SCUBA Travel News

Researchers from Florida State University have found that Red Grouper (Epinephelus morio) dig out and maintain complex structures at the bottom of the sea. They remove sand, exposing hard rocks that are crucial to corals and sponges and the animals that rely on them. The work demonstrates that Red Groupers modify their environment, much as beavers do, creating habitat for many other animals including lobster and commercially important fish.

"Watching these fish dig holes was amazing enough,” says Felicia Coleman, lead researcher, “but then we realised that the sites served to attract mates, beneficial species such as cleaner shrimp that pick parasites and food scraps off the resident fish and a variety of prey species for the Red Grouper. So it's no surprise that the fish are remarkably sedentary. Why move if everything you need comes to you?”

“The research is incredibly valuable because it demonstrates how interconnected species are in the sea,” says Dr. Susan Williams, a professor at the University of California, Davis. “Red Groupers are the 'Frank Lloyd Wrights' of the sea floor because they are critical habitat architects. The species that associate with them include commercially valuable species- such as vermilion snapper, black grouper, and lobsters. If the groupers are overfished, the suite of species that depends on them is likely to suffer.”

Working along the West Florida Shelf, the authors observed the excavating behaviour of the Red Grouper during both their juvenile stage in inshore waters as their adult stage at depths of 100 m. The study serves to document this behaviour and its apparent impact on the biological diversity of the ocean. Their article on the study, “Benthic Habitat Modification through Excavation by Red Grouper, Epinephelus morio, in the Northeastern Gulf of Mexico,” is published in the most recent issue of the journal The Open Fish Science Journal.

Red Grouper (Epinephelus morio) is an economically important species in the reef fish community of the southeastern United States, and especially the Gulf of Mexico. It is relatively common in karst regions of the Gulf.

As juveniles, Red Grouper excavate the limestone bottom of Florida Bay and elsewhere, exposing “solution holes” formed thousands of years ago when sea level was lower, and freshwater dissolved holes in the rock surface. When sea level rose to its present state, these solution holes filled with sediment. By removing the sediment from these holes, Red Grouper restructure the flat bottom into a three dimensional matrix.

Spiny lobsters are among the many species that occupy these excavations, especially during the day when they need refuge from roving predators.

“What are the consequence of overfishing these habitat engineers?” asks co-author Koenig. “You can't remove an animal that can dig a hole five meters across and several meters deep to reveal the rocky substrate and expect there to be no effect on reef communities. The juveniles of a species closely associated with these pits, vermilion snapper, are extremely abundant around the offshore excavations. It is possible that the engineered habitat is significant as a nursery for this species, which other big fish rely on as food. One could anticipate a domino effect in lost diversity resulting from the loss of Red Grouper-engineered habitat.”

Red Grouper clearly remove sufficient sediment to transform an otherwise two-dimensional area into a three-dimensional structure below the seafloor, providing refuge for themselves and for other organisms. In the process, they expose hard substrate, thus creating settlement sites for corals, sponges, and anemones, allowing the creation of three-dimensional structure above the seafloor as well. Addition of these roles to their contribution as resident top predators suggests that they might have a disproportionately large per capita influence on the ecosystem within which they live.

Red Grouper have been harvested in the United States since the 1880s and are currently the most common grouper species landed in both commercial and recreational fisheries of the Gulf of Mexico.

Excessive fishery removals can and often do have cascading effects in marine communities that ultimately result in the loss of many species. This situation arises when the captured species has a disproportionately large influence on the system within which it lives. The Red Grouper has been shown to be one such species.

Further Reading:
Benthic Habitat Modification through Excavation by Red Grouper, Epinephelus morio, in the Northeastern Gulf of Mexico
pp.1-15 (15) Authors: Felicia C. Coleman, Christopher C. Koenig, Kathryn M. Scanlon, Scott Heppell, Selina Heppell, Margaret W. Miller
doi: 10.2174/1874401X01003010001
Florida State University

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Labels: America, coral, fish, marine biology, research, SCUBA News

This common species - Cerianthus lloydii - is not a true anemone but a tube anemone. Instead of attaching itself to a rock it lives in a soft felt-like tube protruding above sand or mud. The anemone's tentacles are usually all that is visible. The inner set circle the mouth and are short and stiff. The long, flexible and attractive outer ones, over 100 of them, sweep prey inwards. When disturbed the whole anemone shoots back into its tube, like a tubeworm. The tentacle crown measures up to 10 cm across.

The animals live from the shallows down to 100 m. The tentacles may be white, brown, green or banded.

You can find the burrowing anemone around the British Isles and in North West Europe to the Bay of Biscay.

Further Reading:
Great British Marine Animals, by Paul Naylor, Deltor (2003)

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Labels: SCUBA diving

A new genetic analysis of Antarctic minke whales concludes that population of these smaller baleen whales have not increased as a result of the intensive hunting of other larger whales – countering arguments by advocates of commercial whaling who want to “cull” minke whales.

Antarctic minke whales are among the few species of baleen whales not decimated by commercial whaling during the 20th century, and some scientists have hypothesised that their large numbers are hampering the recovery of deleted species, such as blue, fin and humpback, which may compete for krill.

This “Krill Surplus Hypothesis” postulates that the killing of some two million whales in the Southern Ocean during the early- and mid-20th century resulted in an enormous surplus of krill, benefiting the remaining predators, including Antarctic minke whales.

But the new analysis, published this week in the journal Molecular Ecology, estimates that contemporary populations of minke whales are not “unusually abundant” in comparison with their historic numbers.

The Southern Ocean is one of the world’s largest and most productive ecosystems and in the 20th century went through what Scott Baker, a whale geneticist at Oregon State University, called “one of the most dramatic ‘experiments’ in ecosystem modification ever conducted.” The elimination of nearly all of the largest whales – such as the blue, fin and humpback – removed a huge portion of the biomass of predators in the ecosystem and changed the dynamics of predator-prey relationships.

Blue whales were reduced to about 1-2 percent of their previous numbers; fin whales to about 2-3 percent; and humpbacks to less than 5 percent. “The overall loss of large whales was staggering,” Baker said.

“It is possible that the removal of the larger whales would have meant more food for minkes,” Baker said, “but we don’t know much about the historic abundance of krill and whether the different whale species competed for it in the same places, or at the same time. It is possible that there might have been enough krill for all species prior to whaling.”

The scientists also say that current minke whale populations may be limited by other factors, including changes in sea ice cover.

“The bottom line is that the Krill Surplus Hypothesis does not appear to be valid in relation to minke whales and increasing hunting based solely on the assumption that minke whales are out-competing other large whale species would be a dubious strategy,” Baker said.

Further Reading: Oregon State University

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Labels: marine biology, research, SCUBA News, whale and dolphins

New acoustic sensors are being used in research and conservation projects around the world, with some very important practical results. Among them is improved monitoring of endangered North Atlantic right whales in an effort to reduce ship strikes, a leading cause of their deaths.

Sofie Van Parijs is one of many researcher whose work is decribed this month in the journal Marine Ecology Progress Series. Her paper is one of about a dozen in a special theme issue focused on acoustics in marine ecology. Van Parijs, who currently heads the NEFSC's Protected Species Branch, is also a co-author of a related paper on acoustic interference or masking, in which marine animals alter their use of sound as a result of changing background noise.

Van Parijs and her colleagues focus on two types of acoustic sensors, real-time and archival. Real-time sensors are mounted on surface buoys, usually anchored or cabled to the ocean bottom, or deployed as arrays towed from a surface vessel. Archival sensors are affixed on bottom-moored buoys equipped with hydrophones to continuously record ocean sounds for long periods of time, often up to three months, before the sensors are temporarily recovered and their batteries refreshed. Some archiving sensors can be mounted of individual animals.

“Marine animals live their lives and communicate acoustically across different time and space scales and use sound for different reasons,” said Van Parijs. “We need to use the right tool in the right place for the right need. There is no ‘one size fits all’ when it comes to using technology in the ocean.”

Large whales move and communicate over great distances, while smaller whales and dolphins tend to communicate over smaller areas. Pinnipeds, the group of marine mammals that includes seals, walrus and sea lions, can breed on land, on ice or in the water, and move and communicate from small to medium distances. Human-produced sounds complicate the sensing problem by adding sounds to what can be a very noisy environment.

The use of passive acoustic monitoring is increasing as improved reliability and lower hardware and software costs provide researchers with a set of tools that can answer a broad range of scientific questions. This information can, in turn, be used in conservation management and mitigation efforts. While most of the new technologies have been applied in studies of whales and dolphins, the researchers say the sensors can also be used in studying pinnipeds, sirenians (manatees and dugongs) and fish.

Further Reading: Northeast Fisheries Science Center

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Labels: environment, technology, whale and dolphins