Species description of Amorphinopsis excavans

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Species description of Amorphinopsis maculosa

A focus on its filtering capability

James Eccles 2017

Summary

Amorphinopsis maculosa is an encrusting leuconoid sponge found in the intertidal zones of tropical regions. Despite A. maculosa’s recent taxonomic classification and lack of species-specific biological descriptions, I have described as many relevant aspects to its biology based on current literature. Information on A. maculosa’s physical description, ecology, life history and behavior, anatomy and physiology, distribution, and evolution have been formulated into this species page. I have added an extended focus on the sponges filtration ability and A. maculosa’s response to increased sedimentation. Overall, A. maculosa is an interesting demosponge despite the lack of scientific studies.

Acknowledgements

A special thank you to Bernie and Sandie for offering their guidance with this species page. Massive thanks to all the tutor who were all a huge help, and to John Hooper of the Queensland Museum for the species identification.

Physical Description

General Morphology

The A. maculosa specimen is thickly encrusting (200-300mm thick), with irregular ventral extensions of the pinacoderm attached to substrate. The A. maculosa specimen takes the form of a leuconoid sponge with a body size of around 100mm long and 50mm wide. The surface has convoluted ridges and short projections that house discreet oscula of various diameters (Alvarez & Hooper 2011).

Alive specimens are yellow in colouration both internally and externally. The variation in colour towards the ventral side is due to the encrusting behaviour and accumulation of substrate.

A. maculosa’s external surface is a dermal membrane (skin) with a lumpy, net appearance that looks smooth (Alvarez & Hooper 2011). The sponge tissue is firm but crumbly when compressed or segregated. This texture is due to the skeleton arrangement which consists primarily of spicules.

Spicules

A. maculosa is comprised of abundant siliceous spicules, they are oxea shaped spicules of the monaxon biradiate type. The oxeas have a large size variation (207-994 µm x 5-38 µm) and occur much more frequently than the small ectosomal styles (139-274 µm x 3-8 µm) (Alvarez & Hooper 2011).

Figure 1

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Ecology

Lifestyle

A. maculosa is a sessile, benthic, filter feeding animal (Brusca et al. 2016; Bell 2008). They have an aquiferous system, a system of canals that allows them to filter large volumes of water efficiently and obtain considerable amounts of food and nutrients (Brusc et al. 2016). The aquiferous system of A. maculosa is supported by the characteristic leuconoid body form. This body form allows all sponges to reach considerable size which can have large consequences and significant influence on the surrounding environment.

Ecosystem Function

Demosponges have a large geographical distribution and can reach considerable size, as a result, they are extremely abundant and have many functional influences on the ecosystem (Bell 2008). Sponges have been known as important agents of the benthic substrate, and in the case of encrusting demosponges like A. maculosa, they have a role in stabilising substrate which prevents fragmentation of coral and boulders (Wulff & Buss 1979; Bell 2008). Substrate stabilising leads to longevity of the ecosystem and reduces the impact of disturbance (Bell 2008; Wulff & Buss 1979). One well studied and extremely important function that sponges perform is the cycling of nutrients and linking the pelagic communities with benthic communities (Butler et al. 1995; Corredo et al. 1988; Bell 2008). This link is known as bentho-pelagic coupling and its due to sponges ability to remove food and other nutrients from the water column (Bulter et al. 1995; Bell 2008). Particle removal provides a means of carbon cycling, silica cycling and nitrogen cycling (Bell 2008; Corredo et al. 1988). Sponges provide an important link between the benthic habitat and the pelagic which undoubtedly fortifies the structure of many ecosystems in the marine environment. Many of the functions performed by sponges have a major influence on ecosystem function and allow them to be highly valuable members of these systems (Bell 2008).

Symbiosis

Sponges act as a refuge site for a variety of organisms (Wulff 2006; Bell 2008; Brusca et al. 2006). The pores and canals of the sponge make ideal habitats for opportunistic invertebrates and even fish (Wulff 2006). Most of the habitants pose a commensal symbiotic relationship where they utilise the canals of the sponge for protection and the suspended food particles that the sponges draws in (Wulff 2006; Bloom 1975). The A. maculosa specimen had a number of inhabitants on both the outer surface and in the canals (see figure 4 & 5). Crabs and other invertebrates, like bivalves, utilise encrusting sponge species like A. maculosa for protective camouflage to aid in predator avoidance (Brusca et al. 2016; Wulff 2006; Farren & Donovan 2007).

Sponges also have a symbiotic relationship with bacteria and algae (Wulff 2006; Bell 2008). The sponge matrix has been shown to be an ideal area for bacterial growth and results in a mutualistic relationship as the sponge can consume the bacteria for nutrients (Brusca et al. 2016). Other forms of mutualistic symbiosis occur with cyanobacteria and algae which assist in primary production and the energy requirements for the sponge (Brusca et al. 2016; Bell 2008; Wilkinson 1987; Wulff 2006).

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Aquiferous System

The aquiferous system is a distinct, derived trait of all sponges, and is considered the most important characteristic that unites the Porifera phylum (Cavalcanti & Klautau 2011). The aquiferous system is responsible for supplying nutrition, waste removal, reproductive processes and gas exchange, it is at the center of all sponge physiology and cellular activity (Cavalcanti & Klautau 2011). In a leuconoid sponge, like A. maculosa, the aquiferous system is a network of canals within the sponge body (Windsor & Leys 2010; Brusca et al. 2016). It consists of chambers that lie between the incurrent and excurrent water flow direction. These chambers a lined with choanocytes that generate the unidirectional movement of water in and out of the sponge (Windsor & Leys 2010; Brusca et al. 2016). Water enters the sponge through the ostia (dermal pores) which line the exterior of a leuconoid sponge and is expelled through the larger osculum (see figure 7) (Windsor & Leys 2010; Brusca et al. 2016; Ruppert et al. 2004).

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Figure 7

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Nutrition

The specific means in which A. maculosa acquires nutrients has not been explored. Therefore, the methods mentioned in this section applies to most sponges, with a particular focus on shallow inhabiting demosponges.

As mentioned earlier, sponges filter food particles from inflowing water and digest food intracellularly through phagocytosis (Rupper et al. 2004; Brusca et al. 2016). Through the aid of the aquiferous system, a constant supply of microscopic food particles is brought into the series of canals and acts as a multilayer sieve (Brusca et al. 2016). Sponges are size-selective feeders and can consume particles ranging from 5µm - 50µm in diameter (Brusca et al. 2016; Rupper et al. 2004), all particles larger than 50µm cannot pass the dermal pores (with a few exceptions). Choanocytes and archeocytes are both capable of phagocytosis, however, choanocytes can only partly digest the food before they typically move the food to the archeocytes for further digestion (Brusca et al. 2016; Ruppert et al. 2004). Pinacocytes that line the external surface area of the sponge are also capable of phagocytosis and digestion of food particles (Brusca et al. 2016).
Phagocytosis is an important method for food capture and digestion, however, sponges deploy other mechanisms to obtain the required nutrients. Many sponges harbour photosynthetic endosymbionts like dinoflagellates and cyanobacteria (Rupper et al. 2004). This relationship enables primary productivity and can contribute between 30-80% of the sponges metabolic needs (Ruppert et al. 2004; Brusca et al. 2016; Pawlik et al. 2015). Typically, the use of photosynthetic endosymbionts is associated with shallow water sponge species (Ruppert et al. 2004). Recently, sponges have been shown to play a role in the cycling of dissolved organic matter (DOM) (Rix et al. 2017; Pawlik et al. 2015). Pinocytosis allows DOM to be taken up from the aquiferous system and is thought to be a major food source for the many microbial symbionts within the sponge (Brusca et al. 2016; Rix et al. 2017; Pawlik et al. 2015).

For information on the various cell types, see section on cellular organisation and function.

Figure 10

Filtration and Experiment

Sediment Environments

Nutrition and food accessibility is an extreme selective force and has proven to be a key factor in the distribution of sponges (Pawlik et al. 2015). With this, changes in environmental conditions can have major consequences, not only for food availability but also on a sponges ability to filter water (Bell & Smith 2004; Pawlik et al. 2015; Tompkins-MacDonald & Leys 2008). Sponges lack neurons and nervous systems that would allow them to close off from the environment, as a result, they have evolved other responses for dealing with changes in environment conditions (Brusca et al. 2016; Tompkins-Macdonald & Leys 2008). Sediment deposition has major impacts on benthic communities, it causes burial effects on benthic communities and alters the physical and chemical properties of sea water. Natural factors influence the fluctuations of sediment particles, such as wind- wave and tidal actions, anthropogenic process also have major impacts on the level of sedimentation like agriculture and coastal development (Carbalo 2006). Sedimentation has been seen to affect sponges both indirectly, by changing the nutrient availability, and directly by altering the sponges ability to filter feed (Carbalo 2006).

Amorphinopsis maculosa excurrent being expelled through the osculum.

Sponges are capable of pumping a volume of water equal to its body every 5 seconds (Rupper et al. 2004). They have been shown to retain up to 80% of the particles that flows through their aquiferous system (Stabili et al. 2006). However, in environments with high turbidity and sedimentation, sponges have been shown to alter the rate of filtration to suit the conditions (Rupper et al. 2004; Pawlik et al. 2015; Cardenas et al. 2012). I performed a study to determine whether the environmental conditions in which A. maculosa is naturally exposed too, enforces any restriction on its ability to filter feed. The A. maculosa specimen was collected at an intertidal mud flat, these habitats are exposed to high amounts of sedimentation twice daily. A. maculosa was exposed to a high sediment condition and a low sediment condition. The results indicated a distinct decrease in A. maculosa’s ability to filter algae in a sediment environment. According to Ruppert et al. (2004), sponges are able to slow their overall flow rate in correspondence to adverse environmental conditions. This response prevents an influx of inorganic particles that potentially could cause blockages in the aquiferous system (Tompkins-MacDonald & Leys 2008). Sponges are able to alter the flow rate of water by changing the diameter of the osculum, closing ostia or adjusting choanocyte beating rates (Tompkins-MacDonald & Leys 2008; Ruppert et al. 2004). Although the direct effects of sedimentation have been negative for A. maculosa, sponges have been seen to benefit from the resuspension of DOM (Tompkins-MacDonald & Leys 2008). Therefore, for shallow water inhabitants where the levels of sedimentation and other environmental conditions are high, although seemingly a restrictive situation, sponges have evolved methods for coping and even benefiting from these conditions.

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Life History and Behaviour

Reproduction

The reproductive processes associated with A. maculosa have not been exclusively explored. Therefore, the means of reproduction for this species will be mention as part of a general process for all marine Demosponges.

Asexual

Asexual development is interpreted as a general consequence of the sponges ability to reorganise constantly and is an efficient way to distribute multiple copies of similar individuals (Hammel et al. 2009; Zillerberg et al. 2006). All sponges are capable of asexual reproduction either by budding or fragmentation from abiotic processes (Hammel et al. 2009; Corriero et al. 1996; Zillerberg et al. 2006). In any case, the resulting dislodged piece of the sponge will regenerate on the sea floor into a new individual. Fragmentation is considered the most primitive mode of reproduction in sponges (Hammel et al. 2009). It is an important aspect of population dynamics and extremely maximises dispersal capabilities (Hammel et al. 2009; Cardone et al. 2010). Additionally, asexual budding for marine sponges includes the formation of reduction bodies (asexual reproduction bodies), budding, and possibly formation of larvae (Hammel et al. 2009; Maldonado & Reisgo 2008). Reduction bodies are a cluster of archaeocyte cells enclosed with spicules and spongin on the outer surface of the sponge (Brusca et al. 2016; Maldonado & Reisgo 2008; Schroder et al. 2004). These reduction bodies will then undergo hibernation while the parent sponge usually stops feeding and eventually dies (Brusca et al. 2016). Reduction bodies are extremely resilient and resistant to a range of stressful conditions, as such, they are usually produced when environmental conditions become unfavourable (Schroder et al. 2004; Brusca et al. 2016; Fell & Levasseur 1991).

Sexual

Sexual reproduction in sponges is performed by two methods, sponges are recognised as being either viviparous and/or oviparous. Oviparity is the process of sperm and eggs being released into the water column through the aquiferous system and external fertilisation results in a free-swimming larva (Reisgo et al. 2014). Viviparity occurs when the sperm enters another sponge through the aquiferous system, finds a way into the mesohyl, and internal fertilisation is achieved (Reisgo et al. 2014; Hooper & Van Soest 2002). In viviparous species, the embryos are released as larvae through the osculum of the parent sponge (Reisgo et al. 2014; Maldonado & Reisgo 2008). Both methods of sexual reproduction have been observed for sponges belonging to the order Halichondrida (Hooper & Van Soest 2002). As stated earlier, A.maculosa’s reproductive mode has not been observed specifically, although, Amorphinosis spp. belong to the Halichondrida order so it is likely they exhibit one, if not both, strategies.

Figure 13

Life Cycle

Demosponges, like all poriferans, exhibit a biphasic life cycle which includes a distinct larval and adult form (Degnan & Degnan 2006; Bishop & Brandhorst 2003). The biphasic life cycle of sponges is the pelago benthic life cycle, in which, a pelagic larvae will live amongst the plankton before settling on the benthic substrate (Degnan & Degnan 2006). Once settled, the larvae will undergo metamorphosis into an adult.

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Anatomy and Physiology

Cellular Organisation and Function

Like all sponges, demosponges are comprised of two single cell thick layers that encapsulate a middle layer called the mesohyl. As the size and complexity of sponges increases, the cell layers remain the same thickness while the mesohyl thickens (Brusca et al. 2016). The inner surface of the sponge is made up of cells that form to be the choanoderm. The choanoderm is comprised of choanocyte cells that are multifunctional cells involve in the pumping, feeding, gas exchange and waste removal (Brusca et al. 2016). In the leuconoid condition, the choanoderm is folded and the surfaces that are lined with flagellated choanocytes form distinct oval chambers (Brusca et al. 2016). The outer surface of the sponge is called the pinacoderm and it is lined with pinacocyte cells. The pinacoderm is separated into two forms, a cuticle-like layer over the external surface of the sponge (exopinacoderm) and within the interior cavities of the dermal pores or ostia (endopinacoderm) (Brusca et al. 2016). The exopinacoderm of demosponges has an extracellular matrix beneath it to aid in the structural integrity of the pinacocytes (Brusca et al. 2016). The mesohyl is embedded with various cell types as well as spicules and collagen fibers (Brusca et al. 2016). Majority of the cells are ameboid, meaning they can change their form and function while freely moving about in the mesohyl (Brusca et al. 2016). The various cells include contractile cells called myocytes, multifunctional archeocytes, spherulous cells that contain chemicals and other cells that are involved in the secretion of the sponge skeleton (Brusca et al. 2016).

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Skeleton structure

Sponges require a support system that allows them to maintain configuration while living in moving water. The sponge skeleton is primarily an aspect of the mesohyl layer which incorporates collagen fibers, spicules and spongin that supports the integument of the sponge (Rupper et al. 2004; Brusca et al. 2016). Demosponges have an organic skeleton meaning that it is made of collagen. The collagen is arranged as a fibrous framework to form what is known as spongin (Brusca et al. 2016), spongin often aids in the cementation of silicious spicules. There are several cells involved in the secretion of the skeleton. Collencytes and lophocytes are responsible for the secretion of collagen fibers (Brusca et al. 2016). Spongocytes produce the spongin framework and sclerocytes are responsible for the production of spicules (Brusca et al. 2016). The stiffness and rigidity of the skeleton is species specific, it depends on the combination and degree of each component.

A. maculosa possess an ectosomal skeleton consisting of tangential to paratangential intercrossing of spicules (Alvarez & Hooper 2011). The ectosome is an outer thickening of the mesohyl (Brusca et al. 2016). The choanosomal skeleton of A. maculosa has a confused makeup with little collagen and a lot of spicules (Alvarez & Hoper 2011). The choanosomal skeleton supports the choanocyte chambers and the overall integument of the sponge.

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Defenses

The sessile nature of sponges makes them prone to a number of potential threats, both physical and non-physical. The primary defense mechanisms of sponges is through the production of spicules and biochemical agents. Biochemical compounds associated with antifouling, respiration, cardiovascular, gastrointestinal, anti-inflammatory, antitumor, cytotoxic and antibiotic actions have all been produced by sponges (Abbas et al. 2011; Kelly et al. 2005). Biochemical compounds occur through the production of secondary metabolites which, in sponges, is due to the symbiotic relationship sponges share with prokaryotes (Wiens et al. 2003). These can take the form of potent biotoxins that are used in predator avoidance, competition for space, inhibiting settlement and prevention of infections (Kelly et al. 2005; Brusca et al. 2016; Swearingen & Pawlik 1998; Ivanisevic et al. 2011). The production of secondary metabolites varies considerably between species. The variance can be seasonally due to trade off with other important biological functions like reproduction or altered to react to changes in environmental conditions (Ivanisevic et al. 2011). Sponges ability to produce biochemical agents has led to extreme interest from chemists and certain biologists interested from a pharmaceutical point of view (Brusca et al. 2016; Abbas et al. 2011).

Biogeographic Distribution

A. maculosa is a tropical sponge that resides in the intertidal zones and shallow ocean depths (6-28m). Little data has been recorded for their exact locality and it most likely could be due to incorrect identification as Amorphinopsis fenestrata, both species occupy similar habitats (Alvarez & Hooper 2011). The specimens that have been recorded were found in the Gulf of Carpentaria in Northern Australia, and in Papua New Guinea (Alvarez & Hooper 2011).

Evolution and Systematics

The systemic placement of sponges has gone through constant change and been difficult to form robust phylogenetic reconstructions (Erpenbeck et al. 2012). Traditionally, the taxonomy and identification of sponges have been based on morphological and reproductive characteristics, particularly spicule and skeletal architecture (Hooper & Van Soest 2002; Redmond 2013; Boury-Esnault 2006). However, the difficulty arises with the lack of such characters and high levels of plasticity displayed by sponges (Redmond 2013; Boury-Esnault 2006). Molecular phylogenetic techniques have been employed during the 21^st century in an attempt to rectify much of the uncertainty in current sponge systematics (Morrow & Cardenas 2015; Redmond et al. 2013; Erpenbeck et al. 2012).

Amorphinopsis maculosa is currently classified to the order Suberitida (formally Halichondrida) and within the family Halichondriidae (Cardenas et al. 2012; Morrow & Cardenas 2015; Alvarez & Hooper 2011). Halichondrida was abandoned because it’s main definition was of shared negative characteristics, and lacked any definite synapomorphies (Morrow & Cardenas 2015; Erpenbeck et al. 2012). Molecular phylogenetics confirmed the reclassification of the families within Halichondrida, and Halichondriidae helped form the new Suberitida clade (Morrow & Cardenas 2015). The distinction of Halichondriidae is based primarily on a few skeletal characteristics like the presence of an ectosome, disorganised choanosomal system, absence of microscleres, and the properties of oxeas and styles (Alvarez & Hooper 2011; Morrow & Cardenas 2015). Subsequently, the classification of Amorphinopsis spp. is as follows:

Phylum: Porifera

Class: Demospongiae

Order: Suberitida

Family: Halichondriidae

Genus: Amorphinopsis

Species: Amorphinopsis maculosa

Figure 20

Conservation and Threats

Currently, A. maculosa has not been listed with a conservation status and can be interpreted as a non-endangered species. However, the IUCN Red List of threatened species does not list any concerns for the entire Porifera phylum. This can be misleading due to little knowledge for most described sponge species, and the lack of endangered status assessments (Bell et al. 2015). In any case, there are a number of potential threats associated with sponges. Anthropogenic process are repeatedly a concerning area for all animals, factors like overfishing, eutrophication from agricultural runoff, physical damage from trawl nets and coastal development have a major influence on the survival of sponges (Bell et al. 2015). Human threats coupled with extreme environmental conditions like rising temperature and cyclones pose potential problems to sponge abundance and richness. The conservation status of sponges, however, is mostly unknown and appear unthreatened in most parts of the world (Bell et al. 2015).

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