Underwater naturalists, in a holiday setting, are often perceived as a bit weird. “Look! Why is this person staring at the algae for so long?” or “Hey! Seen this? Somebody is taking pictures in the mud with a huge camera all the time!” It’s a bit the same with the photos these people take “from the mud.” In scientific books, the underwater photographers are often mentioned in small fontsize on the last pages, where they are difficult to find – they run kind of a poor second.

In this book, it’s different. Here, the naturalists and photographers speak up and show why they love nature watching so much and why they sometimes even direct their cameras into the not so attractive corners of the sea ‒ to go after the secret stars, the hidden life invisible to the unexperienced eye – marine micro­worlds. By doing so, they follow a long tradition of watching marine life in the wild that dates back to the earliest diving biologists, e. g. Filippo Cavolini in the 18^th century and Anton Dohrn in the 19^th. First, this book is meant to celebrate the little masterpieces of nature found in the Adriatic, their magnificent diversity and their historico-cultural importance, be it as sex symbols, money or food. Second, we want you, dear reader, to fall in love with these miniature beauties of the seafloor. Consider this content advertisement for them, since they need protection. The man-made threats of life in the ocean are massive, and therefore this book is meant as a contribution to its defence, including not only the macroworlds, but also the microworlds of marine life.

Into the black 6
Into the blue 7
Some basics about the microworlds of the sea floor 8
How this book was created 11
The sources: benthic algae and plankton 12
Porifera – sponges 16
Ctenophora – comb jelly fish 32
Cnidaria ‒ polyps, sea anemones, corals and jellyfish 34
Plathelminthes – turbellarians or flatworms 62
Mollusca – snails, slugs, cuttlefish and clams 70
Polychaeta – marine ringed worms 138
Pycnogonida ‒ sea spiders 162
Crustacea – mantis shrimps, decapods, mysids (opossum shrimps), isopods (marine woodlice) and others 164
Echinodermata – sea stars, sea urchins, sea cucumbers, serpent stars and feather stars 226
Bryozoa – moss animals 250
Tunicata – sea squirts and synascidians 258
Teleostei – fish 278
Elasmobranchii ‒ sharks and rays 312
Epilogue, dedication and acknowledgements 316
The photographers’ suggestions for further reading 317
Species list 318
The underwater photographers 320

The reader of this introduction might wonder why the present book, meant to celebrate the beauty of marine life in the Northern Adriatic, its diversity, and a multitude of life habits, begins with a tantrum. The answer is simple: It is necessary. Human intervention in nature is resulting in dramatic biodiversity and habitat loss in vast swaths of the ocean. In these zones, marine life as we know it is currently passing away. Man’s global and regional activities have pushed whole ecosystems out of equilibrium, like coral reefs, seagrass meadows, and algal belts. Nature can compensate for slow, natural changes but not the fast, excessive, detrimental impact of the technical civilization established by man – a voracious mass organism, the first species ever that has the power to destroy life on earth since cyanobacteria changed the atmosphere to an oxidizing one about 2.5 billion years ago. For nature, for biodiversity, the sum of human activities from heating the planet to using the ocean as Cloaca maxima to anchoring in a seagrass bed is equivalent to a disastrous meteorite impact or a supervolcano eruption. It leads to a massive die-off of species and communities. When a seagrass bed or an algal forest dies, hundreds of species living in them also will go. And they are wonderful, all of them. How sad if they would go extinct! We, the people who made this book, think these organisms need defense, they need advertisement, they need humans to change into guardians of nature, not its destroyer. If not, mankind in the future might be living in a virtual environment on a dystopic planet from which too many of the wonders of life have been eradicated. This book has been made as a contribution to preventing this nightmare from becoming reality. Maybe we can change our minds from ignorance or pure utilitarianism to respect for the organisms’ independent right to exist. Perhaps we change our attitudes from apathy to interest as distant as we can in our own little world, even if it is far away from the sea.

It may be sad to say, but marine life is threatened globally and regionally. Some of the contributors to this book have been studying the northern Adriatic for decades and have noticed some large or small incidents happening, like algal pests and anoxia calamities, strongly inflicting life in the sea. But there were also signs of improvement in the years around the Millennium. For example, fresh shoots of seagrass appeared at a couple of localities and kept on growing for some years. However, some ten years ago, we noted that a new wave of deterioration had begun. We have seen seagrass beds and algal forests dying at large parts of the coast, corals have bleached, plankton cycles have thoroughly changed, species have disappeared and the sea became murky at times of the year when it was supposed to be clear. Man strangles the ocean by all means possible, e. g., overfishing, eutrophication, pollution, usage of poisons, sewage discharge, marine traffic, mass tourism, causing turbidity of the water by construction sites, and increasing water temperatures due to climate change. Marine scientists agree that the sum of all the man-made factors is the final straw resulting in the observed die-offs.

Dr Bastian Brenzinger is a postdoc at Bavarian State collection of Zoology (SNSB-ZSM). His main research topic are interstitial gastropods in the sediment and related micromolluscs.

Prof. Dr Martin Heß works and teaches at the systematic zoology workgroup, University of Munich (LMU). His reserach interests are animal vision and imaging, his taxonomic interest focuses on marine groups. He gives courses in marine Biology in Rovinj, Sylt, Roscoff, Banjuls, Calvi and Giglio since 1991.

Dr Tobias Lehmann is a postdoc at the MPI for Neurobiology in Munich where he does research on sensory systems of invertebrates. In addition he is a pycnogonid taxonomist and long-time observer of nature in the Adriatic.

M. Sc. Tihomir Makovec is head of the diving unit at the Marine Biological Station in Piran (NIB). He is doing field work on the biodiversity of the Adriatic, his taxonomic interest focuses on marine invertebrates and fishes.

Dr Borut Mavrič is a scientific associate at the Marine Biological Station in Piran (NIB). His research focus is the biodiversity of the Adriatic, his main taxonomic interest are Decapoda and Opisthobranchia. He gives courses in marine Biology in Piran since 2011.

Prof. Dr Roland Melzer is curator for Arthropoda varia at the Bavarian State collection of Zoology (SNSB-ZSM) and teaches at the systematic zoology workgroup, University of Munich (LMU). His research focus is morphology, evolution, and speciation, his taxonomic interest focuses on Pycnogonida and Decapoda. He gives courses in marine Biology in Rovinj and Piran since 1992.

Dr Roland Meyer is an alumni of the Arthropoda varia workgroup at the Bavarian State collection of Zoology (SNSB-ZSM). He has been a dedicated marine naturalist for many years. His main research and taxonomic interest are Decapoda.

M. Sc. Manuel Staggl is a PhD student at the University of Vienna (univie). His main research and taxonomic interest focuses on Chondrichthyes.