Plant Conservation

Mike Maunder , in Encyclopedia of Biodiversity (Second Edition), 2013

Mosses have developed during the past 20 years as a key component of plant conservation (Hallingback and Tan, 2010 ). Mosses and liverworts (Bryophytes) play a fundamental role in ecosystem services. Peat moss ( Sphagnum) has a direct economic value as peat and plays a huge role in carbon sequestration as peat bogs by holding billions of tons of carbon as peat. Mosses play a key role in water cycles (particularly in temperate rainforests) and their value in medicine is being investigated. The Bryophyte Specialist Group is leading a global red list initiative and promoting their conservation. The Bryophyte Specialist Group has produced harvesting guidelines for commercially harvested species and is identifying centers of bryophyte endemism. A particular concern is the lack of trained moss taxonomists and ecologists in nations with rich bryophyte floras.

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Mosses (Bryophytes)

S.K. Rice , in Encyclopedia of Inland Waters, 2009

Introduction

Bryophytes, the second most diverse land plant group behind only the flowering plants, achieve ecological success in habitats that span marked water (desert to aquatic) and temperature (tropical to arctic) gradients. Recent taxonomic treatments segregate the three major bryophyte clades into distinct phyla: the hornworts (Anthocerophyta, approx. 150 species), the liverworts (Marchantiophyta, approx. 6000–8000 species), and the mosses (Bryophyta, approx. 10  000 species). Bryophytes retain characteristics of the earliest evolved land plants and differ fundamentally from more recently derived vascular plant groups ( Figure 1 ). For example, bryophytes lack roots, an efficient internal conducting system, a well developed cuticle, lignin, and structures like stomata that regulate water loss. Consequently, bryophytes achieve favorable water and carbon balance in unique ways and generally rely on external capillary transport and ample water storage ability. In addition, many bryophytes can equilibrate with a dry atmosphere and return to normal metabolic function following rehydration. Even in wetland and stream habitats, bryophytes make use of this capability during times of low water.

Figure 1. Organization of Sphagnum fallax plants. Variation in mictotopography (a), canopy organization (b), plant structure (c), branch morphology (d), leaf shape (e) and hyaline cell anatomy (f) contribute to differences in physiological function in bryophytes. Note that stippled area in (f) represents photosynthetic cells and enlarged cells are hyaline cells that contain only a cell wall. Illustration by S. Webb.

The lack of lignin and reliance on external water conduction restrict the stature of bryophytes and their ability to compete for light with larger plants. Consequently, many bryophytes succeed in habitats not easily colonized by vascular plants like rock and other hard substrates, tree bark, and in deep organic soils. In many forested and nonforested wetlands and in streams and lakes, bryophytes may dominate ecologically and contribute to or control community and ecosystem function. The success of bryophytes in these conditions results from their unique physiology and life form. In this chapter, the nature of these characteristics will be reviewed as they relate to commonalities among bryophytes and also to functional and ecological diversity within the group. The latter will be discussed as it relates to the distribution and ecological role of bryophytes in peatlands (bogs and fens) and in streams and lakes.

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Microbes and Plants

Walter K. Dodds , Matt R. Whiles , in Freshwater Ecology (Third Edition), 2020

Nonvascular plants

Bryophytes (mosses and liverworts) are abundant in some freshwaters. Traditionally, they received little study relative to their importance in some systems, but appreciation of their importance is increasing ( Arscott et al., 1998). Bryophytes can be important components of streams, particularly in alpine and arctic regions, where they can be productive and provide important structural habitats for invertebrates (Bowden, 1999). Aquatic mosses can be divided into three orders (Hutchinson, 1975): the Sphagnales, the Andreales, and the Bryales. The Sphagnales and Bryales have numerous aquatic representatives, and the Andreales has few. The Sphagnales contains only one genus, Sphagnum.

Species of the genus Sphagnum are often a dominant component of the vegetation in the shallow acidic waters of peat bogs and can be very important in many high-latitude wetlands. The total global biomass of Sphagnum is greater than that of any other bryophyte genus (Clymo and Hayward, 1982). Carbon deposition in these peat bogs may be important in the global carbon cycle. The moss promotes acidic conditions because microbial breakdown of organic material produced by Sphagnum produces organic acids. The acidity leads to a stable dominance by the acid-tolerant moss and slows breakdown of organic material. Thus, peat accumulations are significant in the bogs where Sphagnum dominates. We discussed peat and bogs in more detail in Chapter 5.

The Bryales includes several interesting aquatic genera, including Fontinalis, which can be collected up 120   m deep in Crater Lake, and Fissidens, which occurs to 122   m deep in Lake Tahoe (Hutchinson, 1975). Thus, among plants, the mosses can inhabit some of the deepest habitats.

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Macrophytes and Bryophytes

William B. Bowden , ... Tenna Riis , in Methods in Stream Ecology (Second Edition), 2007

B. Bryophytes: An Overview

Classification and Life Cycle of Stream Bryophytes.

Bryophytes include liverworts (Marchantiophyta = Hepatophyta, formerly Hepaticae), hornworts (Anthocerotophyta, formerly Anthocerotae), and mosses (Bryophyta, formerly Musci). Bryophytes have only one set of chromosomes, lack lignin for support, do not have tracheids, and lack true roots. The liverworts differ on their upper and lower surface, whereas mosses are similar all the way around the stem and may grow upright or horizontally. Most (but not all) stream mosses have a horizontal growth form. Identification of bryophytes to the level of species can be technically involved, depending on the species present. Nevertheless, Appendix 18.1 is a simple key that can be used to identify important and common genera of aquatic bryophytes based on morphological characteristics that are reasonably easy to see.

Interestingly, the bryophyte plant that one sees in a stream has only one set of chromosomes (i.e., it is haploid) and is actually either a "male" plant or a "female" plant (as in Fontinalis), or both on the same plant (as in Schistidium). More highly evolved plants like macrophytes have two sets of chromosomes (i.e., they are diploid). Bryophytes are unusual in having "generations" that alternate between a relatively long haploid generation and a relatively short and less prominent diploid generation. At maturity, the female part of the bryophyte population produces sexual organs called archegonia that produce eggs, and the male part of the population produces sexual organs called antheridia that produce sperm. The egg and sperm are both gametes and so this stage is part of the haploid gametophyte generation of the bryophyte life cycle. Sperm cells from the antheridia fertilize eggs in the archegonia to produce the diploid sporophyte, which remains dependent upon the gametophyte, another feature that is unusual in bryophytes. The mature sporophyte is composed of a stalk (seta) and a spore case (capsule). These are often covered by a cap (calyptra), which keeps the capsule closed until the spores are ready for dispersal. Physical characteristics of the sporophyte (some of which can be quite subtle) are key characteristics used to identify bryophyte species. However, these capsules are seldom present in aquatic species.

Although sexual reproduction is clearly important in bryophytes, they can also reproduce vegetatively. That is, pieces of the "plant" may break off when disturbed (e.g., by floods) and the pieces can float downstream to establish in a new location. Vegetative reproduction may be particularly important for stream bryophytes and is a major means by which some species disperse.

Liverworts have two general forms: thalloid or leafy. Thalloid liverworts have no true stems or leaves and cells form an apparently disorganized mass (the thallus), although in some species there may be some internal differentiation (see Appendix 18.1). Antheridia and archegonia may be imbedded in the thallus or raised on a stalk made of thallus tissue. Leafy liverworts, in contrast, have a definite stem with leaves that are one cell thick (see Appendix 18.1). The leaves are arranged in two rows, giving many taxa a flattened appearance that may trend up toward the tip (incubous) or down from the tip (succubous). A third row of usually smaller leaves may be present on the ventral surface. Characteristic pockets, folds, lobes, or other forms of leaf modifications also may be present on the lower surface of the paired leaves and are important characteristics used to identify some species. Both liverwort forms (with a few exceptions) have a distinct "up-down" (i.e., dorso-ventral) construction, unicellular rhizoids (threadlike structures that aid in attachment and absorption), and capsules with elaters (threadlike structures that are generally thought to aid in dispersal) among their spores.

Mosses differ from liverworts in lacking the dorso-ventral orientation, although many species lie prostrate across the substrate and produce rhizoids only on the lower surface. True mosses always have differentiated leaves and stems (see Appendix 18.1). Antheridia, archegonia, and capsules are borne at the apex (acrocarpous) in the upright taxa or on short lateral branches (pleurocarpous) in the more prostrate taxa. No elaters are present in the capsules, but most capsules have teeth (peristomes) at their opening to help regulate dispersal. Their leaves are seldom two-ranked, with a spiral arrangement being more common. Moss species are typically identified on the basis of the shape, color, and texture of leaves and leaf cells and (when present) the appearance, shape, and structure of the sporophyte. The presence of rhizoids, which are multicellular, seems to be habitat-dependent. Terrestrial and stream mosses tend to have rhizoids, but mosses in quiet water often fail to produce them, although Lodge (1959) showed that some of these taxa will produce rhizoids when the plants are out of the water. Many moss taxa have rudimentary internal conducting cells (hydroids and leptoids), but these cells are generally absent among the aquatic species.

Excellent summaries of the general structure, life cycle, and classification of bryophytes may be found in the North American field guides by Conard and Redfearn (1979) and Vitt et al., (1988). These field guides are widely available and serve as useful entries to more technical taxonomic keys, which are listed as general references in these two publications. The authoritative taxonomy of North American bryophytes is the two-volume set by Crum and Anderson (1981). Although oriented to the Eastern United States, it is useful in other locations in North American and beyond. For fieldwork in North America and Europe, the short key provided in Appendix 18.1 will help identify some of the bryophyte genera most often encountered in stream environments.

Distribution of Stream Bryophytes.

Stream bryophytes do not have true roots and are poikilohydric and thus they rely entirely on absorption of water through their leaves. As for terrestrial bryophytes, aquatic bryophytes use a C3 photosynthetic pathway (Bode 1940, Bolhar-Nordenkampf 1970, Rundel et al., 1979, Bain and Proctor 1980, Rudolph 1990). They cannot use bicarbonates as a direct carbon source, unlike many algae and higher aquatic plants, including stream macrophytes (Steeman-Nielsen 1942, 1947, Steeman-Nielsen and Kristiansen 1949, Bain and Proctor 1980, Allen and Spence 1981, Maberly 1985, Raven 1991, Madsen et al., 1993). Thus, bryophytes are often restricted to acidic stream waters (Frahm 1992) where dissolved CO2 is abundant. They are known to exist in waters with pH < 3 (Hargreaves et al., 1975) and can be the dominant plants in acidic environments (Sand-Jensen and Rasmussen 1978). However, other species like Fissidens grandifrons and Cratoneuron filicinum are calciphiles and seem to prefer nonacidic environments.

In contrast to stream macrophytes, stream bryophytes tend to live in faster and shallower water, in part due to their need for constant replenishment of carbon dioxide and nutrients directly from the water. They also prefer hard-bottom substrates (e.g., cobble, boulders, and ledge) because they attach to the surface of substrates via rhizoids and not by roots that penetrate soft sediments. As a consequence, bryophytes are often abundant in riffles, in the splash zone of emergent rocks and stream banks, and in turbulent cascades and waterfalls.

Bryophytes are primary producers (autotrophs) like benthic algae and macrophytes and so they require light to grow. Light influences bryophyte growth and distribution in much the same way as it does macrophytes. However, many bryophytes have an ability to continue to photosynthesize at relatively low light levels, although most of what we know about this characteristic of bryophytes comes from lake rather than stream literature (e.g., Middelboe and Markager 1997, Riis and Sand-Jensen 1997, Sand-Jensen et al., 1999, Schwarz and Markager 1999). Thus, unlike macrophytes, bryophytes may be abundant even in forested headwater streams with dense leaf canopies (Glime 1970, 1984).

Individual bryophyte species can be widely distributed around the world. This seems to be especially true of the more limited set of bryophytes species that are most often found in aquatic habitats. Similar, or even the same, species can be found in North America, Europe, and Austral-Asia.

Ecology of Stream Bryophytes.

The literature on the role of bryophytes in stream ecosystems is especially sparse, which suggests that this is an area that is ripe for future research. Because of their ability to bind ions internally and externally, bryophytes have been used to clean up streams and to monitor for intermittent spills (both intentional and accidental) that cannot be detected by chemical means because of their unpredictable nature ( Glime and Keen 1984, Cenci 2000). Since stream bryophytes are perennial and resistant to decay, they can remove nutrients and heavy metals and sequester them for a very long time (Ozimek 1988, The Stream Bryophyte Group 1999, Samecka-Cymerman et al., 2002). They also have high contents of secondary compounds that discourage both herbivory and microbial breakdown, which prevents substances that have been sequestered by bryophytes from reentering the water column or food chain (Davidson et al., 1989, Liao & Glime 1996). These characteristics can have major impacts on the nature of a stream ecosystem.

Many of the statements about the ecology of macrophytes in streams are equally true of stream bryophytes (Figure 18.1). Both provide an extensive surface for colonization by algae and bacteria. Both can affect the flow velocity in streams and, thus can affect sediment dynamics. Both provide habitat for invertebrates and, so, can be a rich source of food for fish (though it is less clear that this is always the case when bryophytes are abundant). However, much less is known about the production, decomposition, and nutrient turnover in bryophytes compared to macrophytes. The scant literature that does exist suggests that the trophic structure and ecological functions of streams that are dominated by bryophytes should be substantially different from those in which bryophytes are not abundant. The review by the Stream Bryophyte Group (1999) discusses these differences at length and provides a convenient entry point to this literature.

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Microbes and Plants

Walter K. Dodds , Matt R. Whiles , in Freshwater Ecology (Second Edition), 2010

Nonvascular Plants

Bryophytes (mosses and liverworts) are abundant in some freshwaters. Traditionally, they received little study relative to their importance in some systems, but appreciation for their importance is increasing ( Arscott et al., 1998). Bryophytes can be important components of streams, particularly in alpine and arctic regions, where they can be productive and provide important structural habitats for invertebrates (Bowden, 1999). Aquatic mosses can be divided into three orders (Hutchinson, 1975): the Sphagnales, the Andreales, and the Bryales. The Sphagnales and Bryales have numerous aquatic representatives, and the Andreales has few. The Sphagnales contains only one genus, Sphagnum.

Species of the genus Sphagnum are often a dominant component of the vegetation in the shallow acidic waters of peat bogs and can be very important in many high-latitude wetlands. The total global biomass of Sphagnum is greater than that of any other bryophyte genus (Clymo and Hayward, 1982). Carbon deposition in these peat bogs may be important in the global carbon cycle. The moss promotes acidic conditions because microbial breakdown of organic material produced by Sphagnum produces organic acids. The acidity leads to a stable dominance by the acid-tolerant moss and slows breakdown of organic material. Thus, peat accumulations are significant in the bogs where Sphagnum dominates. Peat and bogs were discussed in more detail in Chapter 5.

The Bryales includes several interesting aquatic genera, including Fontinalis, which is found to 120   m deep in Crater Lake, and Fissidens, which has been found to 122   m deep in Lake Tahoe (Hutchinson, 1975). Thus, among plants, the mosses are found in some of the deepest habitats.

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LAND PLANTS

Shum-qing Wu , in The Jehol Fossils, 2008

Bryophytes

Bryophytes (Bryophyta) are the most basal group among the land plants. They include small green plants of simple construction with unlignified conducting tissue and without roots. They are distinguishable from all other land plants in having a dominant gametophyte and a very simple sporophyte that is born on the gametophyte (in other land plants the sporophyte is the dominant and the conducting tissue is lignified). The gametophyte is typically upright with dichotomous branching and small leaf-like appendages, or in liverworts it may be flattened and thalloid. The unbranched sporophyte is born on the gametophyte and produces a single terminal sporangium. Bryophytes mostly inhabit shady and humid environments. In the Jehol Biota they are represented by four species in two genera. Both leafy and thalloid types are present ( Figs. 224, 225).

224. Muscites tenellus, a bryophyte. 3.15 cm long.

225. Thallites riccioites, a bryophyte. 1.1 cm long, round print probably representing the regetative-reproductive organ gemma cups.

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Bioseparation Engineering

M. Azuma , ... H. Ooshima , in Progress in Biotechnology, 2000

2.2 Cd2   + release from the moss

The moss was suspended in Cd2   + solution (100   μg/ml) for 120   min, as described above, recovered by filtration, and washed quickly with 20   ml of deionized water (pH   6). About 100   mg dry weight of the moss was suspended for 120   min with 20   ml of 10   mM phosphate buffer in the pH range of 3.5 to 6.0, and separated using a 0.45 um filter. The filtrate was analyzed using the ICPS-1000TR. The amount of Cd2   + release (%) was determined on the basis of Cd2   + amount in the moss prior to suspending with phosphate buffer.

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Macrophytes and Bryophytes

William B. Bowden , ... Tenna Riis , in Methods in Stream Ecology, Volume 1 (Third Edition), 2017

Abstract

Macrophytes and bryophytes are plants that have structures that are usually more complex, interdependent, and physically substantial than benthic algae. In this chapter, we describe the characteristics and roles of macrophyte and bryophyte species that can thrive in submerged and flowing conditions. Macrophytes and bryophytes are often important components of stream ecosystems, providing an important physical substrate for periphyton, habitat, and refuges for benthic macroinvertebrates and fish, and ultimately detritus that provides food and fuel to heterotrophic bacteria. Individual macrophyte and bryophyte species are differentially responsive to environmental conditions and have been widely used to define stream community types and to monitor responses of stream ecosystems to terrestrial and anthropogenic drivers. In this chapter, we describe the specific characteristics that define macrophytes and bryophytes, discuss their role in stream ecosystems, and provide instructions for common methods to sample them.

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Refuges of Antarctic diversity

Peter Convey , ... Claudia S. Maturana , in Past Antarctica, 2020

Contemporary Antarctic terrestrial biodiversity and biogeography

Bryophytes are the most diverse plants in Antarctica today, represented by around 111 moss and 27 liverwort species, with the majority of these being found in the milder and wetter maritime Antarctic and only 25 mosses and one liverwort in the continental Antarctic ( Convey, 2017; Ochyra et al., 2008). Only two higher plant species, the grass Deschampsia antarctica and the pearlwort Colobanthus quitensis, are native on the continent, both restricted to the Antarctic Peninsula and Scotia Arc archipelagoes, and both also occurring in southern South America and the Andes (Convey et al., 2011). Thus, overall species diversity is low both compared to the nearest continents and globally. Moss diversity is also low relative to that of the Arctic, for instance around 40% and 20% of that known from Svalbard (Frisvoll and Elvebakk, 1996) and Greenland (Goldberg, 2003), respectively. This likely results from a combination of contemporary extreme conditions, the scale of glacial extinction of pre-existing flora, and the geographical isolation of Antarctica.

In contrast, lichens (representing the fungal kingdom) are widely distributed within the continent, reaching the southern-most ice-free mountain exposures (Broady and Weinstein, 1998; Green et al., 2011). More than 380 species are recorded (Øvstedal and Smith, 2001), over half of which are currently thought to be endemic, with the proportions of endemic species increasing and cosmopolitan species decreasing at higher latitudes within the continent. However, despite the proportion of endemism being strongly suggestive, there do not as yet appear to be phylogeographic studies available in the literature to support this. These numbers also do not include the cryptoendolichens (De Los Ríos et al., 2005). Macrofungi are poorly represented, with no more than 90 species, however almost 400 microfungal species have been described (Bridge and Spooner, 2012; Olech, 2004), including about 54 lichenicholous fungal species on King George Island (Olech, 2004, and references therein).

Similar overall patterns are apparent in the terrestrial and freshwater fauna which, with the exception of the sheathbill, a scavenging bird closely associated with marine vertebrate colonies, is entirely composed of invertebrates (Convey, 2017). There are only two higher insects (both Diptera), which, like the higher plants, are restricted to the Antarctic Peninsula and/or South Shetland Islands. One of these, Belgica antarctica, is endemic to this region while the other, Parochlus steinenii, also occurs in sub-Antarctic South Georgia and southern South America (Convey and Block, 1996; Chown and Convey, 2016). The remaining elements of the fauna are small and cryptic, including the micro-arthropod groups of Acari (mites) and Collembola (springtails), and the micro-invertebrate groups of nematode worms, rotifers and tardigrades (water bears). Freshwater ecosystems are mainly dominated by crustaceans (Dartnall, 2017; Díaz et al., 2019), with Boeckella poppei (Calanoida) being the most widespread species occurring across five ACBRs (Bayly, 1992; Maturana et al., 2019; Pugh et al., 2002) as well as in sub-Antarctic South Georgia and southern South America (Maturana et al., 2018; Menu-Marque et al., 2000). A feature of all of these invertebrate groups is the high level of endemism to either the Antarctic as a whole or to specific regions within it (Pugh and Convey, 2008), which approaches 100% in the micro-arthropods (Greenslade, 1995; Pugh, 1993) and nematodes (Andrássy, 1998; Maslen and Convey, 2006). A particularly striking element of this is the almost complete or complete lack of overlap at species level in the mites, springtails and nematodes between the Antarctic Peninsula and remainder of the Antarctic continent. This distinction is strongly indicative of an ancient biogeographical divide, comparable with the well-known Wallace Line of Southeast Asia, and led Chown and Convey (2007) to define the Gressitt Line, which is located across the base of the Antarctic Peninsula.

Unlike most invertebrate groups, very few Antarctic bryophytes (~   10%) are thought to be endemic to the continent, although examples do exist particularly in the genus Schistidium (Biersma et al., 2018b; Ochyra et al., 2008). Rather, a high proportion (~   45%) of currently recognized Antarctic moss species have bipolar or amphitropical distributions, although only ~   5% are cosmopolitan (Ochyra et al., 2008), indicating the importance of very long distance dispersal (LDD) events (as yet with unconfirmed mechanism). The few recent molecular studies of Antarctic colonization rates in such species point to these events being rare and occurring on hundreds of thousands to million-year timescales (Pisa et al., 2014; Biersma et al., 2018b; Zaccara et al., 2020), although examples of more recent arrivals have been found as well (Biersma et al., 2018a; Kato et al., 2013). However, as in many small and morphologically conserved groups, species richness of bryophytes is likely to be underestimated, through the phenomenon of cryptic speciation. While the low apparent endemism levels and relatedness to other regions could be argued to be consistent with more recent (re-)colonization of the continent, the existence of Antarctic endemic species, the possibility of cryptic speciation, and evidence for much more ancient colonization events indicate that this can be questioned. Nevertheless, the good LDD characteristics attributed to mosses and lichens, particularly wind dispersal of spores and other propagules (Muñoz et al., 2004; Winkworth et al., 2002), does suggest a greater possibility of long distance linkage with other continents than is the case for most invertebrate groups.

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Moss Animals

James H. Thorp , D. Christopher Rogers , in Field Guide to Freshwater Invertebrates of North America, 2011

I Introduction, Diversity, and Distribution

Moss animals are widely distributed but a rarely noticed group of colonial animals in the mostly marine phylum Ectoprocta. Their evolutionary origin is unclear, but they seem related to members of the small marine phylum Phoronida, which use ciliated tentacles to obtain food like bryozoans.

These microscopic creatures living in macroscopic colonies are commonly encountered in lakes and streams but are usually not recognized by nonscientists as animals, which is perhaps not surprising given their old common name "moss animals." Instead, colonies of bryozoans resemble anything from amorphous strings to massive gelatinous mounds weighing several kilograms. These benthic suspension-feeders are most easily found during warmer months attached to rocks, submerged branches, or even to the underside of floating docks.

A bryozoan colony consists of individual animals connected internally by a fluid-filled cavity and externally by a secreted nonliving protective coating. A prominent feature of moss animals is their often U-shaped lophophore (Fig. 12a). This structure contains ciliated tentacles, which are employed to filter organic matter from surrounding water.

Fig. 12a. Anatomy of a bryozoan colony.

Only about 24 bryozoan species have been identified from North America, all collected from east of the Mississippi River and north of the 39th latitude (about the level of Washington, DC); most of these are found around the Great Lakes states. Only one species, the brackish water Victorella pavida, is restricted to more southern latitudes. Scientists have published little about populations of bryozoans west of either the Mississippi River or the province of Ontario, and few agencies have recorded their presence. However, species in several genera are known from Arizona, California, Colorado, Nevada, Oregon, Utah, Washington, and British Columbia. About a quarter of the known species are considered rare.

Despite their general northern distribution, bryozoans are most commonly found in warmer months in areas where water temperatures reach around 15–28°C. Despite such preferences, some species can be collected in winter when temperatures are in the single digits and a few taxa in tropical countries survive temperatures of at least 37°C.

Some bryozoans were formerly nuisance species because they fouled intake pipes of water distribution systems. This problem largely declined when many utility companies started drawing water through sand filters, and now only some untreated intake systems face periodic difficulties in warmer months. Moreover, this fouling problem is now considered minor compared to the havoc wreaked by invasive clams and mussels (see Chapter 10).

Bryozoans superficially resemble members of the unrelated phylum Entoprocta (note the difference in spelling of the first syllable), with whom they have been erroneously classified at various times in the past. The confusion arose because both possess ciliated tentacles and an incomplete separation of budded units (zooids); however, the resemblance ends there. The latter phylum contains perhaps 60 species worldwide, but the only entoproct bryozoan in freshwaters of North America is Urnatella gracilis. Like other entoprocts, it has an external segmented stalk which supports the body. For the remainder of this chapter, however, all references to bryozoans pertain to the more diverse ectoprocts.

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