ABYSSAL STATION (STA. N 4100M)
Here, in the depths of the Northeast Pacific, vast assemblages of suspension feeders cling to the spicules of glass sponges (Beaulieu, 2001a). This particular genus, Hyalonema (Figure 9), is known as the “glass rope sponges” due to the spiralled column of spicules that protrude from them. In this genus, the spicule anchors the sponge in a vertical position up to a height of 1m (Beaulieu, 2001b).
As with other species of glass sponge, these twisted columns remain intact long after the death of the sponge. Those who were present in the underwater research vessel, “Alvin”, noticed that the stalks gathered particles much like a tree captures snow in winter. These sponges have been identified in all of the world’s oceans at a depth of >1000m and this specific station lies 4100m deep.
When collected and studied, it was clear that these glass sponge stalks were rich with species and covered in organisms. The stalks even showed some form of zonation with regards to the attached suspension feeders. The larger suspension feeders resided at the top of the stalks and were present all the way towards the bottom of the column up to a few cms from the sea floor. Below this, polychaete tubes and hydroid branches gave columns a “shaggy” appearance. (Beaulieu, 1998). The base of the stalks appeared to be home to solitary epifauna and encrusting foraminifera (Beaulieu, 2001a).
So what is the cause of this zonation? One factor could be that the flow velocity increases as the distance from the sea floor increases. For example, an organism living 5cm from the sea floor experiences half the flow velocity than an organism living at 50cm height (Beaulieu, 1998). However, the environmental conditions of the deep ocean are very calm.
PORCUPINE SEABIGHT, SOUTH WEST OF IRELAND
Pheronema carpenteri (Figure 10) form dense colonies at a depth of 1000-1300m off the coast of Ireland (Rice et al., 1990; Gordon et al., 1996). This species resembles a birds nest, hence its common name – the bird’s nest sponge. The nest-like appearance forms due to the short, thin spicules that surround the osculum. The presence of this species has been observed to positively correlate with biomass of megabenthos (Bett and Rice, 1992). Within this aggregation, approximately a third of the sea floor was covered by spicule mats. One particular sample (with the highest spicule volume) showed abundance of macrobenthos that was almost an entire order of magnitude higher than areas found without spicule mats.
The substratum created by this glass sponge enables a variety of demosponge species to settle. Polychaete worms also take advantage of the glass sponges and have shown association with the amount of sponge fragments present (Bett and Rice, 1992). Meanwhile, ascidians and ophuriods have been noted to utilise the elevated position gained from settling on the sponge species. The reason for this is thought to be the higher flow rates that this position would entail which is advantageous for suspension feeding (Bett and Rice, 1992).