2014 Intertidal Ecology Survey
Laguna Point, MacKerricher SMCA, Fort Bragg CA
Field Survey Report
James Landers, June 14, 2014 (Rev. November 30, 2014)
Abstract. Laguna Point is on the western perimeter of MacKerricher State Park near Fort Bragg CA. MacKerricher is marine reserve designated as an State Marine Conservation Area under the California Marine Life Protection Act (MPA) and provides limited protection for intertidal life. Laguna Point is open coast with a western exposure that is frequented by tourists, abalone divers, and shellfish harvesters. The area was settled by Pomo and other hunter/gatherers thousands of years ago and at Laguna Point their descendents continue the old traditions of harvesting from the sea.
At minus tide, the area just south of Laguna Point’s north margin becomes a small inlet (where on higher tides doghole schooners loaded lumber in the 1880s) below a marine terrace composed of Quaternary sedimentary deposits. Abalone are common in the inlet and the Indians take them by hand from under exposed rocks. Much of the intertidal rock surface is encrusted by marine algae including Endocladia, Neorhodomela, Mastocarpus and Petrocelis. As with other sites in this survey, marine herbivores ̶ limpets, littorines, and chitons ̶ seemed low in proportion to the amount of rockweed, turfweed, and other algae that predominate here. Mussel beds exist outside of the inlet where they are exposed to the open ocean.
Introduction. This document is the final of six survey reports 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 MacKerricher State Park 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 at Laguna Point in MacKerricher State Park near Fort Bragg CA, latitude 39°29’22”.77 N, longitude 123°48’08”.29 W, on the Mendocino County coast 170 miles northwest of San Francisco. Laguna Point is part of the MacKerricher State Marine Conservation Area where some protection is afforded intertidal marine life, but which is open to the public and regularly picked over for abalone and urchins. The location is exposed open coast where at minus tides only a small inlet remains between rocks on the north and a low eroding marine terrace on the south. The substrate is composed of eroded and weathered Quaternary sedimentary deposits with an upper layer of brown sandstone and a lower layer of dark gray clay or mudstone. There is little protection from winds out of any quarter. A sand beach at the east end of the inlet is accessed by boardwalks and wooden stairs from the parking area. West outside the inlet but still within the reserve there are mussel shoals exposed to the open sea.
The survey was conducted on Saturday, June 14, 2014 between 6:30am and 11:30m. A 10-meter transect was set out in an area incorporating Zones 2 and 3, and 9 quadrats were surveyed. Counts in Zones 1 and 4 were estimated from direct observation without the use of transects and quadrats. The early morning was cool and clear with little surf inside the inlet and changed to sunny and warm without wind as the morning progressed. Water quality was clear. The tides for this date were:
Maximum tidal ranges for this year on this coast 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: 54.0° Fahrenheit (12.2° centigrade).
Temperature stratification: not taken.
Salinity: 37.5 ppt.
Specific gravity: 1.028.
Methods. Mapping of the site was confirmed by reference to California Geological Survey, and National Oceanic and Atmospheric Administration (NOAA), maps. The total survey area was about 2 acres, or about 8000 square meters. Within the survey zone there was about 12 square meters of bare rock surface. Counts for invertebrates found inhabiting bare rock surfaces were averaged for this 12 square meter area and are less then densities in particular locales but still yield reasonable numbers for overall density. As with other sites, marine algae nearly completely covered the sedimentary substrate, and some specimens did not occur evenly distributed over a level substrate, so in all zones the less rigorous approach of visual observation and scaled estimation of species abundance was employed where counts of individuals were impractical (Murray, et. al., “Methods for Performing Monitoring….”).
Data for each Zone were recorded separately.
Zone 1. Only a small area of about 12 square meters was within this zone and it was populated by the acorn barnacles Balanus glandula and Chthamalus dalli/fissus distributed in abundance over vertical rock faces, along with occasional rough limpets, Lottia (Acmaea) scabra, and ribbed limpets, L. digitalis, and a rare periwinkle, L. planaxis. The counts for the acorn barnacles of ±3.6 per square meter for B. glandula and ±25.34 per square meter for C. dalli/fissus were worked up from photos of areas from 1/3 square foot to 1 square foot, converted to metric and estimated for a square meter, then distributed over the estimated 12 square meters of Zone 1. Identification of these barnacles 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 across the terga or scuta of the operculum not present in C. dalli/fissus.
Zone 2. Marine algae predominates in this zone, leaving little room for sessile attachment by marine invertebrates. Petrocelis encrusts 25 percent of rock surfaces. Black pine rockweed, Neorhodomela larix, averages 18 percent of the algal cover, with even greater amounts of turfweed, Endocladia muricata (23 percent), and Turkish towel, Mastocarpus papillatus (22 percent). Brown turban snails, Tegula funebralis, are common in the vicinity of Mastocarpus. Fucus, Egregia menzieii, Ulva and encrusting algae make up a smaller presence in this zone. Anthopleura elegantissima are not so much in evidence at this level, rough limpets, L. scabra, and ribbed limpets, L. digitalis, appeared here less often than in Zone 1, and only one shore crab was observed.
Zone 3. Tegula funebralis abundance leaped in this zone, in a roughly 20 square meter area south of the survey transect, numbering an average 80 per square meter, with much higher density in crevices. At this location, the character of Zone 3 substrate changed from vertical algae covered rock to a more flat, wide and open area with less dense algal cover, Mastocarpus and Ulva predominating. E. muricata and Petrocelis diminished to 15 percent or less. A. elegantissima appeared in small colonies, and occasional giant green anemones. Anthopleura xanthogrammica, were found at the base of rocks. Small amounts of coral weed, Corallina, encrusting red algae, other rockweed (Fucus), and surf grass (Phyllospadix) were present.
Zone 4. Surf grass, Phyllospadix, was assumed to be the principal identifier for Zone 4, where it began at the lower margin of Zone 3 and continued on into lower water, accompanied by Corallina, Saccharina, and smaller amounts of Egregia, Ulva, and encrusting red algae. A gumboot chiton, Cryptochiton stelleri, was also encountered at this level.
Discussion. 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.
Algal cover. In Zones 2 and 3 of the inlet at Laguna Point marine algae covers 30 percent and more of the available rock surface, the predominant representatives being turfweed, E. muricata, black pine rockweed, Neorhodomela larix, and Mastocarpus. Petrocelis encrusts as much as 35 percent of rock surfaces, with only a few invertebrates and other algae found on top of the Petrocelis. The preceding chart Species by Relative Zonal Occurrence shows counts of marine herbivores ̶ limpets, littorines, and chitons ̶ that are low in proportion to the amount of E. muricata and appear insufficient to impact colonization of open space by E. muricata, N. larix , Mastocaspus, Petrocelis and other algae.
Species diversity. While Laguna Point had an abundance of acorn barnacles on rocks in the upper zone, there was a remarkable absence of sea stars (Pisaster), shore crabs, and urchins. Urchins may still be recovering from a catastrophic algal bloom in 2011 that killed great numbers of intertidal creatures (Rogers-Bennett, 2011), and they may also be subject to extraordinary human predation. Mussels are not present within the Laguna Point inlet, but are abundant in shoals outside the inlet. Between Pacific Tides (1985) gives the range of owl limpets as from Neah Bay in Washington State south to Bahia Tortugas in Baja California, however no owl limpets were observed in this survey. Fenberg (2010, 2011) states that owl limpets are very rare on the California coast above San Francisco, and a Pacific Rocky Intertidal website states the range as “Washington to Baja California (Morris et al. 1980). Scarce north of San Francisco.”
Microhabitats. We observed that the landscape changed as we moved laterally through the same intertidal zone. In the first location, the substrate was composed of large rocks and rock benches that rose up through Zone 3 into Zone 2 and displayed species zonation on vertical rock faces, mostly algae without many invertebrates. Nearby in a second location, the substrate in the same intertidal zones was broad and flat and surfaced with smaller rubble on which algae such as Mastocarpus had settled; this substrate hosted a large population of Tegula. These two locations may represent separate microhabitats in the same single intertidal zone, influenced by a vertical emersion gradient in the first location with wave action, temperature and oxygenation varying from that of the horizontal emersion gradient of the second location (UK Marine SACs, 2001).
Anecdotal observations. In conversation with Pomo Indians who have frequented Laguna Point for many years harvesting abalone, in particular the Pomo elder “Elliot,” the following anecdotes were offered. Elliot had been coming to take his limit of abalone at Laguna Point each year for nine years.
Abalone. Each of twenty Pomo Indians gathering abalone that morning take their annual limit of eighteen abalone at Laguna Point, so a ballpark estimate of the annual catch produced here would be at least 350 to 400 abalone.
Algal cover. Nine years ago the area surveyed had rockweed and turfweed much as it does now.
Shore crabs. In the past there were many shore crabs in the inlet, but that now there are none.
Urchins. In the third week of April this year, 2014, Elliot observed many purple sea urchins at Laguna Point, but that a short time later “a swarm of Asians came in and picked them all up and took them out,” and that now a single urchin could not be found.
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