Lagiacrus Ecology

Disclaimer: This is merely a plausible explanation for the monster(s) in this article, and should not be considered canon.

Taxonomy
There is a possibility of this creature being distantly related to crocodilians.

Habitat Range
Island and Submerged Forest.

Ecological Niche
Top predator of its habitat.

Biological Adaptations
Lagiacrus is a blue Sea Serpent that mostly dwells in the sea/deep bodies of water and comes onto beaches to sunbathe. They have hood-like crests on their necks similar to the hoods of real-life Cobras to aid in sunbathing and to allow them to control whether or not they want to float on the surface or sink to bottom and rest. This crest may also be used to attract a mate, similar to a peacock. No difference between males and females are known, but we are only speculating at this point. They also have a crocodile-like gait that differs from Fatalis' gait (which is bipedal) and the dermal spikes on its back glow white when it is in rage mode, suggesting that it has an organ similar to the Electro Sac of a Khezu beneath each spike to generate electricity.

When a Lagiacrus is fully sunbathed it turns a dry grayish blue color and its dermal spikes turn a pale red, but when it returns to the water it regains its striking deep blue coloration and its spikes return to their original color of a very light beige. Also the color pattern of a Lagiacrus is similar to that of a Great White Shark, Blue on top so prey from above won't see it coming and whitish on the bottom which mimics the sun hitting the surface so prey from below won't see it coming.

While Lagiacrus is very well adapted to the sea, it is also found in the murky river beds and steamy, wet jungles of the Flooded Forest. Here it's main prey of Espioth, Ludroth, Roarudorosu, Aptonoth, Qurupeco, and Kelbi are still hunted and new food items like arrowana, catfish, and Gobul are also added to the menu. This states that Lagiacrus, like some crocodiles lives a perfect life in both fresh and salt water.

Behavior
If food such as smaller sea serpents or fast moving fish is too quick for this massive predator to catch, it will cast out electricity to incapacitate its prey. However, it can also catch prey in a crocodilian fashion. Lying in wait for prey such as an Aptonoth, Jagii, Jagiinosu, Dosujagii, or Qurupeco to come and take a drink or a swim and then strike, clamping down with tremendous jaw pressure, crippling and sometimes killing its prey on impact.It has also been known to come ashore to hunt, usually if food is scarce or if a particularly wanted prey is seen. This is demonstrated in the Monster Hunter Tri trailer, when it attacks a Rathalos.

This serpent is highly adept at underwater combat, but its weakness seems to be the fact that it cannot defend its back well. And, when on land, it is very clumsy, albeit with devastating attacks. To lure it ashore would make slaying it much, much easier.