Under the radar: Sessile epifaunal invertebrates in the seagrassPosidonia australis

Abstract

Despite the current global decline in seagrass, sessile epifaunal invertebrates inhabiting seagrass ecosystems, particularly sponges and ascidians, have been poorly studied due to their taxonomic complexity. Understanding patterns of distribution of sessile epifaunal communities in seagrass meadows is an important precursor to determining the processes driving their distribution and species interactions. This study (1) identified the sponge and ascidian assemblage associated with Posidonia australis meadows and (2) determined distributional patterns of these invertebrates at a hierarchy of spatial scales in Jervis Bay, Australia. We used a fully nested design with transects distributed in the seagrass (10s m apart), two sites (100s m apart), and six locations (km apart). Within these transects, we recorded the abundance, volume, diversity and substratum used for attachment by sponges and ascidians. We encountered 20 sponge species and eight ascidian species; they were sporadically distributed in the seagrass meadows with high variability among the transects, sites and locations. A few sponge and ascidian species dominated the assemblage and were widespread across the largest spatial scale sampled. The remaining species were mostly rare and sparsely distributed. Sponges attached to a variety of substrata but most notably shells, P. australis and polychaete tubes. No obligate seagrass species were recorded although three species predominantly used P. australis as a substratum. These sponge species relying heavily on seagrass for their attachment are likely prone to disturbances impacting their host habitat. Examining the response of sessile epifauna to the degradation of their seagrass habitat remains a key challenge for the future.

Spatiotemporal variability in the structure of seagrass meadows and associated macrofaunal assemblages in southwest England (UK): Using citizen science to benchmark ecological pattern

“…Variability in faunal community structure may be due to the fact that seagrass offers increased structural complexity (Gartner, Tuya, Lavery, & McMahon, ; Webster, Rowden, & Attrill, ) and habitat area (Attrill et al, ), refuge from predation and disturbance (Peterson, ), elevated food availability (Vizzini, Sarà, Michener, & Mazzola, ), altered sediment characteristics (Frost, Rowden, & Attrill, ), and increased retention of particles, such as propagules and particulate organic matter (Christoffer & Erik, ; Thorsten, ). In the current study, we recorded consistently higher abundances of sessile taxa (e.g., cnidarians, bryozoans) in areas containing seagrass, most likely as seagrass populations offer biogenic substrate for settlement and growth of these organisms (Balata, Nesti, Piazzi, & Cinelli, ; Demers, Knott, & Davis, ; Mabrouk, Ben Brahim, Hamza, & Bradai, ).…”

“…Bootstrapping and tmMDS based on Bray-Curtis distance matrices constructed from 4th-root transformed data Location C (Vizzini, Sarà, Michener, & Mazzola, 2002), altered sediment characteristics (Frost, Rowden, & Attrill, 1999), and increased retention of particles, such as propagules and particulate organic matter (Christoffer & Erik, 2000;Thorsten, 1998). In the current study, we recorded consistently higher abundances of sessile taxa (e.g., cnidarians, bryozoans) in areas containing seagrass, most likely as seagrass populations offer biogenic substrate for settlement and growth of these organisms (Balata, Nesti, Piazzi, & Cinelli, 2007;Demers, Knott, & Davis, 2015;Mabrouk, Ben Brahim, Hamza, & Bradai, 2015).…”

Short Communication: Diversity of sponges associated in seagrass meadows at coastal area of Pacitan District, East Java, Indonesia

“…from Banyuwangi beach that inhabited a sandy substrate type associated with the T. hemprichii seagrass habitat. Furthermore, when we compared our results to other studies by Sivaleela et al (2013), Prabhakaran et al (2013), Demers et al (2015) and Ismet et al (2017) two genera: Calyspongia and Haliclona were also discovered in the other ecosystems with seagrass meadows (Table 2). The existence of conspicuous shallow-water sponges Calyspongia and Haliclona (Table 2) presumably indicates the suitability and adaptability of morphological characters to seagrass meadows i.e., a larger oscula of the sponges is presumed to provide greater protection and shelter against predation (Wulff 2008).…”

“…and Toxochalina sp. sponges and Posidonia australis seagrass found in Australia (Demers et al 2015) and several other sponge and seagrass species found in Pulau Seribu, Indonesia (Ismet et al 2017). Due to the few studies conducted in the Indo-Pacific region despite its high sponge diversity, more explorations are needed in this region.…”

Dragging the chain: Quantifying continued losses of seagrasses from boat moorings

“…Although fragmentation of seagrass habitats is not on the same spatial scale as fragmentation of terrestrial vegetation (see Saunders, Hobbs, & Margules, 1991), the ramifications might still be great. Fragmentation of seagrass meadows will have a range of subsequent effects on, for example, sediment stability and wave hydrodynamics (Colomer et al, 2017), nutrient cycling in sediments (Ricart, Dalmau, Pérez, & Romero, 2015), and invertebrate assemblages (Demers, Knott, & Davis, 2015;Hovel, 2003;Tanner, 2005). Some of the species associated with seagrasses are themselves threatened (e.g.…”