Daily Archives: October 6, 2016

Smith lab and colleagues find that Crown of Thorns (COTS) larvae can take up organic matter derived from corals

Crown-of-Thorns Starfish Larvae can feed on Organic Matter Released from Corals

Ryota Nakajima, Nobuyuki Nakatomi, Haruko Kurihara, Michael D. Fox, Jennifer E. Smith, and Ken Okaji

Abstract: Previous studies have suggested that Crown-of-Thorns starfish (COTS) larvae may be able to survive in the absence of abundant phytoplankton resources suggesting that they may be able to utilize alternative food sources. Here, we tested the hypothesis that COTS larvae are able to feed on coral-derived organic matter using labeled stable isotope tracers (13C and 15N). Our results show that coral-derived organic matter (coral mucus and associated microorganisms) can be assimilated by COTS larvae and may be an important alternative or additional food resource for COTS larvae through periods of low phytoplankton biomass. This additional food resource could potentially facilitate COTS outbreaks by reducing resource limitation.

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Do different species of herbivorous fish have unique grazing roles on coral reefs, or are they all grazing alike?

Coral reefs are home to a large diversity of organisms.  The herbivorous fishes, those fish that eat algae in competition with corals, are no exception to such diversity.  But do the many species of herbivores have unique grazing roles on reefs or are all herbivorous fishes grazing alike?

 

This was the focus of a study recently published in Oecologia by marine ecologist Emily Kelly and colleagues in the Smith and Sandin Labs of the Center for Marine Biodiversity and Conservation at Scripps, along with researchers at the Hawaii Division of Aquatic Resources, and NOAA’s Coral Reef Ecosystem Program in Hawaii.

 

The research team quantified fish foraging behavior, stomach contents, and feeding selectivity to determine the role of individual herbivore species on a reef in Maui, Hawaii.  They found important differences across herbivores in the types of algae different fish consumed and the impact of each bite.

 

“At first pass we often think about all herbivores consuming the same algae in the same way on coral reefs- these fishes are the lawn mowers of reefs, mowing down algae that competes with coral.  But what we find is that in fact these herbivores could be seen as many different types of gardening tools, each with a slightly different function in grazing. Therefore, understanding the role of individual herbivorous fish species is important for knowing how the herbivore community as a whole can influence reef composition and reef health,” says Kelly, lead author of the study.  “This finding is especially important given that we as humans put a lot of pressure on coral reefs, including through overfishing.  Knowing that herbivore species are grazing different algae and in different ways is important for managing a diverse community of herbivores to promote healthy reefs,” she says.

 

Further, the researchers found that using only one method of inquiry into feeding suggested that all fish were grazing similarly on the reef, but using three methods revealed more differences in feeding across fishes.

 

Along with Kelly, Scripps researchers Yoan Eynaud, Samantha Clements, Molly Gleason, and Jennifer Smith were co-authors on the study.

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Investigating functional redundancy versus complementarity in Hawaiian herbivorous coral reef fishes
Kelly, E.L.A., Eynaud, Y., Clements, S.M. et al. Oecologia (2016). doi:10.1007/s00442-016-3724-0
scripps oceanography uc san diego