Rob W. M. Van Soest; Nicole Boury-Esnault; Jean Vacelet; Martin Dohrmann; Dirk Erpenbeck; Nicole J. De Voogd; Nadiezhda Santodomingo; Bart Vanhoorne; Michelle Kelly; John N. A. Hooper

“ This high level of biodiversity in the Mediterranean Sea is a reflection of special efforts undertaken by a Mediterranean team to find new tools to discriminate between cryptic species. It is predictable that a high diversity of homoscleromorph sponges is present in other regions such as the Caribbean and the Indo-West Pacific.
The Homoscleromorpha are considered too difficult to differentiate at the species level due to lack of diagnostic characters, especially in genera without skeleton (Oscarella) , resulting in the perception that many species are cosmopolitan. ”

“ Megabenthic species may form high-density aggregations in many shelf edge and seamount regions playing a so far unexplored role in deep-sea ecosystems. These are only a few general features of the ecosystem services provided by the global sponge community [14] – [15] .
Although sponges have been known to mankind since the earliest civilizations (4000 YBP, see [16] ) they were not recognized as an independent metazoan lineage until well into the 19th century, when Robert Grant [17] first observed their unique morphology and physiology and coined the name Porifera for them. ”

“ To resolve this using global datasets at the level of realms is at present probably unhelpful, in view of the assumed collection bias, especially when the presently “unknown” (but collected) species are excluded, and without corrections for factors like differential collecting effort and sponge taxonomic research effort between the various regions. Near-future efforts might more productively focus on smaller more manageable regional case studies, whereas the ultimate goal of a global sponge richness assessment is of necessity a distant perspective. ”

“ The spicule skeleton, on which the classification is based, includes monaxonic megascleres that usually include a special type of tylostyle, a mycalostyle, that builds the axes of the body and of the appendages, and a large variety of microscleres, generally chelae and derivatives, to which may be added sigmas, sigmancistras, microstyles and forceps. Interestingly, the chelae microscleres have no known function in other poecilosclerids, but in carnivorous species seem to be used to trap the prey, by lining the surface of body and appendages with the larger hook outwardly directed. ”

“ Regional data systems and online identification tools
Progress of knowledge of global sponge diversity is generated predominantly in many regional efforts, most pre-eminently in the Australian region (Fig. 14) . Similar to, but at that time independent of the WoRMS/WPD global effort was an Australian regional inventory of the “known” sponge fauna from the Australian marine territories (amongst the largest in the world, with 6,819,501 km2 of seabed jurisdiction, and also the largest in terms of the number of described marine species, 32,900 so far [116] ) . ”

“ Knowledge of sponge biodiversity is still largely incomplete. To date, about 11,000 species have been formally described of which approximately 8,500 are considered valid (see below) , but as many as twice that number are thought to exist. Sponges are currently divided among four distinct classes, 25 orders, 128 families and 680 genera [9] , [10] , but many of these higher taxa are under discussion due to new insights obtained from molecular systematic methods and new considerations of their morphological characteristics. ”

“ Phylogenomics has recently suggested solutions for decades of differing class-level hypotheses on poriferan phylogeny by showing that sponges are monophyletic, and that classes Demospongiae and Hexactinellida form a sister group to classes Calcarea and Homoscleromorpha [84] . Recent molecular data also shed new light on the classification and phylogenetic relationships within Calcarea, Hexactinellida and Homoscleromorpha, as briefly mentioned in their respective contributions, but Demospongiae systematics appears to be demanding major changes. ”

“ Global sponge diversity information is mostly generated in regional projects and resources: results obtained demonstrate that regional approaches to analytical biogeography are at present more likely to achieve insights into the biogeographic history of sponges than a global perspective, which appears currently too ambitious. We also review information on invasive sponges that might well have some influence on distribution patterns of the future.
Introduction
Sponges, phylum Porifera, are the oldest metazoan group still extant on our planet. ”

“ Only when species richness is accumulated into large marine realms does a pattern emerge that is also recognized in many other marine animal groups: high numbers in tropical regions, lesser numbers in the colder parts of the world oceans. Preliminary similarity analysis of a matrix of species and marine ecoregions extracted from the WPD failed to yield a consistent hierarchical pattern of ecoregions into marine provinces. ”

“ All in all, we believe that names of all higher sponge taxa and species names for all extant sponges are virtually completely present in the WPD. This does not imply that all combinations of species names and genus names are incorporated, but original combinations and accepted combinations have been entered to the best of our ability. If a combination cannot be found in the WPD it usually means that it is neither an original nor an accepted combination. ”

“ MEOWs with high species numbers may be adjacent to very poor ones, often explained by habitat differences (e.g. the 295 species recorded for the Celtic Sea are contrasted by 140 species of the North Sea for reasons of lack of hard substratum in the latter region) , but very often also because exploration has been differently intense (e.g. in the South Australian MEOWs) . Genus (File S3 part A) and family distributions (File S3 part B) are less extremely different in many MEOWs and probably reflect a more realistic diversity of sponges over the MEOWs more closely than the species distributions. ”

“ We are forced to conclude that current knowledge as laid down in the WPD is likely deficient in showing less than the actual diversity patterns of sponges. Many more areas remain to be explored and many recorded undetermined taxa remain to be named.
Global diversity of the Porifera.Numbers of sponge species recorded in each of 232 marine ecoregions of the world [19] extracted from the World Porifera Database (available: www.marinespecies.org/porifera, accessed 2011 Aug 31) . ”

“ Spongillina are distributed over all continents except Antarctica, and show high endemism with the exception of a few widespread species such as Spongilla lacustris and Ephydatia fluviatilis. The suborder is divided into six families (and an incertae sedis complement) , the largest of which, Spongillidae, contains more than half the number of species. There has been some debate over the likelihood of multiple invasions of the freshwater habitat by sponges, so prudency dictates that the issue remains unsolved [96] . ”

“ There is no differentiation between megascleres and microscleres, and the spicules are usually small (100 μm or less) , not localized in any particular region [52] .
Most of the species are encrusting or cushion shaped and the colour varies from cream to blue, violet, green, yellow, deep brown, orange or red (see Figure 6) . They are often found in dark or semi-dark ecosystems (caves, overhangs, coralligenous substratum) . Homoscleromorpha are generally located in shallow waters, but some species have been found below 100 m [53] . ”

“ For the production of maps and the tracing of species richness patterns, WPD data sets were combined in geographic information system (GIS) software (ESRI ArcGIS v9.3) . A biodiversity analysis aimed at testing the aptness of the MEOW hierarchical system of Marine Provinces and Marine Realms for sponge richness data was carried out using the Bray-Curtis coefficient hierarchical clustering of WPD datasets performed with the PRIMER-6 (PRIMER-E) package. ”

“ The skeleton may also be supplemented by exogenous materials, such as sand grains. Skeletons, when present, are constructed of discrete siliceous or calcareous elements (spicules) and/or organic collagenous fibers (spongin) , and rarely skeletons may be aspicular massive limestone constructions. Depending on the nature and density of these building components, sponge species may variously be soft, compressible, fragile or rock hard in consistency. ”

“ Also, the neglect or lack of effort of the study of major taxa such as the Calcarea and the marine Haplosclerida, respectively 8 and 12% of the total number of species, may have contributed to biased results. Clearly, there is a significant sponge diversity impediment to overcome. ”

“ The shapes of sponges are variable among different species and genera, but also vary to some extent between individuals of the same species in response to environmental factors such as hydrodynamics, light and turbidity.
A great diversity of symbiotic organisms often thrive inside or on the body of a sponge, from microscopic prokaryotes, e.g. ”

“ Species combinations that do not fall under reasons 1 or 2 are considered accepted for the time being, unless they are known insufficiently to assess their genus affinity, in which case they are declared ‘species inquirenda’.
Sponge diversity Numbers of taxa tabulated
Based on the above considerations, Table 2 lists the numbers of WPD entries of species and lower-level combinations (varieties or subspecies) of the four recognized classes. So far (2011 August 31) the number of accepted species of Porifera is 8,553, the vast majority of which (83%) are Demospongiae (Fig. 9) . ”

“ Since then, spongology, the study of all aspects of the biology, ecology, taxonomy and chemistry of sponges, has grown into a discipline attracting a steadily increasing population of hundreds of scientists worldwide, many of whom devote a lifetime career to the study of this group. Increasingly, sponges are studied as part of a broader enterprise attempting to detail the Tree of Life. ”

“ Calcarea
Calcareous sponges have a mineral skeleton composed entirely of calcium carbonate, consisting of free, rarely linked or cemented, diactine, triactine, tetractine and/or polyactinal spicules, to which can be added a solid basal calcitic skeleton. The aquiferous system ranges in complexity from the most simple (asconoid and syconoid) to a more complex arrangement (leuconoid) . The mode of reproduction is viviparous and the larvae are always hollow (blastula) [68] .
Calcarea are also called Calcispongiae in the older literature, and more recently in molecular studies. ”

“ In the Australian context the Atlas of Living Australia (ALA, www.ala.org.au) is the most recent development as biodiversity eResearch infrastructure. A further tool in development focused on collaborative work on raw sponge taxonomic data is SpongeMaps wiki (wiki.trin.org.au/bin/viewauth/Marine/Sponges) , a new tool that has been developed from the TRIN wiki (wiki.trin.org.au) .
Invasive species
As in many other marine groups, there are several cases of sponge species known or suspected to have crossed oceanic or terrestrial barriers and showing disjunct distributions. ”

“ Specialized sponges are important bio-eroders in coral reefs, coralline bottoms and oyster beds and they may compete successfully with other sessile organisms such as corals. Specific groups have an essential function in binding unconsolidated substrate such as coral rubble and pebbles into stable surfaces. Many fossil sponges and a small group of Recent sponges are capable of building extensive reef formations that today, in some locations, shape the contours of the benthos, and now form uplifted terrestrial habitats. ”

“ The sponges use acid produced by special cells to etch small ‘chips’ of calcium carbonate [24] from the substratum and through this activity recycle limestone in e.g. coral reef ecosystems, coralline bottoms and temperate oysterbanks. Rock sponges, “Lithistida” (Fig. 2D) , are a polyphyletic group of sponges with stone-hard silica skeletons composed of intimately interlocking spicules. Many living species are found in deeper waters of tropical and (warm-) temperate regions and are thought to be isolated survivors of a much larger fossil sponge fauna, e.g. ”

“ G. SEM images of a selection of microscleres and megascleres, not to scale, sizes vary between 0.01 and 1 mm. Demosponges demonstrate a tremendous diversity that can only be illustrated with a few iconic examples: The well-known bath sponges (family Spongiidae, Fig. 2A) have excellent properties to appeal to human use as a cleaning or scrubbing tool: a softly compressible consistency and a silica-free resilient skeleton of horny fibres. They grow in warmer waters worldwide and have been exploited to near-extinction in many areas. ”

“ Dendrogram output for hierarchical clustering of 12 Marine Realms.The method used is group-average linking of Bray-Curtis similarities calculated on presence/absence sponge species data. Four assemblage types are identified at various levels of similarity. The dendogram given at Province level (File S8) also does not clearly represent a nested system where the Provinces are clustered within their Realm. Most Provinces are clustered together adjacent to their closest geographical Province. ”

“ Sponges are efficient filter feeders, vital to the health and economics of all marine systems by linking the nutrients of the open water column with benthic communities. Symbionts of sponges play a decisive role in the nitrogen cycle of many habitats and may contribute significantly to organic production in oligotrophic habitats. ”

“ The initial hardcopy publication listed 1,385 valid species-group names and 338 genus-group names. The subsequent online version (the AFD [118] ) currently contains 1,650 species and subspecies in 330 genera and 102 families.
Species richness of regional sponge faunas in western, northern and eastern Australia.Red circles indicate ‘hotspots’ of high species richness (modified from [104] ) . Knowledge of regional marine sponge diversity has expanded considerably over the past two decades in particular, thanks to many new biodiversity discovery initiatives. ”