Abstract
Remote operated vehicle (ROV) dives in the Monterey Bay Canyon
revealed the ubiquitous presence of an unidentified, orange-pigmented
mysid. An analysis of videotape footage taken on numerous ROV dives
during a one year time period was done to examine the distribution,
habitat, and behavior of the mysid. Samples were also taken using a
suction sampler on the ROV and taxonomic and observational studies were
performed on these samples. It was found that the mysid may be a new
species and a proper identification continues to be pursued. A preference
for soft sediment was also found in the mysid, and it is felt that this may
be a reflection of available habitat type and feeding requirements.
Introduction
For the past two years the Monterey Bay Aquarium Research Institute
(MBARI) has been conducting investigations of the Monterey Bay Canyon
using a submersible remote operated vehicle (ROV). Currently the tether
length permits a maximum operating depth of four hundred fifty meters.
Scientists have seen small, orange organisms with golden eyes hovering in
the hyperbenthic zone on numerous dives. They were thought to be mysids,
but as none were in hand to identify them, they were labeled temporarily
as "golden-eyes". Limitations in our knowledge of mysid taxonomy,
ecology and physiology as noted by Krygier and Murano (1988), coupled
with the ubiquitous nature of golden-eyes, make them animals worthy of
study. Additionally, the ROV provides a rare opportunity to view these
animals in their natural environment, and to get live specimens from the
deep ocean. The purpose of my study was to determine an exact taxonomic
label for the mysid and to better understand how they fit into the benthic
microenvironments they inhabit.
An analysis of "golden-eye" distribution by depth and habitat was
done by reviewing videotapes taken during ROV dives. In addition,
specimens were collected using a suction sampler mounted on the RÖV and
observed in holding tanks at the Monterey Bay Aquarium where they
continue to live. Those animals which did not survive the transfer to
holding tanks in the aquarium were preserved for use in taxonomic studies.
Materials and Methods
Golden-eye were recorded on betacam videotape footage taken by a
DXC 3000 Sony camera that was mounted on a remote operated vehicle
(ROV) during dives from March 20, 1989 to March 19,1990. The five
primary dive sites studied cover a range of different areas and habitats in
the Monterey Bay Canyon (Fig. 1). The names and locations for each site
are as follows: Canyon Wall C4-C5 (36 degrees 42'N 122 degrees 00'W),
Soquel Canyon (36 degrees 49'N 121 degrees 59'W), Canyon Wall Meander
(36 degrees 45' N 121 degrees 58'W), Pt. Joe (36 degrees 37'N 122
degrees 01'W), and North Wall (36 degrees 48' N 122 degrees 05'W). The
videotapes were annotated by a technician who recorded the comments of
scientists along with a listing of the organisms seen during the dives. The
video tapes are time coded and tied to a master clock so that annotated
frames are linked to all recorded physical and navigational data. Access
to sets of these data can be gained through a relational computer database.
An analysis of one hundred thirty single frames that had been annotated
with golden-eye and known depth was carried out noting date, site, depth,
number of golden-eye in frame, habitat type, other organisms in
association, and behavior. In order to accurately count all of the
golden-eye in an annotated frame adjacent frames were also examined.
The single frames were recorded on optical disk for easier access and
review at later times in the study.
An estimation of the area captured in a given videotape frame was
calculated setting the length of a sharply focused golden-eye in the frame
equal to the average length based on specimens in hand. This conversion
factor was used in transforming dimensions on the monitor to natural
dimensions. The calculated area was then used to compute golden-eye
density (Harea) for a standardized 25X25 centimeter quadrat.
investigated the relationship of density to habitat type by first
classifying notes on habitat into three categories and then comparing them
with calculated average densities for each frame. The three types of
habitat were classified as follows:
1. Hard substrate- on or within approximately one meter of a
hard, vertical rock wall face
2. Rubble- mixture of soft detritus or sandy sediment and low
lying rocks
3. Soft sediment- detritus or sandy sediment with no large rocks
within one meter
Specimens were collected May 7, 1990 and May 23,1990 at the Canyon Wall
C4-C5 site using the suction sampler mounted on the ROV. The May 7th
dive yielded only one golden-eye from a depth of 370 meters. It was kept
in cold sea water for transport to the Monterey Bay Aqurium, where it was
put in a holding container with circulated water maintained between five
and seven degrees Celsius. The container was then placed in a darkened
room, and we observed the specimen for ten days before it died. It was
then fixed in sea water and10% Formalin, and stored in 70% alcohol. On
the May 23rd dive approximately 30 specimens were collected from a
depth of 340 meters and transported in cold sea-water to an aquarium
holding tank. Six died in the transit and were fixed and preserved in the
same fashion as the one above. These seven organisms were observed
under a dissecting scope, and using a calibrated ocular micrometer, total
body length was measured from the anterior margin of the carapace to the
posterior end of the telson, excluding spines or setae. Illustrations were
drawn using a camera lucida.
The surviving 25 specimens continue to be kept in a cold-water
holding tank. Observations of their behavior have been noted. They are
being fed brine shrimp nauplii and rotifers daily and appear to be doing
very well in holding. Observations continue to be made by a professional
aquarist.
Results
Taxonomic efforts placed golden-eye in the Suborder Mysida, Family
Mysidae, Subfamily Mysinae using Tattersall (1951), Mauchline (1980), and
Kathman (1986). A further classification can not confidently be placed on
the organism at the present time, but identification is being pursued.
Sizes of the seven measured specimens ranged from 6.88 to 8.80
millimeters, with an average of 7.69 millimeters. Camera lucida drawings
of the body parts used in identification of mysids are shown in Figures
24-2F. Distinguishing characteristics of the animal include its orange
pigmentation and large, globular golden eyes with large retinas. The
rostrum is rounded and does not extend far beyond the eyestalks. The
antennal scale is setose all around. Both the endopod and exopod of the
uropod are setose all around, and there is a statocyst on the endopod. The
telson is cleft, and has short spines which begin at about two-thirds of
the total length of the distal margins and run posteriorly through the cleft
region. The pleopods appear uniramous, but ambiguity in the
characterization of uniramity and biramity make it difficult to assess this
trait with confidence.
The analysis of average density by depth in 10 meter intervals for all
of the sites showed the five highest average densities were contained in
the 350 to 390 meter range. The highest average density was 15.1
golden-eye per 625 square centimeter quadrat in the 320 to 330 meter
range. However, this was based on only one frame (Fig. 3). The C4-C5 site
had the highest average density of the five sites with 8.97 golden-eye per
625 square centimeter quadrat. (Fig. 4) Average densities for the three
different habitat types revealed the highest density above soft sediment
(8.01 golden-eye per 625 square centimeters) and the lowest density
above hard substrate (5.89 golden-eye per 625 square centimeters) (Fig.5).
The following is a list of some of the organisms seen in areas with
golden-eye:
Sponges
Hagfish
Holothuroids
Psolus sp.
Eptatretus sp.
Anemones
Parastichopus johnsonii
Stomphia sp.
Opisthobranchs
Gorgonians
Asteroids
Plerobranchia sp.
Sergestids
Rathbunaster caifornicus
Tritonia diametia
Sergestes similis
Stylasterias forreri
There was one golden-eye sitting in the upper rim of a conical-shaped
sponge, and what appeared to be two other golden-eye were further down
in the spiral lying motionless. Golden-eye were seen regularly swimming
in and out of hagfish burrows.
We performed qualitative behavioral observations of the golden-eyes
both from the videotape and the aquarium holding tanks. Golden-eye swim
with a hovering motion just above the substrate. They were only seen four
times, in the 130 frames that were analyzed, to be swimming a significant
distance away from the substrate. In only one frame were they seen to be
quiescent above detritus material. In viewing other frames, a rapid
snapping of the abdominal segments at the juncture to the thorax was seen
when a quick escape response action was initiated. The clearest
illustration of this behavior was seen when a golden-eye swam into an
Anthomastus ritteri tentacle and escaped in a fraction of a second.
When examining one specimen in a dish under a dissecting scope it
began to do something best described as a headstand. Mauchline described
this type of behavior as a modification of the general filter feeding
method. The thoracic exopods are used to generate a water current
capable of moving surface material to the feeding appendages for
filtration from the water (Mauchline 1980). The golden-eye appeared to
have no problems maintaining its orientation from the dish sides, and the
use of the antennal flagellum for this purpose was evident. It also did an
extensive picking process through particles and smaller organisms in the
dish and rapidly discarded most of them posteriorly by a sweeping motion
of the thoracopod endopods.
Discussion
The inability to classify the organism beyond the subfamily level not only
reflects the possibility that it is an undescribed species, but also points
out some of the difficulties encountered in mysid taxonomy. I primarily
used Tattersall (1951), Mauchline (1980), and Kathman's et. al (1986) in
my efforts to key out the organism, and found that all three of these
references lacked too many definitive characteristics at important
junctures to confidently carry the golden-eye through the key. Mauchline
points out that the incomplete collection of mysids, especially male
species, has created problems with classification. There is a real need for
a comprehensive and updated taxonomic review of the Mysidacea with a
sound key and illustrations of all known species.
It is difficult to draw firm conclusions from the data of average
density according to depth due to a lack of sampling at certain depths.
However, the depth range of the mysid appears to start on the shelf break
below two hundred meters. It should also be noted that in a recent dive
golden-eye were found at 450 meters in fairly high densities. The
extension of the RÖV depth range to one thousand meters in the fall of
1990 should be very helpful in determining the lower depth range of the
animal.
An understanding of the benthic habitat and the biology of the mysid
may add insight into the distribution of golden-eyes in the Monterey
Submarine Canyon. The highest density of golden-eye being found at the
C4-C5 site may relate to the patchiness and diversity of suitable habitat
types at that location. The C4-C5 site is characterized by hard, vertical
wall faces, and very rugged, rocky terrain, with patches of rubble, and soft
sediment slopes of variable size. There is also an abundance of detrital
material settled on the non vertical substrate. Golden-eye were often
found swimming at the base of rocky, vertical wall faces, or in and out of
rock crevices. The data show that the greatest densities were near soft
sediment, where detrital accumulation is favored. The high degree of
habitat diversity at the C4-C5 site with many suitable habitat types may
legislate against a dominance by predators which may be distributed at a
different patch scale. The expanded range of the ROV will again be helpful
in investigating the habitat available with increased depth. It will be
interesting to see if the trend of decreased available hard, rock substrate
and substrate relief with increasing depth affects golden-eye distribution
as such conditions have previously been shown to affect hard substrate
communities (Lissner 1989).
Another possible explanation for the low density of golden-eye on hard,
vertical faces is that their methods of feeding favor a softer sediment
habitat. They exhibit two types of feeding: filtration of suspended food
material, and ingestion of large food masses (Crouau 1989). It seems
likely that since filter-feeding is a major means of gathering food that
this activity would be favored in a softer material, because it would be
easier to generate a hydrodynamic current with lighter and less attached
organic material. Additional support for a preference for soft sediment is
the relatively fragile structure of the golden-eye exoskeleton. Normally
benthic mysids have a more robust exoskeleton which protects them it
they go burrowing for food in coarse sediment (personal communication
with Dr. Peter Slattery). The lighter exoskeleton of the golden-eye
suggests that it is not a burrower, and this is corroborated by video and
laboratory observation. Finally, when dives were conducted at the C4-C5
site to collect golden-eye, the golden-eyes were most often found on
plateaus where softer detritus matter was present or near crevices where
rock and soft bottom met.
The great numbers and close proximity of golden-eye to a variety of
organisms and substrate types suggest they may be scavengers or involved
in commensal relationships. This would make a great deal of sense, since
mysid diets are generalized and include a great variety of organic
materials (Mauchline, 1980). More detailed studies of exactly what the
golden-eye are feeding on and further investigations of their interactions
with other organisms are needed and may tell us more about their role in
the benthic environment.
References Cite
Crouau, Y. (1989) Feeding mechanisms of the Mysidacea. Functional
Morphoogy of Feeding and Grooming in Crustacea, Issues 6:153-171.
Kathman, R.D., W.C. Austin, J.C. Saltman, and J.D. Fulton. (1986).
Identification manual to the Mysidacea and Euphausiacea of the
northeast Pacific. Can. Spec. Publ. Fish Aquat. Sci. 93: 411p.
Krygier, E.E. and M. Murano (1988) Vertical distribution and zoogeography
of oceanic mysids from the northeastern Pacific Ocean. Bull. Ocean
Res. Inst. Univ. of Tokyo. 26(1):109-122.
Lissner, Andrew (SAIC, ed.) (1989) Benthic Reconnaissance of Central and
Northern California OCS Areas Vol.1 and II. Prepared by Science
Applications International Corp. and MEC Analytical Systems.
Mauchline, J. (1980) The biology of mysids and euphausiids. Advances in
Marine Biology, 18:1-681.
Tattersall, W.M. (1951) A review of the Mysidacea of the United States
National Museum. Bulletin U.S. Natl. Museum., No. 201, 1-292.
Figure Legend
Figure 1: Map of the Monterey Bay Canyon showing the five major dive
sites where the remote operated vehicle (ROV) was submersed and
operated.
Figure 2: Drawings done with camera lucida of some of the distinguishing
anatomical features of the golden-eye. A. dorsal view, anterior end; B.
antennal scale (41 total setae all around); C. uropod; D. telson; E. 5th
pleopod; F. 3rd endopod.
Figure 3: Graph illustrating average density (4/625 sq. cm) at 10 meter
depth intervals for all of the sites combined. Numbers in parentheses
indicate total number of frames viewed at a particular depth.
Figure 4: Graph illustrating average density (4/625 sq. cm) for all depth
intervals at each site
Figure 5: Graph illustrating average density (4/625 sq. cm) for each of
the three habitat types.
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Tigure 4:
Golden-Ege Average Density By Site
4.77
Meander
5.18
Pt. Joe
631
Soquel
6.18
N. Van
8.97
C4-C
Average Densitg (2/625 sq. cm)
Figure 5:
Golden-Ege Average Density By Habitat Type
Soft sedient
8.01
Rubbl
761
Hard substrate
5.89
Average Density (2/625 sq. cm)
Acknowledgements
would like to thank all those who assisted me in completing this
project. The Monterey Bay Aquarium Research Institute (MBARI) was
generous in providing access to videotape and in allowing some ROV time
to be spent on viewing and collecting golden-eye. Öf particular help at
MBARI were Lynn Lewis, Bruce Gritton, and Chris Harrold. Gilbert Van
Dykhuizen at the Monterey Bay Aquarium was generous in time and
resources with his help in getting holding space and trying to work out the
identification of the golden-eye. Cindy Ashy was very helpful in
suggesting references and supplying equipment. Ladd Johnson provided
assistance in using the camera lucida and offered some insightful
comments in interpreting my data. Alan Baldridge and his library staft
were very helpful and bent over backwards to get needed references.
Finally, I wish to thank my insightful advisor Chuck Baxter. He taught me a
great deal about how science truly works and the value of critical thinking
skills.