Sponge Diversity and Distribution in the Labrador Sea

Abstract

Sponges are an overlooked component of the benthic marine ecosystem, despite being known to perform important functional roles within the ocean. Understanding the distribution, density and population make up of sponge grounds as well as what drives these patterns is imperative to constraining the environmental, ecological and biogeochemical role sponges perform. This thesis uses three studies that take differing approaches the problem. These studies focus on the Labrador Sea, an area that is experiencing rapid temperature change due to global warming and is important for deep water formation.
Firstly, a mathematical modeling study aimed to constrain the role of fluid forcing in sponge distribution. This was done using clustering analysis combined with fluid flow finite element modeling. Clustering patterns were observed for sponges within each sponge ground and were statistically significant. Simulation of flow looking at wake interactions around simplified sponge shapes predict that sponges are changing the mean flow conditions when they are spaced at similar distances to those observed in the sponge grounds. Further simulations using topographic models of the sponge grounds show the generation of a boundary layer of slowed flow caused by sponge wake interactions. This boundary layer could potentially be beneficial for sponge development and its presence may have implications for assessing the impact of anthropogenic damage on sponge grounds. Damage to sponge grounds will change the distribution of sponges and therefore would change or reduce the boundary layer thickness, potential affecting recovery rates.
Secondly, a taxonomic study of sponge samples was carried out from three localities. Samples were collected by Remotely Operated Vehicle enabling the collection of delicate and encrusting sponges and the effective sampling of steep bedrock habitats. Twelve new species are described: Halicnemia flavospina sp.nov., Paratimea marionae sp.nov., Asbestopluma (Asbestopluma) frutex sp.nov., Lissodendoryx (Acanthodoryx) magnasigma sp.nov., Fibulia textilitesta sp.nov., Hymedesmia (Hymedesmia) caerulea sp.nov., Hymedesmia (Hymedesmia) alba sp.nov., Sceptrella matia sp.nov., Clathria (Axosuberites) radix sp.nov., Stelodoryx groenlandica sp.nov., Stelodoryx rictus sp.nov., and Plakina jactus sp.nov. New information on distribution, in situ images and spicule measurements are provided for Hymedesmia (Hymedesmia) crux (Schmidt, 1875) and Phakellia robusta Bowerbank, 1866. In total 68 sponge species were recorded by this survey, 13 of which had not previously been recorded in the Labrador Sea. These results significantly increase our understanding of the sponge biodiversity of the west Greenland shelf and knowledge of how this differs from that seen around Orphan Knoll.
Thirdly a biogeographic study using principal component analysis on sponge species data and in situ environmental data to identify sponge assemblages, and investigate the drivers of their distribution. We show that – within the sponge specimens assessed in this study – there are two distinct assemblages defined by the physical oceanographic conditions they inhabit. We suggest that these parameters, notably temperature, depth, and oxygen concentration, are the primary controlling factors for sponge distribution in the Labrador Sea. Within these sponge assemblages we show that there is a strong secondary grouping based on local ocean nutrient concentrations, which have not been considered in previous studies due to the unavailability of data at suitable granularity. These finding have implications for modelling the distribution of sponges in the Labrador Sea, and provide new insights into the vulnerability of these assemblages to climate change relevant for conservation strategies.
The most pertinent conclusion of these studies and this thesis is how little we understand of these organisms and how vulnerable they are to anthropogenic damage.

Date of Award	21 Jun 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Katharine Hendry (Supervisor), Emily J Rayfield (Supervisor), Claire E. Goodwin (Supervisor) & Jeremy C Phillips (Supervisor)