Monterey Bay Aquarium Research Institute
Marine Botany

Sargassum Field Work

My Goals:

    Map the distribution of Sargassum muticum in Monterey Bay

    Observe the environments in which S. muticum grows

    Compare the fauna of S. muticum to that of native seagrass

Methods

To get an idea of where to look for S. muticum, I talked to people at different marine stations around the bay. Apparently there isn't very much Sargassum in Monterey Bay, so I didn't have many places to visit. I observed three sites: Stillwater Cove in Carmel Bay, Boatworks Beach at Hopkins Marine Station, and the Moss Landing Harbor jetty at the mouth of Elkhorn Slough. I heard of another small patch just north of Santa Cruz that I did not visit.

At each site I observed the substrata on which S. muticum was growing, the relative degree of protection from wave action, and other flora in the immediate vicinity. I also collected samples of S. muticum, which I rinsed with fresh water in a 0.5mm sieve. Using forceps, a dissecting microscope, and an invertebrate key, I counted and identified all the animals I found in the sieve. I measured both the dry and wet weights of each of my seaweed samples in order to more accurately compare results.

Originally I planned to compare the fauna of S. muticum to that of Zostera marina (eelgrass), but since I observed no Z. marina growing with S. muticum at any of my sites, I chose to look at Phyllospadix instead, which is almost always present in S. muticum habitats. I chose to use the Phyllospadix at Boatworks Beach growing right next to the S. muticum I sampled.

Results

Distribution Map

Habitat

Stillwater Cove, S. muticum 3/4/99 15:20-16:20; Low tide at 17:59, 0.6ft

Pebble Beach has a shallow slope criss-crossed with channels and littoral (tidal) pools. An abundance and diversity of algae grow everywhere except on the many loose rocks and on the most exposed regions. S. muticum was attached to bare rock in areas of about 50 percent cover, and always growing amongst or near beds of Phyllospadix. The holdfast detached easily from the rock when pulled. I only saw S. muticum in littoral (tidal) pools, but never in exposed areas, even when Phyllospadix and other algae were present. It grew in large quantities in the pools, and to lengths of about 2ft. Other algae I recognized includes Macrocystis, Gastroclonium, Ulva, Gelidium, and Mastocarpus.

Moss Landing Harbor jetty, S. muticum 3/7/99 16:00-17:00; Low tide at 19:48, 2.2ft

The jetty is a pile of bare boulders with no protection from crashing waves. The submerged regions obviously supported algae like Enteromorpha and Mastocarpus, but the tide was too high for me to see Sargassum growing on the rocks. I did, however, manage to grab a small piece of S. muticum that was floating on the surface and probably came from the jetty. The holdfast was still attached to the stipe.

Boatworks Beach, S. muticum 3/2/99 16:00; Low tide at 16:50, -0.2

The cove between Hopkins Marine Station and the Monterey Bay Aquarium was mostly sand, with rock outcroppings on the shore and intertidal zone. S. muticum was growing in a small patch just seaward of Phyllospadix in the shallow subtidal, and was buried in sand down to at least 7 inches. I could not tell if there was rock below that, but it would defy generally accepted principles if there were not. The area was not protected from waves, but the wave action was not as strong as at the jetty. I could not find the holdfasts. Other algae in the area included Gastroclonium and Smithora.

Boatworks Beach, Phyllospadix 3/8/99 13:00; Low tide 9:58, 1.2

Phyllospadix grew in the intertidal but was submerged when I found it. It was rooted shallowly in sand, and many polychaete worms took advantage of the complex root structure, which Sargassum does not have. Growing on Phyllospadix was large quantities of Smithora (which I included in the weight), and nearby was Gastroclonium.

Associated Fauna

     Stillwater  M.L.H Jetty  B.B, S.mut.  B.B, Phyll. 
     Dry Wt. (g)

     34g

     1g

     25g

     40g

     Amphipod Gammaridea

     90

     10

     64

     378

     Amphipod Caprellidea

      -

     1

      -

     Isopod (elongate)

      -

      -

     1

     6

     Isopod (round)

      -

    -

    4

     Polychaete

     5 (7--12mm)

     1

     18 (50-120mm)

     Ribbonworm

      -

    1

     Gastropod Tricoliad

     54

    -

    2

     Gastropod Lacuna

     1

    -

    -

    -

     Gastropod Littorina

     -

    -

    -

    1

     Gastropod Mitrella

     -

    -

    1

     Gastropod Barleeia

     1

    -

    -

     Egg cases (gastropod)

     -

    1

    1(old) 

     Limpet Lottia(2mm)

     -

     1

     Clam (2mm)

     -

     1

     -

Discussion

Unfortunately, the sample size is not large enough to draw any significant conclusions.  What we can see is that there is variation in associated fauna between Sargassum muticum at different sites, which is probably a function of temperature, currents, and light availability, to name a few of the many ecological variables.  Stillwater Cove appears to have the greatest number and diversity of fauna of the three sites, which is perhaps due to the remarkably calm and protected waters of the cove.

We can tentatively say that this particular Phyllospadix sample has a greater biomass of organisms than any of the S. muticum samples per dry weight of plant material (based on the faunal lengths given in the table), and is tied with the Moss Landing sample for greatest number of amphipods per dry weight of plant material.  It is noteworthy that the Moss Landing sample has a decent diversity of fauna, despite having been torn from its original substratum, which demonstrates the ability of the species to live pelagically.

While the existence of the S. muticum stand in a sandy flat does not match the literature, the types of organisms I found in Monterey are very similar to those named by Norton (1983) as living in Washington, namely the Lacuna genus and the Caprellidea suborder.  In order to draw more significant conclusions, I would like to examine more Sargassum sites in the area to gain a more complete knowledge of distribution, habitat, and associated fauna.  I would also like to find sites where both S. muticum and Z. marina grow and compare the fauna between them.

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Last updated: 05 January 2005         copyright Jacqueline Pratt 1999.  All rights reserved.