5. IN BETWEEN THE ISLANDS
Most of the seashores of Finland are characterized by an exceptionally ragged coastline and the dominance of the coastal zone, in comparison with the open sea. From the outskirts of the Archipelago sea, where the swell of the northern Baltic proper can be felt, to the innermost bays of the mainland the conditions vary from those almost resembling the oceans to those being more akin to the inland lakes. This means variation in the distribution of living conditions in general, of loose bottom materials and both plant and animal species.
Although there are no tides, currents occur locally, like here at the narrow end of a funnel-shaped area of water between two long islands. The bootlace weeds wave in the current which, typically, changes direction every ten minutes. On the surface waves form, when the current is strong, and the rush of the water is clearly audible.
Even in the relatively protected waters of the Archipelago sea the motion of the sea, its currents and waves, lifts and carries materials into different depths according to the openness of the spot and fineness of the particles. Loose filamentous algae are a problem for the wrack and vascular plants alike at the more protected locations. Into the area between the two islands mentioned above strong currents bring organic matter in such amounts as to make the bottom an anaerobic dumping place.
The appearance of the protected bays varies from one place to another. The general principle is, as in the Baltic as a whole, that species from fresh and saltwater origins meet. In the case of plants it means that the common reed, fennel pondweed, perfoliate pondweed, bladder wrack and the alga Monostroma can grow even mixed.
The sea coasts of Finland are still recovering from the weight of the continental ice, retrieved less than 10 000 years ago. The earth’s crust is rising at a rate of 0,5 cm a year, at some parts of the coast even faster. At some spots this rise creates lagoons (called flads) connected with the rest of the sea through one or two narrow openings. In the lagoon a special kind of vegetation develops with fresh water species clearly dominating, as exemplified here by hornworts, water milfoils and freshwater algae Chara tomentosa.
Freshwater plants in the Baltic can be meeting places for animals and plants from both of the water worlds. Drifting filamentous algae and hydras on a fennel pondweed; marine moss animal, at least two species of bivalves and isopods on a milfoil; moss animal skeleton on remnants of a perfoliate pondweed leaf.
Of these four gastropods the first two, a pulmonate of genus Lymnaea and the common Bithynia, are from fresh water and the other two, laver spire shell and Jenkins’ spire snail, primarily from saltwater environment.
The colonial hydrozoan Cordylophora caspia is endemic to the Pontocaspian region, or the Black and Caspian seas, meaning that it is from brackish water. It’s most probably traveled to the Baltic on the hull of a ship.
Embletonia pallida, meet Pelmatohydra ologactis! A poignant example of the special nature of the Baltic animal life: the nudibranch comes from the oceans where its more colorful relatives feed mostly on the coral polyps, while the hydra is a cnidarian, like the coral polyps, but from fresh water.
Two occasional creepers on the soft bottoms anywhere but in the protected waters especially: a sedge larva and a mysid shrimp Neomysis integer. You could easily see the larvae climbing on vegetation, too, and the mysid is very conspicuous when moving in immense shoals in the vicinity of the shoreline.
Definitely one of the typical creepers of soft bottoms but also a burrower, Saduria entomon, a predator feeding on smaller benthic animals or animal rests. These two couples are engaged in what seems like some kind of mating behavior, although it could also be males fighting with each other. From the irregular style of swimming of the third you can see that it’s an activity that it doesn’t do often.
The mud shrimps Corophium volutator will have to do as the representative of all the small burrowing crustaceans that are too evasive to be seen without special arrangements. Of course, the only encounter of a lifetime, it seems, occurred when I was just running out of film (remember the time when it was still being used).
The lagoon cockle Cerastoderma glaucum lives its adult life mostly burrowed but it can move around actively at times. It has two siphons of about equal size, while one of the siphons of the Baltic macoma is noticeably longer. Often the siphon of the macoma is the only thing seen of it, when it searches food around it or discharges its feces.
Broad-nosed and straight-nosed pipefishes come from the vegetation of the oceans and that’s where they are usually found in the Baltic, too. Viviparous blenny is more of a generalist and especially the juveniles frequent just about any type of bottom in shallow water.
The ten-spine stickleback, one of the freshwater fishes of the archipelago, lives true to its stickleback nature and the male builds a nest out of vegetation.
Of the three freshwater fishes here the perch and the ruffe usually move around more widely during the day and come close to the shore to rest for the night. The three-spined stickleback has an even wider pattern of movements: though found generally in great numbers close to shores in summer, it moves to the deeper parts of the open sea for the winter.
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