Bit by bit we circled the entire shore of Lough Hyne, surveying for key organisms in the intertidal and shallow subtidal. We surveyed the lough in sectors, following the historical sectors first designated by Louis Renouf, who is in large part responsible for initiating the long standing scientific interest and research in Lough Hyne. In utilizing the Renouf sectors, we can make direct comparisons between the observations of the past, as reported by Renouf (1920s), Rees (1930s), Ebling (1960s), and Kitching (1980s), and present. (And I must say that it is pretty incredible to be able to survey the exact same locations that I've read reports about from the early 20th century; it's like visiting a historical monument still in use today and thus the same but also ever changing, but underwater.)
Lough Hyne is changing. The North Basin shores, which were historically dominated by the purple urchin Paracentrotus lividus, are now covered in towers of ephemeral algae. The population of Paracentrotus collapsed in 2000 and since that time, several species of algae have increased in abundance and begun a northward migration within the lough. One of the questions we’ve begun to explore is what other organisms might be present that could fill the ecological gap left open by the absence of the urchin. In other words, what else might eat the algae?
This seemed like a pretty straightforward question at first, but it turns out to be more difficult. For the last several years, Dr. Cynthia Trowbridge and colleagues have been surveying the lough and documenting the presence of urchins. The results are dismal. More recently, I outplanted pieces of algae around the lough and documented grazing scars (indicators of some type of grazing organism). Now the tricky part is figuring out what animal caused the damage, particularly in areas where urchins have not been observed for some years.
Lough Hyne is changing. The North Basin shores, which were historically dominated by the purple urchin Paracentrotus lividus, are now covered in towers of ephemeral algae. The population of Paracentrotus collapsed in 2000 and since that time, several species of algae have increased in abundance and begun a northward migration within the lough. One of the questions we’ve begun to explore is what other organisms might be present that could fill the ecological gap left open by the absence of the urchin. In other words, what else might eat the algae?
This seemed like a pretty straightforward question at first, but it turns out to be more difficult. For the last several years, Dr. Cynthia Trowbridge and colleagues have been surveying the lough and documenting the presence of urchins. The results are dismal. More recently, I outplanted pieces of algae around the lough and documented grazing scars (indicators of some type of grazing organism). Now the tricky part is figuring out what animal caused the damage, particularly in areas where urchins have not been observed for some years.
To begin to unravel this mystery, I collected organisms that have either been observed on algae or are known to consume algae, at least as part of their diet. The goal is to begin to develop a reference of typical grazing scars induced by different organisms which can then be compared to the damage observed in the Lough. So far the most likely candidate remains the purple urchin, but the search continues.
One of the candidate organisms is the shore crab Carcinus maenas. These crabs are omnivorous. They have been reported to contain both animal and plant material within their guts, suggesting consumption of plant material. However, these crabs are non-picky eaters. It remains to be determined if these crabs are consuming live and healthy algae, or simple rotting pieces. And so we put out some crab pots, baited with fresh mackerel, to catch some Carcinus.
The first try resulted in prawns and gobies, neither of which are suspects in this mystery. The second try resulted in many shore crabs, but all of which were either missing claws or infected with a parasitic barnacle, Sacculina carcini. As fascinating as these parasites are, they are known to alter in some degree the behavior of their host crab, and thus made the crabs ineligible for use in feeding experiments. That’s two strikes.
One of the candidate organisms is the shore crab Carcinus maenas. These crabs are omnivorous. They have been reported to contain both animal and plant material within their guts, suggesting consumption of plant material. However, these crabs are non-picky eaters. It remains to be determined if these crabs are consuming live and healthy algae, or simple rotting pieces. And so we put out some crab pots, baited with fresh mackerel, to catch some Carcinus.
The first try resulted in prawns and gobies, neither of which are suspects in this mystery. The second try resulted in many shore crabs, but all of which were either missing claws or infected with a parasitic barnacle, Sacculina carcini. As fascinating as these parasites are, they are known to alter in some degree the behavior of their host crab, and thus made the crabs ineligible for use in feeding experiments. That’s two strikes.
We refreshed our pots with more bait, and deployed again. This time was far more successful. The first pot contained the swimming crab Liocarcinus arcuatus, which is another species of interest, so we considered it a win. As the second pot rose out of the water, I heard an exclamation of excitement. Expecting to see a bounty of the shore crab we were hunting, I was surprised instead by two large bullhuss, or large spotted dogfish Scyliorhinus stellaris! Our crab pots caught two sharks instead of crabs, last thing I would have guessed would be in the pots. But there they were, and the mackerel bait was not but a head and spine, everything else licked clean. We of course immediately released them and watched them swim away, back into the depths of the Lough.
And our third pot? Carcinus jackpot. But no sharks.
Sara Edquist
Sara Edquist