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TREASURES OF THE SEA 20.4.–3.10.2021 THE BIOLOGICAL MUSEUM Photo: Mats Westerbom. Mats Photo: TREASURES OF THE SEA The underwater world of the appear together and form a de- Finnish sea areas is extremely tailed mosaic where the various diverse compared to many other habitats with different species coasts by the Baltic Sea. Much alternate. like there are various types of forests, meadows and marshes The Baltic Sea is home to an on land, there are also various unusual variety of species, since types of natural habitats and many marine species requiring a landscapes in the Baltic Sea. high salt content meet freshwa- The more diverse the seabed is, ter species there. Nowhere else the more organisms live there. do the freshwater polyp and the In turn, high species richness sea slug live on the stem of the contributes to the stability of the same plant, or the turbot and the ecosystem, including the ability whitefish get caught in the same to withstand sudden changes. net. In the Baltic Sea, species may form completely unique The underwater landscapes of relationships. the Baltic Sea may be classified by the quality of the seabed, Even though the Baltic Sea is for example. The Finnish coast in poor condition in places, the has a wide variety of sand, coast of Finland still has breath- gravel and mud beds, as well takingly beautiful places worth as reefs, meaning hard seabed protecting. In this exhibition, we that houses species adapted to will take a look at the most valu- these specific conditions. Often, able treasures of the Baltic Sea. the various types of seabed 3 Ditch grasses. Photo: Mats Westerbom, Metsähallitus Parks & Wildlife Finland. The under-water ditch-grass (Ruppia spp.) meadow is bathing in sun. Underwater meadows belong to the most diverse communities in the Baltic Sea. The meadows are composed of eelgrass as well as winding and branching stoneworts and tasselweeds. You can also find red al- gae tufts there as seen in the photo. Meadows provide shelter and feed for many species, for example different invertebrates and fish, especial- ly juvenile fish. Stonewort meadows can be found across the coastline, but ditch-grass meadows are not found north of the Kvarken. 4 5 MEADOWS OF THE SANDY SEAFLOOR The sand feels soft and inviting un- In addition to maintaining biodiver- der the feet. In reality, the sandy sea sity, the seagrass beds also bind bottom affected by the waves is a carbon dioxide efficiently from the very harsh habitat: the movement of seawater, which makes them even the water is constantly whirling the better carbon sinks than forests. sand and settling in is difficult. Once Despite all this, the diverse mead- the most resilient plants manage ows of the sandy bottoms are very to root in the sand, in no time at all vulnerable habitats which suffer par- the wavy seagrass meadows will ticularly from the effects of eutroph- also house a variety of animals from ication. The importance of these mussels to shrimp. On sheltered ar- landscapes has not been known eas, the vegetation may be extreme- for very long. Many of the seagrass ly diverse and provide shelter and meadows are located so close to food to many invertebrates. In turn, shore that you can admire them the diverse species attract aquatic by snorkelling. You do not always birds, which arrive to peck at food in have to travel to faraway places to the meadows swaying in the waves. explore the wonders of the sea. 4 5 Photo: Visa Hietalahti. 6 7 Straightnose pipefish. Photo: Pekka Lehtonen, Metsähallitus Parks & Wildlife Finland. The straightnose pipefish (Nerophis ophidion) is a master of camou- flage. This small and slender, greenish fish is related to seahorses. It can reach a length of max 30 centimeters. Straightnose pipefish has only one small dorsal fin which allows it to move slowly, twisting its entire body. Straightnose pipefish is found on the whole Finnish coastline up to Oulu. The spawning takes place in July. The female attaches the fertil- ised eggs to the male’s abdomen and the male is the one to care for the eggs until they hatch. 6 7 Common eelgrass. Photo: Mats Westerbom. The common eelgrass (Zostera marina) is the only fully aquatic seed plant in the Baltic Sea. Under favorable conditions it can form extensive underwater meadows on sandy bottoms. The root system of the eel- grass binds the mobile substrate in place, which creates a habitat for many species that wouldn’t survive on bare sand. Seagrass meadows maintain the biodiversity of the sea in a considerable way, which makes them one of the key underwater nature habitats of the Baltic Sea. The distribution of common eelgrass in the Baltic Sea extends from the southern Baltic Sea to the central Gulf of Finland and to the northern Bothnian Sea. In the Baltic Sea the common eelgrass reproduces mainly vegetatively and forms meadows of cloned eelgrass. Eelgrass requires light to grow and therefore it is sensitive to changes in the sea- bottom and the eutrophication of the seas. The common eelgrass has been classified as endangered, both as a species and as a habitat. 8 9 Common shrimp. Photo: Olli Mustonen. It is difficult to spot a common shrimp (Crangon crangon) lying still on the sand. Usually only a puff of sand is seen when this shy animal disappears. When sensing danger, the shrimp quickly bounces back or digs itself into the sand. This escape to safety is finalized by using the antennae to gather grains of sand to cover the back so thoroughly, that only the prominent eyes ogle the presumed enemy. 8 9 Photo: Mats Westerbom, Photo: Visa Hietalahti. Metsähallitus Parks & Wildlife Finland. Photo: Visa Hietalahti. Photo: Mats Westerbom. 10 11 SECRET LIVES OF COMMON JELLYFISH The sunlight filtered by the water Northern Quark. Large numbers cuts through the underwater of jellyfish can be found particu- landscape as you notice a trans- larly in late summer, when they lucent figure floating above it all. gather in the coastal waters. It The cnidarian common jellyfish is suspected that these mass (Aurelia aurita) is an enchanting occurrences are related to sight. It drifts in the waves and reproduction, as the jellyfish re- currents, but it is not simply a produce sexually at these times, passive floater. Using its primitive at least on the southwestern senses, the jellyfish can identi- coast. The fertilised eggs first fy directions and the chemical develop inside the female, after qualities of the environment. By which they are released into the contracting its bell, it can dodge water as larvae. When a larva rocks and move away from attaches itself to a solid surface, harmful areas. The organs for it develops into a polyp, which balance, sight and smell are in will start budding tiny jellyfish out the small notches on the edge of of itself. When they are released the bell. into the water, the little jellyfish go with the flow and grow into The common jellyfish is found in adult common jellyfish during the the entire Baltic Sea up to the summer. Photo: Mats Westerbom. 10 11 Bladder wrack, clawed fork weed. Photo: Mats Westerblom,Metsähallitus Parks & Wildlife Finland. The reddish-colored clawed fork weed (Furcellaria lumbricalis) grows among bladder wrack (Fucus vesiculosus). This species appears as growths of branching twigs and takes its Finnish name “fork algae” from its fork-like branching. Individuals growing in shallow areas are usually more branched, compared to the ones growing deeper. Furcel- laria lumbricalis is particularly common at the depth between 4 to 10 meters, where it can often be the dominant species. 12 13 UNDERWATER FORESTS OF ROCKY SHORES At first, a rocky bottom does by the ice. A bit deeper, the not sound like a particularly lush scene is taken over by perennial habitat, but the rocky slopes algae: among the large growths rising from the depths of the sea of bladder wrack and the thick- towards the surface can surprise ets of multicoloured filamentous you with their variety of species algae, there is an immensely and colours. Underwater rocks diverse range of organisms and the seabed patterned by seeking shelter and food, and large boulders are full of life, par- also hunting each other. ticularly in the clear waters of the outer archipelago. On such hard The deep waters, where there is seabed, the organisms live in insufficient light for other spe- zones depending on their need cies, are the realm for various for light, for example. red algae. Out of the reach of sunlight, in the deepest and Closest to the surface, the darkest corners of the rocky movement of the waves and the shores, the surfaces are cov- ice makes life challenging. This ered by blue mussel and polyps. is the best environment for the When they settle in the deeper annual filamentous algae, which waters, they do not need to start growing all over again every compete with algae that require spring on the rocks smoothed light. 12 13 Blue mussel, two-spotted goby. Photo: Olli Mustonen. The blue mussel (Mytilus trossulus) requires a minimum of four per mille salinity. Thus, it occurs throughout the Baltic Sea except for the Bothnian Sea, where the salinity is too low for them. Blue mussels live on the hard bottoms, attached to a rock or to each other with their durable filaments. Their highest densities occur below the zone lit by sunlight, where there is less competition for suitable attachment surfac- es. In the southwestern coast of Finland there can live more than 200 000 blue mussel individuals on one square meter, which is probably one sort of a world record for this species.

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