Blue mussels not yet the bellwether of NE coastal environment

Marcy Cockrell installs cages to protect mussels from predators. In Maine, mussels inside cages faired as well as mussels in the wild. In Long Island Sound and Narragansett Bay it was a different story. Credit: Brown University

Ecologists sometimes look to mussel species, a well-studied and foundational genus in estuaries, as model organisms for assessing the condition of coastal habitats, which are crucial for people and well as the broader environment.

But a new study in the journal Ecosphere suggests that the seemingly simple blue mussel, when studied on regional scale from Maine to Connecticut, harbors at least three specific mysteries that must be solved if the mollusks are to serve as the "canaries in the coal mine" of the Northeast coast.

"Mussels could indeed be a good sentinel species for rocky shores, but what our work suggests is that we need to know a lot more about how they behave in these different estuarine settings to use them as an indicator of ecosystem health," said conservation scientist and study senior author Heather Leslie, the Peggy and Henry D. Sharpe Assistant Professor of Environmental Studies.

For the study, Leslie and former students Marcy Cockrell and Joanna Bernhardt monitored and experimented with mussels at 18 sites in the Casco Bay of Maine, the Narragansett Bay of Rhode Island, and the Long Island Sound of Connecticut and New York in 2010 and 2011 (a region spanning about 600 kilometers of coastline). They measured the abundance of mussels both at adult and larval stages, studied the populations of neighboring rocky shore animals and marine algae, and tracked data on ecosystem factors such as water salinity, temperature, nutrients, oxygen, and local human population density. In the experiments, the team protected some mussels with cages to expose the effect that birds, crabs and other predators have on their numbers.

In the end, the research uncovered three intriguing mysteries of mussel life across the region, particularly in Casco Bay:

Generation gaps: Adults were populous but "recruitment" of young mussels from surrounding waters was low in Long Island Sound and Narragansett Bay. The opposite was true in Casco Bay. There, juvenile recruitment was high but adult populations were low. Few Maine predators: The cage experiments showed a significant role for mussel predators in Long Island Sound and Narragansett Bay, but not in Casco Bay. There, unprotected mussels fared about as well as the protected ones. Inner vs. outer: In each estuary, Leslie's team made measurements at sites nestled well within the bay, as well as at sites closer to the open ocean. Prior research suggested that higher levels of food within the bay would promote growth and abundance for the filter-feeding mussels (due to higher levels of nutrients and phytoplankton at the inner estuary sites). The study results were notably mixed across the whole region, however, providing little support for that hypothesis.

Explanations await further research. Genetic studies could determine, for example, whether the young mussels that are so abundant in Casco Bay may be floating up from the more southerly shores. If so, that suggests that mussel population dynamics can only be understood on regional (or multi-estuary) geographic scale.

Meanwhile, understanding why predator activity seems low in Casco Bay might require learning more about the local predator populations there. The findings could shed light on whether the ecosystem is in balance or other factors are at play.

"We did this because we want to understand how these systems work," Leslie said. "Given their accessibility and how well-studied they have been in other locations, rocky shores are logical sentinel ecosystems. They provide an opportunity to investigate how climate change and other more local-scale human activities are affecting New England's coast."

It may take more work to crack open the mussels' mysteries, but the stakes are high enough to make it worthwhile, Leslie said.

Source: Brown University

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You can hear the coral reefs dying, experts say

A lionfish in an Indonesian reef. Credit: Image courtesy of University of Essex

You can hear the sound of former bustling coral reefs dying due to the impact of human activity, according to new research from the Universities of Essex and Exeter.

Coral reefs are amongst the noisiest environments on our planet and healthy reefs can be heard using underwater microphones from kilometres away.

However, scientists have found that coral reefs impacted by human activity, such as overfishing, are much quieter than protected reefs, which can have a big impact on the fish and invertebrates which rely on the reefs for survival.

Led by Dr Julius Piercy, from the University of Essex, the study, which also involved the University of Derby, involved taking acoustic recordings of coral reefs with different levels of protection around islands in the Philippines. The research found that the noise produced by the few remaining resident fish and crustaceans on unprotected reefs was only one third of the sound produced at bustling, healthy reef communities

This is particularly important to the larval stages of reef fish and invertebrates, which spend the first few days of their life away from reefs and use sound as an orientation cue to find their way back. With less sound being produced at impacted reefs, the distance over which larvae can detect habitat is ten times less, impacting on the replenishment of future generations needed to build up and maintain healthy population levels.

"In an environment where underwater noise plays such an important role in the population dynamics of coral reefs, it is alarming to find such a large effect of human impact on the natural acoustic environment," explained Dr Piercy. "This puts reef sound in the spotlight for the people who manage coral reef ecosystems on two counts. Firstly, that they might need to consider reef sound as an integral part of the design of marine protected area networks to ensure that there is sufficient recruitment of larvae within and between reserves and neighbouring reefs. Secondly, this study shows sound can be useful in monitoring the health of coral reefs."

With growing evidence demonstrating the direct impacts of human-made noise on aquatic life, these findings highlight additional indirect human impacts -- such as overfishing and landscape development -- on natural underwater sounds.

Dr Steve Simpson, from Biosciences at the University of Exeter, added: "Taking sound recordings is a cheap, fast and objective way to get a broad idea of whether a reef is in a good condition or not. While it cannot replace detailed visual surveys conducted by snorkelers or divers, it gives a good account of the cryptic and nocturnal species missed in visual census, and quickly provides a general picture of the state of coral reefs without requiring time-consuming surveys and extensive training."

The researchers also found that reef sounds can be detected further away than predicted, increasing previous estimates of the likely detection zone for recruiting larvae and increasing the potential importance of reef sound in attracting new fish and crustaceans to coral reefs.

The study highlights the need to further characterise reef soundscapes and identify acoustic cues that larvae tune into when seeking a suitable home. Dr Simpson said: "We still know very little about what sounds these animals are listening to and it is likely to be very different between species. Combined with recent findings that fish dislike the smell of impacted reefs (another homing cue used by the larvae), there is a real need to understand how human impacts can indirectly affect the success of future generations of reef organisms."

Source: University of Essex

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