Among them, methylaplysinopsin (1, Figure 1) has shown potent
in vivo antidepressant activity, and was later shown to have
reversible inhibitory activity against MAO (Baird-Lambert et al.
1982). Detailed pharmacokinetic studies followed this study,
which showed the drug-like property of 1. Successive studies
developed synthetic analogs as MAOIs with improved IC50 values
down to 5 nM against MAO-A (Aoki et al. 2001; Segraves and
Crews 2005)

Species: Aplysynopsin sp.
Compounds: Aplysynopsins
MAO-A IC50: 0.0056uM
Synthetic Analogs MAO-A IC50: 0.035 uM

Sponges have three asexual methods of reproduction: after fragmentation; by budding; and by producing gemmules. Fragments of sponges may be detached by currents or waves. They use the mobility of their pinacocytes and choanocytes and reshaping of the mesohyl to re-attach themselves to a suitable surface and then rebuild themselves as small but functional sponges over the course of several days. The same capabilities enable sponges that have been squeezed through a fine cloth to regenerate.[49] A sponge fragment can only regenerate if it contains both collencytes to produce mesohyl and archeocytes to produce all the other cell types.[39] A very few species reproduce by budding.[50]

Gemmules are "survival pods" which a few marine sponges and many freshwater species produce by the thousands when dying and which some, mainly freshwater species, regularly produce in autumn. Spongocytes make gemmules by wrapping shells of spongin, often reinforced with spicules, round clusters of archeocytes that are full of nutrients.[51] Freshwater gemmules may also include photosynthesizing symbionts.[52] The gemmules then become dormant, and in this state can survive cold, drying out, lack of oxygen and extreme variations in salinity.[26] Freshwater gemmules often do not revive until the temperature drops, stays cold for a few months and then reaches a near-"normal" level.[52] When a gemmule germinates, the archeocytes round the outside of the cluster transform into pinacocytes, a membrane over a pore in the shell bursts, the cluster of cells slowly emerges, and most of the remaining archeocytes transform into other cell types needed to make a functioning sponge. Gemmules from the same species but different individuals can join forces to form one sponge.[53] Some gemmules are retained within the parent sponge, and in spring it can be difficult to tell whether an old sponge has revived or been "recolonized" by its own gemmules.[52]

Is there a marine source of DMT?

No source has been found for N,N-dmt, but 5,6-dibromo-dmt and 5-bromo-dmt have been found in sea sponges. I would not be surprised if there is a source as alkaloids from marine organisms are probably very understudied compared to plants.