Saturday, July 31, 2010

Alex Beach Barking Crab Transect Observations and Analysis

Today’s class consisted of a walk around the industrialized inner harbor from Long Wharf to Four Points Channel. Low tide was at 9:20am, about an hour before we started our site visits. For reference, high tide was at 3:32pm, about the time we finished class today (tide times taken from The air temperature started at about 70 degrees and topped out in the mid seventies. It was a very bright, sunny day with a strong breeze.

Our first site was at the intersection of Long Wharf and Christopher Columbus Park. This was just after low tide and almost the entirety of the intertidal zone was visible along a small 20x20 foot cobble beach and a retaining wall of about 15 feet high. The retaining wall was covered with a blackish seaweed up to 4 or 5 feet. The seaweed looked to be growing in clusters and had a fibrous and leafy texture. Above the black seaweed was about another 3 feet of a mossy green velvety plant. From our perspective it looked like just a thin film or covering of the wall with no noticeable braches, stalks, stems, etc. The water seemed to look fairly clear. On a completely subjective scale from 1-10 where 1 is opaque and 10 is my Brita pitcher I thought that it looked to be about a 5, however there was a fairly large and noticeable oil slick on the surface. The bottom of the harbor was visible until about 30 feet off shore. I am going to estimate that the depth at this point was five feet. In the water was another green plant, but this one consisted of filaments long enough to flow in the current. It was a darker green color than the velvety substance on the wall. Small off-white barnacles covered the wall, pipe, and rocks of the intertidal zone.

The second site was between the south side of the aquarium and the Harbor Tower. There was no exposed shoreline at this site and the Harbor Tower cast a shadow that covered most of the area. There was noticeable less green velvety moss-like plant than in site one and none of the black seaweed. This is probably due to the lack of sunlight that the intertidal zone gets here because of the tower. In my opinion, however, it looked as if there was a higher concentration of barnacles on this wall than at site 1. Perhaps there was more wall space because of the lack of large black seaweed clumps. The water was deeper at this site and I could not see the bottom. Just under the pier and in the northwest corner by the wall was a small school of baitfish. They looked to be long and slender like anchovies, perhaps 3-4 inches long, with a silver sheen on their sides. A rough estimate puts their numbers at 50-75.

Site 3 was the floating docks at the Barking Crab restaurant. These docks are located in the Four Points Channel in what is called the Roxbury Connector. This site was 100-200 meters upstream from the open harbor and would therefore be a brackish environment. I forgot to taste the water for saltiness while on site and am hoping that someone else did. Especially at low tide, the water there should have been composed more of fresh water sources than seawater. At this point in the day the tide had started to rise and was about 1/3 of the way between low and high tide. Group 3 chose the second dock from the shore in a completely sun-drenched area. From the other groups we learned that the water depth was about 18 feet, the surface temperature was 74 degrees and the temperature at depth was 71 degrees (isn’t collaboration great?). The floats that the dock was resting on went to a depth of no more than one foot. In some locations chains attached certain floats to the bottom on the channel. At first glance it was obvious that there was a tremendous amount of biodiversity on such a small section of substrate. Below is a list of the organisms that we saw. This list is comprised of my original hypotheses as to the types of organisms with further analysis and identification to come later (ie I originally thought that the orange daisy shaped things were algae) :

1. Blue Muscles: the largest being 2 inches long. Dead. No meat inside. Attached directly to the floats

2. Smaller muscles: ¼ to ½ inches long. Shaper looking shells. Dark brown/blue/black in color. Attached to the Blue Muscles

3. Barnacle: white to Mother of Pearl in color, 5 sections, ½ inch across. Attached to Blue Muscle

4. Green leafy seaweed: semi translucent, long strands, 3-4 inches in width, wavy texture like that of green leaf lettuce. A bit slimy to the touch. Attached to Blue Muscles, chains, and float itself

5. Red leafy seaweed: same description as number 4 but red/brown/plum in color

6. Dark red fibrous plant: looks like very diffuse, fibrous, and high density concentration of roots. Deep red/plum in color (more so than red seaweed). Growths no more than 2 or 3 inches long. In patches. Attached to Blue Muscles mostly and a bit to the floats.

7. Brown shrimp-ish crustacean: smallest creatures visible, brown in color, no more than ¼ of an inch for the largest ones. Living amongst fibrous root-like plant

8. Black and yellow shrim-ish creatures: slightly larger than the brown ones. Black and yellow sections of their bodies, also living in the fibrous plant.

9. Crab: grey and brown in color. Very small, possibly a juvenile, living in fibrous plant

10. Long skinny shrimp: the largest individuals were about an inch long, looked like a walking stick bug, brown/orange in color, brown spots, long slender appendages, in fibrous plant

11. “bubble wrap” plant: deep green in color, growing on float and chains, a foot in length, has the shape of divergent tree trunks with finger like “leaves” as the end of each branching section. Sacs at the tips, lighter green in color than rest of the plant, ¼ to ½ inch long, they would pop with a pretty resistive snap when squeezed

12. Orange algae: growing on Blue Muscle. ¼ inch in diameter. Bright orange in color. Looks like the pedals of a daisy. Grouped in clusters

13. Orange spongey stuff: growing on Blue Muscles and float. A bit mucusy in texture. More of a pale yellow brown orange than number 12

14. Bait fish: seemed to be the same as seen at site 2

15. Smaller bait fish: golden sheen, ½ to 1 inch long

Select Attempted Identifications:

A. Long skinny shrimp: I know in class we spent considerable time trying to identify this creature but I still had my doubts. The Audubon guide book had three varieties of skeleton shrimp listed. Based on the pictures the ones we saw looked most like the Smooth Skeleton Shrimp. However, these are Pacific shrimp and can therefore be ruled out. The descriptions given of the Long Horned Skeleton Shrimp and the Linear Skeleton Shrimp seem to favor a Long Horned identification. My hesitation with this choice is a result of the size of the samples we found. As an entire class we were able to see a fairly large sample size of long shrimp like individuals. The longest ones we saw maxed out at about one inch. The guide book says that the Long Horned variety and get over 2 inches in length, whereas the Linear variety grows to ¾ of an inch. Granted individuals of a species vary in size but I would have thought that based on our sample size we would have seen one larger specimen. One of my group members suggested that perhaps the floats were a refuge for the juvenile members of the species, that they all gestated at the same time and had not fully matured yet, or the larger members of the species lived in deeper water. According to the Encyclopedia Britannica website, long horned skeleton shrimp only grow to about 1 inch long. This would be much more consistent with our observations. I am not sure why there are the conflicting descriptions of the same species. My guess is that the Audubon book, published in 1981, might be outdated. Perhaps changing ocean conditions such as warming over the past 30 years have altered the environment that long horned skeleton shrimp live in causing them to become slightly smaller than their ancestors. After browsing Google images on both species to see more examples I am feeling more comfortable deciding that this animal is indeed the Long Horned Skeleton Shrimp.

B. The barnacle we saw on the Blue Muscles was ½ inch across and looked to have 5 plates. The first barnacle listed in the guide book is the Bay Barnacle. It is described as having 4 paired plates overlapping 1 unpaired plate, ½ across, and white in color. It says that these barnacles attach to pilings, rocks, docks, and hard shelled animals in brackish estuarine waters. This description seems to describe fairly accurately the environment we were looking in.

C. All day we had been referring to the muscles found as Blue Muscles simply because they are common in these parts and Professor Burman hinted at this identification. While I would like to trust our peer-review, collaborative system I wanted to make sure for myself that we were correctly identifying these organisms and it was not another intentional misdirection from Prof Burman. According to the guide book Blue Muscles grow to 4 inches long and 2 inches thick. While we did not find any that large the ones that we did were still in that 2x1 proportion. They are Blue-black to black in color with a shiny interior, brownish foot, and have a rounded triangular shape. All of these characteristics support our working hypothesis that they were indeed Blue Muscles.

D. Well I was wrong about the orange organisms that I thought were algae. While looking through the encrusting animals section of the guide book they seem to look identical to the image of Pacific Star Tunicates. Unless the Pacific variety has greatly increased its range in the past 30 years since the guide was written that cannot be a correct identification. The guide’s description of Golden Star Tunicates fits very well but the picture was a bit off. I would like if the guidebook had multiple phenotypes pictured because between the Hitchhikers handout and Google Images it is pretty clear that what we saw were indeed Golden Star Tunicates.

E. The other orange organism we saw was nowhere to be found in the guidebook. After reading the Hitchhikers handout it became obvious why it was not listed by Audubon. This organism was a “Mystery Tunicate” and was introduced to the Boston area from the Pacific (so maybe Pacific Star Tunicates could be introduced and survive here too?). More information can be found on this great MIT page about exotic species in the area (

F. The “bubble wrap” plant we saw was not hard to identify as Rock Weed aka Bladderwrack. This plant is very common in these areas and information can be found in multiple sources including the New England Aquarium’s Educators Guide from Blackboard. This plant is more accurately a type of algae that belongs to a group of brown seaweeds.

G. The green sheet like seaweed we saw is most likely a variety of sea lettuce called Ulva lactuca ( It is a common type of algae that grows in shallow intertidal zones on rocks, shells, piers, practically any hard surface or just free floating. According to the above link from URI, sea lettuce grows especially well in areas with sewage contamination and other pollution and can be used as a good indicator of water pollution levels. The Four Points channel and Roxbury Connector can sometimes carry sewage to the docks at the Barking Crab. It would be interesting to monitor the sea lettuce populations there after large rain storms and see how they react to the introduction of more sewage.

H. The Red leafy seaweed has to be a type of brown algae. There are over 1000 species of brown algae and as of 11:30 I am unable to identify the more specific type of brown algae that the Barking Crab specimen might be. Hopefully someone else had better luck. I have also been unable to identify the deep red/purple fibrous plant specimen. Considering that plant was the habitat for numerous other species that we saw it would be interesting to know what it was. Again I turn to my peers for further insight.

Well I am dehydrated, sunburnt, and tired but enjoyed it immensely. Time for bed so I can do it again in a few hours. Goodnight.

Alex Beach

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