Worm Reefs Research Articles

Musical Chairs on Temperate Reefs: Species Turnover and Replacement Within Functional Groups Explain Regional Diversity Variation in Assemblages Associated With Honeycomb Worms

Reef-building species are recognized as having an important ecological role and as generally enhancing the diversity of benthic organisms in marine habitats. However, although these ecosystem engineers have a facilitating role for some species, they may exclude or compete with others. The honeycomb worm Sabellaria alveolata (Linnaeus, 1767) is an important foundation species, commonly found from northwest Ireland to northern Mauritania, whose reef structures increase the physical complexity of the marine benthos, supporting high levels of biodiversity. Local patterns and regional differences in taxonomic and functional diversity were examined in honeycomb worm reefs from 10 sites along the northeastern Atlantic to explore variation in diversity across biogeographic regions and the potential effects of environmental drivers. While taxonomic composition varied across the study sites, levels of diversity remained relatively constant along the European coast. Assemblages showed high levels of species turnover compared to differences in richness, which varied primarily in response to sea surface temperatures and sediment content, the latter suggesting that local characteristics of the reef had a greater effect on community composition than the density of the engineering species. In contrast, the functional composition of assemblages was similar regardless of taxonomic composition or biogeography, with five functional groups being observed in all sites and only small differences in abundance in these groups being detected. Functional groups represented primarily filter-feeders and deposit-feeders, with the notable absence of herbivores, indicating that the reefs may act as biological filters for some species from the local pool of organisms. Redundancy was observed within functional groups that may indicate that honeycomb worm reefs can offer similar niche properties to its associated assemblages across varying environmental conditions. These results highlight the advantages of comparing taxonomic and functional metrics, which allow identification of a number of ecological processes that structure marine communities.

The sedimentary dynamics of Sabellaria alveolata bioconstructions (Ostia, Tyrrhenian Sea, central Italy)

Sabellaria alveolata (Linnaeus 1767) is a polychaete able to build bioconstructions of different thickness, size and patchiness, in intertidal and subtidal environments. Its biological features have been the object of numerous studies worldwide. The worm reefs are formed by millions of tubes built by sand and shells (whole or in fragments) bonded together with a strong glue produced by the worm itself. Hence, Sabellaria alveolata represents a sedimentological asset for the coastal protection, since it contributes to create natural barriers against storm waves and erosion, and supplies the beach with new sandy deposits. This work shows a multidisciplinary approach to studying a bioconstruction of Sabellaria alveolata along the Latium coast (Ostia, Tyrrhenian Sea, central Italy), proposing image analysis as a novel technique to investigate worm reefs, along with classical sedimentological/ecological tools. The Sabellaria bioconstructions have been analysed at different scales of observation, suggesting the more appropriate strategies to develop a reliable model illustrating the different growth steps of these bioconstructions.

Very high-resolution mapping of emerging biogenic reefs using airborne optical imagery and neural network: the honeycomb worm (Sabellaria alveolata) case study

ABSTRACTBiogenic reefs provide a wide spectrum of ecosystem functions and services, such as biodiversity hotspot, coastal protection, and fishing practices. Honeycomb worm (Sabellaria alveolata) reefs, in the Bay of Mont-Saint-Michel (France), constitute the largest intertidal bioconstruction in Europe but undergo anthropogenic pressures (aquaculture-stemmed food/space competition and siltation, fishing-driven trampling). Very high-resolution (VHR) airborne optical data enable cost-efficient biophysical measurements of reef colonies, strongly expected for conservation approaches. A synergy of remotely sensed airborne optical imagery, calibration/validation photoquadrat ground-truth (202/101, respectively), and artificial neural network (ANN) modelling is first used to map S. alveolata relative abundance, over the largest bioconstruction in Europe. The best prediction of S. alveolata abundance was reached with the infrared–red–green (IRRG) spectral combination and ANN model structured with six neurons (R2 = 0.72, RMSE = 0.08, and r = 0.85). The six hyperbolic tangent formulas were applied to the three input spectral bands (IRRG) in order to build six hidden neuronal images, resulting in VHR digital S. alveolata abundance model (6547 × 6566 pixels with 0.5 m pixel size). The innovative model revealed undescribed spatial patterns, namely a reef polarization (perpendicular to the shoreline) of S. alveolata abundance: high abundance on forereef and low abundance on backreef.

Mediterranean Bioconstructions Along the Italian Coast.

Marine bioconstructions are biodiversity-rich, three-dimensional biogenic structures, regulating key ecological functions of benthic ecosystems worldwide. Tropical coral reefs are outstanding for their beauty, diversity and complexity, but analogous types of bioconstructions are also present in temperate seas. The main bioconstructions in the Mediterranean Sea are represented by coralligenous formations, vermetid reefs, deep-sea cold-water corals, Lithophyllum byssoides trottoirs, coral banks formed by the shallow-water corals Cladocora caespitosa or Astroides calycularis, and sabellariid or serpulid worm reefs. Bioconstructions change the morphological and chemicophysical features of primary substrates and create new habitats for a large variety of organisms, playing pivotal roles in ecosystem functioning. In spite of their importance, Mediterranean bioconstructions have not received the same attention that tropical coral reefs have, and the knowledge of their biology, ecology and distribution is still fragmentary. All existing data about the spatial distribution of Italian bioconstructions have been collected, together with information about their growth patterns, dynamics and connectivity. The degradation of these habitats as a consequence of anthropogenic pressures (pollution, organic enrichment, fishery, coastal development, direct physical disturbance), climate change and the spread of invasive species was also investigated. The study of bioconstructions requires a holistic approach leading to a better understanding of their ecology and the application of more insightful management and conservation measures at basin scale, within ecologically coherent units based on connectivity: the cells of ecosystem functioning.

Reducing the data-deficiency of threatened European habitats: Spatial variation of sabellariid worm reefs and associated fauna in the Sicily Channel, Mediterranean Sea

Biogenic reefs, such as those produced by tube-dwelling polychaetes of the genus Sabellaria, are valuable marine habitats which are a focus of protection according to European legislation. The achievement of this goal is potentially hindered by the lack of essential empirical data, especially in the Mediterranean Sea. This study addresses some of the current knowledge gaps by quantifying and comparing multi-scale patterns of abundance and distribution of two habitat-forming species (Sabellaria alveolata and S. spinulosa) and their associated fauna along 190 km of coast on the Italian side of the Sicily Channel. While the abundance of the two sabellariids and the total number of associated taxa did not differ at any of the examined scales (from tens of centimetres to tens-100 of kilometres), the structure (composition in terms of both the identity and the relative abundance of constituting taxa) of the associated fauna and the abundance of several taxa (the polychaetes Eulalia ornata, Syllis pulvinata, S. garciai, Nereis splendida and Arabella iricolor, and the amphipods Apolochus neapolitanus, Tethylembos viguieri and Caprella acanthifera) varied among locations established ∼50–100 km apart. Syllis pulvinata also showed significant variation between sites (hundreds of metres apart), analogously to the other syllid polychaetes S. armillaris and S. gracilis, the nereidid polychaete Nereis rava, and the amphipod Gammaropsis ulrici. The largest variance of S. spinulosa, of the structure of the whole associated fauna and of 56% of taxa analysed individually occurred at the scale of replicates (metres apart), while that of the dominant bio-constructor S. alveolata and of 25% of taxa occurred at the scale of sites. The remaining 19% and the total richness of taxa showed the largest variance at the scale of locations. Present findings contribute to meet a crucial requirement of any future effective protection strategy, i.e., identifying relevant scales of variation to be included in protection schemes aiming at preserving representative samples not only of target habitats and organisms, but also of the processes driving such variability.

Climate and environmental changes driving idiosyncratic shifts in the distribution of tropical and temperate worm reefs

An increasing number of studies have forecast the potential responses of marine life to future climate change. This study predicts how the distributional range of temperate and tropical worm reefs (WRs) might respond to climate and environmental changes (CECs). Compared with current distributions, the tested hypotheses were: (i) under a low CO2concentration and active atmospheric carbon capturing scenario (RCP2.6), both tropical and temperate WRs will maintain their current distributions and face only slight multi-directional biogeographic changes along the century; and (ii) under a high CO2concentration scenario (RCP8.5) WRs will shift toward higher latitudes, with marked changes for tropical species and slight changes for temperate species, specifically at the end of the 21st century. The hypotheses were tested using species distribution modelling, and exploratory statistical analyses were performed to tune model settings. Under scenario RCP2.6, in the middle of the century, areas of suitable habitat are predicted to slightly increase for the temperate WRs and conversely contract for tropical WRs. At the end of the century, multi-directional shifts without range retraction were predicted for both species, but tropical WRs showed major changes in their distribution. Under scenario RCP8.5 and throughout the century, multi-directional shifts increased the areas of suitable habitat for temperate WRs, whereas tropical WRs experienced shifts toward high latitudes and significant retraction at low latitudes. Results indicate that biogeographic range shifts are idiosyncratic for temperate and tropical WRs depending on the CECs scenarios considered.

Sedimentological features of Sabellaria spinulosa biocontructions

Sedentary polychaete Sabellaria spinulosa (Leukhart, 1849) is a suspension feeder that builds tubes by cementing together terrigenous particles. Under a set of environmental conditions, S. spinulosa can form reefs (consisting of hundreds or thousands of worm tubes) that can vary greatly in thickness, size and patchiness. The more-developed reefs form in areas with a large and continuous supply of sand, turbulent water, nutrient availability and rocky seafloor. Recently, for the first time in the Mediterranean area, a large reef of S. spinulosa has been discovered along the northern Gargano coast at Torre Mileto (Adriatic Sea, southern Italy). In this paper, we will detail the main sedimentological data of this worm reef. In order to evaluate the kind of terrigenous particles involved in the worm tube constructions, detailed grain-size and petrographic analyses were carried out on both reef and soft-sediment substrate samples. It is demonstrated that S. spinulosa selects sands on the basis of their grain size and shape, and not their composition. It is also shown that some seasonal variations of these parameters are the result of the interplay between reef growth and degradation periods mainly related to physical processes. In particular, the degradation stages seem to be induced mainly by storm wave action, while the reef growth is the result of the complex interaction between ecological and physical processes.

Ecological Correlates of Green Turtle (Chelonia mydas) Abundance on the Nearshore Worm Reefs of Southeastern Florida

ABSTRACT Stadler, M.; Salmon, M., and Roberts, C., 2015. Ecological correlates of green turtle (Chelonia mydas) abundance on the nearshore worm reefs of southeastern Florida. Juvenile green turtles (Chelonia mydas) differ in abundance on nearshore reefs, but why some sites are preferred over others is unknown. Our study had two objectives: to quantify site-specific differences in turtle abundance over time (1 y) and to determine what ecological factors were correlated with those differences. We conducted quarterly surveys on reefs in Palm Beach and Broward Counties, Florida, and compared reef sites with respect to (1) water depth, (2) algal abundance, (3) algal species richness, and (4) fluctuations in reef area caused by sand burial (which kills the algae used as forage by the turtles). Turtles were most abundant on reefs located in shallow water and exposed to bright ambient light. More turtles were also seen at sites where algae were both abundant and composed of many species. Reefs with those characte...

Measuring nearshore variability in benthic environments: An acoustic approach

Hardbottom and sedimentary habitats in the nearshore are continually affected by natural and anthropogenic disturbances. Currently used monitoring practices rely on visual techniques, aerial and underwater photography, which are conducted on an annual basis. These practices do not allow for rigorous assessment of the effects of human-induced or natural events on the distribution and composition of these habitats. We investigated the use of an acoustic ground discrimination system (RoxAnn) to determine changes in benthic habitats in the nearshore area of northern Indian River County, FL where hardbottom outcrops occur. It was determined that this method was precise and repeatable when deployed in a highly variable surf zone environment. Multiple surveys assessed temporal and spatial changes in bottom types. Spatial distributions of several bottom types were identified: bare rock surfaces, Sabellarid worm reef, sponge covered rock, and rock covered with two dominant algal species. Short-term (weekly) changes in the distribution of sand coverage were detected during a relatively calm hydrodynamic period. At one site (R-15), there was an increase of 11% in sediments, which attributed to approximately 2 750 m2 of coverage; 2.1 km south (R-22) there was a 6% decrease in sediments in six days. The latter equates to a change of almost 1 500 m2 of available habitat. These results suggest that the current practice of annual surveying is limited for assessing the magnitude and impact of episodic disturbances on benthic habitats. Based on these data, acoustic ground discrimination systems provide an unbiased, technology-based data collection method to distinguish benthic habitats in the surf zone. Employing this method will benefit researchers and coastal resource managers.

Backbeach Deflation Aprons: Morphology and Sedimentology

Backbeach deflation aprons are heterogeneous, coarse clastic deposits associated with active transverse dune fields. The apron comprises variously angular, rounded, fractured, cracked, polished, and ventifacted clasts of bedrock (local and exotic), beachrock, and bioherm fragments (coral and worm reef). Terrestrial and anthropogenic clasts (from archeological sites, deflated dunes, flotsam, and shipwrecks) are also present. The unit forms as a lag deposit on top of a gently sloping (ca. 0.008), planar sandy deflation surface and is typically only one clast thick. It is up to 100 m wide and extends for tens of kilometers along the coast. It is replaced landward by a steep (ca. 0.1) deflated soil surface armored with a layer of iron concretions. Backbeach deflation aprons are compound deposits that result from marine storm, eolian, and human activity since the mid- Holocene. The depositional model proposed involves periodic storm deposition of coarse clasts (of beachrock, bedrock, and biogenic origin) and flotsam (shipwreck and other floating debris) on the backbeach or dunes. Some clasts are deposited directly into interdune depressions and enter the deflation plain immediately. Others are deposited initially on dune surfaces. Dune migration results in winnowing of the storm-deposited coarse clasts (together with rhizoliths and any other coarse material in the dune) until they come to rest on the deflation surface. The lag deposit is subsequently buried and uncovered multiple times by dune migration, during which time it is exposed to polishing and subaerial weathering. Consequently, the lag comprises a variety of materials that reflect both storm and eolian processes. The clasts exhibit variable degrees of rounding, polishing, and ventification according to how long they have been in the deposit.Backbeach deflation aprons are characteristic of sandy beaches along approximately 475 km (. 10% of the total length) of the South African east coast. They develop in association with large-scale transverse dunefields on the backbeach, which in turn depend on reversing shore-parallel winds and high sediment abundance. The variable degree of polishing and weathering, planar surface, low elevation, and back-beach location along extensive shoreline distances distinguish backbeach deflation aprons from tsunami or marine storm deposits.

Persistence and Distribution of Temperate Intertidal Worm Reefs in Delaware Bay: A Comparison of Biological and Physical Factors

The sandbuilder worm Sabellaria vulgaris is widely found along the Mid-Atlantic region of the USA, but occurs in dense, reef-like structures in only one estuary. Reef formation and persistence was monitored in lower Delaware Bay along the western shoreline between 2001 and 2009 using ground surveys and aerial photography. These observations were combined with field larval settlement studies, laboratory low temperature susceptibility experiments, and an examination of the physical properties of the individual beaches to attempt to explain the location and persistence of the reefs. Neither exposure to temperature minima during spring low tides nor yearly variations in recruitment accounted for the observed reef distribution patterns. This study suggests that two physical factors, the distance from the beach to the 2-m isobath and the presence of coarse substratum >2 mm explain the greatest amount of variation in the observed distribution of intertidal S. vulgaris reefs and small aggregations.

The strength of biogenic sand reefs: Visco-elastic behaviour of cement secreted by the tube building polychaete Sabellaria alveolata, Linnaeus, 1767

Mechanical properties of the biomineralised cement from tube-building marine worms are poorly known. Secreted from an organ connected to the polychaetes specialised glands, the cement glues sand grains and calcareous shell fragments of a given size and, on a larger scale, ensures the resistance of the reef to waves. In this study, three kinds of mechanical tests were performed with worm tubes to establish the nature of the cement behaviour. Results obtained show that cement behaves like a visco-elastic material. This property allows the tubes to dissipate the mechanical energy from the waves to which they are subject and to reduce the mechanical stress transmitted inside the tubes to the polychaetes. Comparison of “fresh” and “dry” cements highlights that the visco-elastic behaviour of the cement is maintained after five years. The viscosity of the cement is therefore not related to moisture but to its chemical composition. More generally, these results offer a better understanding of the role of cement on worm reefs strength and their persistence in the geological record.

The Ecological Importance of a Recently Discovered Intertidal Sabellariid Reef in St. Croix, U.S. Virgin Islands

Abstract. In Florida, the reef-building polychaete Phragmatopoma lapidosa is important in enhancing local biodiversity via the shelter it provides for various fish and invertebrate species. While the range of P. lapidosa extends south to Brazil, it is rare to find well-established populations in the Caribbean islands. In this study, we examined an intertidal worm reef recently discovered in St. Croix, U.S. Virgin Islands. The worm species was positively identified as P. lapidosa (also known as P. caudata). Analyses of measured worm lengths and mound photographs revealed multiple size cohorts that likely included recent recruits, and mature adults. An examination of the organisms living within small worm clumps collected from the reef, revealed a number of invertebrates including various mollusks, crabs, shrimp and echinoids. Combined, these data suggest that continuous recruitment is likely to maintain this worm reef which is similar to Florida worm reefs, and likely to enhance local biodiversity in St. C...

Burial tolerances of reef-building Sabellariid worms from the east coast of Florida

Sabellariid worms, such as Phragmatopoma lapidosa, are sessile suspension feeders that attach to exposed hard bottom and serve as foundation species for worm reefs which are complex, multifaceted habitats. While worm reefs are adapted to dynamic sedimentary environments, burial of these habitats by beach nourishment projects is a concern. This study determined duration and depth of burial that can be tolerated by P. lapidosa without death. Worm rock samples were buried in sand at 1–10 cm (1-cm intervals), and at 15, 25 and 40 cm for the duration of 72, 144, and 216 h and then surveyed for initial mortality after burial and one week after removal of sediment (latent effects). Initial mortality was similar across all burial depths for the 72-h duration with values ranging from 8.3% (±0.8 SE) for 1 cm to 24.0% (±8.0 SE) for 10 cm of sediment. As burial duration increased to 144 h, mortality generally increased as burial depth increased with an average mortality for 2 cm of sediment of 23.5% (±5.3 SE) increasing to 96.0% (±14.3 SE) with 40 cm of sediment. The mean percent mortality for burial samples in the 216 h treatment varied from a low of 71.2% (±3.3 SE) for 1 cm depth to a high of 100% (±0 SE) for 10, 15, 25, and 40 cm depths. Mortality for most treatments also increased over time after removal of sediment indicating latent effects of burial stress.

Tubulanus riceae new species (Nemertea: Anopla: Palaeonemertea: Tubulanidae), from South Florida, Belize and Panama

Specimens of Tubulanus riceae new species (Nemertea: Palaeonemertea) were collected from a Phragmatopoma worm reef in the surf zone at Fort Pierce (Florida, USA) and from sublittoral rubble at Carrie Bow Cay (Belize) and Bocas del Toro (Panama). They have well‐developed lateral sensory organs, form a cellophane‐like tube and appear to have ocelli‐like structures. The latter, if confirmed as ocelli, would be the first reported for a tubulanid. The new species is characterized by a unique color pattern, resembling that of Tubulanus rhabdotus, but it is distinctive in its milky‐tan ground color with annular bands of brown pigment bounded by white margins and in having up to six to eight dorsal, longitudinal, but broken, reflective white stripes.

Feeding habits and phenotypic changes in proboscis length in the southern oyster drill, Stramonita haemastoma (Gastropoda: Muricidae), on Florida sabellariid worm reefs

The southern oyster drill, Stramonita (= Thais, Kool 1987) haemastoma, is a common intertidal and subtidal predator in the southeastern United States. It uses specialized feeding structures and foraging strategies to bore holes through the shell of its bivalve prey. However, on the east coast of Florida, S. haemastoma, is common on sabellariid worm reefs constructed by the polychaete Phragmatopoma lapidosa (Walton Rocks Beach, Florida, 27°17′N, 80°12′W), a habitat where the snail’s typical prey are scarce. From 1999 to 2001, we examined the feeding habits of S. haemastoma on sabellariid reefs and the behavioral and morphological responses of S. haemastoma that accompanied switching from a diet of bivalves to sabellariids. On worm reefs S. haemastoma feeds on P. lapidosa by inserting the proboscis deep into a worm’s tube. Worm-feeding snails had longer proboscises (~3.7 times shell height) than bivalve-feeding conspecifics (~2.0 times shell height). Snails raised on different diets showed significant differences in proboscis length suggesting that the proboscis length is phenotypically plastic. Whereas typical oyster drills must bore holes for days before ingesting prey, S. haemastoma on worm reefs avoids boring and attacks and consumes worms in 15–50 min. In the laboratory, oyster drills consumed 1.7 worms per day, spending <1 h each day feeding. On sabellariid reefs, differences in feeding, handling costs, and prey value, are likely to have a significant effect on the ecology and life history of S. haemastoma in this habitat.

Peracáridos associados aos bancos de Phragmatopoma caudata (Kröyer) (Polychaeta, Sabellariidae) na Praia de Caiobá, Matinhos, Paraná

A study about composition, relative abundance and densities of peracarid populations associated to worm reefs of P. caudata (Kroyer, 1856) from Caioba Beach, Matinhos, State of Parana (25o51'S and 48o 32'W) was carried out. Monthly samples were obtained from August/1997 to July/1998. The density was calculated as the number of individuais per liter of worm reef. Three amphipod and three isopod species were obtained. The total density of the amphipod populations varied from 3.85 ind./l (July) to 70.56 ind./l (December) and that of the isopod from 0.25 ind./l (May) to 11.73 ind./l (March), The annual fluctuation of the amphipod densities was closely related to the weight fluctuation of the associated algae. The most numerous amphipod species was Elasmopus pectenicrus (Bate, 1862) followed by Hyale media (Dana, 1853) and Ericthonius brasiliensis (Dana, 1853). The isopod Paradynoides brasiliensis Loyola e Silva, 1960 was the most numerous followed by Excirolana armata (Dana, 1852) and Dynoides castroi Loyola e Silva, 1960. All amphipods and two isopod species were considered as constant species and they showed continuous breeding all year round. The occurrence of males, females (including ovigerous ones) and juveniles in the most amphipod and isopod populations in the present study indicates that these peracarids perform a complete life cycle within the Phragmatopoma caudata reefs. These constitute an alternative substrate to peracarids living on phytal and sandy habitats.

Crustáceos decápodos associados aos bancos de Phragmatopoma caudata (Kröyer) (Polychaeta, Sabellariidae) na Praia de Caiobá, Matinhos, Paraná

A study about species composition, relative abundance, densities, size composition, reproductive and recruiting periods, sex proportion and species diversity of the decapod populations associated to worm reefs of P. caudata (Kroyer, 1856) was carried out. Monthly, samples of worm reef were obtained from August/1997 to July/1998 from Caioba Beach, Matinhos (25o51 'S and 48o32'W), Parana State, southern Brazil. Air temperature oscillated from 14.5oC (July) to 31.0oC (February), surface water from 18.0oC (July) to 28.0oC (January and February), and the salinity from 22%0 (February) to 34%0 (September). Eigth decapod species were found: Petrolisthes armatus (Gibbes, 1850); Pachygrapsus transversus (Gibbes, 1850); Panopeus americanus Saussure, 1857; Eurypanopeus abbreviatus (Stimpson, 1860); Menippe nodifrons Stimpson, 1859; Pilumnus dasypodus Kingsley, 1879; Eriphia gonagra (Fabricius, 1781); and Alpheus heterochaelis Say, 1818. The total density varied from 1.66 ind./l (September) to 33.93 ind./l (January). Petrolisthes armatus was the most numerous species. Six species were constant, one was accessory, and another accidental. Shannon-Wiener diversity index was the lowest when compared with other similar habitats. Ovigerous females occurred in six species, but no species showed continuous breeding all year round. The majority of the associated decapods were smaller than those reported in the literature.

Pione lampa , a bioeroding sponge in a worm reef

A bioeroding sponge was found in a sabellariid worm reef in Florida, USA. The sponge was investigated with standard techniques for species identification (tissue digestion, microscopy techniques, examination of spicules) and was identified as the clionid Pione lampa (De Laubenfels, 1950). This species is extremely similar to Pione vastifica (Hancock, 1849). Morphological and ecological similarities and possible dissimilarities are discussed. Arguments for conspecifity were found to be weaker than evidence of P. lampa and P. vastifica being separate species. The sampled sponge contained asexual reproductive elements: superficial buds and internal gemmules. Buds were very delicate, consisting mainly of a radially-oriented mesh of collageneous threads. They further comprised abundant granular material and acanthose microrhabds. Numerous choanosomal gemmules were found in the sponge body attached to erosion chamber walls. They were subspherical to lenticular and had an aspicular, unstructured, smooth and rigid coat. It enclosed dense cell material and various spicule types. Whereas buds are interpreted to function as dispersal elements, gemmules will primarily ensure survival under adverse conditions such as smothering, exposure to air and high temperatures. Gemmules from this site might occasionally be freed and scattered, since the Florida reef can suffer heavy damage during periods of increased wave activity such as that created during hurricane season. Bioerosion activity of the sponge increases the chance to free gemmules, as the sponge not only etches into calcareous particles cemented into the matrix produced by the worms, but also into the matrix itself. This ability enables the sponge to utilise the reef as substrate. Within the Clionidae, Cliona annulifera and three species of the genus Pione are the only species known to produce typical gemmules. Possible reasons are: (1) reproduction of bioeroding sponges is understudied and asexual bodies may have been overlooked in other species, and (2) clionid gemmules are an adaptation to survive life in risky environments. Sponges of the genus Pioneare comparatively successful in environments in which they are close to their physical limits or in potentially unstable or mobile substrates.

Population structure and breeding period of Pachycheles monilifer (Dana) (Anomura, Porcellanidae) inhabiting sabellariid sand reefs from the littoral coast of São Paulo State, Brazil

The purpose of the present study is to examine the population structure and the breeding period of Pachycheles monilifer (Dana, 1852) inhabiting sabellariid worm reefs in the littoral of São Paulo State coast. The specimens were obtained at 2-month intervals from September/94 to July/95. The study sites were located at the rocky shores of Tenorio and Paranapuã Beaches. Individuals sampled showed a total averaged 4.4 ± 1.4 mm carapace length. Ovigerous females were more frequent in September. Despite clear differences regarding the arrangement of these sabellariid colonies, they are extremely important to the establishment and maintenance of P. monilifer.