Allan Eisemann One of the most common red algae of the rocky shore in California is Rhodoglossum affine. Another red algal species, Gigartina papillata, overlaps R. affine in its vertical range, though it extends somewhat higher in the intertidal zone. To- gether with other less abundant algae these species form a low forest or turf in the midtide zone. The larger animals of this zone are well known (e.g. Ricketts and Calvin, 1968), and the community of smaller organisms inhabiting the Balanus glandula- Endocladia muricata zone in the upper intertidal has been studied in some detail (Glynn, 1965). However, the mesobiota of the mid¬ tide algal forest has received little attention. This biota is the subject of the present investigation. Studies were directed toward determining whether the mesofauna of these algae forms a relatively consistent associa¬ tion or community. Specifically, the following questions were asked. In the zone occupied by the main population of Rhodo- glossum affine, (1)What animals occur on R. affine, what forms on G. papillata, and in what numbers are they present? (2) Does the mesofauna of R. affine differ from that of G. papillata? (3)Is there a significant difference in the nature and abundance of mesobiota in samples taken from low, medium, and high regions of the R. affine belt? (4) Considering R. affine and G. papillata individually with regard to the composition and numbers of the mesofauna: (a)Do differences exist between the mesofauna popu¬ lations in different areas, exposed to different conditions? -2- -3- Allan Eisemann and (b)Where differences exist, what factors are correlated with these differences? All studies were carried out in April and May, 1979, on and about Mussel Point, Pacific Grove, California, within the research reservation around the Hopkins Marine Station. Three sampling areas were chosen, each with a good population of R. affine but each exposed to a different degree of wave action (figure 1). Area A is the least protected, as it faces the open surf. Area C, protected by the rocky islets to the north, re- ceived a moderate degree of wave action. Area B, located on the lee side of a small offshore island, received virtually no wave action. Degree of wave action was estimated by observing the study sites at high tide on six occasions and counting the num¬ ber of waves breaking or impacting directly on or near the site. Field sampling techniques were as follows. Standing three feet behind the inshore border of the R. affine forest, I established a benchmark and starting there, measured off a square area two hundred inches on a side, with each side divi¬ ded into ten units, each twenty inches long. This provided a square containing ten quadrats, each 20x20 inches square. With¬ in each sampling area, arandom numbers table was used to select particular quadrats for study. It was desired to sample one quadrat from the low, medium, and high regions of the R. affine belt. After the first 20x20 inch quadrat was chosen, ran¬ dom coordinates were generated until a quadrat from each of the other two heights had been selected. Positions of quadrats chosen for study were marked by tying yellow plastic surveyors tape to algae at the four corners. Within each selected quad¬ rat, a sampling frame was used, divided into one hundred 2x2 -4- Allan Eisemann inch squares. A random numbers table was used to choose par¬ ticular 2x2 inch squares within the 20x20 inch quadrat. If R. affine was absent from one of the selected 2x2 inch areas, coordinates for another square were randomly chosen until six samples were taken from each quadrat. If six samples could not be collected from the quadrat, a new quadrat was chosen. To sample each 2x2 inch square, a plexiglas sampler (figure 2), having an inside area of four square inches, was firmly pressed onto the substrate at the site of the randomly selected square. A foam rubber rim provided a good seal to the rock surface in most areas. A rubber bulb and plastic tube were used to squirt two to three ounces of hot (+30° C.) fresh water into the sam¬ pler to kill any animals that might otherwise escape during sam¬ pling. The water containing the small organisms was immediately sucked back up into the plastic tube and deposited into a la¬ belled collection bag. The erect algae, including their hold¬ facts, and any sediments present were then removed with a sharp knife and deposited in the same bag. In each of the three sam¬ pling areas, three 20x20 inch quadrats were chosen and six 2x2 inch samples of the R. affine forest were taken per 20x20 inch quadrat for a total of fifty-four samples. In the laboratory, the samples were placed in finger bowls and examined under a dissecting scope. Counts were made of all animals present in the size range 0.25-11 millimeters. The mesofauna of G. pap- illata was sampled from the same sample areas, and from the same 20x20 inch quadrats previously sampled, using the same tech¬ niques. In cases where six samples of G. papillata could not be taken from a marked quadrat, random numbers were generated -5- Allan Eisemann to determine from which immediately adjacent 20x20 inch quadrat the remaining G. papillata samples would be taken. All samples of algae and sediments were dried for twenty-four hours on open foil plates in an oven at 50° C. and then weighed on a Mettler scale accurate to 0.Ol grams. Algae and sediments were dried together as it was often difficult to completely separate the two. Very small numbers of mesobiota might have remained at¬ tached to either the algae or sediments during the drying and weighing processes. The results obtained are shown in figures 3-9. The major findings are indicated and discussed below. Figure 3 compares the composition of the mesobiota of R. affine and G. papillata, based on the pooled data of all samples taken. No major qualitative differences occur in the fauna associated with the two plant species. In terms of num¬ bers of individuals, Nematoda are the most abundant animals on both algae, comprising 1/3 and 1/4 of the total fauna ofR. affine and G. papillata, respectively. Copepoda make up approximately 1/5 of the fauna in both algae, and the small gastropods Tri¬ colia pulloides (Carpenter, 1865) and Barleeia haliotiphila Carpenter, 1864, comprise between 1/6 and 1/10 of the mesobiota, with the relative abundances of these snails reversed in the two algae. Mites make up 1/10 of the G. papillata mesofauna. Other forms are found in lesser abundance. While the upper and lower boundaries of the R. affine belt were not specifically examined, the samples from low, med¬ ium, and high regions within the main R. affine belt were stud- ied for possible differences in the composition and abundance Allan Eisemann -6- of mesobiota. No significant variations were found. One pos¬ sible explanation of this is that the R. affine belt itself is narrow in the study sites, on the average extending vertically for about three feet in the lower midtide zone, from about mean lower low water to approximately the three foot level. All parts are submerged twice a day, and in a given area receive roughly the same degree of turbulence and exposure to other en¬ vironmental factors. Since no significant differences were found between means of samples from each 20x20 inch quadrat in each sampling area, data from the three quadrats in each area were combined and examined together. In order to determine whether there were differences between sampling areas A, B, and C in the abundance of mesobiota associated with R. affine and G. papillata, pooled data for the quadrats in each area were examined (figures 4 and 5). In figure 4, for R. affine, only the four most abundant taxa are plotted, and the three sampling areas, A, B, and C, are ar- ranged in order of decreasing mean counts of individual organ¬ isms per four square inch sample. This order, A, C, B, also corresponds with a decreasing degree of wave action in the sam¬ pling areas, and decreasing mean amounts of sediment per sample of R. affine. Significant differences (p-0.01) occur between sample areas A and B and also C and B in Nematoda, and between sampling areas A and B in Tricolia pulloides. In general, high mean counts per sample correspond to greater wave action and larger amounts of sediment per sample. I did not expect to find more trapped sediment in the region of a greater wave action. However, perhaps the greater wave action results in more sediment Allan Eisemann in suspension, and R. affine grows in such thick, even lawns, that it appears to trap coarse sediments well even where the surf pounds over the plants at high tide. For G. papillata (figure 5) the situation is different. The sampling areas are arranged in the order of decreasing mean amounts of sediment per sample, and only the four most abundant taxa are shown. In G. papillata, the mean amount of sediment per sample did not correspond directly or inversely with the de¬ gree of wave action. Significant differences (p-0.01) exist be¬ tween sampling areas C and B in Nematoda, Copepoda, and Barleeia haliotiphila and between sampling areas C and B in Tricolia pulloides. The trend from high to low mean counts per sample varies more or less with the amount of sediment per sample ex¬ cept in the case of Tricolia pulloides. However, area C, with the greatest amount of sediment per sample, still has the high¬ est number of gastropods, and in addition, the mean number of Tricolia pulloides per square is low in both areas B and A. In general, the mesofaunal population of G. papillata seems to vary directly with the amount of sediment present. For G. pap- illata, area A, the most wave swept, has the lowest amount of sediment per sample. Area C, which receives a moderate degree of wave action, has the highest amount of sediment. A possible explanation of this is that the sediment in area C, mainly sand, is trapped more readily by G. papillata than is the sandy and shelly sediment mixture common to area A. In order to determine more directly the relation between mesofaunal abundances and sediments, I made qualitative analyses of the amount of sediment per sample by estimating the sediment Allan Eisemann -8- coverage over the bottom of the three inch diameter finger bouls in which the algal samples were placed. Complete coverage was termed a large amount of sediment, partial coverage, moderate. sparse coverage, small, and no sediment, zero. Figure 6 shows a comparison of the mean numbers of individuals of the four most abundant taxa per four square inch sample. The samples are ar¬ ranged in order of decreasing amount of sediment per sample. For R. affine, significant differences (p=0.01) exist between samples with large and small amounts of sediments for all four taxa, and for G. papillata, between large and small and large and zero samples. The figure does not present a comparison be¬ tween R. affine and G. papillata. Rather, it examines the dif- ferences, within each algal species, between samples containing different amounts of sediment. The data show clearly that, for both algae, the number of animals present varies directly with the amount of trapped sediment. A direct comparison of the mean numbers of individuals per gram dry weight of sampled material (algae plus holdfasts and associated sediments) for the two plant species is shown in figure 7. Significant differences (p-0.01) exist between R. affine and G. papillata in the numbers of animals of the five most abundant taxa, Nematoda, Copepoda, Barleeia haliotiphila, Tricolia pulloides, and Lasaea cistula, Keen, 1938, per gram dry weight of sampled material. The fact that R. affine is more effective in trapping coarser sédiment particles than G. papillata suggests the pos¬ sibility that it might provide a safer refuge than G. papillata for larger animals, although the same mesofaunal taxa occur in Allan Eisemann both plants. Figure 8 compares the sizes of the animals found in R. affine and G. papillata. No significant differences in size were found. Figure 9 compares R. affine and G. papillata with re- spect to the mean numbers of individuals per unit area for the four most abundant taxa. Significant differences (p-0.001) exist between R. affine and G. papillata in all three sampling areas for Nematoda, in areas A and B for Copepoda, and in area A for Tricolia pulloides. There is a significantly greater num¬ ber of animals per sample in R. affine than in G. papillata. Perhaps R. affine contains more individuals than G. papillata because R. af Fine grows in thick, even lawns which not only trap sediments well but also offer a habitat better protected against wave action and dessication. In contrast, G. papillata is more sparsely branched, forms sparser patches on the granite substratum, and does not trap sediments as well. Fine organic detritus is found clinging to the blades of both algal species, but more is probably trapped, along with sediments, by R. affine. Detritus and associated microorganisms are probably a main food source for Nematods, Copepods, and Lasaea cistula, three of the most abundant taxa, and they may contribute, at least in part, to the diets of other organisms present in the R. affine belt. SUMMARY 1. The mesofauna associated with the red algae R. affine and G. papillata, in the lower midtide zone, includes, in order of abundance: Nematoda, Copepoda, Barleeia haliotiphila, Allan Eiisemann -10- Tricolia pulloides, Lasaea cistula, Mites, Polychaeta, Ostracoda, Nemertea, Isopoda, and Amphipoda. 2. Although the same taxonomic groups of small animals are present in R. affine and G. papillata, mesofaunal popula- tions per unit area of R. affine are nearly twice those found in G. papillata for the more abundant taxa. 3. Populations of mesobiota in both plants appear to vary most directly with the amount of sediment present. 4. No size differences exist between mesobiota in R. affine and G. papillata. ior. ACKNOWLEDGMENTS With humble gratitude I wish to thank Robert Craig and William Magruder for their time and help securing materials necessary for this project, Alan Firestone for statistical advice, and Dr. Robin Burnett for his good humor and wise counsel. I extend the deepest appreciation to Dr. Donald P. Abbott, my advisor, whose guidance, patience, and wisdom will forever be remembered. LITERATURE CITED Glynn, Peter W. 1965. Community composition, structure, and interrelation¬ ships in the marine intertidal Endocladia muricata-Balanus glandula association in Monterey Bay, California. Beaufortia 12 (148): 1-198. (29 January 1965) Pearse, John S. and Lowry, Lloyd F. 1974. An annotated species list of the benthic algae and invertebrates in the kelp forest community at Point Cab¬ rillo, Pacific Grove, California. The Veliger 17(2): 73; mimeo (3 November 1974) Ricketts, Edward F. and Calvin, Jack 1968. Between Pacific Tides. v-xii + 614 pp; illus. Stanford, Calif. (Stanford University Press) Allan Eisemann -13- FIGURE EXPLANATIONS Figure 1 Map of Mussel Point, Pacific Grove, California, show¬ ing sampling areas A, B, andC. (map modified from Pearse and Lowry, 1974) Figure 2 Plexiglas sampler with foam rubber seal Figure 3 Percent composition of mesobiota by taxonomic groups; based on 54 samples of each plant species. Total numbers of individuals counted for R. affine, 2640, for G. papillata, 1022. Figure 1 R. affine: differences in populations of mesobiota from sampling areas A, B, and C, arranged in descend¬ ing order of mean numbers of individuals per four square inch sample, for all 54 samples. Vertical bars show range, mean, and standard deviation. Figure 5 G. papillata: differences in populations of mesobiota from sampling areas A, B, and C, arranged in order of decreasing amount of sediment per four square inch sample, for all 54 samples. Vertical bars show range, mean, and standard deviation. For R. affine and G. papillata individually, com- Figure 6 parison of mean numbers of individuals per four square inch sample, arranged in order of decreasing amounts of sediment. Vertical bars show range, mean, and standard deviation. Figure 7 Comparison of body lengths of animals associated with R. affine and G. papillata. Vertical bars show range, mean, and standard deviation. Numbers above bars show the number of individuals measured. Allan Eisemann -14- FIGURE EXPLANATIONS Figure 8 For R. affine and G. papillata, mean numbers of in- dividuals per gram dry weight of sampled material, algal blades, holdfasts, and sediment, for all 108 samples taken. Figure 9 For R. affine and G. papillata, numbers of individuals per unit area of substratum in sampling areas A, B, and C, based on all 108 samples taken. Vertical bars show range, mean, and standard deviation. 0 6) R u 2 — O . 38 8 00 8 . DO Pergcyo 2170 — R GRérRaab5 210 21 eeggen 2/. 9 80 QTUER PELECPORA1 poa 17. H — O X O 3 5 3 L ane e i a- a ee a E. . a e eieie ieiei e i ed iine niite a P kaaaaa a 8 — — takka- a . O o NN 40 aon a — - — kaaaaa . aa 98 — — 9 + N N • . * + — — aaaa- P aa — — a — — + aaaaaaaaa ta kkaaaa- — kaaa- aaa- O 10 f 00 V GUNGINIGNO DNN o95 DM . 1 7 o 10 2 . . - P . M aaa aaa P ka a- kaaaa- eein e e ine ti eenee k — 5 N4 N' 4 39WON wo 40 2 O— — 1 og o — 97 og + O9 Og O S) + L o og og OL + og ka- OS M — — og a- O O2 os — os OS aaaa 91. - — Wo) 8 — — — k — — P - Ooo Lasen a 6 13 O— NéATopt NeelTeA POLYCAAETA MITEg OTRKopA COPepopA AP4PoD9 OTHER Peldéyfo Tetota pollodeg 5 hal.tl OTMER CA5T20Po gi nale e 1-fade MOONT SET DR E1647 (gran) Qus da 2 2 11 o o o 0.67 o 61 0. Rhodoglossom afine Preda a2 1 10 1 2 os o Puadt 3 k- 2 o 50. 8 + 5.67 3.33 RAW DATA no Lvren Jua 61117 JEMATODA NEMERTEA PoLyCAAETA MIT6S osTRAopA COréPODA 150FoDA AUPA PopA Lasaed Lgiyla oTUER VEtEOJPoA oup BAREEA tp 5. Sterle AMOONT E SE 0- 2650 WE47 Gas) 1 2 Gigato Papillata sa- a 2 e. 2 22 o o 18 10 2 6 12 o 2 o 96 o o O o 1 Alan Szmane Spandeg. Ongendite. fil ndte td ish g.