"Algunos animales viven en la profundidad del mar."
Translation:Some animals live in the depths of the sea.
Being wordy or overly literary does not make something incorrect. I think you should bear in mind, the purpose of this site is to teach you how to translate text. So if it sounds like a text, not speech, that's not a problem. Translating it incorrectly, "deep in the sea" or "in the deep sea" is a problem. IMHO.
Actually, the observation that "the purpose of this site is to teach you how to translate text" is not an argument against "in the deep sea" in favor of "in the depths of the sea"--if in English the first one both (1) captures the meaning of "en la profundidad del mar," and (2) does so in a more colloquial way. After all, you wouldn't say that "Tengo hambre" should be translated as "I have hunger" instead of "I"m hungry"--even though the former is structurally closer to the source text.
There's something to both points of view. However, I believe the major problem with assuming anything that "captures the meaning" (especially if it's colloquial?) allows for a nearly infinite variety of translations. No one in their right mind would attempt to program around that possibility. So, given the practical limits of CPU processing power, Internet bandwidth, and programmer resources, it makes no sense to assume you can enter any phrase you want that effectively means the same thing in a given context.
Your example of "tengo hambre" is interesting because it provides an example of an idiomatic difference between English and Spanish rather than a substitution of a (common) colloquialism for a more literal translation. English speakers just don't say, "I have hunger," and Spanish speakers just don't say, "Estoy hambriento." That difference between the languages is not the same as simply rephrasing something to words you prefer. The Spanish phrase "Tengo hambre" means the same thing as the English phrase "I'm hungry." That would be the translation without any other context. That shouldn't mean Duo must allow "tengo hambre" to be translated as "I'm starving" or "my stomach feels so empty that I should get something to eat," etc.
As someone else pointed out, changing the phrase in these ways actually changes the meaning. Just because you don't like a particular phrasing doesn't mean you should substitute something else. It's even more problematic when your substitution alters the meaning of the original.
While "deep in the sea" comes close to the original, "in the deep sea" does not. The original phrase "depths of the sea" is quite specific about where these animals live (i.e., close to the bottom). The other two phrases lack that absolute sense of deep. Animals can live at the surface of the deep sea and still live "in the deep sea." Likewise, animals can live "deep in the sea" without reaching the depths, the deepest part of the sea.
If you really, really don't want to say "the depths," you should at least speak of the deepest reaches of the sea. Simply saying "deep" is not sufficient. That said, I doubt Duo would accept, "Some animals live in the deepest parts of the sea."
Since you have del (de el) profundidad in the Spanish phrase does indicate that 'of the' might figure somewhere in the answer. However that said, if Duo had more closely followed the more common way of indicating 'the depths of the sea/the bottom of the sea' by pluralising 'profundidad' perhaps we might have avoided this confusion. It difficult to understand why Duo wouldn't do that!
Algunos animales viven en las profundidades del mar
Good points. I wonder if using the singular is common enough in Spanish that the English use of a plural is what's unusual. I've seen it both ways in Spanish. So, I don't know what is most common.
In the end, I'm not sure that will overcome the confusion. I believe some people just don't want to say "depths of the sea" and think that they can use "deep sea" instead. The real confusion is among those who don't seem to grasp the differences between these English phrases.
I wrote "in the depth of the sea" and it was not accepted. I reported it as an error; however, I concede that the plural form is more prevalent in English literature. Still, if the plural is used among native Spanish speakers, then it should be used here. Generally we try to translate as literally as possible within the bounds of what sounds normal to the native speaker.
Can someone please explain me these two cases: La observación tiene un límite - if translated as The observation has a limit it is marked wrong saying THE shouldn't be there but here: "Algunos animales viven en la profundidad del mar." - in the depths of THE sea. If I omit THE the sentence is wrong