Pico acuario recuperado (septiembre 26)

A LITTLE MEDITERRANEAN

ECOSYSTEM

(Field notes on an 8-litre pico aquarium)

Nueva roca viva, que ha venido plagada de habitantes, algunos diminutos y otro no tanto. Gracias a ChatGPT he identificado gran parte de la increíble vida que aloja un mini sistema mediterráneo de tan solo 8 litros de agua.

1. Aquarium profile

- The aquarium is a small, approximately 8-litre marine pico tank containing natural Mediterranean seawater collected from the same general location as the original rock. It has a small pump and filter, a covered top, and is kept in a room reported to range between 20 and 25 °C.

- Volume: Approximately 8 litres. Water: Natural Mediterranean seawater.

- Equipment: Small pump and filter. Cover covered.

- Room temperature: 20–25 °C

- Light: led, 10w

Important context: an 8-litre aquarium has very little water volume, so temperature, salinity, oxygen and waste levels can change quickly. A covered tank should not be airtight; maintain surface movement and ventilation. Check ammonia and nitrite regularly, and avoid adding food or supplements unless there is a clear need and water quality is being monitored.

2. Organisms observed

The list below separates what is visible in the photographs from the confidence of the proposed identification. No species-level identification should be treated as confirmed at this stage.

- Red rounded colony on rock Colonial ascidian (Class Ascidiacea /Tunicata). Possible *Synoicum* or another colonial tunicate. The red lobes and dark openings are suggestive, but species cannot be confirmed from the images.

- Cream fan with a hard tube: Tube-building polychaete; likely a serpulid worm (Family Serpulidae). A feathery crown that retracts into a hard calcareous tube fits a serpulid. The exact genus/species is unknown.

- Tiny white star-like polyps on glass. Hydroids (Class Hydrozoa) are a possibility. The tentacles were later observed moving. This supports a living polyp, but a close macro view is needed for a more

precise identification.

- Orange-yellow cluster in a shaded crevice. Possible colonial cnidarian A zoanthid such as *Parazoanthus* was suggested, but the photograph is too small/soft to confirm. Do not touch it.

- Tiny white spiral structures on glass: Spirorbid tube worms (Family Spirorbidae) are very likely. Small attached calcareous spirals are characteristic of spirorbids. They are tiny relatives of larger tube worms.

- Small crabs: Hermit crabs (infraorder Anomura; family unknown)

- Snails

- Dark burgundy, finely branched tufts. Red algae; *Polysiphonia* is a possibility. The tufted branching appearance is compatible with filamentous red algae, but genus-level confirmation would require a sharper close-up.

- Purple-pink hard patch on glass. Possible crustose coralline alga. The chalky, stone-like, firmly attached crust is compatible with coralline algae. An encrusting bryozoan or other calcified growth remains possible.

- Short, dense, dark brown tufts. Unidentified filamentous growth. Could be a compact algal turf, but the image does not establish that it is algae rather than a small colonial animal.

3. Brief natural-history notes

- Colonial ascidians. Ascidians are tunicates: marine animals that filter water through specialised openings. In colonial species, many small zooids are embedded in a shared tissue. The red colony's openings and clustered lobes make this a reasonable working identification, but the species name previously suggested should remain unconfirmed.

- Tube worms. Serpulid worms build hard calcareous tubes attached to rock. Their feathery crown is used for feeding and gas exchange, and is withdrawn rapidly when disturbed. Spirorbid worms are much smaller relatives that build tight spiral tubes.

- Hydroids and possible zoanthids. Hydroids are colonial or solitary cnidarians with small tentacled polyps. The tiny white stars on the glass may be hydroids.

- The orange-yellow cluster could also be a cnidarian, but it is not possible to tell whether it is a zoanthid from the available photograph.

- Algae and encrusting growth. The burgundy tufts may be filamentous red algae, possibly *Polysiphonia*.

- The hard purple-pink crust may be coralline red algae, which deposit calcium carbonate, but this remains tentative. The short brown tufts are not yet identified.

Nombre en español

- Colonial ascidian (Ascidiacea) Ascidia colonial; también se dice tunicado colonial o sinascidia (según el

grupo).

- Serpulid tube worm (Serpulidae) Gusano tubícola; gusano plumero o gusano de tubo calcáreo.

- Hydroids (Hydrozoa) Hidrozoos; pólipos hidroideos.

- Possible zoanthid / colonial cnidarian Zoántido; anémona incrustante (nombre descriptivo, no confirmado).

- Spirorbid tube worms (Spirorbidae) Gusanos espirórbidos; pequeños gusanos tubícolas espirales.

- Filamentous red alga; possible Polysiphonia Alga roja filamentosa; posible *Polysiphonia*.

- Possible crustose coralline alga. Alga coralina incrustante; alga roja calcárea.

- Unidentified brown tuft. Mata de filamentos pardos; posible alga parda filamentosa.