Ecological Assessment of Invertebrates

The Invertebrate Team

The invertebrate team of the Coral Reef Ecosystem Division (CRED) monitors noncoral marine invertebrate fauna in coral reef ecosystems. We focus our monitoring efforts on targeted macroinvertebrates and the diverse, small, and little-known community of organisms called cryptobiota.

Macroinvertebrates

CRED monitors sea urchins, sea cucumbers, giant clams, and crown-of-thorns seastars (COTS) with towed-diver surveys to address basic questions about the distribution and abundance of these ecologically and economically important taxa.

Sea Urchins

Echinothrix diadema at Kingman Reef. NOAA photo by Scott Godwin.
Echinothrix diadema at Kingman Reef. NOAA photo by Scott Godwin.

Sea urchins play an important role on reef systems as algal grazers. Some urchins also are bioeroders, which means that they scrape and erode limestone rock when they feed on associated algae.

Sea Cucumbers

Chocolate chip sea cucumber (Holothuria sp.) at Johnston Atoll. NOAA photo by Molly Timmers.
Chocolate chip sea cucumber (Holothuria sp.) at Johnston Atoll. NOAA photo by Molly Timmers.

Sea cucumbers are important detritivores, which means that they scavenge the ocean floor for organic debris (e.g., dead animals, plants, fecal matter). They consume and filter sediments, thereby recycling nutrients back into the food web. Both sea urchins and sea cucumbers are harvested for food in some regions of the Pacific.

Giant Clams

Tridacna maxima at Kingman Reef. NOAA photo by Molly Timmers.
Tridacna maxima at Kingman Reef. NOAA photo by Molly Timmers.

Giant clams are harvested not only as food but also for their beautiful shells. Some species of giant clams, such as the Tridacna gigas, are endangered because of overharvesting in the past century. During our surveys conducted as part of the Pacific Reef Assessment and Monitoring Program, we predominantly have observed Tridacna maxima.

Crown-of-thorns Seastars (COTS)

Acanthaster planci> at Kingman Reef, consuming a coral. NOAA photo by Molly Timmers.
Acanthaster planci at Kingman Reef, consuming a coral. NOAA photo by Molly Timmers.

The COTS (Acanthaster planci) is considered one of the greatest present-day threats to coral reefs when individuals aggregate in large numbers. To learn more about COTS and its effect on reefs, click on the photo below.

Cryptobiota

Reefs are built from the skeletal remains of organisms and reworked by processes such as dissolution, bioerosion, cementation, growth, and sedimentation that create a complex, 3D framework—the reef matrix. Much of the biomass and most of the biodiversity of reefs are found within the complex architecture of the reef matrix. We monitor this community of organisms, collectively known as cryptobiota, to help us understand the diversity and community composition of reef ecosystems across spatial, environmental, and human impact gradients and the role that diversity plays in ecosystem organization, functioning, and resilience in a changing environment. Cryptobiota community includes shrimps, crabs, worms, snails, hermit crabs, brittle stars, sponges, and tunicates to name a few. Representatives of virtually all of the phyla in the animal kingdom are a part of this community.

Deployed ARMS at Kingman Reef. NOAA photo by Molly Timmers.
Deployed ARMS at Kingman Reef. NOAA photo by Molly Timmers.

We monitor cryptobiota with autonomous reef monitoring structures (ARMS). CRED developed ARMS in conjunction with the Census of Coral Reef Project (CReefs) of the Census of Marine Life (CoML). They are long-term collecting devices that mimic the structural complexity of coral reef habitats and attract colonizing invertebrates. The key innovation of this method is that ARMS sample biodiversity over precisely the same surface area in the exact same manner. Thus, the use of ARMS is a systematic, consistent, and comparable method for monitoring the cryptobiota community overtime.

ARMS comprise nine gray, type 1 PVC plates (23 x 23 cm) stacked in alternating series of open and obstructed formats and attached to a base plate of 35 x 45 cm. The entire structure is affixed to the sea floor with four stainless steel stakes, weights, and zip ties. These structures typically are deployed on mid-depth (10 m) forereef habitats in replicate sets of three ARMS at three sites (3 x 3) per island or location. They remain on the bottom for 3 years during which time they become colonized with marine organisms. To learn more about the ARMS project, click here.

For information contact the Benthic Program.