Ecological Patterns of Distribution and Cover of Sponges and Ascidians on Coral Reefs in Kimbe Bay 

Saúl González-Murcia
Biography: Saul was born in the smallest continental country of Latin America, El Salvador. He studied General Biology at the Universidad de El Salvador (University of El Salvador), and conducted his honours research studying zonation patterns in tropical rocky intertidal fishes. After finishing his studies, Saul worked as Research Assistant at the Universidad de El Salvador (University of El Salvador), UDP Ciencias Neotropicales (UDP Neotropcial Sciences) and University of California, Merced. In 2013 Saul was awarded with the Australian Awards Scholarship to study his Master’s degree at JCU and returned to El Salvador to work with Fundación Naturaleza El Salvador (Nature of El Salvador Fundation) and the University of California, Merced developing projects of population genetics in insects and intertidal fish. Since 2018 he has been studying regime shifts caused by sponges and ascidians in tropical reefs and their impact on coral reef associated fishes.
Ecological patterns of distribution and cover of sponges and ascidians on coral reefs in Kimbe Bay
Saúl González-Murcia (1,2), Amy Coppock (1,2), Chirstopher Battershill (3), Geoffrey P. Jones (1,2).
1. Marine Biology and Aquaculture, College of Science and Engineering, James Cook University, Townsville, QLD 4811, Australia
2. Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia
3. University of Waikato Coastal Marine Field Station, Sulphur Point, Tauranga, Unit 4, 58 Cross Road, Sulphur Point, Tauranga, New Zealand 3114
Abstract: Disturbed coral reef ecosystems can shift toward alternative stable states dominated by algae, cyanobacterial mats, sponges and ascidians. Sponges and ascidians are strong competitors for space and can overgrow corals, due to their rapid growth, fast recovery, and sexual and asexual modes of reproduction. Typically, benthic reef surveys record coral cover alone and neglect the contribution of other taxa. However, given the decline of coral cover on reefs around the world it is crucial to establish baselines for the distribution and cover of other significant taxa that can aid to identify shifts in benthic community composition. In this study, we surveyed benthic communities on 6 inshore reefs in Kimbe Bay, Papua New Guinea, that are exposed to different influxes of sediment. At each reef, we ran four 50m point intercept transects (100 random points for each transect) at depths of 5m, 10m and 15m at the sheltered (landward) and exposed (seaward) side and recorded the cover of hard corals, encrusting sponges, massive sponges, erected sponges, colonial ascidians, solitary ascidians, soft coral, algae, hydroids, anemones, gorgonians, giant clams, dead coral, rubble, rock and sand. Tissue samples of sponges and individual of ascidians were collected to aid in species identification. Corals had the highest percentage cover [31% ±1.20%SE], followed by algae [14% ±1.01%] and sponges [13% ±0.85%]. We have potentially identified a total of 110 species of sponge and 17 species of ascidian. The percentage cover of sponges varied significantly among reefs, reef sides and depths (ANOVA F=2.429, p=0.001). Ascidians had very low benthic cover [0.21% ±0.05%] and a very scattered distribution with no significant differences among depths, sites or reefs. The most abundant species of sponges were Dysidea cf. granulosa and Dysidea cf. fragilis. The most abundant species of ascidians were Polycarpa aurata and a yet unidentified ascidian. Overall, we conclude that sponges represent an important and spatially variable component of the biotic substrata on inshore reefs in Kimbe Bay. Our study represents the first assessment of the biodiversity, abundance and ecology of ascidians and sponges in Kimbe Bay and provides a baseline against which trends in the abundance of benthic taxa and species diversity can be assessed.
Banner Photo: Samantha Aird