take about a month to hatch into free-swimming planktonic larvae.
Although the individual I filmed was quite small, I was able to detect something attached to its rostrum or forward section of the head region. In researching this column, I learned that these crabs will often pluck a tender morsel of algae and attach it there using hooked setae. It can later detach and snack on it. No need to stop at McKelp en route for food!
Both species of kelp crab are good climbers, and can be found up in the giant kelp munching away... or mating. I also discovered how tenaciously they can hold on when I transferred this individual to my gloved hand to give my readers and viewers a better perspective on its size. It would cling tightly to the kelp... or my glove... until it decided it was time to jump off onto the reef and hide.
Image caption: Silhouette of a northern kelp crab showing spines, crab on my glove and showing tender tidbits attached to rostrum and the southern kelp crab for comparison.
Sightings of a large shark at our harbor mouth a while back did little to "dampen" my desire to night dive that evening. I had two things going for me. First, I was carrying a camera. You never see anything that spectacular while carrying a camera, only when you dive without one. Second, I meditated prior to the dive focusing on seeing this shark. You almost never see what you are looking for. I felt pretty secure I'd be perfectly safe.
Indeed, not a single shark appeared before my eyes or camera. However, I was not even ten feet down when I caught an interesting sight out of the corner of my eyes. There was a crab clinging to a kelp blade as it swirled around in the surge. Even though I had only a momentary glimpse, I knew this crab was not just the ordinary variety I encounter in the dive park at night. In fact, it was a northern kelp crab (Pugettia productus) rather than the southern kelp crabs (Taliepus nuttallii) I see on almost every night dive.
I did a quick 180 using a strong kick from my good German legs (and American fins), and relocated the blade with the kelp crab on it. It was quite small, about the diameter of my thumb, and difficult to film due to the surge whipping the young giant kelp plant around and around and around. I almost got seasick trying to keep it in my camcorder's viewfinder!
The northern kelp crab differs significantly in shape from the southern kelp crab. It's carapace (which "houses" the body) is shaped like a policeman's shield: a broad forward section with several obvious, pointed spines along the edge. The southern kelp crab's carapace is more globular in outline, narrowing towards the front and lacks the obvious spines. The northern species I filmed was olive in color but may also be greenish brown to maroon depending on its food source. The southern kelp crabs in the dive park are all a beautiful red color. Northern kelp crab male may reach a carapace width of over 3 1/2 inches with the females being slightly smaller.
Northern kelp crabs range from Alaska to Asuncion Point in Mexico while the southern species is from from Santa Barbara to Magdalena Bay in Baja. Thus both overlap here in SoCal. The northern species frequents rocky shores and kelp forests, and may be found as deep as 950 ft.
Food for this species consists largely of algae, frequently the larger kelps including giant kelp, feather boa kelp and certain species of Sargassum. They may also feed on red algae. The color of their exoskeleton is known to be dependent on the type of food they are munching. At times when their preferred algae is scarce such as warm El Ninos, they may eat barnacles, mussels, hydroids or bryozoans. Traveling up the food chain, they must fear predators like cabezon, sculpins and sea gulls as well as sea otters in the northern part of their range.
It is reported that during fall the northern kelp crab migrates to deeper water where they group together and mate. The newly extruded eggs are bright orange, but turn red and later a grayish-purple before they hatch. There may be as many as 80,000+ depending on the size of the female. Eggs may be seen carried by her under her broad telson ("tail") almost any time of year and take about a month to hatch into free-swimming planktonic larvae.
Although the individual I filmed was quite small, I was able to detect something attached to its rostrum or forward section of the head region. In researching this column, I learned that these crabs will often pluck a tender morsel of algae and attach it there using hooked setae. It can later detach and snack on it. No need to stop at McKelp en route for food!
Both species of kelp crab are good climbers, and can be found up in the giant kelp munching away... or mating. I also discovered how tenaciously they can hold on when I transferred this individual to my gloved hand to give my readers and viewers a better perspective on its size. It would cling tightly to the kelp... or my glove... until it decided it was time to jump off onto the reef and hide.
Image caption: Silhouette of a northern kelp crab showing spines, crab on my glove and showing tender tidbits attached to rostrum and the southern kelp crab for comparison.
