2014 Intertidal Ecology Survey
Gerstle Cove Marine Reserve, Salt Point State Park CA
Field Survey Report
James Landers, May 16, 2014 (Rev. November 28, 2014)
Abstract. Gerstle Cove State Marine Reserve is located within the boundary of Salt Point State Park, seven miles north of Fort Ross CA, and is part of the Salt Point State Marine Conservation Area. Gerstle is a small protected cove facing open coast. Public access is through Salt Point State Park. The survey site in the cove is frequented by divers, park visitors, and harbor seals.
Purple shore crabs (Hemigrapsus nudus) are plentiful along the higher margin of the rock-littered beach, acorn barnacles (Balanus and Chthamalus) are abundant in a few small crevices, and barnacles and limpets (Lottia) are sparsely distributed over middle to higher zone rocks. No mussels (Mytilus californianus), sea stars (excepting one bat star, Asterina miniata) or sea urchins were observed. Endocladia muricata is present in small amounts, and Petrocelis is common, however two unidentified rockweeds are the prominent cover in middle zones of the intertidal and occupy much open space. Marine herbivores ̶ limpets, littorines, and chitons ̶ seemed low in proportion to the amount of these unidentified rockweeds.
Introduction. This document is the fifth of six that report the findings of our 2014 study of the ecology of intertidal invertebrate and marine plant communities from below Point Conception to above Point Arena on the central California coast. The primary objective of the study is to record detail of environmental conditions and catalogue invertebrate species at selected survey sites. Secondarily, further evaluation will be made of one species, the owl limpet Lottia gigantea, previously observed in 2001 at Fitzgerald Marine Reserve in Moss Beach CA. Finally, related topics of previous research on the intertidal ecology of the California coast will also be considered as opportunity permits.
The data underlying this report is in the accompanying Gerstle Cove Marine Reserve Field Data Sheet. That document contains detail observations of conditions and specimens in each of the four intertidal zone, as well as photographs of the specimens cited here.
Survey Site. The site surveyed for this report was in Gerstle Cove at Salt Point State Park north of Fort Ross CA, latitude 38°33’54”.00 N, longitude 123°19’39”.00 W, on the Sonoma County coast 90 miles northwest of San Francisco. The cove is a protected marine reserve patrolled by Fish and Game wardens and park rangers and frequented by classes of students learning to dive, and park visitors, but is not easily accessible due to poor footing on the beach. Abalone divers are allowed only outside the cove along the open shoreline of the state park.
The location is enclosed north and south by thirty-foot Tertiary Eocene marine terraces with a high intertidal shingle of many rounded and weathered sandstone rocks. The bluffs offer some protection from all but westerly winds. The intertidal is strewn with many rounded weathered sandstone and conglomerate boulders from small to three-foot diameter and larger, averaging two-feet in diameter, closely compacted around Zone 1 shoreline, with only narrow strand of exposed sand at the minus tide waterline. A drain pipe empties onto the shingle from the bluff above the east side of the cove.
All counts were estimated from direct observation without the use of transects and quadrats. The survey was conducted on Friday, May 16, 2014 between 6:30am and 11:30am. The morning was overcast and cool, without wind, and no surf inside the cove. Water quality was clear. The tides for this date were:
Maximum tidal ranges for this year at this location are:
|Highest level||Lowest level|
The following environmental conditions at the start of the survey period were recorded.
Air temperature: 48° Fahrenheit (8.8° centigrade).
Water temperature: 56.5° Fahrenheit (13.6° centigrade).
Temperature stratification: not taken.
Salinity: 37.25 ppt.
Specific gravity: 1.027.
Methods. Mapping of the site was confirmed by reference to California Geological Survey, and National Oceanic and Atmospheric Administration (NOAA), maps. The survey area was about 20 meters by 50 meters, or 1000 square meters. In all zones the less rigorous approach of visual observation and scaled estimation of species abundance was employed in an environment where marine algae nearly completely covered the granitic substrate and specimens did not occur evenly distributed over a level substrate [Murray, et. al., “Methods for Performing Monitoring….”].
Data for each Zone were recorded separately.
Zone 1. This zone is composed of well-weathered shale, sandstone and conglomerate boulders eroded from sedimentary layers. There is a large population of purple shore crabs (Hemigrapsus nudus) living at the rocky east end of the cove, along the small rock-covered beach, averaging about 10 crabs per square meter in an area of 50 square meters. Larger crabs with a carapace over 50mm wide are about 10% of the population.
The acorn barnacles Balanus glandula and Chthamalus dalli/fissus are abundant in a few small crevices, and sparsely distributed over the middle to higher rocks of this zone. A count of the population was estimated from an average over about 250 square meters, which included a few locations with heavy density, and many locations of low density; B. glandula numbered about 32 per square meter, and C. dalli/fissus numbered about 24 per square meter, a ratio of roughly 3 Balanus for 2 Chthamalus. Identification of these individuals was confirmed by reference to discussions of them at Thomas Carefoot’s website A Snail’s Odyssey and a UCSC Pacific Rocky Intertidal website, where in photos B. glandula is distinguished by size, shape, color, and ridges [fissures] across the terga or scuta of the operculum not present in C. dalli/fissus.
The encrusting tar spot algae (Petrocelis) occurred over about 20% of the middle to lower Zone 1 rock surface; other algae were sparse above the lowest boundary of this zone. Rough limpets, Lottia (Acmaea) scabra, and ribbed limpets, L. digitalis, were found in small numbers on lower rocks, but over the entire survey area merited only the rating of “occasional.”
Zone 2. Endocladia muricata prolific at other sites is replaced here by thick mats of two unidentified brown rockweeds that cover as much as 40 percent of the rock surface. Petrocelis encrusts 30 percent, and Mastocarpus occurs over about 10 percent of surfaces here; the number of Tegula, turban snails, appears proportionally small if they are assumed to consume Mastocarpus. A species of what appears to be Acrosiphonia, Green rope, an algae with bright green tufts that cling to rock, is common along the beach. Sea lettuce (Ulva), the brown rockweed Fucus, and calcified encrusting coralline algae, make up a smaller portion of the plants in the lower area of Zone 2. Rough limpets, L. scabra, and ribbed limpets, L. digitalis, appeared here more often than in Zone 1. Several colonies of Anthopleura elegantissima, aggregating anemone, occupied vertical rock faces in numbers averaging 30 per square meter.
 Tentative identification by Kathy Ann Miller, UC Berkeley, based on photo review only.
Zone 3. The thick mats of the two unidentified brown rockweeds noted in Zone 2 were still present in Zone 3, covering perhaps 20 percent of rock surface, together with large amounts of Ulva. Lesser amounts of Coral Weed, Corallina, encrusting red algae, other rockweed (Fucus), and surf grass (Phyllospadix) were present. E. muricata, Mastocarpus, and Petrocelis diminished to 5 percent or less. Limpets L. scabra and L. digitalis were found in some places on the rocks, A. elegantissima appeared in smaller numbers along the upper boundary of the zone, occasional giant green anemones (Anthopleura xanthogrammica) were at the base of rocks, and a rare bat star (Asterina miniata) was submerged in the algae at the bottom of this zone.
Zone 4. Within the survey area, Zone 4 was settled by large amounts of surf grass, coral weed, Ulva, and “splendid iridescent seaweed” Mazzaella splendens. Small amounts of encrusting red algae and golden rockweed (Silvetia compressa) were seen, along with several A. xanthogrammica between 10 and 14 centimeters in diameter. Beyond the survey area in Zone 4, abundant stiff-stiped kelp (Laminaria setchellii) broke the water’s surface along the low intertidal.
Plankton. This is the only time we were able to sample plankton in a survey area. A sampling was taken at a depth of four feet using a plankton net with catch bottle. The results were examined under a 30x binocular microscope. Among the detritus of algae several distinctive specimens could be tentatively identified by reference to plankton image charts. A drawing was made under the microscope of the last entry, Unidentified plankton, and, while it would seem to be a decapod larvae of a crab or lobster because of the chelae, this drawing shows two chelae in addition to five thorax segments, and head and tail segments, which together makes the count of legs and chelae twelve, too many for a decapod.
(The small scale of observation for this survey is understood to be inadequate to support any substantial conclusions. Larger samples studied over time will always yield more useful data. Therefore, discussion here is intended more as a point of departure for further inquiry.)
2010 UCSC Gerstle Cove Biodiversity Survey. The findings of this survey are useful for comparison and can be found online at Pacific Rocky Intertidal Monitoring: Gerstle Cove Biodiversity Survey Findings. Below, It is referred to as the 2010 UCSC Survey. Judging from the photograph at the Gerstle Cove survey home page it would appear that their survey area was located at the south entrance to the cove, about 150 meters from the location of our survey.
Acorn barnacles. In earlier surveys, we were not much aware of the different barnacles in the splash zone, and still less of how to tell them apart. This time around, we searched out an article at Thomas Carefoot’s website A Snail’s Odyssey that shows the convoluted fissure demarking the north and south of the terga and scuta of the plates of the B. glandula operculum, and its diamond-shaped opening. An article on the same subject at a UCSC Pacific Rocky Intertidal website shows the oval-shaped opening of C. dalli/fissus and confirms the absence of fissures in its operculum. In the photographs we took of barnacles at Gerstle Cove these differences are quite clear and B. glandula and C. dalli/fissus can easily be distinguished.
Algal cover. Once more we find that E. muricata is not always the predominant rockweed in the California intertidal, being challenged at Gerstle Cove by two prolific rockweeds we have not yet been able to identify, and at Fitzgerald Marine Reserve by black pine rockweed (Neorhodomela larix). These two unidentified rockweeds (shown below), one of which seems not unlike Neorhodomela oregona (see example at Seaweeds of Alaska), are about 40 percent of algal cover in Zone 2, and 20 percent of algal cover in Zone 3, while E. muricata is never more than 5 percent of the algal cover in either zone. Petrocelis is quite prevalent in Zone 1 and Zone 2, occupying 20 percent and 30 percent respectively of rock surfaces, and both A. elegantissima and calcified encrusting coralline algae, as well as Mazaella splendens, Ulva, and limpets were observed on top of the Petrocelis.
Unidentified brown rockweeds. 2010 UCSC Survey found Odonthalia flocosa, Sea Brush, to be the most abundant algae at their survey site. We researched O. flucosa hoping it might be one of our two unidentified rockweeds, and distant photos of mats of O. flucosa do appear similar (as do other rockweeds from a distance), however in close-up the two algae do not look alike. The stringy quality of the one of our unidentified rockweeds seems quite different from any other algae indexed online.
“Albino” anemones. Unique specimens of anemone were found on the underside a rock ledge in Zone 3. They were out of the water, with mantles closed and tentacles drawn inside, and were white in color with a pink ring around the disk at the base of their tentacles. Above, on the face of the same rock, there was a colony (about 10 per square meter) of Anthopleura elegantissima with individuals of about the same size and shape, and otherwise similar to those under the ledge except that those outside were all olive green in color. We expect those under the ledge also are A. elegantissima and live where the photosynthetic symbionts in the their tissues do not have the direct sunlight needed to produce the green pigment that gives color to the epidermis of anemones living in sunlight (Ricketts and Calvin, 1985, p. 89). Also, anemones with pink tentacles are not rare. In this case, we might say we encountered examples of “albino” anemones.
Purple shore crabs. Ricketts said that purple shore crabs (Hemigrapsus nudus) live in the middle intertidal (Between Pacific Tides, 1985, p. 58) and that the striped shore crab (Pachygrapsus crassipes) is found in the high intertidal (p. 42). So we checked again our photo of the representative shore crab found in the high intertidal at Gerstle Cove and verified that the crab in our photo does not have the striped carapace of P. crassipes, and does have the speckled chelae of H. nudus. Why H. nudus would extend its range upward to live in dry round boulders instead of among the succulent algae of the lower intertidal we will not hazard a guess; why, for that matter, are there hundreds of such crabs gathered together in the tiny high intertidal amphitheater of Gerstle Cove when we have not seen enough to count on one hand at our other five survey sites this Spring? The 2010 UCSC Survey found an average of 0.25 H. nudus per square meter; this difference from our survey might be expected if their survey site was on the south point of the entrance to the cove rather than at the east end of the cove.
Carefoot, Thomas H., Pacific Seashores: A Guide to Intertidal Ecology, University of Washington Press, Seattle, 1977.
Carefoot, Thomas H., A Snail’s Odyssey website.
Cowles, Dave, Pachygrapsus crassipes, Walla Walla University, College Place WA, 2005,
Friday Harbor Laboratories (FHL), University of Washington, “Endocladia muricata, The Brillo Pad Algae.”
Glynn, P., Ecological studies on the Endocladia muricata-Balanus glandula association in the intertidal zone in Monterey Bay, California, Beaufortia 12: 1-198, 1965.
Holsinger, Kent, Species Interactions and Biodiversity Conservation, 2005.
Hunt, Luke John Hoot, The Rise Of Endocladia Muricata: Punctuated Change At An Abrupt Range Edge, PhD Dissertation, Stanford University, 2006.
Littler, M. M. and D. S. Littler, 1985, Nondestructive Sampling, Pages 161-175 in M. M. Littler, and D. S. Littler, editors. Handbook of Phycological Methods, Cambridge University Press, Cambridge, UK.
Lutz, Joe, Algaebase, Mastocarpus papillatus.
Metaxas, A., & Scheibling, R.E. (1993), Community structure and organization of tide pools, Marine Ecology Progress Series, 98, 187-198.
Murray, S.N., Effectiveness of marine life refuges on southern California shores, California and the World Ocean, 1453-1465, 1997.
Murray, Steven N. et. al., Methods for Performing Monitoring, Impact, and Ecological Studies on Rocky Shores, U.S. Department of the Interior, Minerals Management Service, Pacific OCS Region, Camarillo CA, and Southern California Educational Initiative, Marine Science Institute University of California, Santa Barbara, CA, March 2002, .
N. Scott Rugh, Differences in Shell Morphology between the Sibling Species Littorina scutulata and Littorina plena (Gastropoda: Prosobranchia), Department of Biology, San Diego State University, The Veliger, October 1 1997.
O’Clair, Rita M. and Sandra C. Lindstrom. North Pacific Seaweeds, Alaska: Plant Press. 2000, referenced at https://depts.washington.edu/fhl/mb/Endocladia_Laura/ecology.html.
Raimondi, Pete, et. al., Monitoring of rocky intertidal resources along the central and southern California mainland, 3-Year Report for San Luis Obispo, Santa Barbara, and Orange Counties (Fall 1995-Spring 1998), OCS Study, MMS 99-0032, U.S. Bureau of Energy Management, Regulation, and Enforcement, Pacific OCS Region, 1999.
Ricketts, Edward F. and Jack Calvin, Between Pacific Tides, 3rd ed. and 5th ed., Stanford University Press, Stanford, CA, 1939 and 1985.
Rogers-Bennett and Patyten, Abalone and Red Sea Urchins Die During Red Tide in Northern California, DFG Marine Management News, October 2011.
Walder, Ronald K., The persistence of open space in the rocky intertidal Endocladia muricata assemblage, Master’s Thesis, San Francisco State University, 1999.
UCSC, Endocladia (Turfweed), Pacific Rocky Intertidal Monitoring: Trends and Synthesis, UCSC website, 2012.
UCSC, Gerstle Cove Biodiversity Survey Findings, Pacific Rocky Intertidal Monitoring: Trends and Synthesis, UCSC website, 2012,