Nematodes and Other Aquatic Invertebrates in Eurhynchium oreganum from Mary's Peak, Oregon Coast Range

Abstract

Bryophytes provide microhabitats for aquatic invertebrates, many of which are capable of anhydrobiosis. Densities of nematodes, tardigrades, rotifers, and other invertebrates recovered from Eurhynchium oreganum (Sull.) Jaeg, were determined for over one year at an Oregon Coast Range site. Extraction efficiency of Baermann funnels was evaluated by collection on subsequent days followed by squeezing and agigation of moss. Densities of the nematodes, Eudorylaimus spp. and Plectus spp., varied significantly between sampling dates, but densities of Monhystera spp., Tylenchus spp., and Prionchulus muscorum Dujardin did not. Total tardigrade and mite densities differed significantly between sampling dates, but rotifer, amphipod, and turbellarian densities did not. Nematode densities were within the low range of densities previously reported from mosses. Motility efficiency may affect nematode distribution within mosses. Baermann funnels were effective in recovering nematodes and tardigrades, but not rotifers from moss. Nutrient cycling by moss-dwelling aquatic invertebrates is implied by the diversity of their feeding strategies. Bryophytes are a large and significant component of Pacific Northwest forests (Franklin & Dyrness 1988). Estimates of living epiphytic bryophyte and lichen dry weight in old growth coniferous forests exceed that of canopy foliage and of herb and small shrub biomass combined (Nadkarni 1984). Some common bryophytes in Pacific Northwest forests are commercially harvested for the floral and nursery industries, but because their ecological role is virtually unknown, their presumed functions require definition for forest managers and all concerned with forest health and diversity to plan for inevitable sustained exploitation (Peck 1997). The ecological role of bryophytes can be addressed by determination of their water-holding capacity and the effect of this moisture on litter decomposition and erosion control as well as debris accumulation, mycorrhizal relationships, host-parasite relationships, provision of habitat for algae and of food and habitat for invertebrates, the identity and density of these organisms, and their function in nutrient cycling. Bryophytes provide invertebrate habitat because their structure shapes available air spaces within a framework of plant tissue (Gerson 1969), they provide insulation against rapid temperature and humidity changes (Gerson 1969; Kinchin 1994), and they retain large quantities of water and thus retard substrate drying (Gerson 1982). Moss plants are temporary bodies of water that can support an aquatic fauna, holding water within the interstices of the cushion and in the leaf axils (Kinchin 1994). Many mosses can survive in regimes of varying moisture availability because they can dry almost as rapidly as the environment and resume normal metabolic activity upon remoistening (Richardson 1981). Many aquatic invertebrates surviving in mosses are capable of anhydrobiosis, an adaptation to a regime of repeated drying and remoistening. Anhydrobiosis is a latent metabolic state induced by removal of water from an animal by evaporation (Crowe 1975). Dehydrated animals may remain viable in this state for years, and they rapidly swell and resume active life when free water becomes available (Crowe 1975). Since humidities over 80% are required for survival during the dehydration process (Crowe 1975), the environmental mitigation by moss enables moss-dwelling anhydrobiotic invertebrates to successfully enter this latent state. Nematodes, tardigrades, and bdelloid rotifers are the dominant aquatic moss-dwelling invertebrate groups, and all require free water for activity (Gerson 1982; Overgaard 1948) but are all capable of anhydrobiosis to tolerate periodic drought (Crowe 1975; Gilbert 1974; Nicholas 1975; Wright 1991). Although physiological adaptations to survive periods of drought are not characteristically present in typical freshwater nematodes and tardigrades, they are pronounced in typical moss-dwellers (Crowe 1975; Overgaard 1948) and so could be said to be a characteristic of the aquatic bryofauna. Coiling by nematodes and tun formation by tardigrades, both through active antero-posterior contraction, reduce the rate of evaporative water 0007-2745/98/505-511$0.85/0 This content downloaded from 207.46.13.160 on Mon, 17 Oct 2016 05:15:33 UTC All use subject to http://about.jstor.org/terms 506 THE BRYOLOGIST [VOL. 101 loss by removing areas of high permeability in the cuticle from direct contact with the air (Crowe 1975; Crowe & Madin 1974; Wright et al. 1992). Bdelloid rotifers also undergo considerable anteroposterior contraction which dry and shrink their body contents and cuticle to the smallest possible volume (Hyman 1951; Kinchin 1994; Pennak 1978). Eurhynchium oreganum (Sull.) Jaeg. is one of the moss species most often harvested commercially in Pacific Northwest forests (Peck 1997). A common pleurocarpous woodland species growing on Coast Range forest floors, woody debris, and trees, it is characteristic of Group 3 periodically desiccating mosses of shady or humid sites away from direct sunlight (Mihelcic 1954-1955). Due to this poikilohydry, recovery of invertebrate groups characterized by anhydrobiosis from E. oreganum was expected. The objectives of this study are to determine densities of nematodes identified to genera, total tardigrades, and total rotifers in E. oreganum through a one year study period; to enumerate other aquatic taxa present; to compare nematode, tardigrade, and rotifer occurrence and density with previous moss studies; and to investigate the extraction efficiency of Baermann funnel recovery of nematodes, tardigrades, and rotifers from moss. MATERIALS AND METHODS The study area was a Pseudotsuga menziesii-Alnus rubra second growth forest on the northwest slope (533 m) of Mary's Peak, Benton County, in the Oregon Coast Range. Eurhynchium oreganum was the dominant forest floor moss, covering virtually all large and small woody debris, litter, and tree bases in a homogeneous loose mat. Small, isolated areas of Rhytidiadelphus loreus (Hedw.) Warnst. and Rhizomnium glabrescens (Kindb.) T Kop. occurred infrequently on rotting logs but were not included in samples. On ten dates between 6 October 1990 and 25 September 1991, approximately 5 cm diameter samples of the moss E. oreganum were removed at 4to 6-wk. intervals from ten stations, all approximately 1.6 m apart, on the upper surfaces of three abutting parallel rotting logs. Samples from each site on different dates were collected adjacent to previous collections. Moss samples were stored in sealed polyethylene bags under refrigeration for a maximum of 48 hr. Debris was separated from moss plants by hand, and each sample was then weighed at field moisture content. Whole moss plants were then placed on modified Baermann funnels (BF) (Ingham 1994), in which samples were placed on Rapid-Flo milk filters (Filter Fabrics, Inc., Goshen, IN 46526) and immersed in water for five days (Hooper 1986a). Invertebrates collected at the bottom of the funnels were drained into 250 ml glass sample bottles and stored under refrigration until the animals were identified and counted. Nematodes were identified to genus in all cases, and the Prionchulus species was identified as P. muscorum Dujardin, using a compound microscope. Tardigrade and rotifer characteristics were examined using dissecting and compound microscopes. Nematode genera, total tardiTABLE 1. Moisture content of Eurhynchium oreganum as a percentage of dry weight, 1990-1991. n = 10.