Learn Hardcore Indonesian: Pemandu menjelaskan bahwa terumbu karang adalah rumah bagi ikan kecil dan parasit laut. - The guide explains that coral reefs are home to small fish and sea parasites.

In many contexts, especially in tourism, pemandu is short for pemandu wisata = tour guide.
More generally, pemandu can be:
- pemandu acara – host / MC
- pemandu sorak – cheerleader
- pemandu lagu – karaoke operator

In your sentence, with coral reefs and fish, pemandu naturally means a tour guide (probably a snorkeling or diving guide), even though the word wisata is not written.

How is menjelaskan formed, and what is its basic meaning?

The verb menjelaskan means “to explain”.

It comes from the base adjective jelas = clear.

Morphology:

jelas – clear
menjelaskan – to make something clear → to explain
penjelasan – an explanation

So:

Pemandu menjelaskan... = The guide explains / explained...

The meN-...-kan pattern is very common for causative verbs:

besar (big) → membesarkan (to enlarge, to raise)
jelas (clear) → menjelaskan (to clarify, to explain)

What is the function of bahwa here? Could we just drop it?

Bahwa introduces a “that-clause” (reported content), like “that” in English:

Pemandu menjelaskan bahwa...
= The guide explained that...

Yes, in everyday Indonesian you can usually drop bahwa:

Pemandu menjelaskan terumbu karang adalah rumah bagi ikan kecil dan parasit laut.

This is still natural and common in speech.

Nuance:

bahwa is more formal / explicit, common in writing, news, speeches.
Without bahwa, it sounds slightly more casual but still correct.

Don’t confuse bahwa with kalau:

kalau literally means if/when, but in very informal speech some people use kalau where standard Indonesian would use bahwa, e.g.
Dia bilang kalau dia sakit.
This is common, but bahwa is the more formal and “textbook” choice for reported statements.

Why is it terumbu karang and not karang terumbu?

In Indonesian, when you have two nouns together, the head noun usually comes first, and the modifier comes after.

terumbu karang
- terumbu = reef
- karang = coral
  → literally “reef (of) coral” → coral reef

So:

terumbu is the main thing (reef),
karang explains what kind of reef (coral).

You would not say karang terumbu for “coral reef”; that sounds backwards and unnatural.

Other examples:

rumah sakit – hospital (literally “sick house”)
kaca mata / kacamata – glasses (literally “eye glass”)
minyak goreng – cooking oil (literally “frying oil”)

When do we need adalah? Could we omit it in this sentence?

Adalah is a kind of copula used mainly in formal Indonesian when:

the subject is a noun phrase, and
the predicate is also a noun phrase (or sometimes a pronoun).

In your sentence:

terumbu karang = coral reefs (noun phrase)
rumah bagi ikan kecil dan parasit laut = a home for small fish and sea parasites (noun phrase)

So formally:

terumbu karang adalah rumah... = coral reefs are (a) home...

In spoken or less formal Indonesian, adalah is often dropped:

terumbu karang rumah bagi ikan kecil dan parasit laut.

This is quite natural in speech. Using adalah makes it sound more bookish / formal / explanatory. In your sentence, including adalah is perfectly correct, just a bit on the formal side.

Why is it rumah bagi instead of rumah untuk? What’s the difference between bagi and untuk?

Both bagi and untuk can often be translated as “for”, but they differ in tone:

bagi:
- more formal / written
- often highlights the recipient or beneficiary
- common in explanations, official language, academic texts
untuk:
- more neutral / everyday
- very common in speech

In this sentence:

rumah bagi ikan kecil dan parasit laut
= a home for small fish and sea parasites (slightly formal tone)

You could also say:

rumah untuk ikan kecil dan parasit laut
This is still correct and sounds a bit more neutral.

In many cases they are interchangeable, but bagi is avoided in very casual speech where untuk feels more natural.

Why isn’t there any plural marking like ikan-ikan kecil? Does ikan kecil mean one fish or many fish?

Indonesian usually does not mark plural the way English does. Context tells you whether it is singular or plural.

ikan kecil can mean:
- a small fish
- small fish / small fishes (in general)

If you really want to emphasize plural, you can use reduplication:

ikan-ikan kecil = small fish (clearly plural, many small fish)

In your sentence, since we’re talking about coral reefs as habitats, it is obviously plural in meaning:

rumah bagi ikan kecil dan parasit laut
= a home for small fish and marine parasites (many of them).

So ikan kecil here is understood as “small fish (in general / many)”, even without reduplication.

Why is it ikan kecil, not kecil ikan? Where do adjectives go?

In Indonesian, adjectives normally come after the noun they describe.

Pattern:

noun + adjective

So:

ikan kecil = small fish
orang tua = old person / parent
baju merah = red shirt

Putting the adjective before the noun, like kecil ikan, is not standard. It would sound wrong unless you are doing poetry or deliberately breaking the rules for style.

Your sentence follows the basic pattern:

ikan kecil – small fish
parasit laut – sea parasites (here laut functions like a noun modifier: “of the sea”)

What exactly does parasit laut mean? Is it “sea parasite” or “marine parasite”?

Parasit laut literally means “sea parasite”:

parasit = parasite
laut = sea

Together, parasit laut can be translated naturally as:

sea parasites
marine parasites

Both are acceptable in English. The structure is just noun + noun:

main noun: parasit
modifier: laut (of the sea)

If you want to emphasize that there are many parasites, you can say:

parasit-parasit laut – sea parasites (clearly plural) But as with ikan, plurality is usually left to context.

Could the sentence be Pemandu menjelaskan terumbu karang adalah rumah bagi ikan kecil dan parasit laut without bahwa? Is that still correct?

Yes, that version is grammatically correct and common, especially in speech:

Pemandu menjelaskan terumbu karang adalah rumah bagi ikan kecil dan parasit laut.

Here, the clause “terumbu karang adalah rumah bagi ikan kecil dan parasit laut” functions as the object of menjelaskan, even without bahwa.

Differences:

With bahwa – more formal, more explicit:
- Pemandu menjelaskan bahwa terumbu karang adalah rumah...
Without bahwa – more natural in spoken Indonesian:
- Pemandu menjelaskan terumbu karang adalah rumah...

How do we show past tense here? The English translation probably uses “explained”, but there is no tense marker in Indonesian.

Indonesian verbs usually do not change form for tense. Menjelaskan can mean:

explains
explained
is explaining depending on context.

To show time more clearly, Indonesians typically add time expressions:

Pemandu tadi menjelaskan bahwa...
Earlier the guide explained that...
Kemarin pemandu menjelaskan bahwa...
Yesterday the guide explained that...
Sekarang pemandu menjelaskan bahwa...
Now the guide is explaining that...

So in your sentence, menjelaskan can be understood as present or past; the English translation chooses “explained” based on context, not on verb form.

How would I say “The guide explained that the coral reef is a home for small fish and sea parasites”? There’s no “the” or “a” in Indonesian.

Indonesian doesn’t have articles like “a / an / the”. The noun phrase:

terumbu karang
can mean:
a coral reef
the coral reef
coral reefs (in general)

The same Indonesian sentence can be translated in several natural ways in English:

The guide explained that coral reefs are homes for small fish and sea parasites.
The guide explained that the coral reef is a home for small fish and sea parasites.
The guide explained that a coral reef is a home for small fish and sea parasites.

To make it definite in Indonesian, you may add itu:

Pemandu menjelaskan bahwa terumbu karang itu adalah rumah bagi ikan kecil dan parasit laut.
→ The guide explained that that coral reef / the reef is a home...

But often, context alone decides whether English should use “the” or “a”.

Can I replace pemandu with a pronoun, like dia, and keep the same structure?

Yes. You can use a pronoun as the subject without changing the grammar:

Dia menjelaskan bahwa terumbu karang adalah rumah bagi ikan kecil dan parasit laut.
= He/She explained that coral reefs are a home for small fish and sea parasites.

Also possible:

Mereka menjelaskan bahwa... – They explained that...
Ia menjelaskan bahwa... – He/She explained that... (slightly more formal than dia)

The rest of the sentence stays the same.