In early November, there were reports of seahorses washed ashore and caught in traps in southern Maine. These charming fish are quite rare in the Gulf of Maine, with only a few reports off the Scotian Shelf. Initially, I suspected a connection with hurricane Sandy, or perhaps a warm-core ring. Earlier this week, however, I heard reports of seahorse sightings throughout the summer in midcoast Maine.
In October, I was out sampling with a group of Bowdoin students. I had hoped to show them the wonders of copepods--an important lesson for all aspiring oceanographers. However, our zooplankton samples were mysteriously devoid of them. We even ran some 10-micron-filtered samples through a FlowCAM, and didn't see a single nauplius. Instead, net after net came to the surface with voluminous orb-shaped ctenophores.
This beroe sp. was almost as large as my fist. The ecosystem we observed, with its large ctenophores and inscrutable lack of copepods, was quite different from what I had expected. Recently, I have heard reports of these large ctenophores throughout Casco Bay all autumn.
The question remains as to how significant these anomalies are. Gelatinous species, like ctenophores, can bloom suddenly then vanish. They can also settle in for the long term and dramatically reshape the ecosystem, as Mnemiopsis leidyi famously did in the Black Sea. Some ecologists have even forecast a "jelly ocean" following the collapse of global fisheries. The basic idea is that gelatinous species out-compete fish for crustacean prey.
The "jelly-ocean" prediction is a debated one, as there are huge gaps in our knowledge of gelatinous species. They are undersampled, and there is much we don't know about them. Most models don't account for them, and they even thwart some the underlying assumptions in ocean ecosystem theory, such as the nice trophic size structure of marine ecosysems (that is, large eats small). For example, as you can see in the image below, ctenophores like beroe can be prey for tiny crustaceans. We are even still discovering new families in the Gulf of Maine (see Pages et al. 2006, Scientia Marina).
These changes often occur more quickly than we can understand or even sample them. Keep your ears peeled for other strange happenings, and unexpected visitors. And we encourage you to let us know what you happen upon. We'll need many eyes on the sea if we hope to solve this puzzle.
-Nick Record, signing off